Transcriber’s Notes

Obvious typographical errors have been silently corrected. Variations in hyphenation have been standardised but all other spelling and punctuation remains unchanged.

The original makes extensive use of „. This has been replaced by the original text in some cases where this improved clarity or layout.

The mathematical and chemical formulae accurately represent the original but have not been error checked.

HYGIENE:
A MANUAL
OF
Personal and Public Health

BY
ARTHUR NEWSHOLME, M.D., F.R.C.P., Lond.,
UNIVERSITY SCHOLAR IN MEDICINE; DIPLOMATE IN PUBLIC HEALTH, UNIV. LOND.; MEDICAL
OFFICER OF HEALTH OF BRIGHTON; MEMBER OF THE COUNCIL AND EXAMINER TO THE
SANITARY INSTITUTE; EXAMINER IN STATE MEDICINE TO THE UNIVERSITY OF
LONDON; LATE EXAMINER IN PREVENTIVE MEDICINE TO THE UNIVERSITY OF
OXFORD, AND PRESIDENT OF THE INCORPORATED SOCIETY OF MEDICAL
OFFICERS OF HEALTH.

NEW EDITION, 1902. ILLUSTRATED.

LONDON:
Geo. Gill & Sons, Ld., Minerva House, Warwick Lane.

[PREFACE.]

The writing of a preface is perhaps superfluous for a book which has had a large and steady sale for nearly twenty years, and which has evidently met with the approval of a large constituency. A few words of introduction appear, however, desirable in view of the facts that the present edition has been almost entirely re-written; that a large amount of new matter has been introduced; and that, so far as is known, the comments on each subject represent the most recent and authoritative knowledge upon it.

An attempt has been made to meet the requirements of medical students, as well as of science students and general readers, for whom former editions were chiefly intended. A large class of medical students and practitioners do not require the detailed statement of the subject contained in the larger text-books. For them, and, it is hoped, also for a large number of candidates for diplomas in public health and in sanitary science, the present edition will prove to be useful. At the same time, the subject has been treated as non-technically as is consistent with accuracy, in order to retain its suitability for non-medical readers. A large number of new illustrations have been introduced.

The new chapters dealing with Dietetics, Trade Nuisances, Meteorological Observations, Tuberculosis, Disinfection, and Vital Statistics will, it is believed, enhance the value of the book.

Attention is also drawn to the solutions of mathematical problems in the different branches of hygiene, of which a table of contents is given on page viii.

In its new form, it is hoped that this work will be found to have retained its value as a plain and straightforward account of its subject for the general public and for science students; and to have become a practical guide to sanitary inspectors and to medical students, whether preparing for a diploma in public health, or studying hygiene as an important branch of medicine. The use of smaller type for specially technical matter of less general interest will facilitate discriminative reading.

ARTHUR NEWSHOLME.

Brighton,
February 28th, 1902.

TABLE OF CONTENTS.

SPECIAL TABLE OF CONTENTS FOR ARITHMETICAL PROBLEMS IN HYGIENE.

HYGIENE.

[CHAPTER I.]
INTRODUCTORY.

In classical mythology, Æsculapius was worshipped as the god of Medicine, while his daughter Hygeia had homage done to her as the sweet and smiling goddess of Health. The temples of these two deities were always placed in close contiguity; and statues representing Hygeia were often placed in the temple of Æsculapius. In these statues she is represented as a beautiful maid, holding in her hand a bowl, from which a serpent is drinking—the serpent typifying the art of medicine, then merely an art, now establishing its right more and more to the dignity of a science.

That considerable attention was paid in very early times to matters relating to health, is also shewn by the elaborate directions contained in the Mosaic law as to extreme care in the choice of wholesome foods and drinks, in isolation of the sick, and attention to personal and public cleanliness. It is not surprising, therefore, to find that the Jews, throughout the whole of their history, have apparently enjoyed a high standard of health.

In this country great ignorance of the laws of Health has prior to the last fifty years prevailed, and consequently preventible diseases have been rampant, and have claimed innumerable victims. Each century has been marked by great epidemics, which have swept through the country, scattering disease and death in their course. In the fourteenth century, for instance, there was the Black Death, a disease so fatal that it left scarcely one-fourth part of the people alive; while Europe altogether is supposed to have lost about 40 millions of its inhabitants, and China alone 13 millions. A century and a half later came the Sweating Sickness (though there were a score of minor epidemics in between). This was carried by Henry the Seventh’s army throughout the country, and so great was the mortality, that “if half the population in any town escaped, it was thought great favour.” Considerable light is thrown on the rapid spread of this disease after its importation, when we remember that there were no means of ventilation in the houses; that the floors were covered with rushes which were constantly put on fresh without removing the old, thus concealing a mass of filth and exhaling a noisome vapour; while clothing was immoderately warm and seldom changed; baths were very seldom indulged in, and soap hardly used.

In the sixteenth and seventeenth centuries there were five or six epidemics of The Plague, and it was only eradicated from London, when all the houses from Temple Bar to the Tower were burned down in the Great Fire of September 2nd, 1666, which destroyed the insanitary and necessitated the building of new and larger houses.

Scurvy, jail-fever, and small-pox, are other diseases which were formerly frightfully prevalent. Jail-fever, the same disease as the modern typhus-fever, has now become practically extinct in its former habitat, owing largely to the noble work of John Howard, “whose life was finally brought to an end by the fever, against the ravages of which his life had been expended.” This disease was fostered by overcrowding, ill-ventilation, and filth.

Scurvy formerly produced a very great mortality, especially among sea-faring men. In Admiral Anson’s fleet in 1742, out of 961 men, 626 died in nine months, or nearly two out of every three, and this was no solitary case. Captain Cook, on the other hand, conducted an expedition round the world, consisting of 118 men; and although absent over three years, only lost one life. He was practically the first to demonstrate the potency of fresh vegetables in preventing scurvy.

The striking facts respecting small-pox will be found on page 293. The general death-rate has also greatly declined. Thus while the annual death-rate in London 200 years ago was 80 per 1,000, it only averaged 18.8 in the four years 1896-99; and the death-rate of England and Wales has declined from 22.4 in 1841-50 to 18.7 per 1,000 in 1891-95 and 17.6 in 1896-99.

That much still remains to be done is evident on every hand. There is little doubt that the general death-rate might be reduced to 15 per 1,000 per annum, instead of the present 18, were the laws of health applied in every household and community. It has been estimated that on the average at least 20 cases of sickness occur for every death; therefore nearly half of the population is ill at least once a year. A simple calculation will show how much loss the community annually suffers from this vast mass of preventible sickness. It amounts to many millions of pounds, leaving out of the reckoning the suffering and distress which are always associated with sickness. For details relating to special diseases, see page [297].

In the prevention of this mass of sickness, the knowledge of its causation is half the battle; when once a disease is traced to its source, as a rule, the agency which produces it can be avoided.

The reason why even more progress has not been made in the prevention of disease is not far to seek. In order to prevent a disease it is necessary to remove its causes. The causes of disease can only be ascertained by a careful investigation of its phenomena; and it is only within the last century that these have been studied to any large extent scientifically. Such knowledge of morbid processes not only results in improved measures of treatment, but in more rational and complete measures of prevention. Thus, not only is the number of diseases which are curable becoming gradually augmented, but the number preventible is even more rapidly on the increase.

Inasmuch as the preservation of health involves the prevention of disease, Hygiene, the science of health, is sometimes called Preventive Medicine.

The subject of Hygiene naturally divides itself into two parts, the health of the individual, and that of the community, or Personal and Public Health.

The former treats of the influence of habits, cleanliness, exercise, clothing, and food on health; while the latter is concerned with the interests of the community at large, as affected by a pure supply of air and water, the removal of all excreta, the condition of the soil, and with the administrative measures required to secure the removal of evil conditions. It is obvious, however, that these two divisions are not mutually exclusive. What is important to the health of the community, is equally so to each individual member of it. The purity of air and water, for instance, is of immense importance both personally and collectively.

It will be convenient to study first the three main factors in relation to health—food, water, and air—subsequently considering other matters of importance to health (see pages 4-157).

[CHAPTER II.]
FOOD.

Physiological Considerations.—All substances are foods which, after undergoing preparatory changes in the digestive organs (rendering them capable of absorption into the circulation), serve to renew the organs of the body, and maintain their functions. Foods have been classified as tissue producers or energy producers, the first class renewing the composition of the organs of the body, and the second class supplying the combustible material, the oxidation (or more correctly the metabolism) of which is the source of the energy manifested in the body. The two main manifestations of energy in the body are heat and mechanical motion, which are to a large extent interchangeable.

All foods come under one of these heads; they are either tissue or energy producers. They may be both, and in many cases are so. Thus, all nitrogenous foods (as meat, legumens, etc.) not only help to form the nitrogenous tissues of the body, but their largest share becomes split up into fats and urea, and so forms a source of heat to the body. Similarly fats may possibly, after assimilation, enter into the composition of the various tissues containing fat (of which the brain is the most important), though they usually supply an immediate source of heat. Proteid foods are, however, the tissue producers par excellence, other foods serving as the immediate sources of energy when metabolised in the body.

Certain foods do not directly serve either as tissue or energy producers, but are useful in aiding the assimilation of food. Such are the various condiments which may be classed as adjuncts to food. Salt is so necessary to the assimilation of food and to the composition of the various tissues, that it may be ranked as an important food. Water, again, though already oxidised, and so not an immediate source of energy, is absolutely necessary to the assimilation of food, to the interchange between the various tissues and the blood, and to the elimination of effete products.

Classification of Foods.—Inasmuch as milk supplies all the food necessary for health and growth during the first year of life, it may reasonably be expected to afford some guidance as to the necessary constituents of a diet for the adult; although the conditions of life being altered in the latter, we can hardly expect the same proportions of the different materials to hold good. In the infant rapid growth and building up of new tissues and organs are going on, involving the necessity for a larger proportional amount of nitrogenous food than in the adult.

The following is the average composition of 100 parts of

It is evident from this analysis of milk that our food must contain (at least) representatives of all the above divisions. We have, therefore:—

• 1. Nitrogenous Foods.
• 2. Hydrocarbons or Fats.
• 3. Carbohydrates or Amyloids.
• 4. Salts.
• 5. Water.

Condiments and stimulants (tea, coffee, alcohol) are not foods in the strict sense of the word, and will be discussed in a later chapter.

Nitrogenous Foods include albumin, casein, gluten, legumen, fibrin, and gelatin. They all agree in consisting of a complex molecule containing many atoms of carbon, hydrogen, oxygen, and nitrogen, with the addition of smaller quantities of sulphur, and in some cases phosphorus. The nitrogenous substances used as food may be divided into two groups, (a) those containing gelatin, and (b) numerous bodies which receive the common name of proteids or albuminoids.

The percentage composition of gelatin is:—

The percentage composition of all proteids lies within the following limits:—

Proteids also contain a small amount of phosphorus, chiefly as phosphate of lime, but also in minute quantity in their essential structure. Various proteids are used in food, e.g. serum-albumin in the blood and tissues of animals; egg-albumin in the white of eggs; myosin in flesh; casein in milk; legumin, or plant-casein, in the seeds of leguminous plants; gluten in wheat-flour, etc.

Proteid foods are pre-eminently important, as they construct and keep in repair the tissues of the body. They are not used solely for this purpose. A large share of the energy of the body is derived from the metabolism of proteids. The amount required for these purposes will be discussed on page [32]. Meanwhile, it may be said that it is not found to be compatible with efficient health simply to supply an amount of proteid food which will suffice to replace the wear and tear of the tissues, leaving fats and carbohydrates to supply the energy of the body. Deficiency of proteid food always leads to ill-health; and it would appear that in all cases proteid food determines, to a large extent, the metabolism of non-nitrogenous food, and so is favourable to all vital action. The action of nitrogenous food in thus increasing metabolism may make it, when in relative excess, a tissue waster. Banting’s cure for corpulence is founded on this principle, lean meat alone being taken, all starchy and saccharine foods being carefully avoided.

By metabolism is meant the changes undergone by food before it reaches the state in which it is finally eliminated from the body. It is commonly spoken of as oxidation, but this word less exactly represents the facts. The complexity of the changes undergone by food in the body may be better appreciated by a glance at the following schematic statement, which only gives an approximation to the truth:-

Hydrocarbons, or fats, consist of three elements, carbon, hydrogen, and oxygen, the amount of oxygen present not being sufficient to oxidise completely either the hydrogen or the carbon. Thus the molecule of stearin, which may be taken as a typical fat, has the formula C₃H₅ (C₁₈H₃₅O₂)₈.

In respect to their comparatively unoxidised condition fats compare favourably with starch and sugar, C₆H₁₀O₅ and C₆H₁₂O₆ respectively. It is evident that in starch the H₁₀O₅ = 5H₂O, and that in sugar H₁₂O₆ = 6H₂O, so that in both cases only carbon remains uncombined with oxygen. Dried fats produce by their oxidation 2¼ times as much heat as a corresponding amount of sugar or starch; but the relative advantage of fat is not quite so great as would appear from this comparison, inasmuch as metabolism within the body is not identical with oxidation.

The fat obtained from food is not simply deposited in the body as such, to form a store of combustible matter, and to fill up the interstices between the different tissues. If this were so, the kind of fat deposited would vary with the food, which is not the case. The fat of the body is probably not formed directly from fatty food, but as the result of the metabolism of nitrogenous foods when this metabolism is incomplete. In the formation of milk this can be distinctly proved: the fat cells are formed from the protoplasm of the cells of the mammary gland.

Possibly carbohydrate food may be a source of fat, as well as nitrogenous and fatty food. This appears to be the case in the Strasburg goose, which is kept penned up in a warm room, and fed entirely on barley-meal, in order to produce an enormous fatty liver for the delicacy termed pâté de foie gras. But it may be that the large accumulation of fat in the liver is due to the warmth and inaction of the goose diminishing metabolism, and producing a fatty degeneration of the nitrogenous material of the liver.

Fats and carbohydrates, unlike proteids, do not excite metabolism in the system, and so, if in excess of the requirements of the system, can be stored up with comparative ease. Quiet and warmth, diminishing metabolism, conduce to the accumulation of fat in animals being fed for the market; and the same applies to human beings.

Carbohydrates or amyloids include the various starchy and saccharine foods. They are inferior to fats in nutritive power, but, being very digestible, are in much greater favour. In the process of digestion, starch is converted into grape sugar, and starch and sugar are practically equal in nutritive power.

Even when carbohydrates are entirely absent from the food, they may be produced in the organism by the breaking up of nitrogenous matter. This certainly happens in diabetes, in which the nitrogenous food rapidly becomes converted into sugar and urea.

The deprivation of carbohydrate food is much better borne than that of fats, because in the latter the hydrogen is not completely oxidized, and because fats aid the assimilation of other food.

Salts, and especially common salt (chloride of sodium), are essential to health. An average adult human body contains about seven pounds of mineral matter, of which about five-sixths is in the bones. On analysis the whole body yields about five per cent. of ash.

Chloride of sodium is necessary for the production of the acid (hydrochloric) of gastric juice, and of the salts of bile; half the weight of the ash of blood consists of it. An adult requires 150 to 200 grains of salt per day; a large part of this is taken in meat, bread, etc.; and but little need be taken as a condiment. Potassium salts form an important part of milk, muscle juice, and the blood corpuscles. They are obtained from bread and fresh vegetables and fruits. It has been maintained that deficiency of potassium salts causes scurvy (see page [28]); but this is now discredited, and probably potash is chiefly useful because of the vegetable acids with which it is associated in fruits and vegetables, which when oxidised, help to maintain the alkalinity of the blood, e.g., tartrates, citrates, and malates, which become carbonates in the circulation. Calcium phosphate (bone earth) is essential for the growth of bones, and is very important for the young. The best source for it is milk. There is more lime in a pint of milk than in a pint of lime water. Next to milk, come eggs, and then cereals, especially rice as a source of calcium. Lime salts and phosphates as drugs do not benefit like the same substances taken in natural food, and rickets is not curable by taking such drugs.

Oxide of iron is always present in the ash of blood and muscles, and in smaller quantities in milk. Fish and veal are usually deficient in it, while beef and yolk of egg are foods richest in iron. The amount of iron required in food is minute, and it is amply supplied by ordinary diet.

Phosphorus is an essential building material for the body. It is contained in foods chiefly in organic combination. The foods richest in it are yolk of egg, sweetbread (thymus), fish-roe, calves’ brains, and the germ of wheat. Milk and cheese are very rich in phosphates.

Water forms an important article of diet. This is evident from the fact that 80 per cent. of the blood consists of it, and 75 per cent. of the solid tissues; and from the fact that the daily loss of water from the system averages 50 ounces (2½ pints) by the kidneys, and about 40 ounces by the skin and lungs. Water is not simply received into the system as a liquid. It forms a large proportion of the solid food taken. Thus, 87 per cent. of milk, 78 per cent. of fish, 72 per cent. of lean meat, 38 per cent. of bread, 13 per cent. of peas, and 92 per cent. of cabbage, consist of water.

Solid food is dissolved in the alimentary canal by the watery secretions derived from the blood. Water swallowed as food, begins to pass on into the intestine at once. The statement that free consumption of water at meals delays digestion by diluting the gastric juice is therefore not well grounded. In the blood, water serves to carry nutrient materials to all the tissues; and, at the same time being circulated all over the system, equalises the temperature, favours chemical changes, and washes all the tissues. By water again, the effete matters which have been separated by the kidneys are washed out of its tubes.

The Oxygen of the air, in a broad sense, forms one of the foods of the system. This will be considered later.

Besides the above classification, foods have also been classified as follows:—

1. Inorganic food—Oxygen, salts.
2. Organic foods		Animal		Nitrogenous.
				Non-nitrogenous.
		Vegetable		Nitrogenous.
				Non-nitrogenous.
Or, as—
1. Solid foods		Animal		Nitrogenous.
				Non-nitrogenous.
		Vegetable		Nitrogenous.
				Non-nitrogenous.
2. Liquid foods		Water.
		Milk and its products.
		Tea and similar beverages.
		Alcoholic beverages.
3. Gaseous foods—Air.

[CHAPTER III.]
THE VARIETIES OF FOOD.

Nitrogenous Animal Foods.—These are divided into two groups, the one containing gelatin, and the other all the proteid or albuminoid substances, which are taken in the flesh of various animals, and in milk and eggs.

Gelatin is obtainable from bones, and from connective tissue wherever found. Being easily digested, and absorbed, it has been very popular as an invalid’s food; but the fact that animals cannot sustain life on it without the addition of proteids proves that its value is limited. It is incapable of building tissues, but is a valuable proteid-saver, being able to save from metabolism half its weight of proteid, or twice as much as is spared by an equal weight of carbohydrate. Its utility in this direction is, however, limited, because of the dilute form in which it is taken in ordinary foods. It is useful for invalids, partly because it forms a bulk, and prevents the evil tendency to give their food in too concentrated a form; partly because it forms a source of easily metabolised material, and so prevents tissue-waste; and partly because it commonly contains phosphate of lime, derived from the bones forming the source of gelatin.

Gelatin as prepared for the table contains a considerable proportion of water; as little as one per cent. of gelatin in water will cause it to gelatinise on cooling. Isinglass obtained from the floating bladder of the sturgeon is an example of the purest kind of gelatin; glue is an inferior sort, made from bones, etc.

Gelatin is only a cheap food when obtained, for instance, from bones which cannot otherwise be utilised. When made from veal it is costly out of proportion to its dietetic value.

The Flesh of various animals is one of the main sources of our nitrogenous and fatty food. Meats may be divided into two kinds, viz., red meat and white meat. These gradually merge into one another. As common examples of red meats, we have beef, mutton, pork, game, wild fowl, and salmon.

The common fowl and turkey, most fishes, rabbits, crustaceans, and molluscs, are examples of white meat. As a rule white meats are more digestible than red, having more delicate fibres, and containing a smaller proportion of nitrogenous matter.

Flesh consists almost entirely of muscular tissue, of which there are two kinds, striped and unstriped.

The striped is the variety most commonly used as food. Unstriped muscle has a softer texture, but is not so easily masticated as striped, and for this reason may be indigestible. Tripe is composed of the unstriped muscle and connective tissue of the stomach of the cow, and if well cooked forms a cheap and easily digested dish.

The influence of feeding on the quality of the meat is great. In ill-fed or old animals, connective tissue is more abundant, and the meat is tougher. Well-fed and fattened meat contains for equal weights much more nutritious matter than non-fattened meat, the fat which is deposited in the muscle replacing water and not proteid. Hence the gain in nutritive value is an absolute one, and is not attained at the expense of the proteid part of the meat. Young animals, again, contain more water and fat and a larger proportion of connective tissue than the full-grown, and are consequently not so nourishing.

Meat ought to be eaten either before the onset of rigor mortis, or near its end, before putrefaction has commenced. During rigor mortis it is denser, tougher, and more difficult to digest than after it.

The proportion of fat in meat varies greatly in different individuals of the same species, in different animals, and in different parts of the same animal. According to Dr. Ed. Smith, the proportion of fat in fat oxen is ⅓, in fat sheep ½, in calves ⅙, lambs ⅓, and fat pigs ½.

Good meat, whether beef or mutton, ought to have a marbled appearance, a medium colour, neither pale pink nor deep purple; its texture should be firm, and not leave the impress of the finger; its odour slight and pleasant, the juice reddish and acid, the bundles of fibres not coarse, and free from foreign particles imbedded in them; and lastly, it should not be taken from an animal killed near the time of parturition, nor in consequence of any accident or disease.

Beef is, as a rule, more lean than mutton or pork; it has a closer texture, and more nutritive material in a given bulk. It is also fullest of the red-blood juices, and possesses a richer flavour than the two others.

Liebig’s beef extract contains little if any albumin or gelatin. It is a useful stimulant to the gastric secretion, as in soups at the beginning of a meal, but is not a food. Its chief constituents are the various extractives of meat, the most important of which are inosinic acid, kreatin (C₄H₉N₃O₂,H₂O), and inosite, or muscle sugar (C₆H₁₂O₆, 2H₂O). Even in substances like Bovril, containing powdered meat fibre mixed with Liebig’s extract, the amount of nutritive material is very small. The white of one egg contains as much nutritive matter as three teaspoonsful of bovril. None of these substances can be trusted like eggs or milk to keep a patient alive for several weeks.

Mutton is regarded as being more suitable for people of sedentary occupation than beef. Lamb is more watery than mutton, and less nutritious.

Veal, as ordinarily prepared in this country, is difficult of digestion; its shreddy, juiceless fibres eluding the teeth, and consequently not undergoing proper mastication.

Pork is not so digestible as beef or mutton, partly because of the large proportion of fat, and partly because its fibres are hard and difficult to masticate. Its digestibility varies greatly with its age, breeding, and proportion of fat.

The Flesh of Birds contains very little fat, and that found separate from the meat is rarely nice. Most birds are edible, but fish-eating birds are apt to be nasty. As a rule, the flavour of the male bird is richer than that of the female. The chief virtues in poultry are their tenderness, and the large proportion of phosphates they contain. They are deficient in fat and in iron. To compensate for the former, one commonly takes with them melted butter and fat bacon or pork sausages; to compensate for the latter, the addition of Liebig’s extract to the gravy is useful. Young, and consequently tender, birds are known by their large feet and leg-joints. When a bird appears at table with violet-tinged thighs and a thin neck, if possible avoid being helped to the leg. Wild fowls are harder and less digestible than tame. In ducks and geese fat is more abundant, and of a stronger flavour; they are, consequently, not so digestible as fowls.

Fish forms an important article of diet. It is easily cooked, and usually very digestible; it possesses a larger bulk in proportion to its nutritive quality, and hence is very valuable for those who habitually take an excess of meat food, which is commonly the case with those leading sedentary lives, and in declining years. There appears to be no foundation for the statement that fish is rich in phosphorus, and is thus a good brain food. Generally, white-fleshed fish is more digestible than red-fleshed (such as salmon), the latter usually containing more fat than the former. When the fat is distributed throughout the flesh, as in the salmon, fish is more satisfying than when it is mainly stored up in the liver, as in the cod-fish. According to Payen, the percentage proportion of fat in soles is only 0.248, in whiting 0.383, conger eel 5.021, mackerel 5.758, eels 23.861. The addition of some fatty food, as melted butter, is very advisable to such meats as poultry, rabbits, soles, whiting, plaice, haddock, cod, turbot, and other fishes; whereas sprats, eels,. herrings, pilchards, salmon, etc., are more or less rich in fat.

A Hen’s Egg usually weighs a little under two ounces. It consists of 74 per cent. of water and 26 per cent. of solid matter. The white of the egg is chiefly albumin, the yolk consists of a very digestible oil, rich in phosphorus and iron, each particle of the oil being enveloped in a form of albumin called vitellin. The salts are chiefly contained in the shell. There is no sugar in the egg, the necessity for such oxidisable material for the chick being obviated by the heat produced by incubation. Eggs, when kept for some time, lose weight, owing to evaporation through the porous shell; similarly, air entering from without sets up decomposition. In a solution of brine containing an ounce of common salt to half a pint of water, fresh eggs sink, stale ones float; rotten eggs may even float in fresh water. Eggs may be preserved by keeping them in brine, or, better still in lime water, or by smearing them over with lard or butter, as soon as possible after they are laid.

Cow’s Milk has a specific gravity of 1028-34, and on allowing it to stand in a long narrow vessel ought to form ten or twelve per cent. of its volume of cream. The percentage composition of human and cow’s milk has been given on page [5]. The legal minimum standard for dairy milk, which is presumably derived from a number of cows, is now 3 per cent. of fat, and 8.5 per cent. of “solids not fat.” This standard is unfortunately very low, and allows a considerable margin of adulteration, which cannot be prevented by legal means. Thus ordinary milk derived from a herd of cows would probably contain 4.5 per cent. of fat; and it is, therefore, practicable to mix pure new milk with a large proportion of separated milk, and yet keep within the legal standard. This is largely done in towns, and infants suffer much from the deficiency of cream in their sole food (see page [28]). The lactometer determines the specific gravity, which should be taken at a temperature of 60° F. In skimmed or separated milk it will be over 1034; watering on the contrary lowers the specific gravity. If the milk has been both watered and skimmed the specific gravity will give an uncertain indication. Measurement of the cream in a tall narrow glass will enable one to detect the second possible source of fallacy; but the composition of milk can only be certainly determined by analysis. This is done (a) by evaporating a weighed amount of milk to dryness and then re-weighing. (b) From a separate amount of dried milk the fat is extracted by ether, the ether then evaporated, the remaining fat weighed, and its percentage calculated. The weight of fat deducted from the total solids i.e. (b) from (a), gives the “solids not fat.” The following example will make the method then followed clear. The sample gives 7.9 per cent. of “solids not fat.” Genuine milk contains at least 8.5 per cent. of “solids not fat.”

Then the sample contains—

100 × 7.9 ∕ 8.5 = 92.9 per cent. of genuine milk,
i.e. 7.1 per cent. of water has been added to it.

Half a pint of milk supplies as much nitrogenous nutriment as two good-sized eggs, and as three and a half ounces of beef. Milk may be deteriorated (1) by skimming or “separating” by machinery, or (2) by the addition of water—the first diminishing the proportion of fats, and the second the total amount of solids.

Skim Milk still contains nearly 1 per cent. of fat, but Separated Milk, in which the cream has been removed by centrifugal apparatus, contains less than ¹ ∕ ₈ per cent.

Skim or separated milk forms a cheap source of nitrogenous food; but when it is sold mixed with new or alone as new milk, the public is defrauded, and infants fed on it are robbed of the fat which is so essential for their growth.

Condensed Milk is milk deprived of a large part of its water. It represents three times its volume of fresh milk. There are in the market (a) unsweetened and condensed whole milk, (b) sweetened and condensed whole milk, and (c) sweetened and condensed skim or separated milk. Unfortunately the latter is most largely sold because cheapest; and infants are thus often robbed of fat, a most important element in their food. Always examine the label of each tin carefully, to ascertain whether the milk has been deprived of its cream. The law requires that this fact should be stated on the label. Tins which have bulged should be rejected. Condensed milk is more easily digested by infants than new cow’s milk, but it lacks the anti-scorbutic properties of new milk (see page 28). Even the condensed whole milk if diluted beyond 1 part of milk to 3 of water is deficient in fat. Sweetened condensed milk has one-third its weight of extraneous sugar added to it, and on this account it tends in children to produce fatness, and a distaste for simple food; in children fed on it alone ossification (formation of bone) is retarded, and resistance to illness is diminished. The only dietetic advantages it possesses over fresh cow’s milk are its freedom from possible disease germs and easier digestibility.

The digestion of milk is preceded by its clotting in the stomach. The same thing happens when junket is formed by the addition of rennet to milk. This is a different process from the curdling of milk, which occurs when milk turns sour. The latter is caused by the splitting up of milk sugar and the formation of lactic acid by certain micro-organisms in the milk. When milk is heated, a skin is formed, consisting of coagulated albumin, in which is also a little casein, fat, and salts of lime. Boiled milk becomes sterilized. Cow’s milk should always be boiled, unless it is quite certain that the cows from which it is derived are perfectly healthy, and that the milk has not been exposed to infection before reaching the house. The disadvantages of boiling which are outweighed by its advantages, are that the taste of the milk is altered, some nutritive matter is lost by the formation of the “skin,” and the casein is not quite so easily digested. Pasteurization of milk, i.e. keeping it at a temperature of 70° C. (158° F.) for 20 to 30 minutes has been proposed as an alternative to boiling. This appears to destroy the bacilli causing tuberculosis (see page [312]). The typhoid bacilli are killed at 60° C. in five minutes when suspended in emulsion. Pasteurization is not, however, so certainly efficacious for other disease-germs as is boiling, and is not so easily carried out in domestic life as boiling. By boiling milk in a double saucepan, i.e. in a water-bath, very little change occurs in the taste of the milk, especially if it be cooled rapidly and strained.

Cheese is prepared by coagulating milk by “rennet,” the mucous membrane of the fourth stomach of the calf, salted and dried before using. By this means the casein is precipitated, carrying down with it the cream, and a large proportion of the salts of milk. The whey, containing the sugar, soluble albumin, and remaining salts, is separated by straining, while the mixed curd and fat are pressed in moulds. Cheese thus consists of casein, fat in varying proportions, water and salts, especially phosphate of lime. It is coloured with annatto, a vegetable colouring matter. When new, cheese is tough; when old, its oils tend to become rancid; the best age is from nine to twenty months. It is probable that cheese in small amount helps the digestion of other foods, though it is itself a highly concentrated and comparatively indigestible food. When toasted it is proverbially indigestible.

There are many different kinds of cheese. The following classification gives the more important varieties:—

(1) Cream cheese is the new curd only slightly pressed, and is more digestible than ordinary cheese.

(2) Next to these are cheeses made with whole milk rich in cream, such as Stilton, Gorgonzola, Cheshire, and Cheddar.

(3) Cheeses made of poor or partially skimmed milk, such as Shropshire, Single Gloucester, and Gruyère.

(4) Cheeses made of skimmed milk, such as Suffolk, Parmesan, and Dutch.

American cheeses may belong to any of these classes; they are generally pure, but occasionally are made from separated milk, margarine being added to take the place of cream. The sale of such cheeses, except under the name of “margarine cheese,” is now illegal.

Non-Nitrogenous Animal Foods.—These are all fats, and the most important are the various meat fats and butter. They possess a higher food value than carbohydrates in the proportion of 2¼; to 1. The composition of the various fats differs somewhat; they usually contain varying proportions of olein, palmitin, and stearin, which are compounds of glycerine with the radicle of a fatty acid (stearin = C₃H₅ (C₁₈H₃₅O₂)₃). Thus mutton suet consists of stearin, olein, and palmitin, with a preponderance of stearin. Beef suet contains less stearin and more olein than mutton suet. The more olein a fat contains the less solid it is. Olive oil is composed almost entirely of olein. Palmitin, which melts sooner than stearin, is the chief solid constituent of butter, while olein is its chief liquid constituent. Butter is specially distinguished by containing 7 to 8 per cent. of “volatile fatty acids,” such as butyric, caproic, etc., combined with glycerine. The presence and amount of these compounds is an important test for the freedom of butter from adulterating fats.

Cod-liver oil is next to butter the most digestible animal fat known. The best cod-liver oil is frozen at a low temperature, by which means the stearin is frozen out, and nearly pure olein is left. Traces of iodine have been found in it, and more commonly a small amount of bile, which probably increases its digestibility.

The temperature at which a fat becomes hard is a fair guide to its digestibility. Thus we know that beef, and still more, mutton fat, would become solid, under conditions in which bacon dripping is still soft. Where digestion is weak, there may be an instinctive loathing of fat meat; for such persons, especially for children, some other fat should always be substituted. Thus the addition of butter to the potatoes makes up the deficiency.

Butter forms 3½ to 4½ per cent. of cow’s milk. It is separated from milk by churning, the oil particles being deprived by this means of their albuminous coats. The more completely the butter-milk is separated the longer the butter keeps. It can be kept longer if salt is added, or in hot weather by keeping it under frequently-changed water. Rancidity indicates the decomposition of traces of the fat of butter into its fatty acid and glycerine.

Cream contains about 30 per cent. of butter fat, Cheshire cheese 25 per cent., and skim milk cheese 7 per cent.

Butter milk differs from skim milk in the presence of lactic acid. It is more digestible than skim milk, the casein being in a more flocculent condition.

The odour and flavour of butter are not due to olein and palmitin, the two chief constituents, but to a smaller quantity of butyrin, caproin, and caprylin fats of a much lower series. Ordinary butter contains a considerable proportion of water, and the presence of about 8 per cent. renders it more palatable; if it is over 15 per cent., the butter is considered adulterated. An excessive amount of salt is sometimes present. The most frequent adulteration is the substitution of foreign fats for butter fat, e.g. lard, palm oil, rape seed oil, or cocoa-nut oil. Margarine is most frequently used for this purpose.

Margarine is prepared from beef-fat by melting, the stearin becoming solid again at a temperature at which olein and margarine still remain liquid. It forms a wholesome and cheap food, being nearly as digestible as butter, for which more expensive food it is often fraudulently sold. When mixed with a small proportion of butter its recognition by smell, etc., is almost impossible, but on careful chemical analysis, it is found to have a higher melting point and a lower specific gravity than butter, and a much smaller percentage of soluble fatty acids than the latter. Thus:—

Cereal Foods.—Gluten is peculiar to plants, and is chiefly found in plants belonging to the great family of grasses. Gluten is to bread what casein is to milk, and myosin to flesh. If one takes a piece of dough made from wheat flour, and holds it under a stream of water from the tap, a large part of it is washed away, while a sticky adherent mass is left behind. This is gluten, and it is its tenacity which enables bread to be made. If the fluid with which the dough was washed is collected, it will be found to contain a large quantity of starch, a small amount of sugar, of albumin, and certain salts. All cereals possess these constituents in various proportions, as may be seen from the following table:—

The proteid varies in character in the different cereals; wheat flour has the largest proportion of gluten (8 to 12 per cent.) and therefore makes the best bread.

Good wheat flour ought to be white, not gritty or lumpy, not acid or musty, forming a coherent stringy dough. Examined microscopically, it should show the absence of any fungi, or acarus farinæ, or of foreign starches, such as barley, maize, rice, potato, known by the different shape of their starch granules. (See Fig. 1.) Alum has been occasionally added to flour, to enable the baker to make a white and porous bread from damaged wheat flour. It can be detected as follows:—Pour over the freshly cut surface of a slice of bread some freshly prepared decoction of logwood chips, and then a solution of carbonate of ammonia. If alum is present, the bread turns a marked blue to violet colour; but if the bread is pure, it is only stained pink.

The wheat grain may be used as food in its entirety. Thus boiled in milk, after having been soaked in water, it forms the chief constituent of frumenty. Usually it is converted into flour by grinding or milling. A grain of wheat consists of three parts, an outer envelope, the bran, consisting chiefly of indigestible cellulose, and composing 13½ per cent. of the grain; the kernel, or endosperm, which makes up 85 per cent. of the grain; and the germ, forming 1½ per cent. of the grain. In the old method of stone grinding, the bran was removed, and the germ left along with the endosperm. In the elaborate processes of modern roller milling, the bran is removed as in the old grinding, because it cannot without the greatest difficulty be reduced to powder; and the germ is also removed, because the oil abundantly present in it is apt to become rancid and spoil the flour, and because the soluble proteids in it are apt to change some of the flour into dextrin and sugar, which become brown in baking and spoil the appearance of the bread. The germ is easily removed, because its toughness causes it to be flattened out in the milling, while the endosperm becomes powdery. The central part of the endosperm is the source of ‘patents.’ It is very rich in starch and is used for making fancy breads and pastry. The outer part of the endosperm is ‘households.’ ‘Households flour’ is subdivided into (a) second patents, or ‘whites’; (b) first households; (c) second households or ‘seconds.’ ‘Seconds’ is richest in gluten, ‘whites’ in starch. Ordinary bread is normally derived from a blend of these three. Some ‘strong’ wheats, e.g. Australian, yield a ‘patents’ which is rich in gluten, and such flour is used for making Vienna bread. ‘Strong’ wheats take up most water in baking, and so yield most loaves per sack. ‘Seconds’ flour yields a bread which is richer in proteid than most other kinds; but the dark colour of the loaf makes it unpopular. Various schemes have been devised to utilise the germ and the bran, which are ordinarily discarded. In the preparation of Hovis flour the separated germ is partially cooked by superheated steam. This kills the ferment contained in the soluble proteids, and thus prevents it from changing starch into maltose and dextrin. The action thus prevented is represented by the following formula:—

STARCH.MALTOSE.DEXTRIN.
10 C₁₂H₂₀O₁₀ + 6 H₂0 = 6 C₁₂H₂₂O₁₁ + 4 C₁₂H₂₀O₁₀.

The germ thus treated is ground to a fine meal, of which one part to three of ordinary flour, forms Hovis flour. Other ‘germ breads’ are also in the market. In the making of Frame food the bran is boiled with water under high pressure. The watery extract, containing the mineral and part of the nitrogenous constituents of the bran, is evaporated to dryness, and forms the basis of various preparations. It is doubtful if this food possesses any great value.

Brown bread is a somewhat vague expression, meaning either an admixture of bran or of germ or of both with flour, or bread made from whole wheat flour. In each of these cases the loaf would be brown. The bran is rich in fat as well as in phosphates. It acts as a mechanical irritant, ill borne by delicate stomachs, but very useful where a tendency to constipation exists. The excess of nitrogenous matter in brown bread and its richness in fat, do not prove its greater nutritiveness, as it is present in a condition in which only a portion is absorbable from the alimentary canal into the circulation.

The harder wheats, such as Sicilian wheat, contain a larger percentage of gluten; and from them macaroni and vermicelli are obtained, which are nearly pure gluten. They are very nutritious and useful foods. Semolina is prepared from wheat, the millstones being left sufficiently apart to leave the product in a granular condition. In malted breads, a syrupy infusion of malted barley (malt extract) is added to the flour. Malt extract contains in addition to malt sugar (maltose) and dextrins, a ferment (diastase) which, like the saliva, is able to convert starch into the soluble substances, maltose and dextrin (see formulæ above). The action of this ferment is stopped by the temperature of baking. Hence even when the malt extract is allowed a considerable time for its operation on the dough, only about 10 per cent. of the starch in the loaf becomes soluble, as compared with 4 per cent. in an ordinary loaf.

Oatmeal, obtained from the common oat, contains very little gluten, and so cannot be made into vesiculated bread. It contains a large proportion of other nitrogenous material and of fat. As porridge and oatmeal cake it forms a very nutritious diet. The husk ought to be carefully removed from the meal intended for human food, as, although very nitrogenous, it acts as a mechanical irritant. Groats consists of oats from which the husk has been entirely removed. The substitution of rolling for grinding in preparing oats for food and the application of heat during the rolling process, have made oatmeal more digestible, as in Quaker, Provost, and Waverley oats.

Barley contains very little gluten; on this account, like oatmeal, it does not admit of being made easily into bread.

Malt is barley which has been made to germinate by heat and moisture and then dried, “diastase” being formed in the process. Extract of malt, containing diastase in an active condition, is useful in cases of impaired digestion and deficient assimilation of food.

Rye is rarely used in this country for making bread. In Germany it is known as “black bread,” but its colour and acid taste make it disagreeable, and it is laxative in its action.

Maize, or Indian Corn, is deficient in gluten, and so not suitable for making vesiculated bread. Like oatmeal, it is made into cakes, called in America “Johnny cake.” It contains much fatty matter, and is largely used for fattening poultry and other animals. Oswego flour and corn flour are maize flour deprived by a weak solution of soda, of its proteids and fat; hominy contains all its constituents. Maize is a cheap and nutritious food. When wheat flour is dear, it is occasionally adulterated with maize. The adulteration can be detected by the forms of the starch granules, examined under a low power of the microscope.

Rice contains less proteids and fat than any other cereal. Its chief value as a food depends on the large amount of starch it contains (table, page [16]).

Leguminous Foods.—The chief seeds belonging to this group are peas, beans, and lentils. They contain a smaller proportion of starch, and a larger proportion of nitrogenous materials than cereals. Thus while flour contains 9.5 and bread 8 per cent. of proteid, lean meat 15.18 per cent., and cheese about 30 per cent., peas and beans contain 21 to 26 per cent. (green peas only 4 per cent., dried peas 21 per cent.) of proteid. The nitrogenous material exists chiefly as legumin, which has been called vegetable casein. Although leguminous seeds contain more nutritive material in a given weight than cereals, dietetically they are inferior, owing to the fact that they are less digestible, often causing flatulence and other dyspeptic symptoms. Cereals, again, are more palatable than leguminous seeds, and are more prolific, and consequently cheaper. In the absence of animal food, legumens form a useful substitute. They are advantageously diluted with oily substances, or with rice. The farm-labourer’s dish of broad beans and fat bacon is founded on strict physiological principles. A mixture of lentil and barley flour is sold under the name of Revalenta Arabica. Lentil flour costs 2½d., Revalenta 3s. 6d. per lb. Green peas, French beans, and scarlet runners are much more easily digested than are dried peas or beans. Lentils contain the largest proportion of proteid of any of the pulses. They also contain very little sulphur, and so do not give rise to the same liberation of sulphuretted hydrogen in the intestine, as other pulses. The ash of the Egyptian lentil is particularly rich in iron.

Amylaceous Foods. Amylaceous or starchy substances are contained in many of the preceding foods; but some other foods consist almost entirely of starch. The chief of these are sago, tapioca, and arrowroot.

Sago is obtained from the pith of the stems of various species of palm; a single tree may yield several hundred pounds. Alone it is easy of digestion. Boiled with milk it forms a light, nutritious, and non-irritating food. Fictitious sagos are frequently sold, made from potato starch.

Tapioca and Cassava are derived from the tubers of more than one species of the poisonous family, Euphorbiaceæ. The juices are removed, and the prussic acid removed by heat. Tapioca only differs from cassava in being a purer form of starch; the latter is more nutritious, and among the Indians takes the place of bread.

Arrowroot is obtained from the tubers of Maranta Arundinacea.

Tous-les-mois is a form of starch obtained from the tubers of a West Indian plant, the Canna edulis.

Fig. 1.—Different Forms of Starch Granules.
Potato. Wheat. Rice.
Oats. Barley. Pea.

The detection of the varieties of starch is usually possible owing to their fairly characteristic appearance under the microscope. Fig. 1 shows the most important starches. It must be noted that in oats, maize, and rice the contour is completely marked by facets or surfaces, while there are less complete markings in tapioca and sago. In wheat, rye, pea, bean, barley, potato, and arrowroot the contour is even, though there are minor differences of size and shape.

Other Vegetable Foods.—Green Vegetables contain comparatively little nutriment, but form valuable additions to other foods. Cellulose, which forms their main constituent, although indigestible, forms a bulk in the alimentary canal, which is necessary to ensure peristalsis. Concentrated nourishment can only be digested in limited quantity, and is very apt to produce digestive disorder. Cabbage contains 92 per cent. of water, and 2½ per cent. nitrogenous matter. Carrots contain 6 per cent. and turnips 2 per cent. of nitrogenous matter; parsnips are intermediate between these. Green vegetables possess valuable anti-scorbutic properties. They may be made an important vehicle for giving fatty food, by adding butter, etc.

Rhubarb and sorrel contain oxalates and tartrates of potash and lime, to which they owe their tartness. Spinach is cooling and laxative, like rhubarb, but not tart. Sea-kale, artichoke, and asparagus are all wholesome vegetables. Asparagus is somewhat diuretic, and gives a peculiar, disagreeable odour to the urine. Salads, such as mustard and cress, water-cress, endive, and the garden lettuce are very useful as anti-scorbutics. Some of them possess a peculiar pungency due to a volatile oil analogous to that contained in horse-radish.

The Potato contains 26 solid parts in 100, of which nearly 20 are starch and 2½ nitrogenous matter. It forms one of our best-appreciated vegetable foods, and as it possesses valuable anti-scorbutic properties, its universal use is, perhaps, the chief cause of the present rarity of scurvy. Alone, it possesses too small a proportion of nitrogenous material to support life, but the addition of butter milk makes up this deficiency; and these two together form a sufficient diet to maintain life and health for a long time.

The Onion, Garlic, Leek, and Shalot, all members of the lily family, are chiefly used as condiments. They contain an acid volatile oil, which gives them a peculiar odour and flavour. By long boiling, this is dissipated (as in the case of the Spanish onion), and the onion is then fairly digestible, as well as nutritious.

Celery possesses a more delicate flavour and odour than the preceding, but even the most tender celery is digested with difficulty; less so, when boiled or stewed, or a constituent of soups.

Only four Fungi are, with us, commonly regarded as safe—mushrooms, champignons, morels, and truffles; but there are many others which are equally edible. The food value of fungi has been exaggerated. They are difficult of digestion and contain little nutritive material. Poisonous fungi usually have an astringent styptic taste and a disagreeable pungent odour. In any doubtful case it is better to abstain.

Oily Seeds contain a considerable amount of fixed oil which renders them unfit for persons of weak digestion. The almond, walnut, hazel-nut, and cocoa-nut are common examples. The sweet almond, when eaten unbleached, occasionally produces nettlerash, and its solid texture and large proportion of fixed oils render it difficult of digestion. The chestnut contains less oil, but a large amount of carbohydrate. It is extensively used as a food in Italy and some other countries. In the uncooked condition it is very difficult of digestion.

Fruits are chiefly used as adjuncts to other foods; but the vegetable salts and the cellulose and sugar which they contain, make them very valuable. Cucurbitaceous fruits are used as vegetables rather than as fruits. Vegetable marrow is wholesome and agreeable, but not very nutritive. Cucumber is most digestible when rapidly grown and freshly gathered.

Stone-fruits or drupes, such as the peach, nectarine, plum, cherry, are rather luxuries than foods, like many other fruits. Before ripening they are unfit for food; when ripening is complete, the acids and astringent matter largely disappear. The date contains chiefly sugar, and forms an important food in the East.

Pomaceous Fruits, as the apple, pear, and quince, are more digestible when cooked; and, speaking generally, all fruit not perfectly ripe should be cooked before eating. The presence of vegetable acids in fruit soon converts the sucrose of cane sugar into dextrose, a less sweet variety of sugar. It is therefore more economical to sweeten after than before cooking.

The chief Berries are the grape, currant, gooseberry, cranberry, and elderberry. The grape is the most important, and 1,500 varieties of it have been described. Its juice contains a large amount of grape sugar (dextrose), and small quantities of glutinous material, bitartrate of potash, tartrate of lime, malic acid, etc.

Besides the above fruits, we have strawberries, mulberries, figs, plantains, melons, etc., which are all refreshing and anti-scorbutic. The orange family furnishes us with the orange, lemon, citron, lime, shaddock, and pomelo, of which the orange is by far the most important, and possesses most valuable refreshing qualities.

Sugar exists in two chief forms, viz. sucroses and glucoses. Sucroses, known chemically as disaccharids (Sucrose = C₁₂H₂₂O₁₁; compare starch = C₁₂H₂₀O₁₀) are exemplified in cane, beet, maple, malt (maltose), and milk sugar (lactose). Cane sugar has been gradually displaced by beet sugar. The two are chemically identical, and equally nutritious. Maltose is given in malt extract as a food, and because of the digestive action of the ferment also contained in the extract on starchy food. Thus:—

STARCH.MALTOSE.
C₁₂H₂₀O₁₀ + H₂O = C₁₂H₂₂O₁₁.

Lactose is comparatively free from sweetness, and is hardly capable of being fermented by yeasts.

Of Glucoses the best example is dextrose = C₆H₁₂O₆, H₂O, which can be seen crystallised in dried raisins; it only possesses one-third the sweetening power of sucrose. Starchy food becomes changed into glucose by the action of saliva and pancreatic juice in the alimentary canal. Grapes, cherries, gooseberries, figs, and honey contain lævulose in addition to glucose (glucose = C₆H₁₂O₆, H₂O, lævulose = C₆H₁₂O₆). Lævulose resembles dextrose except in being uncrystalline, and in its effect on polarised light. Many ripe fruits, such as pineapples, strawberries, peaches, citrons, contain sucrose and lævulose, the latter being not quite so sweet as sucrose.

In the alimentary canal sucroses are inverted into dextrose and lævulose. Thus natural foods containing these sugars are more readily assimilated than those containing sucrose.

The sweetening power of the varieties of sugar depends on their degree of solubility in water. Sucrose is soluble in one-third of its weight of cold, and in rather more of hot water. Dextrose is soluble in its own weight of water; lævulose is more soluble, and therefore sweeter than dextrose. Lactose requires five to six parts of cold and two of hot water, and is therefore not so sweet as the other varieties.

[CHAPTER IV.]
DISEASES DUE TO FOOD.

Diseases may arise from the noxious character or from deficiency or excess of some particular food, or of the food as a whole.

Diseases from Unwholesome Food.—I. The Meat of Diseased Animals.

(1) The flesh of animals which have not been slaughtered should be prohibited from sale, whether death has resulted from accident or disease. The meat from diseased animals is also generally dangerous, sometimes owing to the drugs with which the animals have been dosed before death, e.g. tartar emetic, or opium.

(2) Meat may be unwholesome from the presence of parasites. Of these the most common is—

(a) The cysticercus cellulosæ, which is the undeveloped embryo of the tape-worm; that from the pig becomes the tænia mediocanellata. The cysticercus of the pig is the most common; it forms a cyst about the size of a hemp-seed, commonest on the under surface of the tongue. In hams oval holes are found or opaque white specks, which are the remains of the cysts converted into calcareous matter. When meat containing the cysticercus alive (as in under-cooked or raw meat) is swallowed, it develops into the tape-worm, which consists of a number of flat segments, each capable of producing numerous ova of new cysticerci, with a minute head at the narrow end surrounded by hooklets. A temperature of 174° F. kills the cysticercus. Another kind of tape-worm common on the continent, called bothriocephalus latus, is derived from the cysticercus of fish.

Fig. 2.
Cysticercus (“Measles”) in Pork.
(Natural Size.)

(b) The trichina spiralis is not a solid worm like the tænia, but possesses an intestine. In pork it forms a minute white speck, just visible to the naked eye, which forms a nest, and in this one or two coiled up worms can be seen by a magnifying glass in active movement. They are effectually killed by the temperature of boiling water; but no form of drying, salting, or even smoking at a low temperature is sufficient for this purpose. Boiling or roasting does not suffice to destroy all the trichinæ unless the joint is completely cooked in its interior. When trichinous pork is swallowed, the eggs develop in the alimentary canal in about a week into complete worms, and in three or four days more each female produces over a hundred young ones. These burrow into every part of the body, producing great irritation and inflammation. In one case after death upwards of 50,000 worms were estimated to exist in a square inch of muscle. Most of the cases of trichinosis have occurred in Germany, from eating imperfectly cooked sausages. The pig becomes trichinous by eating offal, and man is infected by eating pork. This disease is rare in England.

Fig. 3.
Trichinæ Capsulated in Flesh.
Magnified.

(3) Tuberculous Meat, from animals suffering from tuberculosis, has been found to cause tuberculosis in small animals experimentally fed on it. Koch has recently thrown doubt on the communicability of bovine tuberculosis to man; but this point must be regarded as still unsettled (see page [312]). Sheep are rarely affected by it, but it is very common in cattle, especially in cows, and it is a serious economical question whether the meat of all such animals should be condemned. The ideal would be to condemn all such animals, as tuberculosis is an infective disease, and the bacillus which causes it (as well as the toxic products of its activity) may be present in meat which shows no actual signs of disease, except in the lungs or other internal organs. In practice, however, the rules laid down by the Royal Commission on Tuberculosis, in 1898, should be followed for the present. These state that:—

“The entire carcase and all the organs may be seized (a) when there is miliary tuberculosis of both lungs, (b) when tuberculous lesions are present on the pleura and peritoneum, or (c) in the muscular system, or in the lymphatic glands embedded in or between the muscles, or (d) when tuberculous lesions exist in any part of an emaciated carcase. The carcase, if otherwise healthy, shall not be condemned, but every part of it containing tuberculous lesions shall be seized (a) when the lesions are confined to the lungs and the thoracic lymphatic glands, (b) when the lesions are confined to the liver, (c) or to the pharyngeal lymphatic glands, or (d) to any combination of the foregoing, but are collectively small in extent.” They also add that any degree of tuberculosis in the pig should secure the condemnation of the entire carcase, owing to the greater tendency to generalisation of tuberculosis in this animal; and that in foreign meat, seizure should ensue in every case where the pleura has been “stripped.” (See also page [312].)

(4) Other Infective diseases besides tuberculosis may render meat wholly or partially unfit for food. Of these pleuro-pneumonia may not require condemnation of the entire carcase; but in the following this course should be adopted, cattle-plague, pig typhoid (pneumo-enteritis), anthrax, and quarter ill, as well as in sheep-pox. In puerperal fever, actinomycosis, and sheep-rot (liver flukes) each case must be decided on its merits.

II.—Decomposed Meat.—Putrid meat has often produced diarrhœa and other severe symptoms. Putrid sausages are especially dangerous, and incipient putridity seems to be more dangerous than advanced.

Tinned Meats occasionally produce severe illness, which has been in several cases fatal. It is important to secure a good brand, and to eat the meat as early as possible after the tin is opened. Tins in which any bulging is present, showing the presence of putrefactive gases, must be rejected; and still more tins which have been pricked and resoldered in a second place. All tinned meats and fruits are stated by Hehner to contain compounds of tin in solution. These do not seem to be perceptibly injurious, unlike lead salts, which are now rarely found.

The general subject of Meat Poisoning has had much light thrown on it during the last few years. Brieger, about 1886, showed that during the cultivation of bacteria, alkaloidal bodies known as ptomaines and leucomaines, were formed, which were virulently poisonous. It was commonly supposed that the poisoning occasionally produced by eating meat pies, sausages, hams, brawn, and similar food, was due to these ptomaines. It is now known, however, that there are far more important toxines than the alkaloidal, which result from bacterial life in meat, etc. (see page 286). These are more closely related to substances of an albuminous or proteid nature than the ptomaines. These toxines may be fatal when as small a dose as a fraction of a milligramme (mgm. = about ¹ ∕ ₆₄ grain) is given subcutaneously. The evidence now shows that neither ptomaines nor other toxines (albumoses) or any other bacterial products besides these, cause the outbreaks of acute poisoning occasionally traced to food, but that these are due to bacteria. There is, in other words, actual infection, as well as poisoning. The microbe chiefly found as the cause of these outbreaks is the Bacillus enteritidis of Gaertner, and some allied microbes. In an outbreak at Oldham, 160 pies made on a Thursday, from the veal of a calf killed on the preceding Tuesday, were baked in several batches, and of the persons eating these pies fifty-four became ill. That the contamination was not introduced after cooking was shown by the fact that several persons were made ill who ate pies still warm from baking. The facts indicated that one batch was imperfectly cooked, the time allowed being only twenty minutes, as compared with fifty minutes allowed in corresponding cooking in domestic life. Experimentally it has been found that an exposure for one minute to 70° C. kills the Bacillus enteritidis of Gaertner. That this bacillus was the cause of the outbreak was subsequently shown by the fact that the serum of blood taken from some of the patients showed characteristic clumping with a pure culture of this bacillus, just as happens with the blood of a patient suffering from enteric fever when a cultivation of the microbe of this fever is mixed with it (see page [301]). In this outbreak the symptoms were usually diarrhœa, vomiting, intense thirst, desquamation of the skin, and a slow convalescence, lasting from three to six weeks. (See page [26] for poisoning by Bacillus enteritidis sporogenes.)

III.—Meat injuries from the food eaten before killing.—Pheasants fed on laurel, hares on rhododendron chrysanthemum, and other animals fed on the lotus, wild cucumber, and wild melon of Australia, have caused dangerous symptoms.

IV.—Fish, especially some kinds, occasionally produce nettlerash and other disorders, especially in warm weather. Leprosy has been ascribed to the eating of decomposing fish, but it occurs in countries where a fish diet is impossible.

Shell-fish and crustaceans (as lobster, crab) are very prone to produce evil results. Shell-fish (mollusca), such as mussels, cockles, and oysters, are dangerous foods. They are generally grown in estuaries, to which the sewage of towns has access; and not infrequently cases of enteric (typhoid) fever, as well as more acute attacks of diarrhœa and vomiting, have been traced to them. Mussels and cockles are seldom sufficiently cooked to render them safe; and oysters are eaten raw. They should never be eaten, unless from personal direct knowledge it is certain that they have been derived from an estuary in which there was no possibility of contamination by sewage.

V.—Milk has been a common carrier of disease. Cows eating the rhus toxicodendron get the “trembles,” and their milk produces serious gastric irritation in young children. The milk of goats fed on wild herbs or spurgeworts has produced severe disorders.

The milk of animals suffering from foot-and-mouth disease, although frequently drunk with impunity, occasionally produces inflammation of the mouth (aphthous ulceration). The milk derived from cows fed on grass from sewage farms is, per se, as wholesome as any other, and its butter has no more tendency to become putrid than that derived from any other source.

The great dangers in respect to milk are of its becoming mixed with contaminated water; or of its absorbing foul odours. The absorptive power of milk for any vapour in its neighbourhood, is shewn by exposing it in an atmosphere containing a trace of carbolic acid vapour: the milk speedily tastes of the acid.

Milk also tends to undergo rapid fermentative changes, especially in warm weather, or when tainted by traces of putrefying animal matter. Diarrhœa in children is frequently due to such a condition, or to the rapid decomposition of milk in an imperfectly cleaned bottle. Milk should always be boiled in warm weather; and it should never be stored in ill-ventilated larders, or where there is a possibility of the access of drain effluvia; nor ought it to be kept in lead or zinc vessels.

Epidemic diarrhœa has been ascribed by Klein to a microbe called the Bacillus enteritidis sporogenes. This is not killed by heating the liquid containing it to 80°C. for twelve to fifteen minutes, as is the typhoid bacillus and other non-spore-forming bacilli. In an outbreak of diarrhœa among the patients in St. Bartholomew’s Hospital, London, there was strong evidence that this microbe taken in rice pudding had caused the mischief. Eighty-four patients and two nurses were attacked, and the patients who had eaten rice pudding were almost exclusively attacked. A portion of this pudding after being kept twenty-four hours was found sour and acid. The Bac. enteritidis sporog. was found in it. Furthermore it was shewn that the temperature at which the rice puddings were cooked never exceeded 98°C., whereas the spores of this microbe withstand 100°F. a considerable time.

Very many epidemics of enteric fever and scarlet fever, and a smaller number of epidemics of diphtheria have been traced to contaminated milk. Usually in enteric fever the contamination of the milk was traced to the use of water “for washing the milk-cans,” derived from specifically polluted sources, and doubtless the water was the real source of the disease. In most of the milk outbreaks of scarlet fever, either there was scarlet fever in the dairy, or persons employed in the dairy were in attendance on patients suffering from the disease; but in an outbreak connected with a supply of milk from Hendon, it was suspected that a certain eruptive disease of the udders of the cow might have been the cause of scarlet fever in man, without infection from a previous case of the disease. This point is still sub judice.

Tubercular disease of the intestines and mesenteric glands may be produced by taking milk derived from tuberculous cows. This was proved in the case of calves (page [311]), and there are strong reasons for thinking that the same is true for infants, though doubt has been thrown by Koch on the communicability of bovine tuberculosis to the human being. The only safe plan is to sterilise the milk (page [13]).

VII.—Vegetable Food (especially greens) is indigestible if stale, and all mouldy vegetables are dangerous. Over-ripe and rotten fruit is liable to produce diarrhœa; but the diarrhœa prevalent in summer is due much less to this than to other decomposing foods, particularly milk.

Poisonous symptoms have been produced by the admixture of darnel (lolium temulentum) with flour.

The eating of damaged maize in Italy is the cause of an endemic skin disease, called pellagra, which commonly proves fatal.

Ergotism is due to the growth on cereals (and most commonly on the rye) of a poisonous fungus, the claviceps purpurea, which produces a deep purple deposit on the grain. If bread made from such flour is eaten for prolonged periods, severe symptoms result; in some cases, a dry rotting of the limbs. There have been several epidemics on the continent, due chiefly to eating bad rye bread.

Starvation Diseases.—Simple Starvation causes death in a period varying with the previous state of nutrition. Usually death occurs when the body has lost two-fifths of its weight, whether this be after days, months, or years (Chossat). A supply of water prolongs the duration of life, to as much as three times what it would otherwise be. Good nourishment doubles the power of resisting disease; while deficient food prepares the way for many diseases. A large share of the decline in the English death-rate during the last forty years is due to free trade, and the great cheapening of wholesome food which has resulted from it.

An ill-balanced is more frequent than a deficient diet. Deficiency of fat is more serious than deficiency of carbohydrates, and deficiency of proteid is most serious.

Scurvy is caused by the absence of fresh vegetables. The use of the potato and the orange, as well as of lime juice (the juice of citrus limetta), has led to its extinction among adults in this country. In former times, it caused more deaths among seamen than all other causes put together, including the accidents of war. In infants fed upon tinned foods, whether condensed milk or patent foods, a form of scurvy still occurs. Infants fed on new-milk never suffer in this way. If, therefore, it is necessary to feed an infant on condensed milk for many consecutive months, potato gruel or raw meat juice or fresh milk must occasionally be given.

Rickets is chiefly due to improper feeding in childhood. The substitution of artificial foods (most of them containing starch) for the natural milk is its chief cause. The lower incisor teeth of an infant appear between the sixth and seventh months. Starchy food given before this age is undigested. Such food likewise leads to less fat and proteid being given, which are essential for growth. Deficiency of lime salts in the food does not cause it, and giving them in food or medicine will not cure it. Enrichment of the diet by cream or failing this by cod liver oil is the best means of preventing and curing it. Abundant fresh air and warm clothing are also necessary.

Relapsing fever generally follows epidemics of typhus fever, and is greatly favoured by starvation. Ophthalmia has been chiefly prevalent in charity schools in which the children are underfed, though its essential cause is contagion.

Diseases Connected with Over-Feeding.—A fire may go out for want of fuel, or from becoming choked with ashes; and it is the latter state of things which occurs in Gout and allied diseases. Weakness is commonly complained of, but this is due to excess of food embarrassing vital action; and abstinence and exercise are required to restore the balance. Excess of nitrogenous food—especially if combined with the use of sweet, or strong, or very acid wines, and beer—is particularly prone to produce gout. In these cases, animal food should only be taken once a day, and vegetable food should be allowed to preponderate.

Obesity is favoured by excess of starchy food and sugar, and by copious drinking of water or other beverages. The plan of curing obesity by restricting oneself almost entirely to meat food is only advisable, however, under certain conditions. Gall-stones are favoured by rich foods and excess of sugar; also by alcoholic indulgence. Dyspepsia is commonly due to loading the stomach at too frequent intervals; but on the other hand, it not infrequently leads to the taking of insufficient food, because of the discomfort produced. The result of this is that a chronic starvation results, with impaired vital powers. Dyspeptic patients should abstain from pastry and from tea and coffee, except in small quantities. Alcohol in any form, as a rule, does harm. Not uncommonly mastication is imperfectly performed, and a good dentist may cure the indigestion which has resisted all other treatment.

[CHAPTER V.]
DIET.

The importance of a duly proportioned and sufficient dietary is shown by its great influence on health and constitution. An ill-proportioned or deficient diet is certain to lead to failure of health. The anatomy of an animal may be modified in the course of generations by altered diet, as well as its character; thus, the alimentary canal of the cat has increased in length to adapt it to its omnivorous habits. In the case of the bee we have a still more remarkable instance. If by any accident the queen bee dies, or is lost, the working bees (which are sexually undeveloped) select two or three eggs, which they hatch in large cells, and then feed the maggot on a stimulating jelly, different from that supplied to the other maggots, thus producing a queen bee.

The food of mankind varies naturally with—

I.—Climate. A cold climate leads to increased metabolism, and consequently a large amount of fatty matter can be eaten without producing nausea. Witness the difference between a Laplander’s and a Hindoo’s diet.

The season of the year has likewise some influence. Vital processes are more active in spring than autumn, and more food is consequently required in the former season.

II.—Occupation. Although muscular exercise is not associated with an immediate increase of elimination of urea, yet as a matter of experience more nitrogenous food is required and can be metabolised by hard workers than by idlers. The trappers on the North American prairies can live for weeks together on meat alone, accompanied by copious draughts of tea. They are constantly in the open air, undergoing fatiguing exercises, in a dry and rare atmosphere. For brain workers no special food is required. Foods containing phosphorus have no special value, so far as is known, for mental work. Such work, however, is apt to affect digestion; consequently the digestibility of food is more important for those engaged in sedentary occupations than its chemical composition.

III.—Sex. As a rule, women require about one-tenth less food than men, but probably this rule hardly holds good in the case of women engaged in laborious work.

IV.—Age. Infants require only milk, and the less they have of any other food before a year old the better. Atwater has calculated that——

• A child under 2 requires ³ ∕ ₁₀ the food of a man doing moderate work.
• A child of 3 to 5 requires ⁴ ∕ ₁₀ the food of a man doing moderate work.
• A child of 6 to 9 requires ⁵ ∕ ₁₀ the food of a man doing moderate work.
• A child of 10 to 13 requires ⁶ ∕ ₁₀ the food of a man doing moderate work.
• A girl of 14 to 16 requires ⁷ ∕ ₁₀ the food of a man doing moderate work.
• A boy of 14 to 16 requires ⁸ ∕ ₁₀ the food of a man doing moderate work.

Vital processes are more active in early life, and food is required not only to carry on the functions of the body, but also to furnish the materials for growth. Hence, while the proportion of proteids to carbohydrates and fats should be—

As 1:5.3 in adults, it should be about as 1:4.3 in children.

After the age of thirty-five or forty, the tendency is to take too much food. All the tissues of the body are established, and excess of food (especially nitrogenous food) is liable to produce tissue degeneration by loading the system with partially metabolised matter, and may lead to gouty diseases. It is much safer to take what may be regarded as too little than too much food after this period.

Times for Eating.—The best arrangement seems to be to have three meals, each fairly nutritious, and containing all the constituents required. The Romans only had two meals daily, prandium and cœna. This is common among the French at present, but it tends to overloading the digestive organs at these meals.

An ordinary full meal has usually passed from the stomach in four hours. Fresh food ought never to be introduced before this period; it is advisable to allow an interval of five hours between meals for the healthy, so as to give time for the digestive organs to rest, and for the absorption of food. The practice of taking tea with the chief meal, or a “meat tea,” is bad. Tea is better taken an hour or two after food.

Regularity in the time of taking meals is important, as the digestive organs acquire habits like other parts of the body. Work ought not, if possible, to be resumed immediately after meals, nor active exercise of any kind. These tend to abstract blood from the digestive organs, and so diminish the efficiency of digestion.

Vegetable and Animal Foods.—The fact that the food we require can be obtained from the vegetable world has led to the proposition that vegetable food should be taken alone. It is urged in favour of this plan, that a large amount of suffering to animals would be prevented. Also that animal food is not so economical as vegetable, land being more economically employed in producing corn than in feeding cattle. Thirdly, there is the indubitable fact that health can be maintained for prolonged periods on vegetable food (including nuts, cereals, fruits, etc.)

On the other hand, the chief objections to a purely vegetable diet are that the undigested refuse is greater than with an equal quantity of animal food; that a longer time and more exertion than for animal foods are required in digesting the most nutritious vegetable foods, such as legumens, while other vegetable foods do not contain a sufficient proportion of nitrogenous material. Also, if one lived entirely on vegetable food, a greater bulk would be required, and owing to the fact that such food is less easily absorbed, satisfaction to the appetite would not so soon be produced. Animal food has a great advantage as regards convenience. Man is not an eating machine; he requires food which is easily converted into the body substance, and this is supplied by the flesh of animals, milk and eggs, with a due proportion of non-nitrogenous food; sheep and oxen work up indigestible vegetable materials into easily assimilable mutton and beef. The greater convenience of animal food as a supply of proteid is shown by the following examples of foods after the removal of water:—

On the other hand, vegetable foods are a cheaper source, not only of carbohydrates and fats, but also of proteids as well. Thus the approximate cost of—

Under the ordinary conditions of town life, there is considerable danger of indulging in an excess of nitrogenous food, and vegetarians may therefore do good by showing that meat is not absolutely necessary, and can often with advantage be largely replaced by vegetable food.

If we include milk, cheese, and eggs in the vegetarian diet, the objections to it partially disappear; and it would be well if it were much more widely known, especially among the poor, that on these, together with vegetables, health can be maintained with the addition of little or no meat.

The Determination of Diet.—The first principle in making a dietary is that it must be mixed, containing all the necessary constituents, proteids, hydrocarbons, carbohydrates, water, and salts. No one of these alone will support life for any considerable period. Carbohydrates (sugar and starch) can be most easily dispensed with; fats, on the other hand, are essential for the maintenance of health.

The next point is to ascertain the proportion in which these different foods are required. Salts are commonly taken with other foods, common salt being the only one taken alone. The amount required is given on p. 7. The amount of water required varies with the season of the year, the amount of exercise and perspiration, and other factors. As a rule, not more than two pints of water are required per day, and still less if fruit is freely taken. We may therefore confine our attention to the carbonaceous and nitrogenous foods, and try to ascertain the amount of each of these required. Every diet must be subjected to the following tests, to fully ascertain its value:—

1. The Chemical Test.—The metabolism undergone by food in the body being essentially a process of oxidation (though partially modified and incomplete), the amount of heat yielded on complete combustion of a food may be taken as a measure of its value as a source of energy, of which heat and work are convertible forms. The standard of heat production is the calorie, the amount of heat required to raise the temperature of one gramme of water 1° C. This is the small calorie. The kilo-calorie (called the Calorie) is the amount of heat required to raise 1 kilo (1 litre) of water 1° C., or 1 lb. of water 4° F. In calculations on this basis, allowance must be made for foods which are incompletely oxidised in the body. Rubner has shown that the heat value of 1 gramme (=15½ grains) of each of the chief food stuffs is as follows:—

The method of applying this standard to a food is as follows: the percentage of proteid or carbohydrate given in the following table is multiplied by 4.1, and the percentage of fat by 9.3:—

Thus for bread—

The total fuel value in Calories of one pound of certain typical foods is given by Hutchison as follows:—Butter 3,577, peas 1,473, cheese 1,303, bread 1,128, eggs 739, beef 623, potatoes 369, milk 322, fish (cod) 315, apples 238.

2. The Physiological Test.—Not only is a proper proportion of proteid, fat, and carbohydrates required, but these must be capable of digestion and absorption and of oxidation in the body. Cheese is a highly concentrated food, but its value is less than its percentage composition would indicate, because of the difficulty of digesting considerable quantities of it. Green vegetables consist largely of cellulose, which is only imperfectly capable of absorption into the blood, although it can experimentally be oxidised by combustion. The proportion between absorbed food and food rejected in the fæces can be ascertained by analysis. Many experiments made on these lines show that on a purely animal diet (meat, eggs, milk) but little nitrogen is lost, while with vegetable foods (carrots, potatoes, peas, etc.) the waste of nitrogen is considerable. Fats are very completely absorbed from the alimentary canal. The amount remaining unabsorbed is greatest with mutton fat (10 per cent.), least with butter (2½ per cent.). Experimentally it has been found that an amount up to 150 grammes (about 5½ oz.) of fat can be absorbed without appreciable loss. Carbohydrates are very completely absorbed, even starchy foods rarely escaping digestion. Completeness of absorption from the alimentary canal is not desirable for all foods; a certain amount of unabsorbed residue is required to stimulate peristalsis. With a purely vegetable diet this amount is excessive, and there is physiological waste of effort.

3. In practical dietetics the Economic test is important. Carbohydrate is by far the cheapest food, and generally vegetable are cheaper than animal foods. Thus a shilling’s-worth of bread yields 10,764 Calories, while the same sum spent on milk would only yield ¹ ∕ ₃, and on beef ¹ ∕ ₁₀ this number of heat units. Similarly a shilling’s-worth of peas contains 572 grammes of proteid, about double as much as the same money’s-worth of cheese; while to obtain the same amount of proteid from eggs would cost more than eight, and from beef more than five times as much as from peas (Hutchison). The market price of foods is no certain indication of their nutritive value. Thus haddock will supply as much nutriment as sole at a fourth of the cost; Dutch as much nutriment as Stilton cheese at less than half the cost. Similarly the most economical fats are margarine and dripping.

4. An Examination of Actual Dietaries under various conditions has strikingly confirmed the results obtained by other methods. It has been found that (a) the potential energy required by a healthy man weighing 11 stones, and doing a moderate amount of muscular work is 3,000 to 3,500 Calories (=310 grains); and that (b) about 20 grammes of nitrogen and 320 grammes (=4,960 grains) of carbon are excreted by such a man. (c) Expressing the 3,000 Calories required in terms of grammes of food, it is found that 125 grammes of proteid, 500 of carbohydrate and 50 of fat are necessary. These facts are expressed in the following table (Hutchison):—

Three of the best known standard dietaries give the amounts in grammes of each food constituent as follows:

Expressing the same facts in English ounces instead of grammes, ⁴² ∕ ₅ oz. of proteid, 2½ oz. of fat, and 18 oz. of carbohydrate, would represent the ounces of each constituent required according to

The chief point of divergence in the above standard dietaries is in the relative proportion of carbohydrate and fat. Probably the correct proportion between these is as 1 to 10; but it will vary according to climate and other circumstances. Detailed examination of a large number of dietaries shows that the amount of daily proteid should be about 125 grammes, or 4⅖ozs. This is contained in 20 eggs, or in 18 oz. i.e. about 4½ ordinary platesful of cooked meat.

It must be noted that the 23-24 oz. of food given above as the standard daily amount represents dry food. This represents 40 oz. or nearly 3 lbs. of ordinary food.

The following example by Waller, gives a rather liberal standard English diet, for a man doing a moderate amount of muscular work.

This divided up into meals works out roughly as follows (Hutchison):—

Breakfast		Two slices of thick bread and butter.
		Two eggs.
Dinner		One plateful of potato soup.
		A large helping of meat with some fat.
		Four moderate sized potatoes.
		One slice of thick bread and butter.
Tea		A glass of milk and two slices of thick bread and butter.
Supper		Two slices of thick bread and butter and 2 oz. of cheese.

From the preceding data, practical problems as to dietaries are easily solved. Thus if it be required to find
how much oatmeal, milk, and butter would be required to give a sufficient quantity of albuminoids, fats, and carbohydrates to an adult male,
the calculation may be based on the figures in the table on p. 32, or the following figures may, for the sake of convenient calculation, be taken as representing the percentage amount of each of these chief food principles contained in the foods named:—

• Let
• o = number of ounces of oatmeal required.
• m = number of ounces of milk required.
• b = number of ounces of butter required.
• Then
• (12o + 4m + 2b ∕ 100 = 4.5 ozs. of albuminoid
• (6o + 3m + 88b)/100 = 3 ozs. of fat
• (60o + 5m)/100 = 14.25 ozs. of carbohydrate,

according to Moleschott’s diet.

When these equations are worked out by substitution and transference—

• o = 19.2 ounces.
• m = 55.4 ounces.
• b = 0.24 ounces.

Similarly if it is required to find how much meat, bread, and butter of the following percentage composition will be required to give a man a sufficient amount of albuminoids, fats, and carbohydrates.

• Let
• m = number of ounces of meat required.
• b = number of ounces of bread required.
• B = number of ounces of butter required.
• Then
• (12m + 8b + 2B)/100 = 4.5 ozs. of albuminoid
• (15m + 1.5b + 88B)100 = 3 ozs. of fat
• 50b ∕ 100 = 14.25 ozs. of carbohydrates

When these equations are worked out—

• m = 6.28 ounces.
• b = 28.5 ounces.
• B = 1.15 ounces.

Relation of Food to Mechanical Work.—In the body the movements of every part are constant sources of heat. It is evident therefore that the potential energy of food can be expressed by (a) the amount of heat obtained by its complete combustion, or (b) by the amount of work capable of being obtained from it. Joule discovered by exact experiment that the mechanical power obtainable from a given amount of fuel is directly proportional to the amount of fuel used, being in fact due to the oxidation of this fuel, the heat produced being transformed into mechanical power. The heat unit or calorie has been already given (p. 32). The gram-metre is the work unit. The heat unit corresponds to 425.5 units of work. Thus the same energy required to heat one gramme of water 1° C. will raise a weight of 425.5 grammes to the height of 1 metre. Conversely a weight of 425 grammes if allowed to fall from a height of 1 metre, will by its concussion produce heat sufficing to raise the temperature of 1 gramme of water 1° C. In England the amount of work done is commonly expressed as foot tons, i.e. tons lifted one foot; while in France it is similarly expressed as kilogrammetres. Gramme-metres can be converted into foot-pounds by multiplying them by .007233, and kilogrammetres into foot-tons by dividing by 311.

Frankland estimated that—

In practical dietetics digestibility of food as well as chemical composition is an important factor. Furthermore metabolism in the body is not in every instance so complete as oxidation outside it. Hence estimates of potential energy can only be regarded as theoretically correct. Examination questions like the following are occasionally asked:—

A man does work equal to 176.8 foot-tons in a day. Supposing that he eats only bread, how much will he require to give the amount of energy required, if bread contains 8 per cent. proteid, 1.5 per cent. fat, and 49.2 per cent. carbohydrate?

On the above basis, from 100 ounces of bread the amount of potential energy obtainable is:—

Let b = number of ounces of bread required to develop 176.8 foot-tons of energy.

Then 8,601: 100:: 176.8: b.

Therefore b = 2.05 ounces.

[CHAPTER VI.]
THE PREPARATION AND PRESERVATION OF FOOD.

Objects of Cooking.—Food may be taken in its crude condition, as directly derived from the animal or vegetable world, or after it has undergone a preparatory process of cooking. Man is the only animal who cooks his food. Many foods, in the uncooked condition are almost entirely incapable of digestion by him—such as the proteid and farinaceous materials contained in the seeds of cereal and leguminous plants. But cooking, as a preparatory help to the digestion of food, is not equally required by all foods. Thus, fruit is commonly taken uncooked, and does not undergo any important alteration on cooking. Salads are taken uncooked, but not for their nutritive properties so much as for a relish to other foods, and for their quasi-medicinal properties. Milk, again, may be taken cooked or uncooked. The oyster is the only animal which is eaten habitually, and by preference, in the uncooked condition; and there is a physiological reason for this universal custom. The large fawn-coloured liver, which constitutes the delicacy of the oyster, is little else than glycogen, associated with its appropriate ferment diastase, so that the oyster is almost self-digestive. When cooked, the ferment is destroyed, and digestion of the oyster becomes more difficult.

Cooking is intended—1. To make the food softer, and in part to mechanically disintegrate it, thus rendering it more easily masticated and digested. In fact, cooking, in the best sense, is an artificial help to digestion; and digestion may well be said to commence in the kitchen.

2. To produce certain chemical changes. Thus, starch is partially converted into dextrine; gelatin is formed from connective tissue, etc.

3. To destroy any noxious parasites present in the food, or obviate any ill effects from putrefactive changes. Diseased meat chiefly produces bad effects when imperfectly cooked.

4. To make the food more pleasant to the eye and agreeable to the palate. The improved savour in cooked meat, for instance, has a very appetising effect, and consequently makes digestion easier.

The Cooking of Flesh.—1. Roasting is, perhaps, the most perfect way of cooking meat. It exalts its flavour more than any other method. In roasting, place the meat at first sufficiently near a brisk fire, so that the albumin on its surface may be readily coagulated, and the juices retained in the interior of the joint. After about fifteen minutes, the joint ought to be removed somewhat further from the fire, and allowed to cook slowly. Frequent basting is desirable to obtain a good result. Brown meats, such as beef, mutton, and goose, require a quarter of an hour per pound weight; veal and pork require about ten minutes additional, to ensure the absence of redness. White-fleshed birds require a somewhat shorter time. The time required in roasting will be a little more if the joint is large, or the fire not very clear. To ascertain if the meat is sufficiently cooked, press the fleshy part; if it remains depressed, it is done; if not done, it retains its elasticity. At the first incision, gravy should flow out of a reddish colour.

The changes undergone during roasting are, that the connective tissues uniting the muscular fibres is converted by the gradual heat into gelatin, which is soluble and easily digested; the muscular fibres, consequently, become more separable, and the myosin of which they consist is rendered more digestible. The fat is partly melted out of its fat cells, and partly combines with the alkali from the blood-serum. Empyreumatic oils (i.e. fat partially burnt), developed by charring of the surface of the joint, are carried off when it is roasted in front of the fire; and so, to a large extent, is acrolein. Acrolein (C₃H₄O) is always produced by the destructive distillation of neutral fats containing glycerine, and is the cause of the intolerably pungent odour accompanying the process. Osmazome, a peculiar extractive matter, on which the flavour and odour of meat depend, is developed better by roasting than by any other method of cooking.

It is useful to remember, in buying beef or mutton, that 20 per cent. must be allowed for bone and 20 to 30 per cent. for the loss during cooking.

The following figures are by Johnston:

Thus roasting is the least economical method of cooking. The chief loss, however, is of water; the dripping and gravy are recoverable.

2. Baking of meat in a closed oven does not produce so agreeable a result as roasting in front of an open fire. The oven ought always to be very hot before the meat is put in, in order to rapidly coagulate its surface. Baked meat may have an unpleasant flavour, owing to its saturation with empyreumatic oils, which escape in open roasting. The unpleasant flavour can be prevented by covering the meat with a layer of some non-conducting material, as a pie-dish or a crust, no empyreuma being then formed. Baked white of egg, as in the dish of fried ham and eggs, is one of the most indigestible forms of albumin obtainable.

3. Boiling of meat requires the same time as roasting. If the flavour and juices are to be retained, the joint ought first to be plunged into soft boiling water, and then, after three minutes, allowed to stand aside in water at 170° Fahr. The preliminary boiling forms a coating of coagulated albumin over the joint. Where there is no thermometer to guide the cooking—after the preliminary boiling for three to five minutes, add three pints of cold water to each gallon of boiling water, and retain at the same temperature for the rest of the process, i.e., at about 170° Fahr. If the meat is boiled in an inner vessel surrounded by water (water-bath), the temperature of the inner vessel does not rise above 160°-170° F. Ordinary “simmering” means that the meat is kept all the time at a temperature of 212° F. and is thus spoilt. The boiling of an egg is an example of the same point. If an egg is kept in water at a temperature of 170° F. for 10 to 15 minutes, its contents form a tender jelly, while an egg kept in water at 212° F. for the same length of time is hard and tough. An egg is more digestible when cooked in water at 170° F. for 10 minutes than when boiled in water for 2½ minutes.

The use of soft water for cooking purposes is always advisable; otherwise a longer period must be allowed. A preliminary boiling for a few minutes renders hard water softer, and the addition of a little carbonate of soda has a like effect.

When meat is inserted in water at a temperature below its boiling point, the juices are gradually extracted, while the meat is left a mass of indigestible fibres. A good soup is produced, but the meat is almost valueless. In order that the soups and broths may be nutritious, the less heat is employed in their preparation the better. If a soup is strained to make it clear, much of the most valuable part is removed.

Stewing is a process intermediate between boiling and baking. It possesses the great advantage over dry baking that no empyreumatic gases are produced, and there is no charring. The temperature of the stew-pan ought never to be above 180° Fahr.; at this heat the roughest and coarsest kinds of meat are made tender. The only objection to stewing is that the meat becomes saturated with fat and gravy, and is too rich for weak stomachs. It is advisable to stew lean meats only.

Hashing is a process of stewing applied to meat which has been previously cooked. The consequence of this double cooking, is that the meat becomes tough and leathery. A modified hash in which the meat is simply well warmed throughout is preferable.

Frying, unless carefully done, renders meat difficult of digestion, each fibre becoming coated with fat. The art is to “fry lightly,” that is, to burn quickly and evenly, so that no charring is produced. Two methods of frying are described. In the first, the substance to be fried, as an omelette or pancake, is placed with a little fat or oil in a frying-pan. This is really a modified process of roasting, the fat merely serving to prevent the object from adhering to the shallow pan. In the second, the substance to be fried is immersed in fat; for this purpose a frying kettle is required. Olive oil or good cotton seed oil is best for use in the frying-kettle. Lard is a bad material for frying; both it and butter are apt to burn unless heated slowly. Dripping is a good substance for frying. The fat used must be heated to from 350° to 390° F., and then the substance to be fried, e.g. a sole, plunged into it and left for two or three minutes. In this process the substance of the sole is really being steamed by the steam generated in the substance of the sole.

6. Broiling and Grilling are really processes of roasting applied to small portions of meat. In grilling, it is important that the gridiron should be hot before putting anything on it. An external coagulation of albumin is produced, as in good roasting and boiling.

The Cooking of Mixed Dishes.—A few instances may be given of common errors in preparing compound dishes. An egg in a custard, or just coagulated in a poached egg, is a light and easily-digested food; baked half an hour in a pudding, it is much less digestible; fried with ham, it is almost as indigestible as leather. Spices, if mixed with a dish before it is boiled, lose nearly all their flavouring power, while they remain irritating. They ought to be added near the end of the cooking process. A soup containing vegetables, as well as meat juices, should be prepared in two parts. The vegetables require prolonged boiling; gravy is spoilt by this. Similarly, the jam in a tartlet, if inserted before baking, loses its proper fruity flavour; and oysters baked in a beef-steak pie are indigestible.

The Cooking of Vegetable Foods.—Bread is either vesiculated or unvesiculated; the latter being what is called unleavened bread. Vesiculation of bread has usually been produced by fermentation of some of the sugar of the flour. The starch first becomes sugar (dextrose) and then the growth of the yeast plant in the dough splits this up into alcohol and carbonic acid gas. The carbonic acid percolates the substance of the dough, rendering it porous. When it has “risen” sufficiently, the dough is placed in the oven. The heat of the latter kills the yeast plant, thus preventing any further fermentation, but at the same time expands the carbonic acid gas in the bread, rendering the latter still more porous, and drives off in a gaseous condition the greater part of the alcohol produced by the previous fermentation.

It is objected to this plan of making bread, that a little of the sugar is wasted in producing alcohol and carbonic acid. To remedy this, another plan is sometimes adopted, as first proposed by Dr. Dauglish. In it the dough is charged with carbonic acid dissolved in water under considerable pressure. The gas escapes in the substance of the dough, and on baking expands as in the ordinary method of making bread. Bread made in this manner, is called “aerated bread.” Nevill’s bread has a solution of carbonate of ammonia incorporated in the dough, which is dissipated by heat, thus causing vesiculation of the bread.

On the continent, a mixture of hydrochloric acid and carbonate of soda is commonly used, carbonic acid and common salt being formed in the dough. Thus NaHCO₃ + HCl = NaCl + H₂O + CO₂. The hydrochloric acid employed should be perfectly pure and free from arsenic. Baking powders are also largely used for making cakes. “Self-raising” flour is flour with which baking-powder has already been mixed. Most baking-powders consist of a mixture of carbonate of soda and tartaric acid or bitartrate of potash, diluted with starch. When wetted, carbonic acid gas is evolved. A few contain alum, which is now an illegal material for this purpose.

Ten pounds of flour ought to make thirteen to fourteen of bread. The use of stale bread is much more economical than of newly-made bread; besides this, it is more digestible. Newly-made bread is more palatable than stale, but it is more cohesive, and does not crumble into separate particles like stale bread. The consequence is, that it is less digestible, being less easily penetrated by the saliva and other digestive juices. The effect of toasting is to render bread more friable, and consequently more digestible. It ought, however, to be thin and eaten soon after it is made; when thick and kept too long, it becomes tough and leathery.

Pastry is less easily digested than ordinary bread. The lard or dripping added renders it more flaky and less easily pulverised; and, in addition, the fat coats over the starch cells; and thus the action of the digestive juices on the pastry is impeded.

Potatoes ought to be boiled in their jackets, or steamed, to avoid loss of nitrogenous material and salts. Moist heat causes the starch granules to swell, and ultimately softens and bursts the cellulose envelopes in which these are contained. Dry heat, as when potatoes are baked, converts starch into a soluble form, and ultimately into dextrine (= C₆H₁₀O₅), an intermediate stage towards the formation of dextrose (i.e. glucose = C₆H₁₂O₆).

Peas and Beans ought to be boiled slowly and for a long time to render them more digestible. If old, they ought to be soaked in cold water for twenty-four hours, then crushed, and stewed. Hard water must be avoided in the cooking of peas and beans as well as of other vegetables, as the lime-salts form insoluble compounds with legumin.

Green vegetables require thorough and prolonged cooking. This renders their tissues softer and more easily attacked in digestion. The members of the cabbage tribe and carrots can hardly be boiled too long. Soft water ought always to be used; this is one reason why steaming is preferable. Before boiling, all vegetables should be well washed in cold water. A little vinegar will remove any insects present.

Cooking Apparatus.—The apparatus required in cooking may be divided into kitchen utensils and cooking ranges.

To ensure good cooking, perfect cleanliness of all apparatus is indispensable. The use of the frying-pan, gridiron, spit, and oven has been sufficiently indicated under the description of the different methods of cooking. The form of stove to be used for cooking meat is gradually being settled against the old open stove. Although this secures a somewhat more savoury joint than when meat is baked, it is extravagant in working. The closed kitchener in which coal is employed is less economical than a gas stove at the present price of gas, if the latter is carefully used.

Various appliances for economising fuel have been devised, and at the same time of allowing of the prolonged action of a moderate degree of heat. These are usually constructed on the principle of an ordinary bath, consisting of a double pan, with a layer of water between the two compartments. Warren’s cooking-pot belongs to this type. The Aladdin oven consists of an iron box with an opening above to let off superfluous steam. This box is surrounded by another composed of non-conducting material, while a lamp below furnishes the heat. Dr. Atkinson has calculated that in an ordinary oven 2 lbs. of fuel must be expended for every pound of food cooked, while in his Aladdin oven 2½ lbs. of fuel will cook 60 lbs. of food. Time is an important element in cooking. Food is most thoroughly cooked and most digestible when subjected to a temperature below that of boiling water for a prolonged period.

The Preservation of Food.—All organic foods tend rapidly to decompose and putrefy. Putrefaction only occurs when a warm and moist substance is exposed to the air. The problem of preserving any food, therefore, may be solved (1) by keeping it at a very low temperature, (2) by desiccating it, or (3) by boiling or steaming it so as to destroy any microbes in the food which would otherwise start putrefaction, and then fastening it in an air-tight case.

Milk is commonly preserved as condensed milk, and in this condition is very valuable. A pure condensed milk is now supplied, prepared without the addition of sugar or any antiseptic, but in which, as in other condensed milks, all disease-producing or decomposition-producing microbes have been destroyed during the process of concentration. Milk may also be desiccated; in this condition it is difficult of digestion.

In addition to the household methods of preserving fruits, large quantities of fruits—both moist and dry—are now imported, protected by syrup or sugar, in sealed canisters; and they retain the original flavour almost unchanged.

The preservation of meat is effected by—

1. Drying.—This must be done rapidly. It is a process which is best applicable to fish, but has been applied also to beef. Dried Hamburg beef is used for making sausages. Pemmican, largely used by Arctic voyagers, consists of a mixture of meat and fat, dried and powdered along with some spices; it is generally eaten with some kind of meal.

2. Cold.—Frozen meat now forms a very large part of the food of the English people. If the meat has been frozen before rigor mortis (rigidity after death) has commenced, it keeps well; if frozen later, it rapidly decomposes after being thawed. Freezing arrests putrefaction and tends to conceal its odour. Hence the bad condition of frozen fish may not be detected until it is cooked. In cooking frozen meat, time should be allowed for thawing to occur, before the meat is placed in the oven. Much of the ill-founded prejudice against frozen meat arises from inattention to this point. Frozen meat is equal in nutritive value to and does not lose more in cooking than fresh meat.

3. Salting may be done with brine or saltpetre (nitrate of potassium); the latter does not decolourize the meat like the former. Salted meats have lost much of their nutritive material, in the form of albumin and salts, and the remaining meat is harder and more difficult of digestion than fresh meat.

4. Immersion in antiseptic liquids or gases, as sulphite of soda, is objectionable, on account of the addition of extraneous, and not altogether innocuous, salts. Boric acid powder is largely used for sprinkling on meat, particularly rabbits, etc., and for preserving hams and other meats. Its use is to be deprecated. All such meats should be thoroughly washed with water, before being cooked.

Solutions of boric acid and borax are frequently added to milk. Their use is objectionable (a) because they tend to conceal incipient decomposition, but do not prevent its possible evil effects, and (b) because they enable the farmer to palm off dirty milk on the public. Were the addition of preservatives to milk forbidden, the farmer could perfectly well keep his milk sweet until it reached the town-consumer by adopting strict measures of cleanliness, and by cooling his milk before it leaves the farm. At the least it should be made obligatory on the milk retailer to declare the presence of preservatives in milk sold by him.

The presence of borax or boric acid can be detected by evaporating the milk to dryness, incinerating and then moistening the ash with a drop of strong sulphuric acid. If a little alcohol be now added, on applying a light, a green flame indicates boric acid. Milk or cream containing boric acid turns blue litmus paper red.

Formalin is also sometimes used as a preservative for milk in very weak solution.

Its presence can be determined by diluting the milk with water in a test-tube, and running strong sulphuric acid down the side of the tube, taking care to prevent mixing. At the junction of the acid and diluted milk a violet ring is seen if formalin is present.

Salicylic acid was formerly used as a milk preservative, but is now seldom used except in beers. All these preservatives are objectionable in milk, although their injurious action may be difficult to prove.

5. Coating with fat or gelatine has only succeeded in conjunction with the exclusion of air. This process is especially applicable to fishes, as tinned sardines. In a modified form, it is useful in coating potted meats, etc.

6. Heating and Air-tight Cases.—Tinned meats prepared according to this method are imported in large quantities. In the process of preparation, the cases are packed with meat and filled up with gravy, and then closed with a cover which is hermetically sealed, except at one point. The case is then heated to 250° Fahr., in order to drive out all air, and destroy any putrefactive germs present. The open point is sealed while the gravy is still boiling, thus making the case completely air-tight. Albumin is coagulated at about 170° Fahr.; the higher temperature, which it is found necessary to employ, overcooks the meat and renders it less digestible (see also p. 40).

[CHAPTER VII.]
CONDIMENTS AND BEVERAGES.

Condiments, etc.—The name condiment is used in various senses by different writers. In its strictest sense it is a substance containing a volatile oil or ether, which may be taken with salt, and the object of which is to excite the senses of taste and smell, and consequently produce an appetising effect. This definition excludes spices, substances allied to condiments, but usually taken with sugar, as cinnamon, ginger, etc.; also flavouring agents, such as vanilla; and acids, such as vinegar and lemon-juice. If we use the word in its widest sense, to include these various groups of substances, we find that all condiments are taken with the object of improving the taste or flavour of food, or of assisting its digestion; but that they are not foods in the sense of supplying any elements towards building up the body or maintaining its heat. The only partial exception is lemon-juice, the salts of which have a quasi-medicinal use.

Taste is usually a compound sensation, the organs of which are the nerves of taste and smell. True taste is confined to the appreciation of sensations of bitter and sweet; but the flavour of meats is nearly entirely appreciated by the sense of smell. This is shown by the fact that meats appear tasteless and insipid, during “a cold in the head.” In the appreciation of acid, astringent, and fiery substances, the sense of touch is also employed. The excitement of these different nerves results in a stimulus which is carried up to the central nervous system, and causes by reflex action an increased flow of the digestive juices. Hot substances, like cayenne and ginger, also cause an increased flow of gastric juice, by directly congesting the mucous membrane. This action is not so desirable as that through the influence of the nervous system. All natural foods are sapid and possessed of flavour, and thus stimulate secretion; but any local irritating effect ought to be avoided.

1. Condiments proper comprise chiefly mustard, pepper, cayenne, garlic, onion, capers, mint, sage, morels, mushrooms, truffles. The last three on the list are also foods, but are more commonly used as condiments.

All these act as stimulants to the digestive organs, and in small quantities aid digestion. The active principle of mustard and horse-radish is sulphocyanide of allyl. Horse-radish is not so wholesome as mustard, the scraped root being apt to adhere to the stomach like the skins of grapes, and produce indigestion. Pepper contains an acrid resin, a volatile oil, and an alkaloidal substance, called piperine. Cayenne contains an analogous substance, called capsicin. Cayenne, unless in extreme moderation, is harmful, as its small particles adhere to the mucous membrane of the stomach, and may set up considerable irritation.

2. Spices are those condiments which contain an aromatic oil, and which harmonize with sugar. They are, as a rule, less irritating to the stomach than those of the pepper group. Cinnamon, cloves, camphor, ginger, and curry powder are the chief of these. Curry powder really belongs to both the first and second divisions. When genuine, it is said to contain turmeric, cardamoms, ginger, allspice, cloves, black pepper, coriander, cayenne, and a few other substances.

3. Flavouring agents, such as vanilla, lemon peel, and fruit essences, are used to give a pleasant flavour to various dishes.

4. Acidulous substances are taken chiefly because of their sharp and agreeable taste. Vinegar is the chief acid employed. It is produced by the action of a fungus (Mycoderma aceti) on alcoholic liquids, as wine, or beer, C₂H₅OH (alcohol) becoming C₂H₄O₂ (acetic acid). It is also produced by the destructive distillation of wood. In small quantities it does not stop digestion, but, by exciting the nerves of taste, may be of actual service. It helps to soften the vegetable fibres in a salad; and is also useful for the same purpose with hard meats, as lobster, etc. In large quantities it diminishes the power to assimilate food.

Good vinegar ought not to contain less than 3 per cent. of acetic acid; and sulphuric acid beyond 1 in 1000 in vinegar is to be regarded as an adulteration. A specific gravity below 1015 indicates the addition of water.

Citric acid and lemon-juice are useful for their refreshing properties, and the latter also because of its alkaline salts.

Oils, such as olive oil, have been sometimes classed under condiments, but as they have great nutritive properties, this is hardly accurate. For the same reason, salt is not classed under this head.

BEVERAGES.

Water is the universal beverage, and for healthy persons is preferable to any other. All other beverages necessarily contain it as their basis.

It will be convenient to consider first aërated and other natural waters; then tea, coffee, and cocoa; and finally, alcohol.

1. Aerated Waters contain carbonic acid (carbon dioxide) in solution, which gives to them their characteristic sharp taste and sparkling character. Thus distilled water charged with gas is sold as Salutaris or Puralis water. Soda water contains three to five grains, and medicinal soda water fifteen grains of bicarbonate of soda to the bottle. Potash water contains fifteen grains of bicarbonate of potash to the pint, in each case carbonic acid being dissolved under pressure. In lemonade, ginger-beer, etc., the basis is sweetened water, rendered tart by the addition of an acid, and finally charged with carbonic acid. Lemonade frequently contains acetic or phosphoric acid instead of citric or tartaric, and ginger-beer the same constituents with some added tincture of ginger. Home-made lemonade prepared from fresh lemons is a much more wholesome drink. Ginger-beer (stone ginger) is produced by the fermentative action of yeast on a solution containing sugar, bruised ginger, tartaric acid, and oil of lemon. It usually contains at least two per cent. of alcohol.

Natural Mineral Waters usually contain common salt (chloride of sodium) and alkaline salts of soda or lime, and are impregnated with carbonic acid gas. Apollinaris, Rosbach, and Johannis possess these characteristics. The carbonic acid in natural waters is partially combined, and is given off more gradually than that in artificial mineral waters.

In all the preceding waters there is considerable carbonic acid. This acts as a sedative to the mucous membrane of the stomach, and is useful in indigestion. An aërated water added to milk renders it more digestible by diluting it, and by preventing the formation in the stomach of a heavy clot of casein. In the making of artificial aërated waters, it is essential that the water employed should be pure, that the acid used in generating the carbonic acid should be free from arsenic or other impurities, and that the water should not be allowed to come into contact with lead at any stage, as in pewter fittings. One per cent. of proof spirit is allowed in temperance beverages by the Excise.

TEA.

Tea is the leaf of an evergreen shrub, the Camellia thea, which is cultivated in China, Japan, British India, Ceylon, Java, and other countries. The tea leaves, as seen in this country, uncurl in hot water. They are lanceolated, with a serrated edge, and the veins do not extend to the edge of each leaf. By these characteristics they may be distinguished from foreign leaves, e.g., the sloe and willow used as adulterants (Fig. 4). The use of old and exhausted leaves can be detected by a determination of the percentage of soluble matter dissolved by boiling water from a given weight of tea. This on evaporation to dryness should be 28 to 30 per cent. of the total weight of the original tea. The presence of clay, iron dust or other forms of dust is detected by igniting a given amount of tea and determining the amount of ash. This should be only about six per cent.

In black tea, the leaves are dried in the sun, rolled and allowed to become soft and to ferment. During this process, some of the tannin appears to be converted into less soluble forms. The leaves are afterwards sun-dried, and these “fired” in a furnace. Green tea leaves are dried in the fresh condition over wood fires. Indian teas have more “body” and astringency than China teas. The smallest and topmost leaves of the tea plant give the finest sort of tea (Orange Pekoe); next to this comes Pekoe; the next largest leaves producing Souchong; after these Congou; while the coarser leaves nearer the base used to yield Bohea, which is now seldom seen.

Tea consists of three important constituents—volatile oil, theine or caffeine, and tannin—and soluble and insoluble extractive matters.

(1) Volatile Oil gives the aroma and flavour to each particular tea. It is this which causes the headache, trembling, wakefulness, and restlessness, occasionally produced by tea, especially by green tea.

Leaves of
(A) Elder. (B) Tea. (C) Tea. (D) Sloe. (E) Elder.
Fig. 4.

(2) Theine or caffeine, is an alkaloidal crystalline principle. Its composition is represented by the formula C₈H₁₀N₄O₂, H₂O. Ceylon tea, broken leaf contains 4·03 per cent., Assam (Indian) tea, broken leaf 4·02 per cent., while Chinese teas contain from 2·89 (Moyune Gunpowder) to 3·74 (Moning, black leaf) per cent. of caffeine (Allen).

Theine is the most important constituent of tea and coffee. It is a stimulant, but unlike alcohol, acts even more upon the central nervous system than upon the heart. It removes the sense of fatigue, and may, especially if taken in excessive doses, produce sleeplessness. Its stimulant action on the heart is followed by increased flow of urine, and it thus helps in the removal of waste products from the system. The effect on the tissue-changes of the body is somewhat doubtful. It has been stated to arrest or diminish the waste, i.e., the metabolism, constantly going on in the system, and so diminish the amount of food required to repair this waste. This is highly improbable; we cannot conceive the likelihood of the development of energy without a corresponding expenditure of material, and that is what would be the case if theine increased the activity of various organs while retarding their waste. The experiments of Conty and Guimarès on the action of coffee show that this (and tea has the same essential constituent) does not diminish tissue waste. It does not prolong life in starvation, though it may lessen the feeling of hunger. Hence tea and coffee, which owe their value mainly to the caffeine or theine contained in them, are in no sense foods.

(3) The amount of Tannin varies from 12·31 in Ceylon tea (broken leaf, Pekoe) to 11·76 in Moning, black leaf, and 9·9 per cent. in Natal Pekoe Souchong (Allen). The difference in tannin between Chinese and Indian teas is not therefore so great as is usually supposed. Tannin is a powerful astringent, and possesses a bitter styptic taste, and a constipating effect on the bowels. Its amount is increased by long “brewing,” as is shown by the following results (Hale White):—

The Mode of Preparation of Tea is important. It is clear that the percentage of tannin to weight of leaf used in making the infusion increases with the protraction of the infusion. On the other hand caffeine is so soluble that it is nearly completely dissolved as soon as infusion has begun. Dittmann found that five minutes infusion of Indian tea extracted 3·63 and ten minutes infusion 3·73 per cent. of caffeine. The Chinese put the tea leaves in a cup, and having poured boiling water on them, drink the resulting infusion after a very short time, without adding anything. The Russians drink the infusion with a squeeze of lemon, and with or without sugar. We add cream or milk and generally sugar, and so render it more nutritious, though the delicate flavour is veiled. The Chinese plan of infusion for a short time is the best, as it ensures the extraction of the aromatic and stimulant principles of the tea with only a proportion of the tannin.

In making tea it is important to use a tea-pot which is quite dry, in order to avoid mustiness; to pour a small quantity of boiling water into the tea-pot and then out again, so that the infusion may be made at the temperature of boiling water; and to use water which has only freshly come to the boil, and so has not been rendered flat, and not to infuse longer than five minutes. For persons of weak digestion, the best kind of tea is that obtained by pouring boiling water on the leaves, and then immediately pouring the resulting infusion into another hot tea-pot. In all cases where tea has to be kept a considerable time, it should be poured into a second tea-pot, the leaves being left behind.

Indigestion is not an uncommon consequence of tea-drinking; caused by the excess of tannin in the tea, by the other constituents of the tea, or more commonly by the practice of drinking tea in small sips, with bread and butter. The tea infusion usurps the place of the saliva, the secretion of saliva remaining partially in abeyance. The presence of tannin in tea renders it an undesirable part of a substantial meal. Tannin coagulates albumin, and retards its solution by the digestive juices. Hence “high teas” and “tea-dinners,” unless the tea is very weak, are objectionable. The practice of drinking tea with every meal is inexcusable.

For quenching thirst during active exercise, and rendering possible prolonged exertions, tea is unsurpassed.

COFFEE.

Coffee is the seed of the berry of the Caffea Arabica. Each berry contains two seeds, or beans as they are sometimes incorrectly called. The coffee is prepared by roasting the seeds until they assume a reddish-brown colour, in which process they lose 15 per cent. in weight and gain 30 per cent. in bulk. During the process of roasting, a volatile oil having a powerful aromatic smell is developed. This is not produced in such large quantities from fresh seeds; the best time for roasting varying, however, for different varieties of coffee.

The amount of Volatile Oil in coffee is much less than in tea. As it is elicited during the process of roasting, this should be done with nicety and care. It is effected in an iron cylinder made to revolve over a fire. After the roasting, the sooner the seeds are ground the better the coffee. When it cannot be immediately used, it should be kept in closed canisters, and not in paper or open jars.

In addition to the volatile oil, which is contained in roasted coffee in the proportion of about 1 part in 50,000, coffee contains caffeine, of which there is ¾ to 1 per cent., and an astringent acid, called caffeo-tannic or caffeic acid, which differs from ordinary tannin in that it does not blacken a solution of an iron salt.

The chief adulteration of coffee is Chicory, which is thought by some to improve the coffee. It is generally harmless, though in some people it produces heartburn and diarrhœa. Chicory is prepared from the root of the wild endive. It contains a volatile oil and a bitter principle, but no caffeine. It is, therefore, of no utility as a stimulant. Its presence can be detected by shaking a little of the suspected coffee on to the surface of the water in a wine-glassful of cold water. Coffee swims on the surface, and gives little or no colouration to the water; while chicory sinks, and gives a deep red tint. The aqueous extract of pure coffee (extracted by boiling water) is, when evaporated, 25 to 30 per cent. of the weight of the original decoction of coffee; while that of chicory is 65 to 70 per cent.; and on this basis, as well as on the fact that a filtered decoction of 10 grammes of coffee in 100 c.c. of distilled water, cooled to 60° F. has a specific gravity of 1009, while that of a similar solution of chicory would be 1021, the proportion of chicory in a mixture of coffee and chicory can be calculated. The microscopical appearances of the two powders differ, coffee showing hexagonal cells and no laticiferous vessels, unlike chicory. There is no law against selling mixed coffee and chicory, if the fact that it is a mixture is stated; and the proportion of the two unfortunately is not required to be stated. As a pound of coffee costs five times as much as a pound of chicory, it is obviously to the purchaser’s advantage to make his own mixture in the proportions desired.

The Preparation of Coffee ought to be effected as in the case of tea—by making an infusion and not a decoction, i.e. by pouring boiling water on the coffee and allowing it to stand, but not continuing the boiling. Continuance of boiling dissipates the delicate aroma.

Inasmuch as coffee contains a much smaller percentage of theine than tea, more of the former must be used to obtain a beverage equally refreshing with tea. Two ounces to a pint of boiling water are required. The infusion thus made should be mixed with an equal part of boiled milk. The coffee ought, if possible, to be freshly roasted.

The colour of coffee is no guide to its strength. Many of the black coffees, especially “French coffee,” owe their colour to the caramel (burnt sugar) contained in the chicory mixed with them.

Coffee has similar properties to tea, with some minor differences. (1) Like tea, it is restorative and sustaining in its action, but seems to act more quickly than tea. (2) Unlike tea, it does not tend to produce perspiration, but rather a dry hot skin. (3) With some it is decidedly laxative; while tea, especially if badly made, has an opposite effect; but this is not always true. (4) It seems to have a greater power of antagonising the effects of alcohol than tea; and is a valuable antidote, after the action of an emetic, in poisoning by opium or arsenic or alcohol.

As a rule, coffee is not so prone to disorder the digestion as tea, but this is not universally true, and in some persons it always produces “biliousness.” When taken in excess, it produces—besides indigestion—palpitation, restlessness, irritability, sleeplessness, and a condition of general nervous prostration; in fact, similar symptoms to those produced by a prolonged over-indulgence in tea.

While the consumption of tea is rapidly on the increase, that of coffee is steadily diminishing. This is partly owing to the greater expense of coffee—a larger quantity being required to form a good beverage; and partly to the greater difficulty in preparing good coffee.

COCOA.

Cocoa, or more properly cacao, is obtained from the seeds of the Theobroma Cacao—a native of the West Indies, Mexico, and the central parts of America. Its name Theobroma was given it by Linnæus, and means the “food of gods.” The fruit is a large leathery capsule, having nearly the form of a cucumber. It contains from 25 to 30 seeds, each about the size of an almond. Before using, these are roasted like coffee berries, and a peculiar aroma is developed in this process as in the case of coffee. The beans or seeds are then manufactured into three different products. (1) They are simply deprived of their husks and broken to pieces; this forms Cocoa-Nibs. (2) They are ground, husk and all, between hot rollers into a paste, and mixed with starch and sugar; this forms Cocoa. (3) They are shelled and then ground into a paste, as in making cocoa; sugar and some seasoning, usually vanilla, being subsequently thoroughly mixed; this paste is Chocolate.

The purest form is the cocoa-nibs. When these are boiled in water, a brownish decoction is formed, with the fat as a scum at the top; this may be removed, and the decoction flavoured with milk and sugar. In this form, cocoa can be taken by invalids with weak digestion, who would be nauseated by the fat of ordinary cocoa or chocolate.

The best cocoa is prepared as above; but the lowest quality contains the husks of the beans, with hardly any of the beans in it; a somewhat better, though still inferior sort, is made from the smaller fragments of the nibs, and a good deal of husk. In some cases the cacao butter is removed during the process of preparation, and starch or sugar substituted. This form is less likely to disagree with dyspeptics than whole cocoa.

The action of the Volatile Oil (not the cacao-butter) developed during roasting, is probably similar to that of tea and coffee, though it is less in amount. The bitterness is greater than that of coffee, but the astringency less than in either tea or coffee.

The Concrete Oil, or fat of cocoa, forms about half its weight. It is white, and not apt to turn rancid, and possesses an agreeable flavour. Cocoa also contains a certain amount of starch and cellulose.

Theobromine is a white crystalline alkaloid, the exact analogue of caffeine. The latter, in fact, is methyl-theobromine—that is, theobromine plus the theoretical group CH₂. Theobromine possesses similar properties to caffeine. It amounts to 1.5 to 2 per cent. of the whole bean. The ordinary preparations of cocoa differ considerably in composition as may be seen from the following table of per centage composition (Ewell). In each instance other nitrogenous and non-nitrogenous constituents go to make up the total 100:

Some of the preparations of cocoa (e.g. Van Houten’s) have added to them alkaline salts to increase their solubility. Cocoa is not such a valuable food as might appear from the large amount of fat in it, because only moderate quantities of this can be taken without deranging digestion. In Vi-Cocoa a certain amount of kola is added, which contains a considerable proportion of caffeine. The addition of such a drug to a beverage is distinctly to be deprecated.

Minor Stimulants.—Beverages containing theine, or some analogous principle, appear to be employed in most countries. In moderate doses, they may assist the assimilation of other foods, but their main influence is on the nervous system. Theine-containing substances may be described as both sedative and exciting. They are sedative, in that they allay nervous irritability, and tend to “take the edge off” the disturbance caused by outward circumstances; and they are exciting, inasmuch as they are known to form an admirable antidote to the stupefying effects of opium or alcohol. The wakefulness from tea is an instance of the same thing, while the allaying of sensations of cold and hunger by a cup of tea is an instance of the sedative effect.

In Brazil, Guarana (from Paullinia sorbilis) is used as a drink; it contains theine, the quantity of which is twice as much as in good black tea, and five times as much as in coffee. Like green tea, a cup of guarana infusion is sometimes extremely valuable in nervous headaches.

In Peru, the natives use the leaves of the Coca plant (Erythroxylon coca), which must be carefully distinguished from cocoa. It is chewed somewhat in the same way as the betel-nut. It contains two alkaloids—cocaine and hygrine, as well as tannin. In its stimulant action it resembles tea and coffee. The active principle of this plant, Cocaine, is a valuable local anæsthetic. Internally it has been taken as a stimulant and restorative. Various wines containing Coca, with vaunted restorative powers, are advertised. They are mischievous when taken frequently. Nature’s remedy for fatigue, whether mental or body, is rest and recreation. Stimulants of this class, even though they enable work to be continued for awhile, eventually increase the exhaustion for which they are taken.

The Kola-nut is used in some parts of Western Africa as a stimulant. It is about the size of a pigeon’s egg, and has a bitter taste. The natives of Guinea generally take a piece of the seeds before each meal, and sometimes nibble it throughout the day.

Kava is prepared from the root of a kind of pepper. The natives of the Fiji islands commonly indulge in it. Its effects resemble those of coffee. In large doses, it destroys the power of walking, and may possibly produce impairment of vision.

The leaves of the Ilex Paraguayense, Ilex Gongorrha, and Ilex Theezans are made into the beverage commonly known as Paraguay tea or maté.

The leaves of the Hydrangea Thunbergii are made into a beverage, which is designated in Japan “the tea of heaven.”

Among certain nations of Asia, the Betel-nut (from a palm called Areca Catechu) is chewed, after mixing small fragments with pepper and quicklime, and rolling in a palm leaf. The saliva is tinged blood-red, and a narcotic effect is said to be produced.

The dried flowering tops of the Indian Hemp (Cannabis Indica) are smoked by the Malays and others, or made into a beverage, called haschisch, which produces a kind of intoxication, in which murder has often been committed (hence, assassins equals haschascheens).

The Kamtschatkans drink an infusion made from a fungus, known as the Fly Agaric (Amanita Muscaria), thus producing an intoxication similar to that from haschisch.

Opium in small doses is a stimulant, in large doses narcotic. The crude drug is sometimes taken, and less frequently the active principle, Morphia. It is frequently smoked, as well as taken internally. It is to be feared that secret opium taking is considerably increasing. The taking of morphia, especially hypodermically, is too common. Generally it has been first prescribed for neuralgia or some other complaint causing acute pain; and the patient, having experienced relief by its means, is tempted to revert to the practice apart from medical advice. Such a line of action is most pernicious. Eventually both the physical and the moral nature of the victim are shattered by it; and to break off this insidious habit, when once thoroughly established, is most difficult.

Tobacco may be conveniently mentioned here, though its usual effects are certainly not stimulant. It is smoked, chewed, or taken as snuff; when indulged in to excess it produces serious depression of the heart’s action, with frequent intermittence. In moderate doses it is sedative as well as slightly laxative. Prolonged indulgence in tobacco has produced many cases of incomplete blindness (tobacco amblyopia), in some cases it comes on with much smaller doses, and in all cases is only curable by ceasing to smoke. There is no sufficient ground for the statement that cigarette smoking is more injurious than smoking tobacco in a pipe or cigar, unless in the former case the smoke is inhaled into the lungs. The practice of smoking is injurious to growing boys, and should be strictly forbidden.

Other Drugs are now not infrequently taken, apart from medical advice. Of these the most commonly used are Antipyrin and Phenacetin, for headaches. Their use is injurious, and should not be entertained as a frequent practice. Sleeplessness frequently leads to the practice of taking chloral or sulphonal, or occasionally the inhalation of chloroform to induce sleep. (See also page [259]). Remedies to induce sleep should never be taken except under immediate medical advice. They are only justifiable in extreme conditions, and if frequently taken tend to aggravate the conditions for which they are given.

[CHAPTER VIII.]
FERMENTED DRINKS.

Properties of Alcohol.—When a saccharine solution is subjected to the influence of warmth and moisture, and exposed to the air, it rapidly undergoes a process of fermentation. The most favourable temperature is about 70° Fahr. The ferment or agent exciting the change in the sugar is derived from the atmosphere; it is a minute fungus (torula cerevisiæ), the spores of which are constantly floating in the air. When once fermentation has started, exposure in the air is no longer necessary; the process continues in closed vessels. The essential change occurring in the vinous fermentation is that grape sugar (C₆H₁₂O₆,H₂O) becomes split up into alcohol (C₂H₅OH) and carbonic acid (CO₂). Thus—

	C₂H₆O		Two of alcohol
	C₂H₆O
C₆C₆H₁₂O₆ =
	CO₂		Two of carbonic acid.
	CO₂

There are other fermentations allied to the vinous. Thus the Acetous fermentation results in the conversion of alcohol into vinegar, as in the souring of beer or wine. The Lactic fermentation leads to the conversion of milk-sugar into lactic acid, with consequent souring of the milk.

Alcohol, or more correctly ethylic alcohol, is a colourless liquid, having a pleasant vinous odour, and evaporating rapidly on exposure to air. It burns with a bluish sootless flame, and is a capital solvent for resins and other substances.

Rectified spirit is absolute alcohol mixed with 16 per cent. of water. Proof-spirit is a mixture of 42·7 per cent. by volume of absolute alcohol, and 57·3 per cent. of water. Thus the ratio of alcohol to proof-spirit being as 1: 1·76, the amount of alcohol in any liquid being given, the amount of proof-spirit can readily be calculated. The fermented drinks containing alcohol may be classed as (1) malt liquors, (2) wines, and (3) distilled spirits. The relative properties of these will be considered afterwards; in the next two sections will be considered the effects of diluted alcohol in whatever form it is taken.

Effects of Moderate Doses of Alcohol on the System.—In studying the physiological effects of alcohol, one has to guard against the fallacy that these are the same, only differing in degree, whatever the dose may be. The effects of large doses of alcohol are almost exactly the reverse of those produced by small doses. It will be necessary to define, therefore, what we mean by a moderate dose. By a moderate dose, we understand the amount of alcohol which can be taken without any alcohol being eliminated in the urine. Dr. Anstie found that 1½ ounces, that is three tablespoonsful, of absolute alcohol, taken in twenty-four hours, caused its appearance in the urine; and Dr. Parkes and Count Wollowicz obtained almost precisely the same result. Anything below some quantity between 1 and 1½ fluid ounces per day can be disposed of in the system, and is probably oxidised like ordinary foods.

The amount of alcohol, in the form of alcoholic beverages, corresponding to this maximum dose of absolute alcohol is approximately as follows:—

It will be understood, therefore, that in describing the effects of a moderate amount of alcohol on the system, an amount below 1½ ounces of absolute alcohol per day is meant, freely diluted, and taken as a rule with meals.

1. Effect on the Stomach.—In very small quantities, alcohol seems to stimulate digestion in the same way as mustard. But like all other artificial helps to digestion, it is best avoided in the healthy condition.

2. The Effect on the Liver is similar to that on the stomach—a temporary redness and congestion being produced; this effect soon disappearing if the dose is small and well diluted. But in all cases where there is a tendency to biliousness, even small doses of alcohol are injurious.

3. The Effect on the Heart and Blood-Vessels is first to increase the force of the heart’s action and the rapidity of the pulse. The stimulation of the heart is rapidly followed by a universal dilatation of the small arteries of the body, which diminishes the blood-pressure. Parkes and Wollowicz found that the daily administration of from 1 to 7½ ounces of rectified spirit raised the pulse rate by ten beats per minute, as compared with other periods; and that this effect was followed by a period of depression in which the beat was both slower and feebler than usual.

4. The Effect on the Nervous System varies. In persons unaccustomed to its effects, even small doses dull the power of thought and the rapidity of perception, owing to the paralyzing effect which it exerts on nerve cells. In most cases, however, it at first produces increased rapidity of thought and excites the imagination, though even here it makes it more difficult to keep to one train of thought. This is clearly owing to the more rapid circulation of blood through the brain. Dr. E. Smith’s experiments show that it diminishes the acuteness of the senses. Its influence even in dietetic doses, on the capacity for mental work, is slightly to diminish it.

5. The Effect on the Muscular System is never beneficial. Even when only small quantities are taken, the power of controlling delicate movements is slightly diminished. For persons engaged in laborious occupations, a small quantity does not produce much apparent effect, but where the quantity exceeds two fluid ounces per day the capacity for strong and sustained muscular work is manifestly lessened (Parkes). This effect is probably due partly to the dulling of the nervous system, rendering the muscles less amenable to the will, and partly to the over-excitation of the heart causing palpitation and breathlessness.

6. The Effect on Metabolism is to diminish it, thus favouring the deposit of fat in the tissues. It acts as a poison to the protoplasm of the cells of the body, diminishing their power to break down the floating nutriment, especially fat and carbohydrate.

The Effect on the Temperature is to lower it; but unless the dose is excessive, this effect is hardly appreciable. The resistance to excessive cold is diminished by even moderate doses of alcohol, still more by large doses. In the Arctic regions, this has been abundantly proved. This effect is produced, notwithstanding the fact that alcohol becomes oxidised in the system. The dilatation of the surface blood vessels leads to a greater loss of heat than that produced by the oxidation of the alcohol.

Effects of Immoderate Doses of Alcohol on the System.—Bearing in mind the definition given of a moderate dose, one is bound to admit that a large number of individuals exceed this amount daily, apparently without any very serious results. The system becomes habituated to large doses, and if the occupation is a laborious one, they may in part be oxidised in the system. Such, however, are exceptional cases. In the majority of cases evil results are by no means confined to those who indulge in very large quantities of alcohol at varying intervals. In fact these very often escape comparatively free, while others who never take a quantity sufficient to incapacitate them for their work, are sowing the seeds of chronic and oft incurable disease. The labourer who has a drinking bout at intervals is thoroughly nauseated; and the condition of liver and stomach induced, enforces abstinence on him for a time sufficient to bring his organs back to a normal condition; while the city merchant who indulges more moderately, but whose organs are almost continuously impregnated with alcohol, becomes gouty and prematurely old.

The Stomach may become acutely inflamed, when a large dose of alcohol is taken. The chronic irritation of alcohol, especially when taken apart from meals, causes atrophy of the walls of the stomach, and a change analogous to that in the liver.

The Liver, when alcohol is daily taken immoderately, becomes seriously diseased. In some cases it becomes large and fatty; in others the chronic irritation excites an overgrowth of fibrous tissue between the lobules of the liver, which, gradually shrinking, squeezes the liver cells and causes them to atrophy, at the same time obstructing the small branches of the portal vein in the substance of the liver. The consequence of this obstruction to the flow of blood through the liver is that all the organs from which the portal vein brings blood become overloaded with blood, and vomiting of blood and dropsy of the abdomen occur at a later period.

The Lungs are irritated to a less extent by alcohol in large doses. The tendency to chronic bronchitis is increased, followed by emphysema, and sometimes an overgrowth of fibrous tissue (cirrhosis) like that in the liver occurs.

The Heart and Blood-vessels tend to become diseased, owing largely to the gouty condition of system developed.

The powers of Metabolism are diminished. Corpulence is, consequently, a common result of alcoholism. There may also be fatty deposit in the internal organs, such as the heart. This must not, however, be confounded with a much more serious condition, fatty degeneration of the heart, in which the substance of the muscular fibres becomes partially converted into fat, and which also is sometimes due to alcoholism.

The Nervous System is more prone to suffer in chronic alcoholism than any other part of the body, except perhaps the liver. The first effect of a large dose of alcohol is to stimulate the nervous system, as already described. This is followed by a dulling of the nervous faculties, which comes on rapidly in proportion to the amount taken. The phenomena of intoxication are unhappily too familiar to require description, mental incoherence and muscular incoordination (lack of control over the muscles) being the most prominent features.

When the dose of alcohol is still larger, a condition of profound unconsciousness is produced (coma), which may be difficult to distinguish from other forms of unconsciousness.

Delirium Tremens is another nervous condition, which may rarely follow a single debauch, but much more commonly affects the chronic toper. In some cases the immediate exciting cause is a mental shock, or lack of food, or a surgical injury. Alcoholic subjects suffering from any acute disease are liable to this form of delirium, and their chance of recovery is greatly diminished.

Insanity of a more prolonged character than that characterising delirium tremens is an occasional result of alcoholism.

Besides the nervous diseases already named, a chronic thickening of the membranes covering the brain and spinal cord, gradually progressing and finally fatal, is often the consequence of prolonged alcoholic indulgence.

Various Degenerative Diseases are produced by alcohol. It has been well called by Dickinson the very “genius of degeneration.” Such degenerations are by no means confined to the intemperate; they are seen in those who are of what would usually be considered moderate habits. The stomach, liver, lungs, and probably the kidneys, are the main organs to suffer in this way. It is probable that the effect on the kidneys only occurs when a gouty condition is developed. In all these cases there is an overgrowth of fibrous tissue, with atrophy of the proper gland structures.

Gout is the common nemesis of those indulging in alcoholic beverages, more especially wine and beer, due to the excessive formation or retention of urate of soda in the body. This produces inflammation of the joints, and other evils—among them the gouty kidney, named above, which is always ultimately fatal. Rigid arteries are likewise commonly due to alcoholism and gout. If one of these bursts in the brain, apoplexy results.

Longevity is diminished by immoderate indulgence in alcohol. The statistics of Temperance Insurance Societies, show much better results among teetotalers than among moderate drinkers. It is only fair to add that although the latter are supposed to consist of moderate drinkers—and particular enquiries are always made on this point before insurance—it is probable that a large proportion of them exceed 1½ ounces of alcohol per day. Making due allowance for this fact, the statistics show a great superiority in the expectation of life of teetotalers.

Factors Modifying the Effects of Alcohol.—1. Age and Sex.—Until adult life is reached, total abstinence from alcohol should be enforced. The delicate nervous system of children is easily disturbed by it, and it appears in some measure to retard growth. Another argument against giving alcohol before adult age is reached, is still more important. It is at this period of life that habits are chiefly formed, and a craving for alcohol may be insidiously produced, destined to have most baneful results.

Old people, if ordered spirits for medical reasons, should drink them well diluted.

Women are much more easily affected by alcohol than men, and if they acquire the habit of excess, the hope of reformation is even less than with men.

2. Exercise has a most important influence in modifying the effects of alcohol. Those of sedentary occupations and living in towns, cannot oxidise as much as those engaged in active out-door work, and are consequently much more prone to suffer. A game-keeper in the Scotch Highlands may possibly live to a good old age, notwithstanding the fact that he consumes an amount of whiskey that would have sent a sedentary man to his grave in the course of a few years.

3. The Condition of the Stomach has also great influence. When the stomach is empty, alcohol produces at once a powerful reflex stimulation of the heart, and becomes quickly absorbed into the circulation. Thus intoxication may be produced by a quantity that would have had little effect if taken with a meal.

4. The State of Concentration or Dilution modifies greatly the action of alcohol, the local action on the stomach and the reflex stimulation being much greater than when it is concentrated, and injurious effects being much more likely to occur.

5. Cold and Heat modify the action of alcohol. A smaller quantity of hot spirits and water will intoxicate than of cold; the heat stimulating the heart, and so making the absorption of the alcohol more rapid. A glass of hot spirits and water will often cause sleep, by drawing the blood towards the abdominal organs. The fact that persons, who have been drinking spirits in a warm room, on going out into the cold air become suddenly intoxicated, seems opposed to what has been already said. But probably this is due to the cold causing contraction of the arteries of the skin, and so driving more of the blood loaded with alcohol to the internal organs and the brain (Brunton).

6. Mental Occupation has some influence in modifying the effects of alcohol. Topers have found that if they try to converse during their debauch—the conversation implying increased functional activity of the brain, and therefore a freer circulation of blood in it—intoxication occurs much more readily, than when the mind is not active.

7. Disease modifies greatly the effects of alcohol. In some diseases, as in inflammation of the lungs and in fevers, it can be given in large quantities without producing intoxication; and in these conditions it lowers the temperature. In other diseases, especially gout and kidney disease, its use is nearly always followed by bad results.

The Advisability of Alcohol as an Article of Diet in Health.—In dealing with this difficult point, two sets of facts require consideration, those obtained as the result of Physiological observations (see page [56]), and those which are the result of Experience. There can be no doubt that the former are much more reliable than the latter. Experience is very prone to give fallacious results, especially when questions of appetite are concerned. In making a trial of abstinence, the mistake has been commonly made of only prolonging the investigation for a few weeks, and then comparing results. Such a method is, however, very unfair, and is certain to lead to an unreliable conclusion.

The records of experience under certain conditions have, however, been so extensive, as to lead to trustworthy results. It has been abundantly proved that prolonged muscular work is best undergone during total abstinence from alcohol; and that the extremes of heat and cold and the exposure and exertions of marching armies, are best borne under similar conditions.

The artificial character of town life is commonly adduced as an argument for the moderate use of alcohol. In the case of healthy workers, this does not hold good; many of our hardest workers and thinkers take no alcohol.

The universality of the habit of taking stimulants is a curious argument on the same side, though if the habit be bad, this can be no more reason for continuing it than can the prevalence of vice be an excuse for indulgence in it.

The two chief physiological points bearing on the advisability of alcohol as a part of one’s daily diet are—its food properties, and its effect on the appetite and digestion.

It has been already stated that a quantity of alcohol under 1 or 1½ ounces may become oxidised in the system, and may thus form a source of heat. But in all probability, although it may be regarded as a food, it is a most inconvenient one, inasmuch as it diminishes the oxidation of other foods. It has been aptly compared in this respect to sulphur, which is an oxidisable material, but which, when it is burnt in a chimney, in which the soot is on fire, will put an end to the combustion of the latter. Its value as a food, under normal conditions, is practically nil.

Its Effect on the Digestive Organs is three-fold. (a) The contact of alcohol with the mucous membrane of the mouth and stomach, acts as a reflex nervous stimulus, which in moderation excites an increased flow of gastric juice. (b) It also increases the activity of the movements of the stomach. In cases of weak digestion, therefore, small doses of alcohol may, at times, be useful. (c) The effect of alcohol on the food taken varies with its degree of dilution. Concentrated alcohol coagulates albumin, and so stops digestion; largely diluted alcohol has no such effect.

The late Dr. Parkes, the greatest authority on the dietetic use of alcohol, has summarised the argument as to the dietetic use of alcohol as follows:—

“But what, now, should be the conclusion as to the use of alcohol in health after growth is completed? Admitting the impossibility of proving a small quantity to be hurtful, and at the same time acknowledging the dangers of excess, there arises an argument which seems to me somewhat in favour of total abstinence. No man can say when he has passed the boundary which divides safety from harm; he may call himself temperate, and yet may be daily taking a little more than his system can bear, and be gradually causing some tissue to undergo slow degeneration. He may be safe, but he may be on the verge of danger.

“This uncertainty, coupled with the difficulty at present of saying what dietetic advantage is gained by using alcohol, seems to me rather to turn the scale in favour of total abstinence instead of moderate drinking. But if any one honestly tries, and finds he is better in health for a little alcohol, let him take it, but he should keep within the boundary line, viz., that 1½ ounces of pure or absolute alcohol in twenty-four hours form the limit of moderation. I do not then think he can do himself any harm.”

The Varieties of Fermented Drinks.—The three chief kinds of alcoholic beverages are malt liquors, wines, and ardent spirits. In addition, we may mention cider and perry, which are the fermented juices of apples and pears respectively; and koumiss, which the Tartars prepare by fermenting mare’s milk, though it may also be made from the milk of other animals.

All Beers, Ales, and Porters are prepared from malt, which is the germinating grain of barley. The fermentation of the sugar in the barley produces alcohol, the amount of which varies in different cases. In Pilsener beer it is 3½ per cent. of absolute alcohol; in stout and porter 5 to 6 per cent. The hop which is added to the fermenting barley, gives to beer its characteristic bitterness.

London Porter is coloured with black or roasted malt; stout is only a stronger form of porter. Bottled ales are generally stronger than those on draught, and being slightly effervescent, may agree better.

The effect of alcohol in beer is modified by the hops, which help in producing drowsiness. Beer has a marked tendency to produce obesity, more so than any other alcoholic beverage. Its influence in the production of gout is also very great.

Substitutes for Malt have been largely used. Thus by the action of sulphuric acid on starch, an artificial form of sugar is produced, which is largely used in place of malt for making beer. Many recent cases of poisoning by arsenic have been traced to the use of impure sulphuric acid in manufacturing this form of sugar.

The detection of arsenic in organic liquids requires great care, as so many compounds of arsenic are volatile, especially in the presence of chlorides, as in beer. To detect arsenic in beer a pint of the beer is evaporated to dryness, and treated with 20 c.c. of strong sulphuric acid, heated, and 20 c.c. of strong nitric acid added drop by drop. Violent action occurs: if possible 20 c.c. more of nitric acid are worked in. Transfer the liquid to a small flask, and expel the nitric acid by boiling. By this means all chlorine is expelled, the arsenic is oxidised and the organic matter destroyed. SH₂ gas is now passed into the acid liquid for some hours, the precipitated sulphur and any sulphide filtered off and extracted with ammonia, which dissolves any sulphide of arsenic. The liquid so obtained is subjected to Marsh’s test. (See page [216].)

In the making of beer from malt, the first stage is to malt the barley, i.e. leave it spread on floors for ten days after soaking. This allows germination to take place, in which process the insoluble starch is converted into starch, dextrine, maltose and glucose. After the dried malt has been screened to break off the sproutings, the brewer places it in the mash-tub, with water, at a temperature of 160° F. This completes the transformation of the starch into glucose. The wort is now boiled to stop the process, and the albumin from the grain is thus coagulated. Hops are added at this stage. The boiled liquid is passed into shallow vessels and cooled. The proper temperature for “top” yeast is 60° F., for “bottom,” or Bavarian yeast, a much lower temperature is desirable. When the desired temperature is reached, the liquid is run into the fermenting tun along with yeast. The varieties of beer are due in part to the degree of completeness of fermentation of sugar allowed. If too complete, the beer does not keep well.

Wines are produced by the fermentation of the juice of the grape. The wine produced may be bottled before or after fermentation is complete; in the former case, an effervescing wine is produced, such as the sparkling wines of the Rhine and the Moselle, or champagne. When the sugar is nearly all fermented a dry wine is obtained, of which Bordeaux and Burgundy, Hock and Moselle, are examples.

The difference in colour between red and white wines is produced by allowing the juice in the former to ferment in contact with the skins, from which the colouring matter is extracted by the alcohol. Both red and white wines may be obtained from either red or white grapes. From the skins also are extracted a salt of iron, and a peculiar form of tannin. Tartaric and acetic acids, and tartrate of potass, are present in varying quantities in wines; in old wines the tartrate separates as bitartrate of potass, forming with tannin and colouring matter the “crust” of port and other wines. The “bouquet” of wines is due chiefly to certain volatile bodies, such as pelargonic ether. The proportion of alcohol in wines varies from 6 to 14 per cent. As fermentation is stopped by the presence of 14 per cent. of alcohol, any larger amount of alcohol than this must have been added to the wine.

Wine, like beer, has a strong tendency to produce gout, especially the sweet and strong wines. It has not, however, the same tendency to induce obesity.

Spirits differ from the two last groups, to begin with, in the amount of alcohol they contain. Thus, English beers contain from 3 to 6 per cent., German beers from 2 to 5 per cent., wines from 8 to 20, and all kinds of spirits from 37 to 58 per cent. of alcohol. They differ in the absence of the bitter principle of beer and much of the salts and sugar and ether of wines. They are all prepared by the distillation of some previously fermented liquor. Brandy ought to be made by the distillation of wine; and then contains, besides alcohol and water, small quantities of acetic, œnanthic, butylic, and valerianic ethers. But much of the brandy sold is simply made from potato spirit, by the addition of acetic ether, burnt sugar, etc. The starch of potatoes is converted into dextrin and dextrose by dilute acids, and then fermentation allowed. By the use of patent stills, all bye-products can be separated, a fairly pure alcohol known as silent spirit being produced. This is largely employed in manufacturing spirits and in fortifying wines.

Whiskey is prepared from malted barley, or from a mixture of grains, to which a sufficiency of malt to convert their starch into sugar has been added. In grain whiskey the distillation is effected by steam in a patent (Coffey’s) still, which separates most of the bye-products (fusel oil, etc.) from the spirit. In malt whiskey, distilled in the old-fashioned pot-still, these bye-products are not separated.

The improvement of whiskey effected by keeping is not due (Bell) to the diminution of fusel oil. Such a diminution does not occur. The percentage of alcohol diminishes by keeping, 6 to 8 per cent. proof spirit being lost by five years’ storage in wood. “Fusel oil” is a mixture of alcohols of higher boiling point than ethylic alcohol (amylic, propylic, etc.). Even in a bad whiskey not more than ¹ ∕ ₁₀ per cent. of fusel oil is present (about one grain in a glassful). Experimentally no marked effects have been produced by fusel oil, when it is less than 1 per cent. Possibly the presence of furfurol, of which there is a trace in malt whiskey, which disappears on keeping, may partially explain the disagreeable flavour of new whiskey. But it is fairly clear that those who argue that it is bad whiskey and not good whiskey which does harm are speaking without knowledge. It is not the quality but the quantity of whiskey which is responsible for so much moral and physical evil.

Gin and Hollands are obtained from barley, and flavoured with juniper berries and other materials. The oil of juniper stimulates the urinary excretion.

Rum is obtained by the distillation of molasses, and is usually kept for a long time in oak barrels. It is said thus to acquire more astringent matters than other spirits contain.

The legal limits of dilution of whiskey, brandy and rum is down to 25 degrees under proof, and of gin down to 35 degrees under proof. (For definition of proof spirit, see page [55]). The amount of alcohol in an alcoholic liquor is determined by distillation of 100 c.c., making up the distillate to 100 c.c. by the addition of distilled water, and then taking the specific gravity of a portion of this liquid by the aid of the specific gravity bottle. The percentage of alcohol corresponding to a given specific gravity is given in tables prepared for this purpose.

Prolonged indulgence in spirits produces the various organic diseases already described, and unless well diluted they are more harmful than beers or wines. They differ from wines and beers in not tending to produce gout, and from beer in not leading to obesity.

[CHAPTER IX.]
WATER.

Uses of Water.—Water is a prime necessity of life. In its absence life can only exist in lowly organised beings, and in them only in a dormant state. From a hygienic point of view, the uses of water are four-fold:—(1) It is an essential part of our food, not only serving to build up the tissues of the body, but also preserving the fluidity of the blood and aiding excretion of effete matters. (2) It is necessary for personal cleanliness, of which the importance can scarcely be exaggerated. (3) In the household it is essential for cooking, as well as for washing the house, the linen, and various utensils. (4) By the community at large it is required for water-closets and sewers, for public baths, for cleansing the streets, and for horses and other domestic animals, as well as in many manufacturing processes. It is obvious that the water to be used for domestic and general purposes, need not be so pure as that for drinking purposes. Hence, a double supply was proposed for London in 1878, by the Metropolitan Board of Works—a less pure river supply for general purposes, and a deep chalk-well supply for drinking purposes. The scheme, however, rightly fell through, because of the expense of a double source of supply, and the danger that the impure water would, through carelessness or ignorance, be often used for drinking purposes, when it happened to be nearest at hand.

Quantity of Water Required.—The quantity of water required for all purposes has been variously stated by different authorities. The quantity required for drinking purposes is found to bear a relation to the weight of the individual, being nearly half an ounce for every pound weight, or 1½ gills for every stone weight. Thus, a man weighing 150 lbs. would require 3¾ pints. Of this water, about one-third is taken in the food; the remainder, averaging 2½ pints, being required as drink. If we add the water required for other purposes, according to De Chaumont, 1 gallon is required for drinking and cooking, 2 gallons (not including a bath) for personal cleanliness, 3 gallons for a share of utensil and house washing, 3 gallons for clothes washing; and if a general bath be taken, 3 gallons more; making a total of about 12 gallons, to which 5 gallons must be added if there is a water closet.

In hot summer weather the consumption is about 20 per cent. above the average of the year; and frost often increases the amount 30—40 per cent. above the average, owing to the bursting of pipes, or the loss from taps foolishly left open to prevent bursting.

Water companies usually reckon 30-60 gallons for each individual, to allow for the water required for scavenging and manufactories and for waste. In large houses and hotels where baths are freely used, often as much as 70 gallons per head is used, and in hospitals the amount averages from 60 to 90 gallons per head. The following is Parkes’ estimate of the daily allowance for all purposes:—

It has been proposed to put a water-meter to each house, so that the rate may be in proportion to the amount of water used. The plan is objectionable for two reasons: 1st—Because it tends to restrict the necessary use of water for purposes of cleanliness. A scant supply of water is always followed by uncleanliness of house and person, with its consequent diseases; at the same time closets may be imperfectly flushed, and may become choked. 2nd—Because of the primary expense of the meter, and of its maintenance.

Sources of Water Supply.—All our drinking water is obtained in the first instance, by a natural process of distillation on a large scale. The sun is constantly causing evaporation from sea and land. The vapour produced, being condensed by a lower temperature, returns to the earth as snow, dew or rain. All these natural products have been at times utilised as sources of drinking water.

1. Dew has on rare occasions been utilised at sea by hanging out fleeces of wool at night and wringing them out in the morning. A much better plan is—

2. The Distillation of Sea-water. This can easily be managed now that steam power is so largely used. It has even been employed on land, when it was necessary temporarily to continue the use of water derived from an impure source. The first part distilled should always be rejected, as it is always impure. Distilled water is “flat” in taste, owing to its containing no dissolved gases. It can be aërated by letting it drop a considerable distance from one cask into another, through small openings in the upper one, and by filtration through charcoal. Non-aërated water is not easily absorbed into the circulation, and occasionally causes illness.

3. The utility of Melted Snow and Ice is obviously very limited. Moreover, its use is not free from danger if the ice is derived from contaminated water. Outbreaks of enteric fever have been traced in the United States to the taking of ice obtained from impure water.

4. Rain-water is a much more important source of water supply, and after passing through the soil it constitutes the chief part of the water we drink. The term, however, is properly restricted to the water collected immediately after its descent from roofs, etc. Its purity depends on three conditions—the character of the air it passes through, the cleanliness of and absence of lead from the channels through which it runs, and the condition of the water-butts in which it is stored. Rain-water is soft; in fact, too soft to be pleasant to the palate. In passing through the air, it carries with it a certain proportion of its constituents; in towns especially ammonia, soot, etc.; near the sea, it generally contains some salt; and being soft and having dissolved oxygen from the air, it dissolves an appreciable amount of lead from roofs or gutters.

The Rivers Pollution Commissioners found that out of eight samples of stored rain-water only one was fit to drink. They came to the conclusion that rain-water, collected from the roofs of houses and stored in underground tanks, is “often polluted to a dangerous extent by excrementitious matters, and is rarely of sufficiently good quality to be used for domestic purposes with safety.” Also, that in Great Britain, and more particularly in England, we shall “look in vain to the atmosphere for a supply of water pure enough for dietetic purposes.”

The use of rain-water for drinking purposes is only justified in isolated country houses where no better source is available; and under these circumstances the greatest care should be taken to prevent contamination with lead or organic impurities.

The amount of water falling on any impervious material obtainable from rain can easily be estimated, if the amount of rainfall and the area of the receiving surface are known. The average annual rainfall in this country is 33 inches (see page [236]).

We may assume the amount practically available to be 20 inches per annum, and the area of the receiving surface 500 square feet. Multiply the area by 144, to bring it into square inches, and this by the rainfall, and the product gives the number of cubic inches of rain which fall on the receiving area in a year. One cubic foot, or 1,728 cubic inches, of water being equivalent to 6·23 gallons, the number of gallons of water can be easily calculated. To calculate the receiving surface of the roof of a house, do not take into account the slope of the roof, but merely ascertain the area of the flat space actually covered by the roof. This may be done roughly by calculating the area of all the rooms on the ground floor, and allowing an additional amount for the space occupied by the walls. It has been estimated that, even if a rain-water supply for towns were desirable, the amount collected from the roofs of houses would scarcely average two gallons per person daily—assuming the average rainfall to be 20 inches, and that there was a roof area of 60 square feet for each individual.

The amount practically available from rain falling on different soils varies with their porosity and slope. Thus, according to Professor Rankine, the proportion of the total rainfall available is as follows:—

• Nearly the whole on steep surfaces of granite, gneiss, and slate;
• From three to four-fifths on moorland hilly pastures;
• From two-fifths to half on flat cultivated country; and
• None on chalk.

By available rainfall is meant the amount remaining after allowing for percolation, etc., which can be stored in reservoirs.

5. Upland Surface Water is the water collected in hilly districts, as on moorlands, at the head of a river. By its utilisation for drinking purposes, the sources of water for the river are interfered with, and any water company or local authority using such a source is, therefore, required to run into the stream a quantity of water equal to a third of the available rainfall. The limited and regular supply thus furnished to the stream is found to be advantageous for industrial purposes as its flow is equalised, and the violence of floods mitigated.

In the utilization of upland surface water the water from the surrounding hills is collected at the bottom of a valley, in an artificial, strongly-constructed lake; or in a natural lake, as in Loch Katrine (from which Glasgow is now supplied).

Upland surface water is nearly always soft. Its use is much more economical than that of hard water. It may be brownish, from the presence of peat, but this is not objectionable, so far as health is concerned. Its occasionally solvent action on lead is a more serious objection. The population of many parts of Yorkshire and Lancashire have suffered severely from chronic lead poisoning, due to the action of certain upland surface water on lead service pipes. Only the waters giving an acid reaction possess this plumbo-solvent power. (See also page [82].)

6. Springs supply water which, originally derived from rain-water, has percolated through the soil until it reaches some impervious stratum, and has then run along this, until it arrives at the point at which the impervious stratum reaches the surface of the soil. A spring is thus the outcrop of the underground water. Springs are divided into (1) land springs, and (2) main springs. The former flow from beds of drift or gravel lying on an impervious stratum. They are very subject to seasonal variation, and may dry up in certain years; while main springs occurring in chalk, greensand, or other regular geological formation, constantly supply a certain amount of water. Springs often occur in connection with “faults” in geological strata, and then may appear on table-lands and high elevations, unlike springs caused by alternation of strata in valleys of denudation. The two kinds of springs are shewn in Fig. 5 and 6.

In the land spring water crops out at the point where the porous stratum ceases. Deep springs may crop out in the same way as land springs, except that they appear at the bottom of deeper strata. Or they may be formed by faults. Both these are shown in water having percolated through the chalk beneath the superficial clay, is stopped at the “fault” by the lack of continuity of the chalk stratum, and is consequently confined under pressure. It therefore makes its way to the surface, forming a spring. In its passage underground, water (owing partly to the carbonic acid it has obtained from the air and soil), is able to dissolve small quantities of chalk, sulphate of lime and of magnesium, and traces of oxide of iron, aluminium oxide, and silica. Spring-water possesses an equable temperature, generally about 50° Fahr., while impounded or river water is always warm in summer and cold in winter. Spring water is well-aerated, while river water, and still more rain-water, are flat.

Fig. 5.—Land Spring.

Fig. 6.
Main Springs formed in Valley of Denudation and by a Fault.

7. Wells may form the best or worst sources of water-supply according to their depth and the means of protection against contamination. There are two kinds—Surface wells and deep wells.

Surface Wells do not usually descend further than 15 or 20 feet, and have no impervious stratum between the source of water and the surface of the well. They catch the subsoil or underground-water, which percolates into them from the surrounding soil, and the character of the water they receive will therefore vary with the nature of their surroundings. If there is a cesspool near, this may simply drain into the well. All the soakage from a considerable distance may find its way into the well. In villages and isolated places the water of surface wells is commonly contaminated. One hole may be dug in the garden for a well, and another for a cesspool, while there is possibly a farmyard near at hand—the soakage from the cesspool and farmyard soaking into the well. Danger may also arise from more distant contamination. The ground water which is tapped by the well is an underground stream flowing towards the nearest brook. Heavy rains swelling the ground water may wash impurities from cesspools, leaky drains, etc., at a considerable distance, and carry these into wells lying between these sources of pollution and the brook into the bed of which the underground water ultimately discharges. The danger of contamination of the water in the well by the contents of the cesspool is much greater in the relative position shown in A than in the position shown at B, Fig. 7. After heavy rain, when the underground water is swollen, the danger of contamination is still further increased. The model bye-laws of the Local Government Board state that a cesspool must be at least 40 feet distant from any well, spring, or stream. Probably this is insufficient for safety; cesspools ought to be entirely forbidden. If necessary to retain a surface well, it should be protected nearly to the bottom with brick, lined with an impervious layer of cement so as to prevent water from entering the well except near its bottom. In modern wells iron cylinders are employed to line the upper part of the well; and large glazed earthenware pipes arranged vertically and with water-tight joints are sometimes used for the same purpose.

Fig. 7.
Showing Varying Danger of Contamination of a Shallow Well, according to Level of Underground Water and Relative Position of Cesspool and Well (after Galton).

Deep Wells are made by digging a surface well, as above, except that the ground water is prevented from entering the well by means of impervious steining; and then boring from the bottom down through the subjacent impervious stratum until a water-bearing stratum is reached. The difference between a surface well and a deep well is shown in Fig. 8 by A and B. Where the water in this stratum is retained under pressure, deep wells are known as Artesian Wells. Such Artesian wells have been sunk in London. Rain, falling on the chalk hills which lie to the south and north of London, percolates through the chalk downwards, and then laterally, until it lies in the concave London basin. Here the clay stratum above it prevents its escape upwards; and being confined under considerable pressure, it rises to the surface, or into a well in the superficial gravel, when the clay is tapped. In Fig. 8, B is an Artesian well if the pressure is such as to make the water rise through the London clay, when this is cut through and the underlying chalk is reached. C is a well in the chalk, which does not pass through an impervious stratum, and therefore comes within the above definition of a surface well; but as regards depth required to be dug before water is reached it is more like a deep well.

Fig. 8.
Showing Difference between Deep and Superficial Well. A.—Surface Well in Gravel. B.—Deep Well, going through Gravel and Clay to Chalk. C.—Well in Chalk District.

Among the deepest Artesian wells are Grenelle (1,800 feet), and Kissingen (1,878 feet.) The sinking of a deep well and severe pumping of its water may exhaust all the neighbouring wells for two or three miles. There is also danger of contamination from neighbouring cesspools when the upper part of the deep well is not properly constructed. The area exhausted by a deep well undergoing pumping is represented by an inverted cone, having a very wide base, and with a convex inner surface pointing towards the well.

For country places deep-well water is much preferable to water from streams, as streams are very liable to be contaminated by the sewage of houses higher up in their course, or even by that of houses close by. A good well should be at least thirty feet deep—preferably fifty feet and should always be lined with impervious material, except near its bottom. The absolutely water-tight and impervious condition as well as the distance of all drains or cesspools in the vicinity should be ascertained before deciding whether the drinking water from a given well is above suspicion. The direction of flow of the underground water should also be determined. This may be done by measuring the level of all the wells in the neighbourhood. Possible sources of pollution at points from which ground water is flowing towards the well are much more dangerous than those nearer than the well to the river towards which the underground water is flowing (see Fig. 7). Steam pumping greatly increases the area from which contamination may be derived.

An excellent plan to obtain water for villages, in a gravelly soil, is to sink a Norton’s Abyssinian tube well for fifty or sixty feet.

In towns it is preferable to trust to the public water supplied, rather than to any private well; and in villages, a general supply from a pure source should also be provided.

The water is obtained from a well by a pump or a draw-well. The former is a safer as well as a less laborious plan. The pump should be fixed some distance from the well, and the aperture through which the pump pipe passes should be rendered water tight. Lead pipes should be avoided, as well water not infrequently has plumbo-solvent properties.

8. Rivers and running streams originate in upland surface water or springs, and their water should be of the same quality as these. Unfortunately, they acquire a large amount of impurities in their course. Towns commonly pour their more or less clarified sewage into them; and the discharge of crude sewage from hamlets and single houses on the banks is still far from uncommon. With the more rigid enforcement of the Rivers Pollution Acts, this pollution of rivers will become less frequent; but river water previously contaminated by even small amounts of sewage cannot be regarded as an ideal source of water-supply.

If no contamination be present in the water of a river, it forms a good source of water-supply; being running water, it is always fairly well aërated, and is not usually so hard as spring-water.

Even if sewage has entered a river, it is asserted that it becomes a safe source of water-supply, after passage through filter beds, the sewage having been got rid of in four ways.

1st.—By subsidence, the organic matter settling to the bottom.

2nd.—By the influence of water-plants, which assimilate ammonia, nitrates, etc., and give out nascent oxygen.

3rd.—Oxidation. Doubtless a large amount of the nitrogenous matter does become oxidised in its course down a river, and in this condition is harmless. The river Seine becomes greatly polluted as it passes through Paris, but so far as chemical analysis can determine its condition, it is purer 30 miles below the city than it was before it received the sewage of the city.

4th.—It is highly probable that the germs (or micro-organisms) of enteric fever and other diseases known to be propagated by polluted water, are practically or wholly destroyed in the struggle for existence with the natural micro-organisms of river-water. When to this is added the fact that river-water supplied to large communities is carefully filtered through sand, after having been stored in reservoirs, in which the chief impurities have time to settle, it is not surprising that the experience of those communities like London, which are supplied with river-water, usually shows no evidence of evil ascribable to drinking this water. For over 30 years the inhabitants of London have been drinking filtered water from the river Lea and from the Thames above Teddington, and this gigantic experiment on a population which has increased from 2½ to 5 millions has not been accompanied by any conclusive evidence of evil effect.

In regard to the comparative merits of the various waters described, it will be useful to give here the classification made by the Rivers Pollution Commissioners in their sixth report:—

Wholesome		1. Spring Water		Very palatable.
		2. Deep-well Water
		3. Upland Surface Water		Moderately palatable.
Suspicious		4. Stored Rain Water
		5. Surface Water from Cultivated Land		Palatable.
Dangerous		6. River Water to which Sewage gains access
		7. Shallow-well Water

Passage through certain geological strata has a great influence in rendering water palatable, colourless, and wholesome by percolation.

The following strata are said by the Commissioners to be the most efficient:—(1) Chalk, (2) oolite, (3) greensand, (4) Hastings sand, (5) new red and conglomerate sandstone. Fissures or cracks in these strata may cause the water to pass through them unpurified by filtration.

[CHAPTER X.]
THE STORAGE AND DELIVERY OF WATER.

The methods of storing and delivering water will vary with its source. In rural districts, deep wells and springs are the best sources of supply; but in large towns they are found to be insufficient for the wants of a rapidly-increasing population; and they can only be multiplied in a given district within certain limits, as every well drains a large surrounding area. The supply from surface wells in gravel or sand beds or in chalk districts is liable to fail in seasons of drought; but deep wells in oolite or chalk formations, and in the new red sandstone, generally yield a constant and abundant supply.

When the water is supplied from upland surfaces, springs, or small streams, a collecting reservoir is required. This is generally a natural valley below the level of the source of supply, but of sufficient elevation above the place supplied to allow the water to be distributed by gravity, without any pumping apparatus. The reservoir should be large enough to hold five or six months’ supply, and its embankment should be perfectly water-tight, and of great strength.

When water is collected from upland surfaces, it is important to know the amount of rainfall to be reckoned on. If we know the area of the surface which drains towards the reservoir, and the average rainfall, the total rainfall is easily calculated. This will, however, differ greatly from the available rainfall, owing to the losses from penetration into the ground, evaporation, and other causes. The amount lost will vary, according to the season, from one-half to seven-eighths of the total rainfall; and according to the soil (page [68]). The proportion of percolation in the chief water-bearing strata surrounding London varies from 48 to 60 per cent. (Prestwich). It is less when the ground is steep and the rainfall rapid, and usually less in winter than in summer.

Water collected near its actual place of fall, and from uncultivated districts, is always purer than that collected further from its source, and from cultivated land.

From the collecting or impounding reservoir, water is carried by the aqueduct or conduit either directly into the service-pipes, or when the pressure is too great, into a second service-reservoir, resembling the impounding reservoir in general structure, and capable of holding a few days’ supply.

This must be high ground, above the level of the highest houses to which water has to be supplied, as water cannot rise above its own level. When this cannot be arranged, the water is pumped into tanks at a higher level, and distributed from them.

The greatest hourly demand for water being double the average hourly demand, the water-mains supplying a town must have double the discharging power that would be required, supposing the demand was uniform. The first requisite of a supply of water is that it should be abundant, and sufficient in amount for any extra strain on its capacities. Water ought to be laid on to every house, and to at least two floors of the house. Anything preventing free access to water, militates against cleanliness.

Cast-iron is the most serviceable material used in the construction of the main water-pipes; it is coated with pitch, or Dr. Angus Smith’s varnish, or with magnetic oxide of iron (Barff). The service-pipes to each house are generally made of lead, and the ease with which this material can be bent and curved, and carried to the different floors of a house, makes its use very convenient. Lead pipes, furthermore, can be easily obliterated in case of bursting, and so any waste of water and flooding of the house minimised. Some kinds of water, unfortunately, act on and dissolve lead; this is especially true of soft waters and those containing organic matter. Shallow wells, being very liable to organic pollution, ought never to have the supply-pipe of their pumps made of lead. With hard waters, lead pipes may generally be used safely. When the quality of the water renders lead pipes objectionable, the use of iron, tin, zinc, tinned copper, earthenware, gutta-percha, and other materials, has been suggested. Of these, cast and wrought-iron pipes are the most serviceable, or pipes composed of an inner lining of block-tin and an outer of lead, a layer of asbestos intervening to prevent galvanic action between the metals. According to Rawlinson, “supply-pipes of wrought-iron are cheaper, stronger, and more easily fitted than service-pipes of lead;” but it is urged against them by Perry, that with soft water they become choked by rust in a few years. If galvanized they are more durable. Cast-iron pipes are rusted less easily than wrought-iron.

When the water-supply is from a river, filtering beds are needed, in addition to the parts of a water-service hitherto described. Moreover, since the river is usually at a low level, the water, after passing through the filtering beds, requires to be pumped into raised tanks, from which it is delivered.

In laying down water-pipes, in the streets and to houses, it is very important to make the distance between them and all drains and gas-pipes as great as possible. Suction of gases or liquids may occur into leaky pipes, even though these contain water, and still more when they are empty; and disease has occasionally been traced to this source. Thus if sewers and water-mains are laid in the same trench, foul matters which have escaped into the soil from the former may be sucked into the latter. This may happen if the water-mains are leaky, even when they are running full. Experiments have shewn that the flow of water causes a partial vacuum and insuction at the defective points. During intermissions of supply when the mains are partially or entirely empty, the danger of leakage into them is still greater. Coal-gas has been similarly sucked into water-mains.

The pipes bringing the water to a house may be kept constantly filled with water, or only for a limited time once or twice a day. The intermittent system of supply necessitates the provision of cisterns or water-tanks, in which water can be stored in the intervals of flow of water. With a sufficient and properly-distributed public supply of water, no cistern ought to be required.

Cisterns.—Cisterns for the supply of potable water may be made of iron, slate, stone, glass, glazed earthenware, or brick lined with Portland cement. Other materials have been used, as timber, lead, and zinc. Timber is inadvisable, as it easily rots; lead is very objectionable, owing to the possible solvent action of the water on it. Zinc or galvanized iron cisterns are also acted on by soft water; but they may be used with most waters. Galvanized iron is iron coated with a thin layer of zinc. Iron cisterns soon rust; but this may be prevented by giving them a coating of boiled linseed oil before they leave the foundry. Stone cisterns are too heavy for use, except in basements. Slate cisterns are good, but are apt to leak; the points of leakage have occasionally been stopped with red lead, which is attacked by the water, and thus lead poisoning results. If the slate is set in good cement (not mortar, as this makes the water hard), it is a good material for a cistern.

Every cistern should have a well-fitting lid, always kept closed, to avoid the entrance of dust of various kinds, or even dead cats, birds, etc. Noxious gases may be absorbed by the stagnant water.

The cistern should be easy of access. If it is indoors, the cistern room should be well ventilated; and in any case the cistern should be periodically visited and cleaned out. When the cistern is full, a ball-tap prevents any further flow of water; and if this does not act properly, an overflow pipe carries off the excess of water.

Cisterns badly arranged or neglected have been in the past a common source of disease. (1) The overflow pipe should not pass into any part of the water-closet apparatus or the soil-pipe, or into the supply pipe to the water-closet.

Where the overflow-pipe discharges into the soil-pipe or closet pan, foul gases or even solid particles may find their way into the cistern.

(2) No water-closet ought to be supplied from the same cistern as supplies drinking water, as the pipe leading down to the closet may when the cistern is accidentally empty carry noxious effluvia into the cistern. A separate flushing cistern capable of discharging two to three gallons of water should be provided for each closet.

With a constant supply of water, cisterns are only required for water-closets and for hot-water apparatus (see pages 168 and 164).

Constant and Intermittent Services.—With an intermittent service of water, during the intervals of supply, water is only obtainable from cisterns, water-butts, etc. The objections against this system are that—(1) The cisterns required are expensive, and liable to get out of order and become foul. (2) Their overflow pipes may improperly communicate with the soil pipe or with some other part of the drainage, instead of opening into the external air. (3) Putrid gases, from neighbouring ventilating-pipes or other parts of the drainage system, are liable to be absorbed by the stagnant water in the cistern. (4) The chief objection to an intermittent supply is that, during the intervals in which the water-mains are empty, foul air and liquids from the contiguous soil and drains are liable to be sucked through imperfect joints into the pipes. (5) In case of fire, the supply of water in the system is insufficient. In certain towns rates of insurance against fire have been reduced on replacing an intermittent by a constant service of water.

On the other hand it is urged that more expensive fittings are required for a constant service; and that, when taps are left open or pipes burst, the waste of water is much greater than with a cistern supply. The balance is decidedly in favour of a constant supply without storage cisterns. Where storage cisterns are in use, the taps for drinking-water should be connected with the “rising-main,” before it supplies the cistern.

The Advantages of the Constant Service may be thus summarised:—

(1) Owing to the absence of cisterns, the risks connected with stagnant water, and with improper arrangement of overflow pipes, are obviated.

(2) The risk of suction into supply mains of external contaminations is reduced to a minimum, since the pipes are never empty.

(3) The pipes are less liable to rust. Air in the presence of a little moisture, causes rapid corrosion.

(4) There is an abundant supply of water in case of fire.

Of course, when there is a temporary stoppage of supply, as for repairs, some of the dangers incurred by an intermittent supply will arise.

[CHAPTER XI.]
IMPURITIES OF WATER.

Properties of Water.—When pure, water is colourless, or bluish when seen in large quantity. It should be quite inodorous. If, after keeping it for some time in a perfectly clean vessel, or if on heating it a smell is developed, the water is bad. Its taste should be pleasant and sparkling from the atmospheric gases dissolved in it. Bitterness generally indicates the presence of sulphate of magnesium (Epsom salts). Saltness is always a suspicious property, except in water obtained in the neighbourhood of salt mines or brine springs, or near the sea. It should be soft to the touch, and should dissolve soap easily. It should be bright and clear, and contain no suspended matters. Clear water is not necessarily pure, but turbid water is always to be rejected; the only exception being the brownish-tinged water from moors, which is not hurtful. In all other cases, printed matter should be legible through at least 18 inches of water in a clear glass cylinder. Thoroughly dissolved organic matter is less dangerous than suspended; the turbidity of water is therefore of great importance. But water may be bright and sparkling and apparently perfectly clear, and yet highly dangerous. The most important of the physical properties of water in regard to health are the absence of smell and turbidity, and these can be ascertained by even the most inexperienced. The chemical tests for the more important impurities are given (pages 85 to 87).

The impurities of water may be classed under four heads—gaseous, mineral, vegetable, and animal.

The gases ordinarily present in water cannot properly be regarded as impurities, inasmuch as they are always present, and greatly increase its palatableness. The dissolved nitrogen and oxygen bear to each other the proportion 1·42 to 1; where sewage contamination occurs, the oxygen will be diminished or disappear, owing to oxidation of the organic matter.

The amount of carbonic acid gas in water varies greatly. It may be considerable in chalk waters, and in contaminated well-water.

Mineral Impurities.—Mineral impurities are dissolved by water in its course through the soil, and so will vary with the character of the latter. 1. The water obtained from granitic formations contains very little mineral matter, often not more than two to six grains per gallon. Clay slate water is also generally very pure, as is the water from hard trap rocks. 2. The water from millstone grit and hard oolite is very pure, often containing only four to eight grains per gallon, chiefly calcium and magnesium sulphate and carbonate. 3. Soft sand-rock waters usually contain thirty to eighty grains per gallon of sodium salts, with a little lime and magnesia. 4. Loose sand and gravel waters vary greatly. They may be almost free from mineral matter, or the solids may be more than seventy grains per gallon, including much organic matter. 5. Waters from the lias clays vary somewhat, but commonly contain a large quantity of calcium and magnesium sulphates. 6. Chalk waters generally contain from seven to twenty grains of calcium carbonate, with smaller quantities of other salts. 7. Limestone and magnesian limestone waters differ from the last, in containing more calcium sulphate and less calcium carbonate, as well as much magnesium sulphate and carbonate in the dolomite districts. 8. Selenitic waters contain calcium sulphate in considerable quantities. 9. Clay waters usually possess the characters of water from surface wells, and are objectionable. 10. Alluvial waters generally contain a large amount of various salts, including the various calcium, magnesium, and sodium salts. 11. Artesian well water varies greatly in composition. It may contain a large amount of sodium and potassium salts, or a small quantity of iron, or calcium salts.

The commonest and most important mineral constituent of water is calcium carbonate, next to this calcium sulphate. These two salts are the chief causes of hardness of water. For practical purposes as regards use in domestic matters and in manufactures, the most important classification of waters is into hard and soft. The degree of hardness varies within wide limits—from rain-water, which has no hardness at all, to the water from new red sandstone rocks which sometimes possesses a hardness of 90 degrees; or wells in the gravel, in which it may be as much as 152 degrees.

The following classification of waters, according to the degree of hardness, beginning with the least hard and gradually increasing in hardness, is from the sixth report of the Rivers Pollution Commissioners:—1. Rain-water. 2. Upland surface. 3. Surface from cultivated land. 4. River. 5. Spring. 6. Deep-well. 7. Shallow-well water.

Calcium carbonate is the most common cause of hardness, and the hardness produced by it is remediable by boiling or chemical means. Calcium carbonate (chalk) is rendered soluble in water, by the carbonic acid contained in the latter, a double bicarbonate being thus formed. The air contained in the interstices of the soil through which water passes, often contains 250 times as much carbonic acid as ordinary air. The water, in percolating through the soil, dissolves this carbonic acid, and thus is able to take up a considerable amount of chalk.

The amount of hardness in any given water is expressed in degrees, one degree being equivalent to a grain of calcium carbonate in a gallon of water. Clarke’s soap test is employed to detect the amount of hardness. It consists of a solution of soap of a known strength. Soft water will form a lather at once with this; hard water will only form a lather after all the calcium salt is neutralised. The amount of Clarke’s solution required before a lather is produced, will give an estimate of the amount of hardness.

To Determine the Total Hardness take 70 c.c. of the water and place in a stoppered bottle. From a burette run in a sufficient quantity of the standard soap solution (of which 1 c.c. equals 1° of hardness), to produce a lather on shaking the water, which remains unbroken after standing five minutes. Thus, if 7·5 c.c. of the soap solution were required, the hardness is 6°·5, as 1 c.c. of the solution is required to produce a lather in soft water. The 6°·5 means 6·5 milligrammes of calcium carbonate in 70 c.c. or 6·5 grains in a gallon of the water.

To Determine the Permanent Hardness boil 70 c.c. of the water in a flask for half-an-hour; allow the precipitated carbonates of calcium and magnesium to settle. Some of the latter will be re-dissolved. Carefully decant, and make up the liquid to the original 70 c.c. with distilled water. Filter through fine filter paper and estimate hardness as above.

The amount of soap wasted in consequence of the hardness of water is very great. Thus, in the case of water of one degree of hardness, as every gallon contains one grain of chalk, 7,000 gallons would contain 7,000 grains—that is, a pound. But every grain of chalk wastes 8 or 9 grains of soap; therefore, a pound of chalk, contained in 7,000 gallons, would waste about 8½ pounds of soap. But nearly all waters are harder than this, and they not uncommonly possess a hardness of 20° or more. If the hardness be 20°, the waste would be 170 pounds of soap. This quantity would be easily used annually in a family of seven or eight persons, if we include the washing of clothes. The amount of money thus wasted can be easily estimated.

Not only does soft water require less soap, but it is much more suitable for making tea and soup, and for boiling meat and vegetables—both time and fuel being saved. The reason why better tea is made when a little carbonate of soda is added to the water is that the chalk is by this means precipitated.

Carbonate of calcium is precipitated from water by boiling it; carbonic acid being driven off, the neutral salt falls to the bottom of the vessel. This is the origin of the “fur” inside kettles, which lessens their conductivity to heat, and renders necessary a greater consumption of fuel.

The chalk may also be removed by adding to the water, while still in the reservoir, some milk of lime—that is, quicklime made into a milky solution with water. This is done on a large scale at various waterworks. The reaction may be expressed thus:—

Calcium bicarbonate + calcium oxide = calcium carbonate + calcium carbonate.

The calcium carbonate, as it is precipitated, carries down with it organic and other matters, thus clearing and purifying the water.

The hardness due to calcium sulphate is not removable by boiling. It is, therefore, called permanent hardness, to distinguish it from the temporary hardness of chalk waters, which is removable by boiling. It may, however, be partially removed by the addition of washing soda to the water, as well as the nitrate and chloride of calcium which are also present. The magnesium salts are not removable by boiling or soda. This is shown by the fact that the “fur” inside kettles does not usually contain magnesium salts.

The amount of hardness varies greatly in different waters. In the deep wells in magnesium limestone, it varies from 14°-57°; in the deep wells from chalk beds, it varies from 13° to 27° and may be higher. In the water from Bala Lake, Wales, the temporary hardness is 0°·1, the permanent hardness 0°·3; in the Loch Katrine water there is no temporary hardness, 0°·9 permanent hardness; in the water from the new red sandstone (Nottingham), the temporary hardness is 9°·6, permanent 10°·2; in a chalk spring at Ryde, temporary hardness 16°·7, permanent 3°·9 (Wanklyn). The total hardness in the metropolitan water supplies from the rivers Thames and Lea, varies from 13°·2 (Southwark Company) to 14°·6 (New River Company); in the Kent Deep Wells 20°·1; in deep wells from the chalk at Brighton it varies from 12° to 13°. In all these, the hardness is chiefly temporary.

The amount of permanent hardness is always great in water from clays, as the London, Oxford, Kimmeridge, and Lower Lias clays; or in places where there are large deposits of calcium sulphate, as at Montmartre, near Paris (hence the name Plaster of Paris, given to desiccated calcium sulphate). Water from fissures in the clay often contains, also, a large amount of organic matter.

Chlorides are always present in small quantities in water. As a rule the presence of more than 1 grain per gallon, i.e. ·7 parts per 100,000 of water, indicates contamination with some animal refuse, unless the water is derived from new red sandstone, or brine springs, or from the neighbourhood of the sea. This rule does not, however, hold universally good. The absence or the presence of only a minute quantity of chlorides indicates the probable absence of animal contamination; but in exceptional cases waters of the highest organic purity may contain more chlorides than the same bulk of sewage.

To determine the amount of Chlorine take 70 c.c. of the water, add a few drops of solution of potassium monochromate (KCrO₄). From a burette run in gradually a standard solution of silver nitrate (of such a strength that 1 c.c. of the solution is equivalent to 1 milligramme of chlorine). The silver solution forms milky chloride of silver (AgCl) by combination with the chlorine of the chlorides in the water. When all the chlorine is thus combined, the next drop of the silver solution forms a deep red tint with the chromate. The number of c.c.’s of the silver solution required to produce this effect, equals the number of milligrammes of chlorine in 70 c.c. of water, or the number of grains of chlorine in a gallon of water. To convert this into parts per 100,000, divide by 7 and multiply by 10.

To express the amount of chlorine in terms of common salt (NaCl), multiply the parts per 100,000 of chlorine by 1·65.

Nitrates in any water are suspicious; but their import varies with the circumstances under which they occur. A minute quantity of ammonium nitrate is present in nearly all waters; and the water of deep wells, especially of wells in the chalk, which, as a rule is perfectly free from sewage, may be highly charged with nitrates. Nitrates, when derived from sewage, represent a completely oxidised condition of its nitrogenous matter. Crude sewage generally contains no nitrates. Nitrites as a rule indicate more recent contamination, and therefore greater danger than nitrates. The presence of more than a trace of phosphates is a strong indication of contamination with sewage matter.

To determine the amount of Nitrites and Nitrates the best known methods are by the indigo, the phenol-sulphuric, the aluminium, or the zinc-copper couple tests. For nitrites the metaphenylene-diamine test is employed (page [85]). The following qualitative tests will suffice for elementary work.

Nitrates. An equal amount of a solution of brucine is added to the suspected water in a test-tube, then a little pure sulphuric acid is poured down the side of the tube. A pink zone is produced if nitrates are present in considerable amount.

Nitrites. A few drops of each of diluted sulphuric acid and of metaphenylene-diamine solution give a red colour with water after standing for a few minutes, if nitrites are present.

Lead is an occasional contamination of slightly acid waters. The purest and most oxygenated waters act most readily on lead; as also those containing organic matter, nitrates or nitrites. Waters containing chlorides also act on lead, the chloride of lead being sufficiently soluble to produce poisonous symptoms. Upland surface waters derived from moorlands in certain districts, e.g. around Sheffield, have been found to be capable of dissolving considerable lead from lead service-pipes. The water taken first from the tap in the early morning is the most heavily charged with lead. Such waters are very soft; but other moorland soft waters do not dissolve lead. It is the water having a slightly acid reaction which possesses this property. The source of this acid, whether sulphuric acid from the products of combustion in a neighbouring town, or an organic acid, is uncertain. The plumbo-solvent action of such water is greatest in autumn, when the amount of acid is at its maximum. The property of dissolving lead is removed by passing the water on a large scale over filters of sand, spongy iron, chalk, or limestone. The addition of a small quantity of carbonate of soda has the same effect. In such districts the use of tin-lined iron pipes for domestic services has been recommended, but these are liable to fracture when bent. Pipes consisting of an outer case of lead and an inner pipe of tin with a layers of asbestos between have also been placed on the market. (See also page [68].)

Hard waters have the least action on lead; a coating of insoluble carbonate of lead being formed on the interior of the pipe, which prevents any further action. Thus the use of lead pipes for water containing carbonates or sulphate, or calcium phosphate, is comparatively safe. Hard water containing carbonic acid gas under pressure will dissolve a small amount of carbonate of lead; this explains the cases of lead poisoning from soda water which was formerly supplied in syphon bottles with lead tubes.

Lead is dissolved much more easily by water if other metals are in contact with it, as iron, zinc, or tin, galvanic action being thus set up. Zinc pipes containing some lead are very dangerous, especially with the distilled water used on board ships.

To determine the presence of lead in water, place a given quantity, say 100 c.c. in a white dish, and stir with a rod dipped in a solution of ammonium sulphide; if the water becomes coloured, this is generally due to the presence of iron or lead. If the colour remains after adding a drop or two of hydrochloric acid, lead is present.

To determine the amount of lead, a standard solution of lead acetate containing ¹ ∕ ₁₀ milligrammes of lead in 1 c.c., is made by dissolving ·183 gramme of crystallised lead acetate in a litre of distilled water. Place 100 c.c. of the water to be examined in a Nessler glass, acidify by a few drops of acetic acid; now add ½ c.c. of a saturated solution of ammonium sulphide. A brownish-black discoloration is produced if lead is present. To a second Nessler glass, containing 100 c.c. of distilled water, the same amounts of acetic acid and ammonium sulphide are added, and then a sufficient quantity of the standard lead solution is added, until the tints of the contents of the two Nessler glasses are identical. The amount of the standard solution added being known, we know the amount of lead in 100 c.c., and the amount per litre (1,000 c.c.) will be tenfold. Thus if 2 c.c. of the solution were required for matching colours, there were ·2 parts of lead per 100,000 of water, or ·14 grains per gallon.

Traces of Iron are sometimes present in water, giving it an astringent taste. Such water is apt to turn brown; and tea made from it is very dark.

Organic Impurities.—Organic impurities may be either vegetable or animal, the latter being by far the most dangerous. The water from moorlands is often brown, but this is not noxious. Growing plants, again, may be beneficial to water, by absorbing dissolved organic matter, and aiding its oxidation. Decaying vegetable matter is objectionable in water, and may set up diarrhœa.

The most important organic impurity of water has an animal origin—from sewage; the liquid or solid excreta (i.e. the urine or fæces) gaining accidental access to the water. Besides sewage, the eggs of various intestinal worms have been swallowed with water; and in a few cases, even leeches. But whatever the source of the organic matter contained in water, it contains nitrogen as an essential constituent; and tends under the influence of warmth, and therefore especially in summer, to undergo putrefactive changes, owing to the action of bacteria. These split up the more complex molecules of organic matter into simpler matter; ammoniacal compounds and salts, of which the most important are nitrites and nitrates, being final products of their activity. The detection of nitrates, and still more of nitrites, is important, as they may indicate the occurrence of previous sewage contamination. These products are quite harmless in water, except as an indication that the water has been polluted, and that possibly a certain proportion of the nitrogenous matter in the form of the complex organic matter forming the germs of such diseases as enteric fever, may still be present. Organic matter may be suspended or dissolved, the former being most dangerous to health. The germs or microbes causing disease consist of suspended, i.e. particulate matter. The amount of organic matter is determined by the amount of free ammonia and albuminoid ammonia which are present (Wanklyn’s process), by Frankland’s combustion process, or by Forschammer’s oxygen process; all of which give indications, rather than an exact estimate of its amount.

METHODS OF WATER ANALYSIS.

The following scheme of qualitative examination may be followed, when an immediate opinion is required as to a water. It can only be trusted when the examination shows pollution. The following results will be obtained, for instance, when a minute quantity of urine is added to a gallon of water.

(1) The water has a faint odour.

(2) Its colour is greenish yellow in bulk.

(3) On adding a few drops of Nessler’s solution, a deep yellow colour appears.

(4) A few drops of an acid solution of permanganate of potassium become yellow when added to it.

(5) Acidify some of the water in a test-tube with nitric acid, then add silver nitrate solution. Distinct cloudiness is produced, much greater than with pure tap water.

(6) Addition of hydrochloric acid and barium chloride solution shows a much greater quantity of sulphates than the same quantity of tap water.

(7) A quantity of the water evaporated in a porcelain dish over a Bunsen’s flame gives a white residue, which speedily turns brown, with a urinous odour.

(8) Ignite the ash and add some nitric acid to oxidise it more completely. Then dissolve in distilled water, and add acid molybdate solution. A yellow colour, followed by a precipitate, indicates high phosphates and sewage pollution.

The Complete Systematic Examination is (a) physical, (b) bacteriological, and (c) chemical. Of the physical tests, colour, which should never be yellow or brown except for peaty water, is important. Taste is a somewhat uncertain guide, but any badly-tasting water should be rejected. The odour on heating to 80° F. in a closed flask may indicate pollution. The degree of hardness can be roughly tested by rubbing between the hands. The absence of turbidity is most important, as suspended impurities are more dangerous than all others. Printed matter should be legible through a column of 18 inches of water.

Microscopally the suspended matter in water which has been allowed to settle should be examined. Particles of vegetable matter, e.g. fibres of cotton, linen, cells of potato, or spiral cells of cabbage, are important as indicating domestic impurities. Bits of wool, hair, wings and legs of insects and epithelium may be discovered. The presence of algæ, diatoms and desmids, or of water-fleas, cannot be held to indicate pollution, as these are found in all running streams and in many wells. The eggs and embryos of worms are much more serious.

Bacteria are almost invariably present in water. The majority of these micro-organisms are harmless. But as they may number among them the germs producing diseases like enteric fever and cholera, the estimation of their number and particularly of any deviation from the number usually present in a given water, and if possible the detection of special disease-producing bacteria, are very important. This method has been made more practicable since Koch’s method of “plate cultivation” of bacteria was discovered. A small quantity of the water to be examined (kept surrounded by ice until this test is applied, to prevent multiplication of bacteria in the bottle), is mixed with sterilised gelatine which has been melted over a water bath. Then the mixture is spread in a thin layer on a glass plate and allowed to solidify, having been covered to prevent atmospheric germs from settling on the gelatine. The bacteria in the water thus become fixed, each growing and forming “colonies” dotted over the plate. These colonies can be recognised by their size and appearance, and by sub-culturing according to recognised methods. The number of such colonies, and the number of bacteria, from which, presumably, such colonies sprang in 1 c.c. of filtered Thames water is usually much below 100; in the water before filtration many thousands are present. It has been suggested that no water should be regarded as wholesome which contains more than 100 bacteria in each c.c.

This standard is, however, obviously arbitrary. Chalk water ought to have a smaller number than this; river waters may have more, and yet be wholesome. Everything depends on the character of the bacteria found. The detection of the Bacillus coli communis, which is present in sewage, and normally in the human intestine, is very suggestive of contamination by sewage. The bacteriological method of examination of water is still in its infancy.

CHEMICAL ANALYSIS.

(1) The total solids are ascertained by evaporating a given quantity of the water to dryness, and weighing.

(2) Determination of Chlorine (see page [81]).

(3) Determination of Hardness (see page [80]).

(4) The Determination of Nitrites is based on the reddish-brown colouration produced when an acid solution of metaphenylene diamine is brought into contact with a weak solution of nitrous acid. 100 c.c. of the water under examination are placed in a clean glass cylinder. Add 1 c.c. of H₂SO₄ solution (1 in 3), then 2 c.c. of metaphenylene diamine solution (5 grains in 1 litre of water with a little H₂SO₄ added). Stir well with a glass rod. If a colouration is produced at once, a smaller quantity of water must be taken, and made up to 100 c.c. with pure distilled water. The quantity of nitrous acid present is measured by introducing different fractions of a c.c. of the standard sodium nitrate solution[3] into similar glass cylinders. Each is then made up to 100 c.c. with distilled water, and the metaphenylene diamine solution and acid added as before. The colour develops slowly; time must, therefore, be allowed in matching.

(5) The Determination of Nitrates can be conveniently made by the following method. When phenyl-hydrogen sulphate solution is poured upon a nitrate, and sulphuric acid is formed, picric acid is formed:—

(C₆H₅)HSO₄ + 3 HNO₃ = C₆H₂(NO₂)₃OH + H₂SO₄ + 2 H₂O.

The addition of free ammonia in excess forms yellow ammonium picrate, the intensity of the colour of which is an index of the picrate, and of the nitrate from which it was produced. (a) Evaporate 25 c.c. of the water under examination, and (b) 5 c.c. of standard KNO₃ solution (containing 1 part N in 100,000) to dryness in two porcelain dishes over the water bath. Add 1 c.c. of phenyl-sulphate solution to each of these as soon as cool, stir well with a glass rod, then add 1 c.c. distilled water to each dish and 3 drops of strong H₂SO₄. Next add 25 c.c. of water to each dish, and after heating for five minutes over the water bath, add solution of ammonia to each dish in excess. A yellow colour is produced in proportion to the amount of nitrate present. Transfer the liquids to glass cylinders, and dilute each to 100 c.c. Take 50 c.c. of the solution showing the least colour, and dilute the other with distilled water, until it has the same tint.

Supposing the 100 c.c. of the sample required to be diluted to 150 c.c.—

Then the amount of N will be ¹⁵⁰ ∕ ₁₀₀ × ⁵ ∕ ₂₅ = ·3 parts per 100,000.

If the two solutions (a) and (b) when diluted have the same tint, then the

Amount of N in the sample = ⁵ ∕ ₂₅ = ·2 parts per 100,000.

(6) Determination of Organic Matter. Frankland’s combustion process involves the use of delicate and costly apparatus, and is seldom employed. In this process the organic carbon is evolved as carbonic acid, and the nitrogen as such.

Wanklyn’s ammonia process is based on the reduction of organic matter to ammonia. Part of this ammonia, free or saline ammonia, is simply combined with carbonic, nitric, or other acids, or is easily derived from the urea of urine, CH₄N₂O + 2H₂O = 2(NH₄)₂CO₃. Another part is only set free when the water is boiled with a strongly alkaline solution of permanganate of potassium. This is called the albuminoid ammonia.

In carrying out this method, a retort is taken, and after having been washed out, first with a little sulphuric acid, and then with some of the water to be analysed, 500 c.c. of the latter is put in, and the retort is connected with a condenser, and distillation begun; 50 c.c. of the distilled water is collected in a cylindrical glass tube called a Nessler glass. To this 1½ c.c. of Nessler’s reagent (mercuric iodide dissolved in a solution of potassic iodide and made alkaline by potass) are added. A rich brown colour is produced, if any ammonia is present in the distillate. The amount of ammonia in the distillate is determined by exactly imitating its colour by adding a known quantity of a standard solution of ammonium-chloride to 50 c.c. of ammonia-free distilled water, and then Nesslerising as before. Each c.c. of the dilute standard ammonium chloride solution is equivalent to ·00001 gramme of ammonia (NH₃).

If the first 50 c.c. of water distilled over gives only a slight colouration with the Nessler solution, no more water needs to be distilled over for free ammonia. If more is present, two more 50 c.c.’s must be distilled over, and the amounts of the standard solution required for imitating the test in each Nesslerised 50 c.c. added together. Thus, if 2 c.c. were needed. This

= ·00002 grm. NH₃, which is contained in 500 c.c. of the water

= ·00002 × 200 = ·004 parts saline NH₃ in 100,000 of water.

The free ammonia having been distilled over, 50 c.c. of an alkaline permanganate solution (containing 8 grammes KMnO₄ and 200 grammes of NaOH in 1100 c.c. of distilled water, boiled until the bulk is reduced to 1,000 c.c.) is poured into the retort, and distillation is begun again. Three successive 50 c.c.’s of water are collected, and then the distillation stopped. Each of these is Nesslerised, and the tint imitated as before with standard ammonia solution. The three amounts of ammonia thus found to be present are added together; and when multiplied by 200, we obtain the amount of albuminoid ammonia in 100,000 parts of water. This test is universally employed by water analysts along with the next test.

The amount of Oxygen Absorbed from permanganate of potassium is regarded as an approximate test of the amount of organic matter in water. Qualitatively this forms a favourite method of testing the purity of water. Two glass cylinders are taken, one filled with distilled water, one with the water to be tested. To each is added a given small amount of an acid solution of permanganate of potassium. The distilled water to which permanganate has been added will retain its pink colour; while, if the water being tested is very impure, it will speedily become decolourised. The rapidity and degree of decolourisation are a rough test of the amount of impurity. A rapid decolourisation proves the presence of organic matter having an animal origin, or of sulphuretted hydrogen, iron, or nitrites. Sulphuretted hydrogen is rarely present, and can be easily recognised by its smell; iron or nitrites are readily distinguished by their appropriate tests. In the absence of these, the rapid discolouration is an indication of animal contamination.

To Determine the Amount of Oxygen Absorbed, two glass-stoppered bottles, each holding about 350 c.c. are required. Into one, 250 c.c. distilled water, and into the other the same amount of the water under examination are placed. To each are then added 10 c.c. of standard permanganate of potassium solution[4] and 10 c.c. of a standard pure 25 per cent sulphuric acid solution. The two bottles, after being shaken, are placed in a water-bath at 27°C for four hours. At the end of this time add a few drops of potassium iodide solution to each bottle. The pink is now replaced by a yellow colour.[5] A standard thiosulphate solution (Na₂S₂O₃, 5H₂O)[6] is placed in a burette. From this the thiosulphate solution is run into the control bottle until the yellow colour almost disappears. Now a few drops of starch solution are added, and a blue colour is produced. The thiosulphate is then added cautiously until all the blue colour disappears. The amount of thiosulphate necessary for this is read off on the burette. The same process is repeated with the bottle containing the sample of water. The starch acts as an indicator. The amount of iodine liberated is an index of the amount of permanganate in the water, which has not been used up by its impurities. The amount of iodine liberated is measured by the amount of thiosulphate required to decolourise the solution. Thus—

2 Na₂S₂O₃ + I₂ = 2 NaI + Na₂S₄O₆.

Suppose that 20 c.c. of thiosulphate solution were required to decolourise the iodine liberated in 250 c.c. of a sample of water, while the distilled water required 25 c.c. Then 25 c.c. thiosulphate represents 10 c.c. of the permanganate solution = ·001 grains of available oxygen.

25-20 = 5

As 25 c.c. = ·001 grm. O, 5 c.c. = ⁵ ∕ ₂₅ of ·001 = ·0002 grm.

This is the amount of O absorbed by 250 c.c. of the sample.

Therefore the amount of O absorbed by 100,000 c.c. of the sample. = ·08 grm.

It is usual to make a similar determination of the amount of oxygen absorbed in fifteen minutes.

The Interpretation of Results of analysis is more difficult than the analysis. A single analysis may be misleading, unless the source of the water is known. Constancy in composition or analysis is almost as important a criterion of purity as the actual character of the constituents. A knowledge of the source is essential in interpreting results of analysis, as the chemical composition of water varies with its source. The following rules are only approximately correct, and are subject to the above general considerations. The total dissolved solids in river-water are usually 10 to 30 parts in 100,000. Shallow well-water may contain from 30 to 200 parts or even more, and deep well-water from 20 to 70 parts.

Saline Ammonia in water is commonly of animal origin, ammonia (NH₃) being one of the first products of decomposition of nitrogenous animal refuse. Upland surface water usually contains about ·002 parts per 100,000, but it may reach ·008 or more if the land over which the water passes has been manured. Shallow well-water may be free from ammonia, or this may be very excessive in amount. Deep well-water may contain no ammonia or any amount up to ·1 per 100,000. Its presence is suspicious if the albuminoid ammonia is above a trace, or if the oxygen absorbed is appreciable in amount. Generally water is suspicious if saline ammonia is up to ·01 per 100,000. Albuminoid Ammonia indicates the amount of organic nitrogenous matter present in the water. It should not exceed ·005 parts per 100,000, while at the same time the saline ammonia should not usually exceed ·01 per 100,000. For Oxygen consumed the following table of the weight of oxygen required for 100,000 parts of water is given by Clowes and Coleman:—

The presence of more than 1 and still more so of 2 grains of Chlorine per 100,000 of water is most suspicious, except in saline districts. Nitrites if present in an appreciable quantity indicate comparatively recent contamination by sewage. In deep well-water they may be produced by deoxidation of nitrates. Nitrates in upland surface waters should not be equivalent to more than ·03 of N. per 100,000; in shallow well-waters the amount varies greatly; in deep well-waters it may be excessive. As a rule it ought not to be equivalent to more than 5 parts of N. per 100,000 of water; but the significance of nitrates depends greatly on the source of the water and on the amount of the other constituents present.

Chemical analysis alone cannot ascertain the safety of a given drinking water. A minute amount of impurity inappreciable to analysis may be competent to produce disease; while another water may be drunk with impunity, which contains considerable organic matter. Chemical analysis “can tell us of impurity and hazard, but not of purity or safety” (Buchanan). An accurate opinion as to the character of a drinking water can only be expressed when one knows the amount of each chief constituent (as above), and whether these amounts deviate from the same water at other times or from other waters in the vicinity.

[CHAPTER XII.]
ORIGIN AND EFFECTS OF THE IMPURITIES OF WATER.

Origin of Impurities of Water.—Parkes classifies impurities of water as:

1. Those Received at the Source.—The character of water varies with the geological structures through which it has passed; with its origin from the subsoil or cultivated land, or deep wells, or graveyards, or near the sea, etc. It is a mistaken policy to commence with an impure water and proceed to purify it; though communities supplied from rivers may be compelled to submit to this. They must then insist on the most stringent measures of purification (see p. 96). Inorganic impurities are of much smaller consequence as regards health than organic; hence the great advantage of deep well-water over river water. It has been suggested, however, that when deep well-water becomes polluted, it is more dangerous than equally polluted river-water, because in the latter the normal bacteria of water are more abundant, and possibly interfere with the continued life in water of disease-producing bacteria. This statement is unproved; and if correct, is rather an indication for further precautions being taken to prevent access of pollution to deep wells, than in favour of the continued use of river-water.

2. Impurities of Transit from Source to Reservoir, acquired during the flow in rivers, canals, or other conduits. These impurities have been broadly divided by the Rivers Pollution Commissioners into “sewage” and “manufacturing;” the former including the solid and liquid excreta, the house and waste water, etc.; the latter including the refuse from manufacturing processes, as from dye and bleaching works, tanneries, etc.

3. Impurities of Storage, whether in wells, reservoirs, or cisterns. Organic impurities are commonly received at this stage. A well, for instance, drains the soil around it in the shape of an inverted cone, with a very broad base, unless the entrance of water from its sides is prevented.

4. Impurities of Distribution. Lead, and occasionally other metals, are dissolved by certain waters. If the pipes are left empty, as with an intermittent supply, sewage may be drawn into them; in a few cases coal-gas has found its way into the water pipes (page [76]).

Effects of Impure Water.—1. Effects of Mineral Impurities. Suspended Mineral matters in unfiltered water occasionally produce diarrhœa. The hill diarrhœa of some parts of India has been traced to water containing fine mica particles in suspension.

Hard water is said by some to be hurtful, but the salts causing hardness are probably innocuous when not amounting to more than 12 or 16 grains per gallon. Persons in the habit of drinking hard water find soft water unpalatable. Hard water has been thought to favour gout and calculus (stone), but this is not so. The salts producing permanent hardness are said to be injurious, producing indigestion, but this is doubtful in the amounts ordinarily drunk.

Goitre, a swelling of the thyroid gland in the neck, is often associated with the use of drinking water from magnesian limestone formations; but that any kind of excessively hard water causes goitre is very doubtful.

Lead dissolved in water may produce serious and lasting ailments, and they are often present for a long time before their cause is detected. The amount of lead capable of producing poisonous symptoms has been as little as ¹ ∕ ₁₀₀ grain per gallon of water (Dr. Angus Smith). According to De Chaumont, ¹ ∕ ₁₀ grain per gallon, that is 1 part in 700,000 is usually required to produce such symptoms. In the well-known case of the poisoning of Louis Phillippe’s family at Claremount, there was ⁷ ∕ ₁₀ grain of lead in a gallon of water; and this affected 34 per cent. of those who drank it. The symptoms produced by lead poisoning are those of indigestion, accompanied by colic; a blue line at the junction of the gums with the teeth; “wrist drop,” a paralysis of the muscles of the forearm, or some other paralysis; and if the poisoning is continued, attacks of gout, followed by its usual consequences, chronic kidney disease. The latter affections chiefly occur when the poisoning is continued for a long time, as in the case of painters or type-setters: poisoning from water is generally discovered before any other than dyspeptic symptoms and colic are produced.

The presence of traces of iron in water may give it a slightly astringent taste; and such water is liable to cause headache and constipation.

2. Effects of Vegetable Impurities.—Living plants are unobjectionable, but decomposing vegetable matter may produce diarrhœa and other severe symptoms.

3. Effects of Animal Impurities.—Animal impurities of water are by far the most important from a sanitary point of view. They are most commonly derived from leaky drains or cesspools, or from surface accumulations of filth. The quality of the contamination is more important than its quantity; and this will explain why water containing a large amount of sewage may be drunk for a prolonged period with impunity, while at another time the least trace, if it contain the active germs of disease, will lead to serious mischief.

Suspended animal impurities are much more dangerous than those completely dissolved. Hence the examination of the colour and turbidity of drinking water is very important. Fæcal contamination is by far the most dangerous of all, and chiefly so when it is derived from a patient suffering from some communicable disease, like enteric fever or cholera.

Certain Parasites occasionally are swallowed with water in the form of embryo or egg. The liver fluke, round worm, and less frequently other kinds of entozoa have been introduced in this way. The occasional swallowing of small leeches has occasionally given rise to hæmorrhage.

Diarrhœa may be caused by animal contamination of water. It most often occurs in summer, when all the circumstances are favourable to active fermentative changes. The summer diarrhœa of infants is caused by similar changes in milk or other foods. The presence of fœtid gases in water may lead to diarrhœa. This may occur when the overflow pipe of a cistern opens into the soil pipe or into the trap of the W.C.

Dysentery, like cholera and enteric fever, may be propagated by water contaminated with the stools of a patient suffering from the same disease.

Malaria or Ague has been stated to be caused by the water of malarious marshes. The evidence on this point requires revision, in view of the part which the mosquito is now known to play in the propagation of this disease (pages 282 and 307).

Enteric (otherwise called Typhoid) fever is most often due to the drinking of water contaminated with sewage.

The balance of evidence is in favour of the view that in order to produce enteric fever water must be contaminated with the stools or urine of a patient who has suffered from this disease. Numerous instances are on record in which villages, the inhabitants of which drink sewage-contaminated water, have remained free from enteric fever, until a patient suffering from it has come to the village, when the spread by water has been very rapid. Occasionally no known contamination from a case of enteric fever has preceded the outbreak of this disease which has been caused by sewage-contaminated water. It must be remembered on this point that the urine of an enteric fever patient may occasionally contain large numbers of the bacillus causing this disease for several months after the patient is well (page [301]).

The contamination of water with sewage may occur in various ways. In country places surface wells and small streams commonly supply the drinking water, and these are frequently contaminated. The illustration (Fig. 9) shows the percolation of excretory matters from an out-door closet through the porous gravel, into a neighbouring well; the result being an epidemic of enteric fever among those who drank the water of the well. Alterations in the level of the subsoil water are sometimes followed by an outbreak of enteric fever (p. 70). A sudden fall of rain occurs, and the excess of water in the soil absorbs the soakings from country privies or cesspools, and carries them into the nearest well. The percolation of tainted water through a considerable tract of land, possibly along fissures, is sometimes insufficient to purify it, as proved by a remarkable epidemic in the small village of Lausen, in Switzerland.

In other cases sewage gains access into leaky water-pipes. Formerly contamination was occasionally due to improper connection between the overflow pipe of the cistern and the soil-pipe, or to the water-closet being flushed by a pipe directly connected with a water-main (as in the Caius College outbreak at Cambridge), or connected with the drinking-water cistern (page [76]).

Milk may, by the admixture of water, become contaminated with enteric matter, and produce widespread epidemics. Where the water is very impure, the small amount used in washing cans may suffice to cause infection.

Cholera was first proved by Dr. Snow, in 1849, to be due to the specific contagium of cholera gaining an entrance into drinking water. This contagium is derived as in enteric fever from the intestinal evacuations, the urine, and the vomit of patients suffering from the same disease.

Fig. 9.

The close connection of the spread of cholera with an impure water supply has been repeatedly shown in this country. The cholera epidemic of 1854 was very severe in the southern districts of London. At that period these districts were supplied with water by the Southwark and Vauxhall Company, deriving its water from the Thames at Battersea, and by the Lambeth Company, having its intake at Thames Ditton, where the water was purer. The two companies were acting in rivalry, so that in many streets their mains ran side by side; and houses in the same street similar in all other respects, received a different water supply. An investigation of the distribution of cholera in these districts gave the following results:—

The facts, when examined in detail, brought out still more strikingly the exemption of the houses supplied by the Lambeth Company; the infection picking out in a given street the houses supplied by the Southwark Company. The great epidemic of cholera at Hamburg in 1892 proves the same point. Hamburg, Wandsbeck and Altona are three towns adjoining each other, and really forming one large community; but while Hamburg suffered terribly, the two other towns had no cases of cholera, except the few that were brought into them. In all respects except water-supply the conditions were alike; but Wandsbeck obtained filtered water from a lake, Altona obtained filtered water from the Elbe below the town, while Hamburg was supplied, previous to the epidemic, by unfiltered water from the Elbe just above the town.

Diphtheria and scarlet fever have never been traced to polluted water.

Effects of an Insufficient Supply of Water.—The influence on personal health is most baneful. Water is used sparingly for purposes of cleanliness, with the necessary results that cutaneous diseases become more common, and the whole body suffers; the linen is imperfectly and infrequently washed; the house becomes dirty; drains are imperfectly flushed; the streets are not cleaned; and the whole atmosphere becomes loaded with impurities. According to Parkes, it is probable that the almost complete disappearance of typhus fever from civilized and cleanly nations, is not merely owing to better ventilation, but also to more frequent and thorough washing of clothes.

Insufficient cleansing of the surfaces of streets and of sewers, owing to a deficient supply of water, has a very important influence on the spread of enteric fever and epidemic diarrhœa. A heavy fall of rain often causes a rapid diminution in the prevalence of the latter disease.

[CHAPTER XIII.]
THE PURIFICATION OF WATER.

When a public water-supply is provided, it may reasonably be expected to be furnished pure and fit for use; but this, occasionally is not so. The reports, for instance, of the condition of the London Water Supply, occasionally show that it is turbid and contains a slight excess of organic matter. This is especially the case when, after heavy rainfall, storm-water is brought into the reservoirs, and owing to deficient storage, sufficient time is not allowed for deposit. Rain-water always and other waters frequently require to be purified before use.

Methods of Purification.—The only certain way of obtaining pure water is by Distillation; but this plan is scarcely applicable to water on a large scale. Furthermore distilled water is not so palatable as ordinary water. The distillation of water is more especially required on board ship, during long voyages. It should be followed by the use of some measure to secure efficient aeration.

2. Boiling water serves to remove the temporary hardness, and the chalk carries down with it a large proportion of any organic matter that may be present. Boiling deprives the water of its dissolved gases, and renders it flat; it is desirable, therefore, to aerate it by filtration or from a gazogene after boiling. All the microbes which are known to produce disease are destroyed by efficient boiling. Certain putrefactive microbes are more persistent of life, owing to the fact that they form spores, which are not killed at the temperature of boiling water. Tyndall showed that by boiling the liquid containing these spore-forming microbes on three successive days, thus giving time for the spores to develop into less resistant microbes, they could be effectually destroyed. Boiled water will not cause enteric fever or cholera, the two chief water-borne diseases.

3. The exposure of water in divided currents to the air by passing it through a sieve has been proposed as a means of purifying water, but it is inefficient when trusted to alone. Plants in reservoirs help to absorb organic matter; and fish, by destroying small crustaceans, have been found useful. Hard waters do not bear exposure to light, as a thick green growth of chara occurs, which may block pipes, and give a bitter taste to the water.

4. The Addition of Chemical Substances.—(1) Clarke’s process consists in adding milk of lime, i.e. an emulsion of quicklime with water, to the water in the reservoir on a large scale. By this means calcium carbonate is precipitated, but no effect is produced on calcium and magnesium sulphates and chlorides. The hardness of the Thames water can thus be reduced from 16° to 3° or 4° (Clarke’s scale). The calcium carbonate carries down with it suspended and possibly dissolved organic matter. In the Porter-Clarke process lime-water, i.e. milk of lime diluted, and the excess of lime separated by settlement or filtration, is mixed with the water to be purified, the water being freed from the precipitated calcium carbonate either by subsidence or by being forced through a filter of stretched canvas.

(2) Carbonate of Soda added to boiling water throws down calcium carbonate, and possibly lead if present. Much less is required when added to boiling than to cold water. Maignen’s process consists in adding anti-calcaire powder, containing chiefly carbonate of soda, lime, and alum.

(3) Aluminous salts are very effectual in removing suspended organic matter, if the water contains calcium carbonate. On the addition of alum, calcium sulphate and aluminium hydrate are formed, both of which fall to the bottom, carrying with them other impurities. The amount of alum required is about 6 grains per gallon of water. If the water is not hard, a little calcium chloride and carbonate of soda should be put in before the alum is added, in order that a precipitable substance may be formed.

(4) Potassium permanganate readily removes the offensive smell of stagnant water, but it gives a yellow tint to the water. The addition of a little alum will help to carry down the decomposed permanganate.

(5) Perchloride of Iron, in the proportion of 2½ grains to a gallon of water, has been found to completely purify water from finely suspended organic matters and clay.

(6) More recently, other substances, such as iodine and hyposulphite of soda, have been recommended. These are supposed to act by sterilizing the water, and iodine in suitable quantities undoubtedly effects this.

Chemical processes for the purification of water, with the exception of the softening process, are not to be recommended for general use. Efficient filtration, or boiling, is safer than chemical treatment; and it would only be justifiable to trust to the latter, when, as in a military campaign, an attempt at purification was necessary, and no means were available for filtering or boiling water.

7. Filtration.—The object of filtration is to remove the impurities of water. The most dangerous impurities are suspended in it, especially the microbes causing infectious diseases. Hence the most perfect filter is the one which most completely prevents the passage through it of microbes. If the water supply is pure, domestic filtration is not only useless, but likely to do more harm than good. This is true for such upland surface waters as those supplied to Liverpool, Glasgow, and Manchester; for such deep well-water supplies as those of Brighton (deep chalk), of Nottingham (new red sandstone), and others, when pumped from wells remote from inhabited houses. For upland surface waters known to attack lead pipes, filtration through charcoal or spongy iron may be advisable; for river water, filtration through a germ-proof filter is best.

Filtration on a large scale is generally carried on as follows:—A preliminary step consists in collecting the water into settling reservoirs, wherein the more bulky substances subside. The water is then filtered through beds of gravel and sand, containing perforated tubular drains below, into which the filtered water flows. The drains are covered by a bed of gravel about 3 feet deep, over which is spread a layer of sand about 1½ to 2 feet deep. Sharp angular particles of sand are the best; and the gravel should gradually increase in its coarseness as it descends.

The effect of this filtration is chiefly mechanical; it separates any suspended matter, whether organic or inorganic. A certain amount of biological action possibly also takes place. Piefke found that a perfectly cleaned and sterilised filter when first used, increases the microbes in water, instead of decreasing them. Gradually a gelatinous layer of slimy matter is formed on the top of the sand; the water now filters through much more slowly, but it gradually becomes freer from microbes, these being intercepted by the slimy layer. It is important that this layer should not be disturbed by too rapid or forced filtration, and that when the surface layer requires to be removed, because the filter has become impervious, time should be allowed for another thin film to form before the filtered water is again utilised. Koch concluded that the rapidity of filtration should never be allowed to exceed 100 millimetres (about 4 inches) per hour; and that the number of microbes per c.c. in the filtered water should never exceed 100. Some oxidation of organic matter, as well as detention of microbes, may take place during the filtration of water, nitrates being formed by the vital activity of certain “nitrifying” microbes in the filter. (On nitrification, see pages 195 and 274.) P. Frankland’s observations show that the number of microbes in Thames water is reduced by filtration through sand and gravel beds, as practised by the London Water Companies, so that only 3·4 per cent. of those originally present remained. He also concludes that the majority of the microbes present in filtered water are derived from post-filtration sources. Thus the number is greater in tap-water than in water derived from near the reservoirs.

Other materials besides sand have been used for filtration on a large scale, but none with proved success.

Domestic Filtration ought, as already explained, not to be needed, but circumstances often arise in which the public supply is open to suspicion, and a second domestic line of defence against infection through the water supply is desirable. When this is so, the form of filter which will best protect the household is one attached to the house-tap, so that all drinking-water is perforce filtered. When filtering involves the transfer of water from the tap to the interior of the filter, opportunity is left for carelessness or forgetfulness. The one essential point of a domestic filter is that it will prevent the passage through it of microbes. Every filter must be tested from this standpoint.

On this point the experiments of Woodhead and Cartwright Wood are conclusive. They first of all experimented on various filters with fine artificial ultramarine containing particles 16 µ to 0·6 µ or even less in diameter in suspension; and milk containing granules and globules of fat 0·5 µ to 30 µ or more in diameter, freely diluted with water.

The number + indicates the relative amount of the experimental substances that made their way through the filtering medium.

Experiments were then made with the actual microbes of certain infectious diseases, and it was found that certain filters allow these to pass. Thus a silicated carbon filter allowed 1,000 out of 15,000 typhoid bacilli suspended in water to pass through its substance; a manganous carbon filter allowed 600 to 800 out of 10,000 cholera vibrios to pass through; Maignen’s filter on the second day of experiment allowed 150 out of 5,000 cholera vibrios to pass through; Lipscombe’s charcoal filter experimentally only reduced typhoid bacilli from 20,000 to 5,000; the magnetic carbide filter only reduced them from 20,000 to 10,000; the spongy iron filter from 20,000 to 3,000; while, on the contrary, the Pasteur-Chamberland and the Berkefeld filter completely stopped all microbes and produced a sterile water. (As to these two, see page [98].)

Of the materials enumerated animal charcoal was formerly regarded as an excellent filtering medium. It is capable of oxidising organic matter dissolved in water, but so far from sterilizing water, it favours the growth of microbes in it. Water filtered through charcoal, after the first few days of use of the charcoal, deteriorates, as the charcoal yields up impurities to it.

Manganous Carbon consists of animal charcoal and black oxide of manganese mixed with oil, and heated strongly together out of contact with the air. The oxidising power of the carbon is said to be thus greatly increased. It shares the objections to carbon.

Silicated Carbon consists of 75 per cent. of charcoal and 22 per cent. of silica, with a little oxide of iron and alumina. It is not an efficient filtering medium.

Spongy iron is prepared by the reduction of hæmatite ore with fusion, so that the iron is obtained in a porous and finely-divided condition. The Rivers Pollution Commissioners found spongy iron to be “a very active agent, not only in removing organic matter from water, but also in materially reducing its hardness, and otherwise altering its character.” It is a powerful oxidising agent, some of the water being decomposed, and hydrogen set free, and the oxygen acting upon any organic matter present. It also removes lead from water. As already seen, it does not, however, fulfil the primary object of water, by depriving it of any microbes contained in it.

Magnetic carbide of iron is obtained by heating hæmatite ore with sawdust. Its action is similar to that of spongy iron.

The Pasteur-Chamberland filter consists of a cylinder of unglazed fine porcelain made from a well-baked Kaolin of a certain degree of porosity and hardness. (Fig. 10.)

The water passes through the porcelain from without inwards, and with the pressure of 1½ to 2½ atmospheres which is usually present in the pipes of a water-service, passes through at the rate of about three quarts per hour. The filter can easily be cleaned by brushing it in a stream of hot water, or by subjecting to the heat of a Bunsen burner. The filtration is entirely mechanical, the filtered water being quite freed of microbes. No chemical action takes place.

Fig. 10.

Pasteur-Chamberland Filter.

A.—Outlet of filtered water. B.—Pasteur tube. C.—Metal tube containing unfiltered water. D.—Unfiltered water delivered through tap.

The Berkefeld filter is cylindrical like the Pasteur-Chamberland filter, and is used in the same way. It is made of infusorial earth, which is soft and friable and liable to break. The cylinder becomes gradually worn thin by cleaning, and it then ceases to filter efficiently. Its sole advantage over the Pasteur-Chamberland filter is the more rapid rate of filtration; and against this is to be set the greater liability to fracture and the lack of continuance of efficient filtration. Woodhead and Wood in the report already quoted, state: “The Berkefeld filter appears to have the largest pores among the efficient filters, as is evidenced by the fact that the water organisms were not apparently weakened, that more species of organisms appeared in its filtrate, and that lowering the temperature to 11° C. did not prevent their appearance. The Pasteur-Chamberland filter, on the other hand, at 11° C. was able to give an apparently sterile filtrate for a prolonged period.” More recent experiments have shewn that pathogenic (disease-producing) microbes contained in water after awhile grow through the substance of a Berkefeld filter, and that this does not happen with a Pasteur-Chamberland filter. The latter is therefore preferable.

In determining the number of bougies required for any filter to secure a given amount of pure water, it is necessary to calculate on the basis of the output after several weeks’ use, not on the original output. If this is done, pure water will be secured without disappointment as to the amount supplied.

[CHAPTER XIV.]
COMPOSITION AND PROPERTIES OF AIR.

An abundant supply of fresh air is necessary at all times. And yet its importance is commonly ignored in practical life. Strenuous efforts are made to ensure a supply of food, and water is commonly filtered or otherwise purified before drinking; but many are content to live in an impure atmosphere, which hardly suffices for the preservation of life, and certainly not of health. Deprivation of food, or even of water, only kills after several days or weeks; deprivation of air kills in a few minutes. Only about three pints of water are required daily, while at least 1,500 gallons of air are necessary every day for carrying on the vital functions.

Composition of Air.—The air constitutes a gaseous ocean in which we live, as fishes live in water. In virtue of its weight, it exerts a pressure of about 15 lbs. on every square inch. This pressure is usually measured by the barometer, and is equivalent on an average to that of a column of 30 inches of quicksilver. (See page [331]).

Chemically, air consists of a mixture of various gases and vapours. These are chiefly Oxygen and Nitrogen; but in addition, there are minute quantities of carbonic acid, argon, hydrogen, water vapour, ammonia, ozone, and suspended matters.

The oxygen and nitrogen exist, in the proportion by volume of 20·9 of oxygen to 79·1 of nitrogen, or of 23·16 grains of oxygen to 76·84 of nitrogen, by weight.

These two gases do not exist in chemical combination, but mechanically mixed. This is proved by the fact, that they do not exist in air in the proportion of their combining weights, or any multiple of these; that the proportion varies slightly at different parts; and that the air which is dissolved in water does not contain the nitrogen and oxygen in the proportion 4 to 1 (as in the atmosphere), but in the proportion 1·87 to 1. This means that oxygen, being more soluble in water than nitrogen, has dissolved in a larger proportion; as it certainly would not have done, had the oxygen and nitrogen been chemically combined. The oxygen dissolved in water supplies fishes with the necessary oxygen for their respiratory processes. Similarly the oxygen in the atmosphere is its most essential constituent, being required in all processes of oxidation (i.e., combustion), whether in living organisms or in the inanimate world. Nitrogen serves as a diluting agent. It is incapable of supporting life alone; and many of the fatal accidents which have occurred through men descending deep wells without first testing, by means of a lit candle held well below them, the quality of the air near the bottom, have been due to an accumulation of nitrogen in the well.

Ozone is a condensed form of oxygen, which is present in minute quantities in pure air, and especially during a thunder-storm or after a fall of snow, and in the air near the sea. In it three volumes of oxygen are condensed so as to occupy two volumes. In this condensed condition it has powerful chemical affinities; often oxidising substances which oxygen cannot attack. It is generally absent from the close air of towns and dwelling houses, having been used up to oxidise the organic matter present in these places. Air without it is said to be “devitalised”; and ozone has been described as the scavenger of the air.

Ozone can be produced by hanging a piece of moist phosphorus in a room; and it is stated by Dr. Daubeny, that part of the oxygen given out by plants, especially by scented flowering plants, is in the condition of ozone. A small quantity is produced when an electrical machine is worked; its presence is evidenced by a peculiar smell (the name ozone is derived from the Greek word for smell).

Test of Ozone in Air.—Traces of ozone in air are detected by exposing strips of blotting paper moistened with a mixture of a solution of potassic iodide and starch. If ozone is present, the paper assumes a blue tint, due to the liberation of iodine, and its combination with the starch. Other acid gases may, however, produce the same effect. A second test should, therefore, be tried. Soak red litmus paper with a very dilute solution of potassic iodide, and expose as before. Potassic oxide is produced if ozone is present, and this turns the litmus blue.

Aqueous Vapour is always present in air, though the amount varies greatly. It is invisible in the ordinary condition, but by condensation becomes cloud or fog, rain, snow, or hail. The quantity of moisture present varies with the temperature of the air; the higher the temperature, the more water can be vaporised, without the point of saturation being reached. An increase of 27° Fahr. doubles the capacity of air for moisture. The amount of moisture that would saturate air at 50° Fahr. only gives 71 per cent. of the saturation amount at 60° Fahr. The amount of moisture is estimated by the hygrometer (page [240]).

Air saturated with moisture at 32° Fahr., holds vapour equal to ¹ ∕ ₁₆₀ of its weight; at 59° it holds ¹ ∕ ₈₀, at 86° ¹ ∕ ₄₀, at 113° ¹ ∕ ₂₀, and at 140° ¹ ∕ ₁₀.

Ammonia in normal air does not exceed one part in a million of air; but it is always present—either as free ammonia or as sulphate, chloride, carbonate, or sulphide of ammonia. From this source, plants derive some of the nitrogen they require as food; some also from the free nitrogen, which is fixed by certain microbes, growing in the nodules connected with the roots of peas, lentils, and other plants (page [274]).

Traces of nitrous and nitric acid are also present in the air, produced by the direct combination of nitrogen and oxygen occurring as the result of the electric spark during lightning.

Carbonic Acid or carbon dioxide is always present in air, in the proportion of 3·36 to 4 parts in 10,000; but in impure air may be present in much larger amount. It is a heavy gas, incapable of supporting combustion, and therefore of supporting animal life. Being a heavy gas, it tends to accumulate where it is produced, as about lime-kilns by the heating of chalk. Thus CaCO₃ (chalk) (heated) = CaO (lime) + CO₂ (carbonic acid). Tramps have occasionally died of carbonic acid poisoning through sleeping near lime-kilns.

It is produced by the oxidation of carbonaceous matters, hence in all ordinary combustion, in many cases of putrefaction and fermentation, and in the respiratory processes of all animals.

Plants diminish the amount of carbonic acid in the atmosphere. Two processes occur in most plants: a process of respiration, as in animals; and a process of assimilation, by which the leaves and all other green parts of a plant under the influence of sunlight decompose the carbonic acid of the atmosphere, fixing its carbon and liberating its oxygen. Plants such as fungi, which are destitute of green colouring matter, cannot decompose carbonic acid; nor can any plants during the night. During the day green plants are air purifiers; during the night all plants vitiate the air to a slight extent.

The Air in Relation to Respiration.—The oxygen of air is absolutely essential for the continuance of life. In every organised animal, lungs or analogous organs are provided, in order to supply the necessary oxygen to the system, and to remove the impure air from it.

The act of breathing occurs in man about seventeen times per minute. While the inspired air is in contact with the interior of the lungs, it undergoes important alterations. It comes into contact with the five or six millions air-vesicles which form the minute dilated terminations of the windpipe, and have an aggregate area of ten to twenty square feet. Each of the air-vesicles has extremely thin walls; and outside these delicate walls lie capillary blood-vessels, full of impure blood. An active interchange now occurs between the air and the gases dissolved in the blood. Oxygen passes through the intervening membrane into the blood, while carbonic acid and other impurities of the blood pass into the air-vesicle. The consequence of this is that the impure dark-coloured blood becomes bright scarlet and pure. This purification is not confined to any one portion of the blood; for the heart contracting 60 or 70 times per minute, pours successive portions of blood into the capillaries surrounding the air-vesicles; while at the same time, pure air is brought into the air-vesicles seventeen times per minute, and so the interchange is constantly kept up.

In view of the incessant character of respiration and circulation, it is clear that all the blood will be purified if the external air is pure; and that if there is any detrimental matter in the air, it probably will come into contact with the blood in the lungs.

The amount of air taken in with each inspiration is about thirty cubic inches. This is called the tidal air, as it is constantly ebbing and flowing from and to the lungs. By means of a very forced inspiration, about 100 cubic inches of additional air can be inspired; and similarly after an ordinary inspiration, one can expire forcibly an additional 100 cubic inches, though there will still be left in the lungs another 100 cubic inches of air. Thus:—

Corresponding to the respiratory changes in the lungs, there are changes in the tissues throughout the body. The pure and oxygenated blood leaving the lungs, is carried to all parts of the system. Oxidation and allied processes are actively carried on, the result of which is the formation of urea, carbonic acid, and smaller quantities of other effete matters. These are then carried by the blood to the excretory organs, urea being chiefly eliminated by the kidneys, and carbonic acid by the lungs.

Examination of Expired Air shows that—1. It is heated; in its passage through the nose and deeper respiratory passages it has acquired a temperature approaching that of the blood.

2. Its moisture is increased. By the skin and lungs from 25 to 40 ounces of water pass off in the twenty-four hours; the relative amount varies somewhat.

3. It contains 4 to 5 per cent. less oxygen, and 4 per cent. more carbonic acid than inspired air. The carbonic acid, instead of being 4 parts in 10,000 of air, becomes over 400 in 10,000, while the oxygen is diminished in a somewhat larger proportion. Thus:—

The amount of carbonic acid expired varies under different circumstances. It is increased by active work, by an increase of food, by a diminution of the external temperature; it is greater when the surrounding air is pure, and when it is moist; and it varies with the season, being greatest in spring, and least in autumn.

Children require more oxygen, and expire more carbonic acid than adults, weight for weight. A child six or seven years old requires nearly as much oxygen as one twice that age. Boys usually require more air than girls, as they are more active and exhale a larger amount of carbonic acid and other impurities.

The average amount of carbonic acid eliminated by a healthy adult is at least 0·6 cubic foot per hour, or 14·4 cubic feet per day. This reckoned as carbon is equivalent to 160 grains per hour, or half a pound of carbon in the twenty-four hours. Liebig gives the amount of carbonic acid expired as 0·79 cubic foot per hour, or 19 cubic feet per day.

4. It contains organic impurities. These are chiefly gaseous, solid particles only being expired during coughing, or possibly during conversation. The danger from the “breath” of patients in infectious diseases is really associated rather with the dried discharges on handkerchiefs, etc., than from the “breath” itself; unless droplets of saliva discharged during speaking, or mucus during coughing, are directly inhaled.

[CHAPTER XV.]
SUSPENDED IMPURITIES OF AIR.

Pure air being essential to life and health, it is important to ascertain the character and origin of the impurities of air. Innumerable substance—in the condition of gases, vapours, or solid particles—constantly pass into it, and deteriorate its quality. To counteract this, certain purifying agencies are at work, the mechanism of which will be considered hereafter.

Impurities are much commoner and more abundant in the air of enclosed spaces than in the external air, as the natural processes of purification cannot be brought to bear so efficiently in the former case. In sick rooms, hospitals, etc., impurities arise, which are not present where only healthy people are collected. The most important impurities are derived from the respiration of animals, and the combustion of gases, candles, or lamps in rooms, from sewage emanations, from various occupations, and the air of marshes, mines, church-yards, etc. These may be classed under two heads—solid and gaseous; the solid being simply suspended in the air in a finely divided condition, or floated about in a coarser condition by currents of air. They are revealed in an atmosphere in which one did not previously suspect their existence, by the passage of a beam of sunlight. Light itself is invisible, but its course is rendered visible by the particles from which its rays are reflected. Tyndall demonstrated the presence of minute particulate matter in the air of all ordinary situations, and showed that a large proportion of this matter consists of germs (microbes). In his experiments with vapours in closed tubes, floating matter was always revealed by a concentrated beam of light, even though the air entering the tube had been first drawn through sulphuric acid and through a strong solution of caustic potash. If this air was then passed through a red-hot platinum tube and across folds of red-hot platinum gauze, it became optically empty; the floating matter had been burnt, and disappeared. It was therefore organic. In subsequent experiments, he took organic solutions, as of meat, turnip, and the like, and rendered them sterile by repeated boiling. They remained sterile when kept in air-tight vessels or in vessels covered with a thick layer of cotton-wool, which would efficiently filter any entering air; but when exposed to the air, they invariably became turbid, owing to an enormous multiplication of germs. Clearly, therefore, air contains organic, matter, and much of this organic matter consists of living germs. Most of these germs are comparatively harmless under ordinary conditions. They are, however, the causes of fermentation, putrefaction, and all the processes of decomposition which occur in organic substances. The importance of the exclusion of the dust of air has received an important application in Lister’s antiseptic and in the aseptic system of treatment of wounds. Formerly accidents and operations were frequently fatal; now vast numbers of lives are saved by improved surgical methods. The original antiseptic method acted on the supposition that some germicidal application to the wounds was necessary; now it is realized that if, during the operation, germs are not allowed to remain in the wound, all that is afterwards necessary to insure rapid recovery is that they shall be prevented from entering the wound from the external air during its process of recovery. By the adoption of such means, large wounds can be made to heal, without the formation of a drop of “pus” or “matter.” (See also page [110].)

Suspended Matters are mineral or organic, the two being commonly associated together. The mineral matters consist largely of fine particles of common salt, silica, clay, iron rust, dried mud, chalk, coal, soot, and similar substances. Not uncommonly the mineral particles are coated by, or mixed with, organic matter, the comparative lightness of the organic matter enabling the mineral matter to float about more easily. The objection to dust is thus intensified, for not only is it irritating to the respiratory passages and generally disagreeable, but it carries with it putrescent and possibly morbific particles. The prevention of infectious diseases resolves itself largely into means for preventing the inhalation of dust.

Organic Suspended Matters in the open air are, most commonly, minute fragments of wood and straw, dried horse litter, fragments of insects, the spores and pollen of plants, and microscopic plants and animals. In addition, there is the putrescent organic matter resulting from respiration and other organic functions.

Indoors, the air commonly contains, in addition, fragments of cotton, linen, silk, or other fibres, fragments of vegetables, starch cells, soot, charred wood, splinters from floors, etc.

In Sick Rooms, products of the morbid conditions may be evolved; thus, pus-cells, particles from the expectoration, blood cells, fat particles, epithelium, or the special germs or microbes to which infectious diseases are due. These are disturbed by the movements of persons, causing the dust to rise; and thus the infection of consumption, and of the acute infectious diseases, is frequently spread.

Flies and other winged insects are important auxiliaries in the diffusion of disease-carrying particles. Receiving some morbid secretions on their limbs, or other parts of their bodies, they have occasionally been the means of spreading erysipelas in hospitals, and glanders in veterinary stables. The specific contagia of cholera, enteric fever, and summer diarrhœa are occasionally conveyed to food by flies which have previously alighted on latrines or privies or other places where the stools of such patients have been deposited (page [281]). The excreta of flies, which are not uncommonly deposited on food, or on articles of furniture, have occasionally being found to contain the minute ova of intestinal worms.

Effects of Suspended Matters.—The inhalation of dust is followed by deleterious effects. We may divide the solid substances inhaled as dust into three kinds:—dead substances, living substances, and the contagia (microbes or germs) of various diseases.

1. Dead Substances inhaled for a prolonged period in various occupations are a common cause of premature death. The potter draws into his lungs a fine silicious dust, which irritates his lungs, and finally produces a fatal disease, known as potter’s asthma.

Mill-stone Cutters and Stone Masons inhale the fine particles of stone given off from the material which is being chiselled. These produce serious disease of the lungs.

Pearl Cutters inhale fine particles of pearl-dust, and as they generally work in close rooms, and the dust is light and tasteless, serious disease of the lungs results.

Sand-paper Makers inhale minute portions of glass and sand; and needle and knife grinders are exposed to similar dangers, and at one time the mortality among them was frightful. It has greatly diminished since the introduction of wet grinding, the use of steam fans, and wearing of respirators.

Hemp and Flax Dressers inhale a dust which is peculiarly irritating. Workers in rags and in wool suffer in like manner from dust. The dust from fleeces of wool, and especially from the alpaca fleece, has produced in many cases (in the neighbourhood of Bradford and elsewhere) an acute disease (anthrax) proving fatal in a few days. The spores of this disease are very persistent of life (page [274]), and remain active for mischief for months after the death of the animal which had suffered from it. The fleece can be disinfected by steam; and the use of fans for diverting the dust created during “sorting” minimises the danger from it.

The miller commonly suffers from a form of asthma, not so severe as potter’s asthma, as the particles in this case are not equally irritating. The hairdresser is liable to inhale the short fragments of hair cut by the scissors, and the mortality of this class of workers is high. Miners in coal have a surprisingly low mortality, when accidents are excluded from the calculation; except in South Wales, where it is slightly higher than for all males in the same district. Coal dust is relatively free from sharp angles, and is therefore not so irritating to the lungs as metallic dust. Consumption is relatively rare among miners.

The Fur-dyer is very prone to suffer from the dust of the dyed furs, great irritation and disease resulting in many cases.

Artificial Flower-makers, and those engaged in colouring arsenical wall-papers, suffer from the inhalation of arsenical vapours, as well as from the irritating effects of its absorption by the skin. These are now seldom seen, owing to the almost complete abandonment of the use of arsenic for wall-pigments.

Cigar-makers are liable to have their lungs irritated by inhalation of the dust of the tobacco-leaf; and may suffer from tobacco-poisoning.

Workers in Lead are very liable to be poisoned by the metal, e.g., house painters, potters engaged in the glazing process, in which the ware is dipped into a solution containing lead, manufacturers of white lead, and others. The lead is partly absorbed by the skin; in some cases it is inhaled as dust; and more often it is swallowed, when the workman eats his meals with unwashed hands. Of the symptoms “painter’s colic” and “drop-wrist” are the two most important, though, in some cases, lead shews its effects more insidiously, leading to gout and chronic renal disease. It is now compulsory on employers to provide in the workshop, complete washing arrangements for the use of workers in lead. Every doctor called to attend a case of lead or phosphorus or arsenic poisoning or anthrax, which has been acquired in an industrial occupation, must notify the same to H.M. Inspector of Factories. This implies inspection of the factory or workshop and the subsequent adoption of further measures of precaution.

Brass-founders occasionally inhale the fumes of oxide of zinc; and diarrhœa, cramp, waterbrash, and other troubles are the result. Those engaged in the manufacture of bichromate of potass, are liable to partial destruction of the mucous membrane of the nose, and to irritation of the skin, with the formation, in some cases, of small ulcers.

Workers with Phosphorus, as those engaged in the making of phosphorus matches, not uncommonly suffer from a gradual necrosis (death) of the jaw-bone. Those having carious teeth are especially attacked by this disease, which is due to the fumes of oxide of phosphorus, attacking the jaw. Improved ventilation of workshops, careful attention to the teeth, and other measures, have greatly diminished this disease; and it has disappeared where safety matches made from red non-volatile phosphorus, have replaced matches made from the yellow variety.

Chimney Sweeps occasionally suffer from irritative skin diseases, as well as bronchitis. In some cases the chronic irritation of the soot has produced cancer of the skin.

The effect of dust on workers can be seen in the mortality returns: Among men aged 25 to 65 years in 1881-90, the comparative mortality figure in England and Wales was as follows, all males throughout the country being taken as a standard and given as 1,000:—

Comparative Mortality Figures.

Remedial Measures.—Means have been taken to diminish the prevalence of the above dust diseases, in several cases with remarkable success. In the case of steel-grinding, for instance, the mortality is greatest with dry grinding, and least with wet grinding. Wet processes have been applied to others of the industries named, with a like success. Where the dust cannot be avoided, the use of steam or electric fans, to deflect the dust away from the workman, has been found successful; and in many cases, free ventilation of the workshops has greatly diminished the mortality. Where none of the above measures suffice, the use of respirators ought to be insisted on. Breathing through the nostrils ought to be carefully maintained, as thus the dust is to a large extent stopped before reaching the lungs.

The dangers of lead poisoning may be avoided by absolute cleanliness, the hands being always washed before taking meals, and the nail-brush used to secure complete cleanliness beneath the nails.

2. Living Substances.—The pollen of plants in some persons produces a distressing form of disease, called hay-asthma, which is apt to recur each year, and is sometimes only curable by living in a town or removing to the sea-coast. The amount of pollen floating about in the atmosphere is considerable; 95 per cent. of it is grass-pollen, and this form and the pollen from pine-trees appear to be the most powerful in inducing hay-asthma. According to some authorities, hay-asthma is rather due to the minute particles constituting the scent of various flowers, than to the pollen; but that is probably not the usual mode of origin of the disease, though it may be in some cases. In some cases, true asthma results from smelling particular plants. Here as in the case of hay-asthma a peculiar idiosyncrasy is involved, only a very small proportion of those exposed to the minute particles suffering from asthma.

The spores of many fungi and of other living organisms are constantly being floated about in the air, until they find a suitable resting place, when they settle and proceed to grow and multiply. The souring of milk, the fermentation of a saccharine solution, the moulding of bread, the presence of mildew, the blighting of corn, and numerous other phenomena are due to the growth of organisms carried by the atmosphere from one part to another.

3. The Contagia (microbes or germs) of the acute infectious diseases are minute living organisms, known as bacteria. Hence these diseases may be carried about by currents of air, some much more easily than others. Some of the contagia have a persistent vitality. Thus the contagia of scarlet fever, diphtheria, or small-pox may infect a room for months, causing the disease in question, when infected articles in the room are disturbed. The contagia of typhus fever and of measles, on the other hand, are short-lived, and do not usually resist free ventilation and exposure to sunlight.

Besides the contagia of the acute fevers, septic organisms may be carried by the atmosphere. Formerly, blood-poisoning from operation and other wounds was common; but Lister, by insisting on absolute cleanliness of wounds, and only allowing air to have access to the wound which had been filtered through layers of gauze and deprived of its septic germs, has secured that wounds can now be kept perfectly “sweet,” the suppuration in them reduced to a minimum, and the danger of blood-poisoning almost annihilated (page [106]). It had often been noticed that recovery from even very severe injuries was common, if only the skin remained unbroken; while the same injuries, with the addition of a rupture of the skin, and consequent access of air, were rapidly fatal. But to Lister is due the great honour of proving that it was not the air which produced the mischief, but the germs it contained, and that filtered air might be admitted with impunity.

Erysipelas and hospital gangrene have occasionally been carried about in hospital wards by dirty sponges and dressings; and if the ventilation is not perfect, particles of epithelium and pus from diseased persons may be carried to other patients at a distance. Some forms of purulent disease of the eyes are transferable from patient to patient, and in children some forms of eczema are also contagious.

[CHAPTER XVI.]
GASEOUS AND OTHER IMPURITIES OF AIR.

Gaseous impurities of the air are very commonly associated with suspended matters, and it is often difficult to separate the effects of the two.

Different gases are also often associated, and so produce modified results. It will be convenient to consider, first of all, certain well-marked gaseous impurities, and then others in which there is a mixture of several gases, or of these with suspended solid particles.

Under the first head the most important impurity is—

(1) Carbonic Acid.—This is reckoned an impurity if amounting to more than 5 parts in 10,000 of air. Owing to the large amount produced in the respiration of animals, in the combustion of fires, gas, lamps, etc., and in other natural processes, it would be much greater in populous parts, were it not for the rapid diffusion occurring in the air, and the purifying action of plants. The following analyses (Angus Smith) illustrate the facts that in towns the amount rises, and is greatest in the most populous parts, while during fogs it is greatly increased.

The effects of carbonic acid gas alone must be carefully distinguished from those of the same gas plus the organic impurities from respiration, with which it is commonly associated. Dr. Angus Smith found that air containing 3 per cent. of carbonic acid produced difficulty of breathing, but he was able to breathe comfortably an atmosphere containing 0·2 per cent. carbonic acid. Other observers have found they could breathe without discomfort air containing 1 per cent. carbonic acid. When the carbonic acid is derived from respiration, headache and giddiness are produced in many persons when the carbonic acid amounts to 0·15 per cent. A fatal result has occasionally occurred from the inhalation of the carbonic acid at the bottom of brewing vats, or about lime-kilns. The gaseous impurity at the bottom of wells is more commonly nitrogen than carbonic acid (page [102]).

The presence of an excess of carbonic acid diminishes the elimination of carbonic acid from the lungs, nutrition and muscular energy being consequently impaired. This is seen in workshops where the air is confined and gaslight is commonly employed; though the air here also contains carbonic oxide, sulphurous acid, and organic impurities, and these probably have a large share in producing the evil results.

(2) Carbonic Oxide in the proportion of more than 1 per cent. is rapidly fatal, and has poisoned when under ½ per cent. Poisoning by its means occurs where charcoal stoves are used, and especially when the charcoal is burnt in rooms with no chimney flue. This is an occasional mode of suicide on the continent. Carbonic oxide is a much more deadly poison than the dioxide (carbonic acid); it forms a stable compound with the hæmoglobin of the red blood-corpuscles, displacing oxygen from them, and is got rid of with great difficulty. Lace-frame makers place a coke stove under their work, and thus inhale the invisible gas. Headache, giddiness, irregular action of the heart, and depression of the general health result. Carbonic oxide is the most poisonous constituent of coal-gas, and is present in much larger quantity in carburetted water-gas with which coal-gas is now commonly mixed, than in pure coal-gas (page [115]).

(3) The inhalation of Sulphuretted Hydrogen produces headache, nausea, and diarrhœa; but in manufactures involving the inhalation of a small proportion of this gas the symptoms are much slighter.

(4) Sulphurous Acid is always present in small quantities in the air of towns, derived from the combustion of coal and coal-gas. Straw-bleachers and the bleachers in cotton and worsted manufactories, often suffer from severe cough and bronchitis due to inhaling its irritating vapours.

(5) Carbon Disulphide when vaporised and inhaled produces headache, general muscular pains, and nervous depression. It is used in the manufacture of waterproof coats, toy balloons, etc.

(6) Ammonia produces irritation of the eyes and bronchial irritation. Hat-makers commonly suffer from its effects, being generally pale and feeble. It is difficult to say how much is due to the ammonia, and how much to the high temperature at which they work.

(7) Acid Fumes are very irritating to the lungs, and in the case of alkali manufactures, they destroy all vegetation for considerable distances. Hydrochloric acid produces great irritation, and chlorine even more so. The fur-dyer is not only subject to the dangers of dust, but also of the fumes of nitric acid, used to remove fat and give certain shades of colour to the fur.

(8) Other Vapours evolved in various processes produce special symptoms. House-painters suffer from the inhalation of turpentine vapour, headache and loss of appetite commonly resulting. The symptoms from the commonly coexistent lead-poisoning are distinct. Brush-makers have a persistent cough, due to the inhalation of resinous fumes, evolved in making brushes.

Workers in paraffin are liable to an irritative disease of the hair-follicles of the body, followed by the formation of scars, almost like small-pox marks.

Workers in quicksilver, as those engaged in making mirrors or thermometers, are prone to suffer from mercurial poisoning. The gums become spongy, and there is profuse salivation, also generally alimentary disturbance; and in some cases nervous affections, resulting in persistent muscular tremblings, etc.

Under the second head—cases of inhalation of mixed gaseous and particulate contamination—we must consider

(1) The Effects of Air Rendered Impure by Respiration.—It has been already stated that an amount of carbonic acid which could easily be borne alone, is intolerable when other products of respiration are mixed with it. These are chiefly organic gases and solids, which (unless removed quickly) render the atmosphere close and “stuffy”—an effect which is readily perceptible by the sense of smell of those entering an occupied room immediately from the outer air. When such a room is inhabited for a few hours, headache, langour, drowsiness, and yawning (which is really a cry for purer air) result. The soporific effects so commonly produced in churches, etc., are commonly due to the vitiated atmosphere, rather than as is supposed to the soothing effects of the sermon.

When the exposure to foul air is more chronic, and occurs day after day, there results a general lowering of strength and vigour—both bodily and mental—even where no actual disease is set up. Oxidation processes are retarded; the consequence is an anæmic sallow complexion, which compares badly with the ruddy complexion of those spending a great part of the day out of doors.

The prolonged breathing of air, foul from the products of respiration, is perhaps more common in workshops and schools than in private houses; but in both, a faint smell is commonly perceptible on entering from the open air, indicating imperfect ventilation and accumulation of organic putrescible matter. The preceding remarks are left as in the last edition. It must be noted, however, that recent research attaches more importance to the particulate matter (dust) in the atmosphere than to the amount of gaseous impurity, though the latter remains a convenient index of impurity. Experiments made by Drs. Haldane and L. Smith on themselves negative the older conclusion that a special organic poison exists in expired air. They were able without any appreciable effect on themselves to breathe air which was vitiated to such an extent as to completely prevent a match from burning; and they conclude that excess of carbonic acid and deficiency of oxygen are the sole cause of danger from breathing air highly vitiated by respiration. This conclusion may be accepted under the conditions of these experiments. Under ordinary conditions, however, the evil effects produced by breathing the air of crowded rooms, are due not only to the excess of carbonic acid and deficiency of oxygen, but also to the dust which is usually associated with them. This dust, which may be derived from handkerchiefs of patients suffering from influenza, consumption, sore throat, &c., or from other sources, is apt to be inhaled by the persons occupying such rooms.

The tendency to catarrhs is greatly increased by living in a vitiated atmosphere. In the causation of “colds” two elements are concerned, the infective agent, and the condition of the patients. “Colds” are caused primarily by infection from previous patients. The nasal discharge of a “cold in the head” contains the contagium. This is dried on handkerchiefs, and is subsequently scattered as dust, and thus conveyed to others. Ordinarily there is considerable resisting power against such catarrhs. When, however, the general vitality or the local vitality of the mucous membrane of the nose, throat, and lungs is impaired by the breathing of impure air or by sitting in wet clothes after exposure to wet and cold, a catarrh is produced.

The close connection of phthisis (consumption) with overcrowding and the breathing of a vitiated atmosphere will be discussed hereafter (page [313]). The polluted air acts in producing consumption by depressing vital functions, and diminishing the powers of resistance against the actual contagium of the disease, which is inhaled as dust, produced by the drying of the expectoration of consumptive patients.

The germs of infectious diseases are propagated very rapidly in an impure atmosphere; and typhus fever occurs almost solely in conditions of overcrowding.

In the cattle-plague of 1866, it was found that nearly all the cows died when crowded together in unventilated sheds, while only a third died when there was free ventilation.

The effects of air containing the products of respiration in a concentrated condition, and of a deficient supply of air, have been shown only too well in the oft-quoted case of the Black Hole of Calcutta. In this case, 146 persons were confined in a space eighteen feet every way, with two small windows on one side. Next morning 123 were found dead, and the remaining 23 were very ill.

In the experience of this country, the highest death-rates are in the most densely populated districts. The death-rate from phthisis, childbirth, and typhus fever for instance, is far higher in cities than in country-places. The fact may be explained in various ways. Density of population commonly implies insufficient or unwholesome food, unhealthy work, and poverty; but especially impurity of the air, uncleanliness, and imperfect removal of excreta. Of these factors, the vitiated air is probably the most powerful for evil. Children suffer more than adults from close aggregation of population, largely owing to the greater ease with which infectious diseases spread in towns.

(2) Coal-gas is obtained by the destructive distillation of coal, free from access of air. The average composition of London coal-gas is hydrogen 50 to 53, saturated hydrocarbons 33 to 66, unsaturated hydrocarbons 3·5 to 3·6, carbonic oxide 5·7 to 7·1, carbonic acid 0 to 0·6, nitrogen 2·5 to 4·1, and oxygen 0·2 to 0·3 per cent. Of these the illuminants are olefiant gas (C₂H₄) and the higher hydrocarbons. Sulphuretted hydrogen and other sulphur compounds are present in small quantities, averaging 12 grains of sulphur per 100 cubic feet of London gas.

The inhalation of coal-gas, even in small quantities, is liable to produce headache, and may lead to chronic poisoning if allowed to continue. Where the escape of gas is more extensive, as when a tap is left turned on accidentally during the night, two dangers may arise. If a light is struck in the room an explosion occurs; or persons may be poisoned in their sleep by inhalation of the gas. The most poisonous gas in coal-gas is the carbonic oxide. The chief product of the combustion of coal-gas is carbonic acid. Some sulphurous acid is also produced, which is irritating to breathe, and injurious to bookbindings, picture-frames, etc. If the flame is imperfect, as when the pressure of gas is too great, some carbonic oxide may also escape.

In recent years Carburetted water-gas has been largely mixed with coal-gas in certain districts. This is made by passing steam over heated coke. Thus

The product is water-gas which burns with a non-luminous flame and has no smell. For illuminating purposes it is enriched with vaporised paraffin oil, which gives it a high illuminating power, and a smell rather like that of coal-gas. In some towns as much as 60 per cent. of this carburetted water-gas is mixed with 40 per cent. of coal-gas. Now as the former contains about 30 per cent. of carbonic oxide, and the latter only 7 per cent., a mixture of equal parts of the two gases would contain 18·5 per cent. of carbonic oxide, and would therefore be much more dangerous than coal-gas. This has been found to be so in actual experience of escapes of gas.

In speaking of these products of different illuminants, it is necessary to adopt a standard of light. In this country the standard has hitherto been a light known as “one-candle power” which is given by a sperm candle burning 120 grains per hour, or in V. Harcourt’s standard flame by a mixture of air and pentane (C₅H₁₂). A good fish-tail or bat’s wing burner for coal-gas gives an illuminating power equal to 16 candles, and burns from 4 to 5 cubic feet of gas per hour. Most flat flame burners known as 4 or 5, and supposed to burn that number of cubic feet of gas per hour, really consume nearly double this amount of gas. In the following table the amount of various products produced and of vitiation of air caused by various forms of illuminants is compared, when an illumination equal to 16 candles is produced in each instance:—

Thus as an adult expires 0·6 cubic feet of carbonic acid per hour, it follows that the amount of carbonic acid produced in one hour by the various illuminants named in the above table, burning so as to give a light equal to 16 standard candles, varies from 4 to 11 times the amount produced by the adult. Candle and oils possess the advantage over coal-gas that no sulphurous acid is produced in combustion. If the pressure in the mains is excessive, some gas may escape through the burner unburnt or carbonic oxide may escape.

In England the flashing-point of mineral oils has been fixed at 73° Fahr. The material of which the reservoirs of lamps are composed should not be glass or other breakable material, and the wick should be contained in a small wick chamber extending nearly to the bottom of the reservoir. Only a tight fitting wick must be used.

The best illuminant for domestic purposes is incandescent electricity, in which no products of combustion are formed, and only a comparative small amount of heat is produced. Electrical illumination possesses the further advantages that there is no blackening of ceilings and no damaging of other decorations as in illumination by gas.

(3) Air Rendered Impure by Exhalations from the Sick. In addition to the ordinary impurities of occupied rooms, special impurities are produced, varying with the character of the disease. They may include infectious particles from the sick. In wards for consumptives and for diphtheria, dust in the room has been found to contain the special microbes of these diseases. Making beds, sweeping floors, &c. may help to scatter infectious dust; hence the importance of adopting means of cleansing which will not scatter dust, and of keeping sick-rooms spotlessly clean. In many diseases e.g. consumption, a patient may re-infect himself with such infectious dust, and thus diminish his own chance of recovery (see page [311]). Hospital wards can scarcely be too freely ventilated; but even more important than ventilation is the strictest cleanliness in every minute detail.

(4) The Air of Sewers, Cesspools, etc., may contain the products of decomposition of sewage, such as volatile fœtid organic matter, carbo-ammoniacal substances, sulphuretted hydrogen, carbonic acid, etc. The amount of these various products varies greatly under different circumstances, such as dilution of the sewage, ventilation of sewers, temperature, etc. The effluvia from cesspools are usually more concentrated than those from sewers. It appears fairly certain that the emanations from sewers or drains may give rise to diarrhœa and gastric disturbances, and to certain forms of sore throat, which favour the production of diphtheria. On the other hand, there is much evidence showing that the danger from sewer-emanations has been exaggerated. Carnelley and Haldane found that the air of the sewers of the Houses of Parliament and of certain sewers of Dundee was not very impure, containing a smaller number of bacteria than external air. There is reason to believe that the emanations from well-ventilated sewers, possessing a good gradient, so that the contents of the sewers are hurried away to the outfall, are free from danger. The chief source of possible danger would be the escape of the bacteria of such diseases as enteric fever or diphtheria, which had been discharged into the sewer from patients suffering from these diseases. But, in the absence of splashing, these bacteria could not escape from a liquid medium. Their escape could only occur when the sewer became dry, and the dust was carried up by rapid currents of air, a very improbable occurrence in sewers. Hence in the majority of instances sewer emanations must be freed from the accusation of producing infectious diseases. Sewer-men usually enjoy good health, and there is no excess of infectious diseases among them.

The emanations from obstructed drains or sewers may cause serious mischief, similarly to that occasionally produced by the emanations from cesspools. Under such conditions, sulphuretted hydrogen, carburetted hydrogen, and other gases are evolved, and fatal asphyxia has been caused by these. In other instances acute sewer-gas poisoning, without pneumonia, has followed.

The exhalations from cesspools or privies while cleaning them out, may produce severe disorders, which are sometimes fatal. When a drain is newly opened or sewer gas gets into a house, a less marked form of poisoning sometimes occurs, chiefly characterised by languor, headache, vomiting, and diarrhœa. In some cases there may be febrile attacks lasting a few days. Children are especially sensitive to such conditions and quickly fall into ill health.

The direct origin of acute infectious diseases from the effluvia from drains or cesspools has occasionally occurred. Leaky and choked drains under a house are especially dangerous. The subsoil becomes contaminated more and more as time goes on; foul gases are aspirated into the house, owing to its interior being warmer than the subsoil; and finally infectious matter may find its way into the house, or carried by insects or vermin, through cracks in the earth.

Diphtheria has been ascribed to emanations from drains and sewers. There is reason to believe that a non-specific form of sore throat may originate in this way; but diphtheria is generally, if not always, spread by personal infection. Diarrhœa has been occasionally ascribed to sewer-emanations. It chiefly occurs in hot weather, and is usually associated with a foul condition of the surface soil, and speedily ceases after this has been scoured by copious rain.

Enteric or typhoid fever, has been frequently ascribed to drain and sewer effluvia. It was formerly thought that putrefactive changes alone, under certain conditions of temperature, etc., would produce it, and Dr. Murchison, one of the greatest authorities on the subject, who adopted this view, proposed for enteric fever the name “pythogenic fever” (i.e. filth-produced). Isolated cases of enteric fever, occurring where there is no system of drainage, support the same view, as does also the fact that, with the adoption of drainage, the enteric mortality has steadily diminished. On the other hand, numerous cases can be quoted to show that emanations from excreta have been breathed, and sewage-contaminated water drunk, for years, without the production of a single case of enteric fever—until a case is accidentally imported. The weight of evidence is clearly on the side of the view that only emanations from the liquid or solid dejecta of previous enteric patients will produce enteric fever, and that it is the solid particles of the urine or fæces, either inhaled as dust or carried on to food by flies, &c., or mixed with food by contaminated water, &c., which cause infection. Furthermore, modern investigation shows that infection by dust is the exception in England; and that the enteric infection is usually swallowed and not inhaled, being taken in infected water or milk or other food.

(5) Effluvia from Decomposing Organic Matter.—(a) The air of marshes contains an excess of carbonic acid, marsh gas, etc., in addition to other organic matters. Malarial diseases are commonly ascribed to the inhalation of the marsh effluvia under certain conditions, though the recent proof of the part played by the mosquito in spreading malaria, puts the inhalation of such effluvia in the background as cause of this disease (page [307]). Some forms of diarrhœa and dysentery have been ascribed, with a less degree of probability, to the same cause. In this case, as in that of emanations from other organic sources, the impurities received by the air are both gaseous and particulate.

(b) The Air of Graveyards contains an excess of carbonic acid. The older intramural graveyards appear to have been a cause of illness; but modern graveyards, kept under good regulations have never been shown to cause illness.

(c) The Effluvia from Decomposing Carcases, especially of horses on the battle-field, have led to outbreaks of diarrhœa and dysentery among the soldiers.

(d) The Effluvia from Manure and Similar Manufactories do not seem to injure the workmen as a rule, but attacks of diarrhœa have been produced in the neighbourhood when the wind has wafted the effluvia towards any particular part. Sore throat, and occasionally diphtheria, have been ascribed to the inhalation of London manure taken into Essex.

(6) The Effluvia from Certain Manufacturing Processes seem to be rather nuisances than actually productive of ill health. The vapours given off by tallow-making and bone-burning processes are most disagreeable, but there is little or no positive evidence of their direct insalubrity.

The air of brickfields and cement works is peculiarly disagreeable.

The Degree of Moisture and the Temperature of air are of great importance in relation to health. Air which is unduly moist or dry, hot or cold, may be injurious apart from any foreign matters it contains.

The relative amount of moisture is of greater importance than its actual amount. An atmosphere which contains aqueous vapour up to the point of saturation is very oppressive; the normal evaporation of insensible perspiration (and with it of the organic impurities removed from the skin) is interfered with; and consequently the “oppressiveness of the day” is complained of.

An unduly hot air is generally productive of pallor and ill health, though it is difficult to know how much to ascribe to the high temperature, and how much to the commonly coexistent vitiated atmosphere. The temperature of living-rooms ought not to be over 60° to 65° Fahr., and of bedrooms not over 60° Fahr.

The devitalising influence of extreme cold is well known. Its effects are more particularly seen in young children and the very old, who require to be carefully tended during severe and long-continued cold weather. Dry, cold weather, with the temperature near the freezing point of water, and a cutting east wind prevailing, is not uncommonly described as “bracing.” This is so far from being the case, that it requires all the vital powers of the strong and healthy to resist its depressing influence, and the feeble of both extremes of age succumb.

[CHAPTER XVII.]
TRADE NUISANCES.

Many occupations are the source of considerable danger to the workers engaged in them. They are chiefly injurious by the inhalation into the lungs of some foreign agent, which produces serious local inconveniences and irritation, and may be also absorbed into the circulation and produce more remote effects.

The injurious agents may be classified under four heads:—

(1) Insoluble particles or dust.

(2) Soluble or partially soluble substances.

(3) Injurious gases or vapours.

(4) Effluvia from offensive trades.

It is evident that, as regards the effluvia named under (4), they might generally be included under the three previous heads, though it is convenient for our present purpose to keep them separate.

The occupations in which dust and soluble substances are productive of injurious effect have already been described, pages 107 to 109.

Injurious gases and vapours have received consideration on pages 111 and 112. The special offensive trades still require attention.

Offensive Trades.—The legal enactments relating to offensive trades are contained in sect. 112 of the Public Health Act, 1875, which states, any person who, after the passing of this Act, establishes within the district of an urban sanitary authority, without their consent in writing, any offensive trade, that is to say, the trade of—

• Blood boiler, or
• Bone boiler, or
• Fellmonger, or
• Soap boiler, or
• Tallow melter, or
• Tripe boiler, or
• any other noxious or offensive trade, business, or manufacture,

shall be liable to a penalty not exceeding fifty pounds in respect of the establishment thereof, and a penalty not exceeding forty shillings for every day on which the offence is continued.

These provisions can only be enforced in rural districts with the sanction of the Local Government Board.

The “other noxious or offensive trades,” in order to be brought within the operation of the section, must be analogous to those which are specially enumerated.

The most exhaustive and authoritative report on this subject is by the late Dr. Ballard, whose report is largely quoted in the following remarks.

We may consider (1) the extent to which the public is inconvenienced by various effluvium nuisances. The majority of the nuisances arise from trade processes in which animal matters are chiefly used. Among the most disgusting are the effluvia from gut-scraping, and the preparation of sausage skins and catgut, the preparation of artificial manures from “skutch” (the refuse matter of the manufacture of glue), the manufacture of some kinds of artificial manures, and the melting of some kinds of fat. Manufacturing businesses dealing with vegetable substances are often offensive, but rarely give out disgusting effluvia. The most offensive vegetable effluvia are probably those thrown off during the heating of vegetable oils, as in the boiling of linseed oil, the manufacture of palmitic acid from cotton oil or palm oil, the manufacture of some kinds of varnish, the drying of fabrics coated with such varnishes, and the burning of painted articles, such as disused meat-tins.

Occasionally offensive effluvia arise in connection with industries in which neither vegetable nor animal matters are used; as in the manufacture of sulphate or chloride of ammonia, and some other processes in which sulphuretted hydrogen is copiously evolved; and in the making of gas and the distillation of tar. The fumes from the manufacture of alkali and bleaching powder are acid and irritating, and produce very injurious effects on vegetation in the neighbourhood.

The distances to which nuisances extend vary greatly according to circumstances—as, for instance, the elevation at which the effluvia are discharged into the air. Discharge from a high chimney may relieve the immediate vicinity of the works at the partial expense of those living at a greater distance. With a damp and comparatively stagnant atmosphere, effluvia have a much greater tendency to cling about a neighbourhood.

(2) The industrial processes in which offensive effluvia are produced are classified by Dr. Ballard as follows:—

1. The keeping of animals.

2. The slaughtering of animals.

3. Other branches of industry in which animal matters or substances of animal origin are chiefly dealt with.

4. Branches of industry in which vegetable matters are chiefly dealt with.

5. Branches of industry in which mineral matters are chiefly dealt with.

6. Branches of industry in which matters of mixed origin (animal, vegetable, and mineral) are dealt with.

(3) It is important to inquire to what extent offensive trade effluvia are injurious to the public health. It is impossible to bring statistics to bear on the inquiry, as other influences, apart from occupation, can scarcely be eliminated. The term “injurious to health” is capable of a double interpretation. It might mean either serious damage to health, or the mere production of bodily discomfort or other functional disturbance by the offensive effluvia, leading by its continuance to an appreciable impairment of vigour, though not to any actual disease.

In the latter sense offensive effluvia have a deleterious effect on health. Such symptoms as loss of appetite, nausea, headache, occasionally diarrhœa, and general malaise are produced by effluvia of various kinds, but agreeing in being all offensive. “A condition of dis-ease or mal-aise is produced.”

There is little difficulty in proving bad effects on the workmen, though the invariable defence of manufacturers is an appeal to the condition of health of their workmen. The workmen only remain such so long as they are healthy, and as they become disabled they necessarily cease to rank among workmen. The decomposition of putrefying organic matters is unquestionably dangerous. The general doctrine of sanitation that filth is one of the chief factors in producing disease is certainly applicable to trade effluvia as well as to general sanitation. It has been alleged on behalf of such effluvia as chlorine sulphurous acid and tar vapours that they are useful disinfectants; but modern research has shown that disinfectants, in order to be of practical use, must be in such a concentrated condition that the air containing them is irrespirable. Probably such septic diseases as erysipelas are favoured by organic trade effluvia.

(4) The means available to prevent or minimise the nuisances arising from trade effluvia vary with the character of the processes. The general principles on which treatment must be founded depend, as Dr. Ballard points out, on a recognition of the following kinds of effluvia:—

Effluvia dependent—

1. On the accumulation of filth on or about business premises, or on its removal in an offensive condition.

2. On a generally filthy condition of the interior of buildings and premises and utensils generally.

3. On an improper mode of disposal of offensive refuse, liquid or otherwise.

4. On insufficient or careless arrangements in reception of offensive materials of the trade, or in removal of offensive products.

5. On an improper mode of storing offensive materials or products.

6. On the escape of offensive gases or vapours given off during some part of the trade processes.

It is evident that under the first two headings the proper remedy is cleanliness. Filth should be removed in impervious covered vessels, at regular intervals. Structural arrangements should be made, which will facilitate cleansing operations. Solid refuse should, as far as possible, be separated from liquid refuse, as thus putrefaction is retarded.

Under the last head important remedies are applicable. In many cases a careful selection of the materials of manufacture will form an effective remedy. Thus much of the nuisance connected with soap or candle works arises from the putrid condition of the fat collected from butchers and marine store dealers, and might be obviated by more regular and more frequent collection of the materials of manufacture. The offensive vapours arising during processes of manufacture may be intercepted before reaching the external air, and so treated that they lose their obnoxious character. Various methods of interception are adopted, according to the processes involved. Occasionally it is necessary to have the air of the entire workshop drawn by means of artificial ventilation in a special direction; usually the interception of air from special chambers suffices. When thus collected, the offensive air may be dealt with by (1) passing it through water or some other liquid capable of absorbing the offensive materials; or (2) passing it through some powder with which it has chemical affinity; or (3) if its offensive materials are capable of condensation by cold, passing them through an appropriate condensing apparatus; or (4) if the evolved matters are organic in nature, conducting them through a fire. (5) Occasionally it is sufficient to discharge the offensive gases into the air from a high chimney; and this always produces a mitigation of nuisance, as compared with discharge at a low level.

It is usually found that the adoption of one or other of these methods is directly or indirectly profitable to the offender.

Nuisances from the Keeping of Animals.—The 47th section of the Public Heath Act prohibits the keeping of pigs in towns so as to be a nuisance, and, as a general rule, it is possible to obtain a magistrate’s order, entirely prohibiting the keeping of pigs in towns. The excreta of the pig have a very offensive and penetrating odour, and however carefully kept, pigs in towns form an intolerable nuisance.

Not only is there nuisance from the accumulation of manure and dirtiness of the piggeries, but also from the storage and subsequent preparation of food. The boiling of hog-wash is often an even greater nuisance than the filth of the styes.

Cow-keeping and horse-keeping in towns are still allowed and, as compared with pig-keeping, form a small nuisance. Mews, if kept clean and well drained, need not be offensive, though it is objectionable for persons to sleep over stables. The removal of manure also constitutes a difficulty. The manure should not be allowed to accumulate in deep wet pits, but in an iron cage-work over a cement paving at or above the ground-level, thus allowing free drainage, and keeping the manure dry, and reducing ammoniacal decomposition to a minimum.

Cowsheds are generally very badly ventilated, as the cowkeeper finds that more milk is produced by the cows when the temperature of the shed is maintained at 65° or higher; and he does not see the necessity for providing artificial means of warmth. The grains which are used so largely for food are stored in a wet condition, and speedily give rise to nuisance. Cowsheds and stables should be well paved and well drained. At least 800 cubic feet should be allowed for each cow in the shed.

Cowsheds are regulated under the Dairies’, Cowsheds’, and Milkshops’ Order of the Local Government Board. This order provides for and insists on the registration of cowkeepers, dairymen, and purveyors of milk, by the local authority. It also provides that no cowshed or dairy shall be occupied as such, unless provision is made to the satisfaction of the local authority, for the lighting and ventilation, including air-space, and the cleansing, drainage, and water-supply of the same; and for the protection of the milk against infection or contamination. With the view of preventing contamination of milk, no person suffering from an infectious disorder, or having recently been in contact with a person so suffering, is allowed to milk cows or take any part in any stage of the business of a milk-seller. The milk of a cow suffering from cattle plague, pleuro-pneumonia, or foot and mouth disease must not be mixed with other milk, must not be sold or used for human food, nor for food for swine or other animals, unless it has been boiled. By the order of 1899 this regulation is made to extend to tubercular disease of the udder.

Slaughtering of Animals.—Nuisance may arise in slaughter-houses from various causes:—(1) the uncleanly way in which animals are kept in the pound or lair before being killed; (2) the insanitary condition, bad paving, lack of lime-whiting of walls, etc., of the slaughter-house; (3) the accumulation of hides, blood, fat, offal, dung, or garbage on the premises; (4) the uncleanly condition of the blood-pits, or the receptacles for garbage; (5) the flowing of blood or offal into the drains and thence into the public sewer.

Private slaughter-houses ought to be abolished, and all animals intended for human food slaughtered in public abattoirs under efficient supervision. When a large number of private slaughter-houses exist in different parts of a large town, it is impossible for the sanitary officials to properly supervise the slaughtering, or to ensure that diseased meat shall not enter the market. The inspector may only have the opportunity of examining the flesh, the internal organs which more particularly show the presence of a diseased condition having been concealed. Such concealment and the consequent foisting of diseased meat upon the public, can only be efficiently prevented by forbidding the slaughtering of any animal intended for food in a private slaughter-house.

Most local authorities have bye-laws regulating the slaughtering of animals. These provide for a cleanly condition of the lairs, and prevent keeping the animals longer in the lairs than is necessary for the purpose of preparation for slaughtering. They also insist on the provision of proper covered receptacles of iron or other non-absorbent material for the reception of garbage, and similar receptacles for blood; for cleansing of the floor, etc. after slaughtering; for lime-whiting of the walls four times a year; and for other matters of detail.

For knackers’ yards similar regulations are applicable. The flesh should not be kept until it becomes putrid before being boiled, and the boiling of the flesh and fat should be so arranged as to avoid the escape of offensive vapours into the external air.

In smoking bacon, the singeing has formed a serious nuisance. Fish-frying in small shops is often a most troublesome nuisance. A hopper over the pan in which the frying is conducted has not been always successful in carrying the fumes up the chimney. The frying should preferably be done in a closed outhouse, close to a chimney with a good up-draught.

The fellmonger prepares skins for the leather-dresser, the chief operations being taking off the wool, liming the skins, etc. The skins deprived of wool are called “pelts.” The pelts are thrown into a pit containing milk of lime, and thence sent direct to the leather-dresser. Nuisance may arise from (1) the odour of the raw skins; (2) the ammoniacal odour from the lime-painted skins hanging in the yard; (3) the emptying and cleansing of the “poke” or tank in which the hides are washed; (4) the foul condition of the waste lime taken from the exhausted lime pits; (5) the odour from the dirty unpaved yards.

The leather-dresser only deals with “pelts,” derived from sheep-skins; the tanner with bullocks’-hides. The skins brought from the fellmonger to the leather-dresser are first deprived of lime, and then soaked in a solution of dog’s dung, called “pure,” until they become soft. In winter this “pure” solution is warmed for use. The odour is very abominable, both from the “pure” tub, and from the discharge of the exhausted “pure” liquid into the drain.

At each stage of tanning nuisance may arise unless great precautions are taken, as when the hides are soaked in lime and water, when the hair is being removed, when the loose inner skin of the hide is being removed, and especially when the hides are soaked in pits containing pigeons’ or other dung. Nuisance may arise again during the passage of offensive hides through the street. Cleanliness is the great rule. If every process is carried on with due precaution, including frequent washing out of receptacles and the free use of disinfectants, little complaint need arise.

The manufacturers of glue and size boil out the gelatine from bits of hides and “fleshings” from leather dressers and tanners, from damaged “pelts,” ox or calves’ feet, horns, and other similar substances. The raw material is apt to be offensive in collection or while accumulating on the premises. The process of boiling causes offence by the effluvia from the steam. The residue remaining after the process is known as “scutch,” and this, unless frequently removed, is a most serious source of nuisance.

Prussiate of Potass is manufactured by heating carbonate of potass with refuse animal matters. In order to avoid nuisance the pot in which the boiling is done should have a pipe to conduct away the steam, first running horizontally and then vertically down to the back part of the fire.

Fat-melting and Dip-candle-making, as usually carried on, give rise to nuisance. The fat which is melted down usually comes from butchers and marine-store dealers in a rancid or even putrid condition, and it may be stored on the premises for some time before it is boiled. The vapours from the melting-vat are very offensive. They should be carried by means of a pipe down until they discharge just under the boiler-fire. The residue from the fat-melting process (known as “greaves”) requires frequent removal to avoid nuisance.

Bone-boiling, in order to extract the fat and gelatine, is most offensive, and most difficult to deal with. After boiling, the bones are apt to give off offensive smells. The vapours from the closed boiler should be condensed as far as possible in a worm condenser, and the remainder passed through a furnace fire.

In the manufacture of artificial manures nuisance is apt to arise (1) from the reception and accumulation of the raw materials, as putrid fish, putrid blood, scutch (the residue from the manufacture of glue), recently boiled bones, etc.; (2) from the preparation of the raw material for use. Thus the drying of condemned fish or meat on open kilns is very offensive; similarly the drying of sewage sludge. (3) From the process of mixing the materials of manufacture, irritant and offensive vapours being evolved, as for instance in the manufacture of manure by crushing bones, and converting into super-phosphate by the addition of sulphuric acid. (4) From the removal of the manure from the hot den, after it has been dried. When sulphuric acid is mixed with coprolites or other mineral phosphates, most irritant and offensive vapours are produced, which may be perceived in some cases at the distance of a mile.

Blood-boiling is now almost obsolete, having been replaced by albumen-making and clot-drying. Nuisance may arise from the blood collected from slaughter-houses being in a putrid state; and from the effluvia evolved during the drying process.

Gutscraping, gut-spinning, and the preparation of sausage-skins are very closely akin. In gut-scraping the putrid intestines are deprived of their interior soft parts by scraping with pieces of wood, and are then, after being cleansed, ready for sausage-skins. In gut-spinning the prepared gut is twisted into a cord. The small intestines of hogs and sheep are used for this purpose. The stench from these establishments is indescribably horrible. Extreme cleanliness is desirable. Immersion of the guts in common salt is useful; so also the use of impervious vessels, early removal of all refuse material, etc.

Brick and ballast burning are a frequent source of complaint in the neighbourhood of towns. Brick burning is conducted either in kilns or clamps. When bricks are burnt in closed kilns comparatively little nuisance arises; but when they are burnt in open clamps the effluvia are very irritating, partly owing to the fact that very commonly house refuse, containing vegetable and animal matters, is burnt with the bricks. Clamp burning should be absolutely prohibited in the neighbourhood of large towns.

In Ballast burning stiff clay is converted by the agency of heat into a brick-like material, which is of use in road-making. The clay is usually burnt in heaps, mixed with ashes and breeze from dust-bins. The process is offensive unless carried on with precautions similar to those for brick-burning.

[CHAPTER XVIII.]
THE EXAMINATION OF AIR.

There are various methods of ascertaining the quality of the air in enclosed spaces, of which not the least useful is the information furnished by the sense of smell, on entering a room from the external air. Besides the evidence given by the senses, chemical and microscopical examination of the air gives important information, while the thermometer and hydrometer ascertain the temperature and degree of moisture.

Examination by the Senses.—The dull grey haze hanging over a town, when it is viewed from a distance, indicates comparative impurity of its atmosphere, and the presence of a considerable amount of suspended matter, including smoke.

The smell of a stagnant atmosphere is a good preliminary guide to its condition. The fact that a room has been occupied for some time without efficient ventilation can be at once detected on entering a room from the external air. The sense of smell is extremely delicate; it has been estimated that the ³ ∕ _100,000,000 part of a grain of musk can be apprehended by it. But nothing is so soon dulled as the sense of smell. An atmosphere which did not appear to be unpleasant while remaining in a room, is intolerable when one returns to it after a few minutes in the open air. It is important not to confound the “closeness” perceived by the sense of smell, with the oppression due to the high temperature of a room. The two are easily distinguished (unless the two co-exist) by a reference to the thermometer, which ought always to be placed in rooms inhabited during the evening. The remedy for a close room is to allow free entry of fresh air, and not allow the fire to go down, as is so commonly done, under the impression that the closeness is due to heat.

De Chaumont has made many experiments, shewing how accurate is the information given by an acute sense of smell. Carbonic acid is destitute of odour, but as its amount is usually proportionate to that of the organic matter producing closeness, it may be taken as an index of the amount of impurity present in living rooms. De Chaumont found that the limit of smell is reached when carbonic acid amounts to 6 parts in 10,000 of air, or half as much again as in the external air. In the following extracts from his experiments, there was a close accordance between the evidence of his sense of smell and the amount of carbonic acid:—

He also found that humidity of the air had marked influence in rendering the smell of organic matter perceptible, even more than a rise of temperature. The sense of smell is doubtless aided in detecting impurities in the air, by the besoin de respirer, a feeling of oppression caused by the deficiency of interchange between the blood and air. The state of cleanliness of the room as well as of the persons in it influences smell; hence there may not be in particular instances exact correspondence between excess of carbonic acid and of organic matter.

Chemical Examination.—The estimation of nitrogen and oxygen in air is usually unnecessary, as these vary but little. The oxygen is, however, reduced in frequently re-breathed air. The ill effects of an often-breathed atmosphere are due not only to deficiency of oxygen, but also to the addition of carbonic acid and organic matters, rendering difficult the interchange between oxygen and the blood.

The Estimation of Carbonic Acid is of great importance, as under ordinary circumstances, its amount is a fairly exact indication of the amount of contamination in the air.

Pettenkofer’s Method.—A carefully dried glass vessel containing a gallon of water is filled with the air to be examined, by emptying the water in the room, the air of which is to be examined. Fifty cubic centimetres of clear freshly prepared baryta water are then added, and the stopper of the bottle then replaced. It is then well shaken, and afterwards allowed to stand for an hour. The carbonic acid combines with part of the baryta to form barium carbonate; and the baryta water remaining is consequently diminished in alkalinity. Given the alkalinity of the baryta water before and after the experiment, and the difference will give the amount of baryta which has combined with carbonic acid.

The alkalinity of the baryta is estimated by a standard solution of oxalic acid, of such a strength that 1 c.c. is the equivalent of 0·5 c.c. of CO₂. The indicator used in making this test is phenolphthalein, which colours baryta water red, but its colour disappears when neutralization is reached.

The following example is taken from “Pakes’ Laboratory Text Book of Hygiene,” p. 292:—

The jar is found to contain 3,950 c.c.

As 50 c.c. baryta water were run into the jar, the air experimented on = 3,950-50 = 3,900 c.c.

On titrating 25 c.c. of the original baryta water, 22·50 c.c. standard acid solution were required to neutralise it.

The baryta water in the jar required 19·35 c.c.

22·50-19·35 = 3·15 c.c. = difference of acid used.

But 1 c.c. acid = 0·5 c.c. CO₂ at 0° C. and 760 mm. of mercury.

Therefore CO₂ taken up by 25 c.c. of baryta = 3·15∕ 2 = 1·575 c.c.

As 50 c.c. were used the CO₂ absorbed by the baryta = 3·15 c.c. This was present in 3,900 c.c. of air. Therefore the CO₂ = 0·80 per cent.

Correction may be required for variations from the normal pressure of 760 mm. and normal temperature of 0° C., in accordance with ordinary rules.

In Lunge and Zeckendorf’s Method, the air to be examined is pumped through a glass bottle in which is 10 c.c. of a N ∕ 500 solution of Na₂CO₃ containing phenolphthalein as an indicator. The air is pumped by a hand pump through this solution until the phenolphthalein is decolourized. The number of times the ball of the pump has been squeezed indicates the amount of CO₂ present in accordance with a table prepared from separate experiments by Pettenkofer’s method.

Dr. Angus Smith’s plan for the estimation of carbonic acid in air is similar in principle to the last calculations. It is based on the fact that the amount of carbonic acid in a given volume of air will not render turbid a given amount of lime water, unless the carbonic acid is in excess.

Table.—To be used when the point of observation is “No precipitate.” Half an
ounce of lime water containing ·0195 gramme lime.

Air at 0° C. and 760 M. M. Barometric pressure.

The foregoing table shows how to apply this method. The first and second columns state the ratio of carbonic acid in a quantity of air which will give no turbidity or precipitate in half an ounce of lime water; the third column gives the corresponding size of the bottle in cubic centimetres; and the fourth column gives the same in ounces. Thus different sized bottles, each containing half an ounce of lime water, will indicate with a fair degree of accuracy the ratio of carbonic acid in the air containing them, by giving no precipitate when the bottle is well shaken. For instance, if a pint bottle is used and there is no precipitate with half an ounce of lime water, it indicates that the ratio of carbonic acid does not amount to ·03 per cent.; if an eight-ounce bottle be used, and there is no precipitate, it indicates that the ratio does not amount to ·08 per cent., and so on. The air of a room ought never to contain more than six parts of carbonic acid in 10,000 of air, or ·06 per cent., i.e. a 10½ ounce bottle full of the air shaken up with half an ounce of clear lime water ought to give no precipitate.

Dr. Haldane has recently described (Journal of Hygiene, No. 1, 1901) a method of estimating CO₂, which, although it appears complicated, is really both simple and convenient. For particulars, see the above Journal.

The Estimation of Organic Impurities may be accomplished approximately by drawing a definite amount of air by means of an aspirator, through a dilute solution of permanganate of potassium of known strength. The result is stated by giving the number of cubic feet of air required to decolourise .001 gramme of the permanganate in solution. Sulphuretted hydrogen, sulphurous acid, and other substances in air likewise decolourise the permanganate; these ought to be separately tested for, and allowance made.

The Estimation of Ammonia, whether free or derived from albuminoid impurities, is a matter requiring very delicate processes. It is accomplished in the same way as the estimation of ammonia in water, the air being drawn through perfectly pure distilled water, and then the analysis proceeded with as a water analysis. The mere presence of free ammonia may be determined by exposing to the air strips of filtering paper dipped in Nessler’s solution, which become brown if there is any ammonia in the air.

Microscopical Examination is required for the detection of suspended matters. These are the most potent for harm, containing sometimes the germs of infectious diseases. The suspended matters scattered throughout the air may be collected by Pouchet’s aeroscope. This consists of a small funnel drawn out to a fine point, under which a slip of glass is placed moistened with glycerine. Both funnel and glass are enclosed in an air-tight chamber, connected by tubing with an aspirator, by means of which when water is allowed to escape from it, air is drawn through the funnel and its particles impinging on the glycerine are there arrested. Glycerine may be objectionable from the foreign particles previously contained in it. Various other plans have been devised, one of which is to draw the air through a small quantity of pure distilled water and then examine a drop of it. By microscopic examination large particles can be detected. For the detection of bacteria and their spores more delicate methods are required.

The Bacteriological Examination of air is usually conducted as follows. Air is drawn through a wide glass tube (Hesse’s tube), which has been previously sterilised, and on the inner side of which liquid gelatine has been allowed to solidify. The air as it passes over the gelatine deposits any germs present in it. The entrance of any further germs is prevented by closing the tube, and it is then left to stand for two or three days. Moulds and colonies of bacteria will develop in the gelatine, and these can be counted and differentiated by their appearance and by further tests. In closed rooms the number of microbes (i.e., bacteria and moulds) ought not to be more than 20 per litre of air in excess of those in the outside air; and the ratio of bacteria to moulds ought not to exceed 30 to 1.

Examination of Temperature and Moisture.—The temperature should be observed at the point most remote from an open fire-place, and compared with the external temperature. For methods of estimating moisture, see page [240].

It may be useful to recapitulate at this point the desiderata in an inhabited room. The temperature should be 60-62° Fahr., the amount of carbonic acid should not exceed ·06 per cent. and the humidity should range between 73 and 75 per cent. of the amount required to produce saturation. The dry bulb thermometer should read 63-65° Fahr., the wet bulb 58°-61° Fahr., and the difference between the two should not be less than 4° or more than 8°.

[CHAPTER XIX.]
THE PURIFICATION OF AIR.

In addition to the artificial measures which will be discussed in the next chapter, various natural agencies are constantly at work for the removal of the impurities discussed in preceding chapters. Of these, the most important are the action of plants, the fall of rain, natural methods of ventilation, and certain natural constituents of the atmosphere.

1. Plants, by virtue of the chlorophyll contained in their green parts, absorb carbonic acid from the atmosphere, liberating oxygen in an active condition. In addition, ammonia and nitrous and nitric acids are dissolved from the air by rain-water, and assimilated by plants. During the night plants only give off carbonic acid.

2. The Fall of Rain clears the atmosphere of any solid particles contained in it, the impurities being transferred to rain-water which generally contains an appreciable amount of ammonia as well as other impurities. Rain not only washes and purifies the air, but by washing the ground, diminishes dust, and prevents its escape into the air. It is the great natural scavenger.

3. Ventilation—that is, the interchange of pure and impure air, is constantly being effected. Before entering on the details of ventilation, we must consider the physical causes at work which tend to purify the air, apart from all artificial contrivances. These are three in number—namely, diffusion, winds, and differences of temperature of masses of air.

(1) Diffusion causes the rapid mixture of gases placed together. Every gas diffuses at a certain rate—namely, inversely as the square root of its density. In any room which is not air-tight, diffusion is constantly occurring, air passing in and out at every possible point. Through chinks and openings in the carpentry-work of a room, the air diffuses rapidly. Bricks and stone commonly allow air to pass through them; diffusion occurs to a slight extent even if the wall is plastered, but very little through paper. Diffusion alone is quite insufficient to purify a room under ordinary circumstances; and solid particles including the organic matter evolved from the skin and lungs, not being gaseous, are unaffected by it. To remove these, the room must be periodically flushed with air, and washing of all dirty surfaces must be carried out.

Diffusion sometimes produces evil results, when the sanitary arrangements of a house are bad. If there is a leakage of sewage under the kitchen floor, the foul gases from it diffuse upwards; occasionally foul air diffuses from the dust-bin through the wall into the rooms of a house. These results are helped by the fact that the internal temperature of a house is commonly higher than the external.

(2) Differences of Temperature cause active movements of air. In fact winds are caused by movements between large masses of air of unequal temperature and consequently of unequal density. Light gases ascend, as familiarly illustrated by the smell of dinner perceived in bedrooms, or the smell of a cigar lit in the hall perceived in the attic. In rooms differences of temperature of the air are caused by the heat of fire, gas, and our own bodies. Currents of air result; the warmer and lighter air ascends up the chimney or towards the ceiling, while colder and denser air rushes in under the door or through the floor, etc. The lighter gases carry with them solid particles in suspension and thus tend to remove the most important impurities. Assuming that the external air is colder, if admitted into the lower part of a room, it produces a draught; if admitted at the top of a room, being heavier, it falls by its own weight on the heads of those in the room. The problem of ventilation is to secure a sufficient interchange of air without the production of perceptible currents.

Movements of air are constantly occurring, so long as the temperature of the air is subject to changes. This cause alone will suffice to ventilate all rooms in which the air is hotter than the external air. It may thus happen that a room with windows and doors closed in winter, may possess purer air than the same room in summer with these thrown widely open. The value of diffusion of air through the walls, and the influence of temperature on this diffusion are well illustrated by some experiments of Pettenkofer.

When the difference between the outside and inside temperatures was 34° Fahr. (66° inside and 32° outside), and the doors and windows were shut, an ordinary room in his house, of the capacity of 2,650 cubic feet, which was built of brick, and furnished with a German stove instead of an open fire-place, had its entire atmosphere changed once in an hour. With the same difference of temperature, but with the addition of a good fire in the stove, the change of air rose to 3,320 cubic feet per hour. On lessening the difference between the external and internal temperature to 7° Fahr. (64° and 71°), the change of air was reduced to only 780 cubic feet per hour. In these experiments, all crevices and openings in doors and windows were pasted up.

It is instructive to note the greater amount of ventilation effected through the walls, etc., than by the draught of the stove.

The amount of ventilation through walls varies with the material of which they are built. Mortar is exceedingly porous when dry; sandstones and bricks are easily permeated by both water and air. Limestone is almost impervious to air, but requires much mortar in building, which effects a partial compensation (see page [206]).

The rise of temperature caused by the bodily heat and by the combustion of illuminating agents, is well shown by some figures of Dr. Angus Smith. He found that the rise of temperature of 170 cubic feet of air in one hour, produced by the bodily heat of one man was 5°·6 Fahr.; by the combustion of a candle 3°·8 Fahr. Thus, in a room 8 feet high, 4 feet broad, and 6 feet long, a man burning a candle would in an hour raise the temperature from 60° to 70° Fahr. This rise in temperature would not only cause currents of hot air towards the upper part of the room, but would probably make the room uncomfortable, and so lead to the opening of a door, etc.

(3) Winds are of great value in flushing rooms with fresh air. They ought to be utilised as often as possible, by throwing windows widely open; without, however, taking the place of constant ventilation in the intervals. They are especially valuable in getting rid of organic matters which are unaffected by diffusion.

The wind will pass through wood, and even brick and stone walls. When it is allowed to pass directly through a room, as from window to door, it produces a more powerful effect than can be produced in any other way. The average rate of movement of winds in this country is 10 feet per second, or about 7 miles an hour. If the surface which a man exposes to this average wind = 6’ × 1½’ = 9 square feet, then 90 cubic feet of air flows over him in one second, and 324,000 in an hour. If 3,000 cubic feet were the allowance for each person indoors—a much greater allowance than is usually given—he only receives ¹ ∕ ₁₀₈ of the air with which he is supplied in the open.

Winds act as a ventilating agent in two ways—directly by perflation, driving impure air before them, or freely mixing with it; and indirectly by aspiration, drawing the impure air along with them. In the last case, the wind causes a partial vacuum on each side of its path, towards which all the air in its vicinity flows. Thus, the wind blowing over the top of a chimney causes a current at right angles to itself up the chimney. In a spray-producing apparatus we have a familiar instance of the same principle, the current of air or steam along the horizontal tube causing the fluid to rise in the vertical tube till it is scattered in spray. In Sylvester’s plan of ventilation, both these forces are used (see page [150]).

4. Certain Constituents of the Atmosphere have an important purifying effect. Of these oxygen is by far the most important. By its means organic impurities become oxidised, and thus rendered harmless. It is probable that much of this oxidation is effected by means of ozone—a peculiarly active and concentrated form of oxygen. A large part of this ozone is probably produced during thunderstorms and similar electrical disturbances of the atmosphere. The ammonia and organic impurities in air become changed into nitrites and nitrates—chiefly of ammonium—and being washed down by rain, form an important part of the food of plants.

5. For Chemical Measures of purification of the atmosphere see page [324].

[CHAPTER XX.]
GENERAL PRINCIPLES OF VENTILATION.

The Amount of Air required.—Ventilation is chiefly concerned with the removal of the products of respiration, just as sewage is chiefly concerned with the removal of the solid and liquid excreta.

In a less degree it is required for removing the impurities produced by the burning of gas, candles, and lamps. The main problem, however, is the removal of the respiratory products.

The amount of carbonic acid in air is usually fairly proportional to that of the other respiratory products. It may therefore be taken as a measure of the impurity of the air. There are, however, certain fallacies in this test. In soda water manufactory, for instance, there would be a comparatively harmless excess of carbonic acid. In dirty rooms, and in hospitals and other institutions where rooms are not vacated for a considerable period, the amount of organic matter present is often in excess of what would have been anticipated, judging by an estimation of the carbonic acid. This is strikingly shown by some valuable researches at Dundee, which are summarised in the following table. If we take the average amount (in excess of outside air) of carbonic acid, organic matter, and micro-organisms respectively in houses of four or more rooms as unity, then in one or two-roomed houses or tenements we have as follows:—

It is evident that in these cases the carbonic acid did not increase in the same proportion as the organic matter and micro-organisms, and that it alone does not form a sufficient test of the impurity of any given atmosphere. The amount of carbonic acid, however, is a valuable and convenient test of the condition of the air of a room, and the problems of ventilation, of which examples are given on page [137], are based on its amount.

The Standard of purity is somewhat difficult to fix. The external air ought only to contain 4 parts of carbonic acid to 10,000 parts; but it is almost impossible to maintain this degree of purity in inhabited rooms. The experiments made by Drs. Parkes and De Chaumont showed that when the carbonic acid is ·06 per cent., or in the proportion of 6 parts in 10,000 of air, the air begins to be perceptibly stuffy (page [125]); this may therefore be taken as the limit of impurity. Pettenkofer has adopted the limit of ·07 per cent.[7]

The problem then is to discover the amount of pure external air (containing ·04 per cent. of carbonic acid) that will be required to pass hourly through a room, for every person in that room, in order to keep the carbonic acid at the ratio of ·06 per cent.

This may be ascertained by actual observation of the air of rooms in which a given number of persons are placed; or by calculations from physiological data.

As the result of numerous experiments on the atmosphere of prisons, barracks, etc., where the amount of fresh air supplied per hour is exactly known, it is found that in order to keep the carbonic acid at ·06 per cent., 3,000 cubic feet of pure air are required per head per hour; 2,000 cubic feet keep the carbonic acid at ·07 per cent.; 1,500 cubic feet at ·08 per cent.; and 1,200 cubic feet at ·09 per cent.

For the removal of the products of combustion of gas, an additional supply of air is required, for the amount of which, see page [116].

Where a number of sick persons are collected, as in hospitals and workhouses, a much freer supply of air is required. Much depends, however, on the cleanliness of the wards, and on whether the ventilation is constant in character. In St. Thomas’s Hospital, the space allotted to each ordinary patient is 1,800 cubic feet, and to each patient in the fever wards 2,500 cubic feet. Thus, by changing the air of the wards twice in the hour, an abundant supply of fresh air is ensured. The mortality after operations, and in all fevers, is much diminished by a free supply of air.

Soldiers are allowed 600 cubic feet of space per head in their sleeping rooms, which involves a change of the air five times per hour, in order that the carbonic acid may be maintained at ·06 per cent. The limit of overcrowding for lodging-houses is usually fixed at 300 to 500 cubic feet, but this is too little.

The amount of pure air required in order to keep the carbonic acid in a room at ·06 per cent., may also be ascertained from physiological data.

An average adult expires ³ ∕ ₅ (·6) cubic foot of carbonic acid per hour. Now as the carbonic acid in air to be breathed must not contain more than two parts in 10,000 (·02 per cent.) in excess of what is present in external air (·04 per cent.), it follows that if x = the amount of fresh air required by an adult per hour in order to keep the carbonic acid in the room down to .06 per cent., then:—

·02 : ·6 :: 100 : x.
x = 3,000 cubic feet.

Relation of Air Required to Cubic Space of Room.—If we accept 3,000 cubic feet of air as the amount required per head per hour, this may clearly be furnished by having a large room with comparatively little circulation of air, or by having a small room with frequent interchanges. Thus, supposing the cubic space allowed to each individual is 1,000 cubic feet—that is, 10 feet in every direction—the atmosphere will require changing three times per hour.

Now, it is found that when a current of air, at the temperature of 55°-60° Fahr., is moving at the rate of less than one mile per hour, it is not perceptible—that is, produces no draught. The rate of a breeze, which is just perceptible, is 18 inches per second, or one mile per hour. As draughts are objectionable, ventilation, in the best sense of the word, means the supplying of abundant fresh air at a rate of less than one mile per hour, or warmed air at a higher rate. Air moving at the rate of 2½ miles per hour, or 3½ feet per second, is perceived as a slight draught by all, at the average temperature of our climate (about 50° Fahr.)

Where natural ventilation is employed, the difficulties of thoroughly ventilating a small space, without draught, are very great.

A change of air three or four times in an hour is all that can be borne under ordinary conditions in this country, and this necessitates a supply of 1,000 or 750 cubic feet of space respectively for each individual. And a change of this frequency is commonly not effected; the ventilating apparatus may fail temporarily, or may be wilfully stopped up, or there may be no means of ventilation; it is essential therefore to have as large a cubic space as possible. A large cubic space, does not obviate the necessity for efficient circulation of air. It is, however, advantageous, not only on account of the initial longer time before the air reaches the limit of impurity, but also because there are less draughts, and there is a larger wall surface and larger windows for unperceived ventilation.

Common Errors as to Ventilation.—(1) In relation to the cubic space of a room, it is most important to note that a lofty ceiling does not compensate for deficiencies in floor-space. One hears, “lofty” and “airy” rooms spoken of as though the two terms were necessarily synonymous. This is by no means the case. The impurities produced by respiration tend to accumulate about the persons who have evolved them, although it is true that in rooms heated by gaslight, a large amount of hot and impure air collects near the ceiling. The necessity of an abundant floor-space is shown by the fact that a space enclosed by four high walls and without a roof, will, if crowded, speedily become offensive. Twelve feet is quite high enough for large rooms in schools, hospital wards, etc., and nine feet suffices for the rooms of a private dwelling-house. There is no objection to a greater height, if it is remembered that in reckoning the practical cubic dimensions of a room, the height should only be reckoned as twelve feet. Supposing 500 cubic feet is the amount allowed per individual, then the floor-space should be forty-two square feet, which would be furnished by a room about 8½ feet long and 5½ feet wide. In barracks, soldiers are allowed fifty square feet of floor-space. In school-rooms the Education Code requires that at least ten square feet of floor-space, and at least 120 cubic feet shall be allowed for each child in average attendance.

(2) It is commonly supposed that a large room compensates for a deficient circulation of air. The cubic space of a room is really of less importance than the capacity for frequent interchanges of air. Even the largest enclosed space can only supply air for a limited period, after which the same amount of fresh air must be supplied, whether the space be small or large. Thus, supposing that as large a space as 10,000 cubic feet per head were allowed, the limit of purity would in the absence of ventilation be reached in three hours, and after that time an hourly supply of 3,000 cubic feet of air would be just as necessary as if the space were only 200 cubic feet.

(3) It must not be overlooked that the furniture in a room must be deducted from the breathing space, as the amount of air is diminished by the space occupied by the furniture. About 10 cubic feet ought to be allowed for each bed, and 3 to 5 cubic feet for each individual in a room; projecting surfaces must be allowed for by subtraction, and recesses by addition. The deductions to be made for furniture are not of any great consequence, if there is a free interchange of air; as the cubic space is of less importance than free ventilation.

General Rules respecting Ventilation.—The two great objects in ventilating being to remove all impurities from the air, and to avoid draughts, it is important that—

1. The entering air should be, if possible, of a temperature of 55° to 60° Fahr. Whenever the temperature of a room differs from the external temperature by 10° Fahr., a draught is certain to ensue. It is impossible at all times to ensure the incoming air being of the temperature of 60°, without some artificial means of warming it. In this country it is seldom necessary to cool the incoming air, but this may be managed in artificial systems of ventilation by passing the incoming air over ice, or by using compressed air which becomes cooled on expansion, or by passing the incoming air through subterranean tunnels.

2. The entering air should be pure. When a room is hotter than the passages and kitchens, air from the latter, whatever may be its character, is drawn into the room. Similarly the ground-air under the kitchen-floor or the air from ash-pits may be drawn into the house, when no other means of ventilation are provided; and this is often followed by evil results.

3. No draught or current should be perceptible from the incoming air, except when it is wished to flush the room with air, by opening the windows wide. It is a common complaint that a room is draughty, and, to remedy this, keyholes are stopped up, and mats are placed at the bottom of the door, etc. The draught can often be remedied by increasing the size and number of the openings through which air is admitted, so that the current of air is not concentrated and rapid. When this does not remedy it, the incoming air should be warmed. A feeling of draught is very often due to the radiation to and from a window, and disappears when a curtain or screen is placed between the radiating surface and the occupant of the room.

4. The entry of air should be constant, not intermittent. The occasional opening of a window or door will not compensate for the lack of a constant interchange of air, although it forms a very valuable adjunct, especially in the removal of organic particles which do not follow the law of diffusion.

5. An exit should be provided for impure air, as well as an entrance for pure air. The chimney furnishes this in most living-rooms, and diminishes the necessity for other means of exit.

If the openings in a room for entrance and exit are properly regulated, a rate of 5 feet per second (about 3½ miles per hour) will provide sufficient air without any unpleasant draught in a room. For instance, if the opening measure 1 square foot, then a rate of 5 feet per second will give five cubic feet of air per second, that is, 18,000 cubic feet per hour. But as only 3,000 cubic feet are required, it follows that an opening one-sixth this size, i.e. 24 square inches, is sufficient for each individual. Reckoning the same amount for means of exit, 48 square inches is the size of the ventilating orifices required by each individual.

6. A number of small divided openings are not collectively equal in ventilating power to one large one having the same area. Thus, when a ventilating orifice is divided into four parts, which have the same collective area as the original orifice, it is found that only half as much air passes through these as through the original orifice. In order to obtain as much air, therefore, each opening must be equal in size to half the original opening. This is in accordance with the rule that the friction for air passing through openings is inversely to the diameter of these openings, i.e. inversely to the square-root of the area of the openings.

7. The most important requirements of perfect ventilation may be recapitulated as follows:—

1st. The maximum impurity of air vitiated by respiration should not exceed 6 parts carbonic acid per 10,000 volumes.

2nd. To ensure the maintenance of this standard, 3,000 cubic feet of pure air must be supplied per head per hour.

3rd. In order to supply this amount of pure air, with ordinary means of ventilation, 1,000 cubic feet at least must be allowed per head in buildings always occupied.

[CHAPTER XXI.]
PROBLEMS AS TO VENTILATION.

The following formula enables many problems relating to ventilation to be solved. Let p = the amount of poison (carbonic acid) in every cubic foot of fresh air, viz. ·0004 cubic foot. Let A = the number of cubic feet of fresh air delivered or available, P = the amount of carbonic acid exhaled, and x = the amount of carbonic acid per cubic foot in the room at the end of a given time. Then—

x = p + P ∕ A, whence A = P ∕ (x - p).

If the carbonic acid in the air of a room is ·75 per 1,000 volumes (that in the outer air being ·4 per 1,000 volumes), and there are five persons in the room, how much air is entering the room per hour?

• Here x = ·00075.
• p = ·0004.
• P = ·6 (i.e. number of cubic feet of carbonic acid expired by each person per hour).
• Now x = p + P ∕ A.
• ·00075 = ·0004 + ·6 ∕ A.

Therefore A = about 1,700.

Thus 1,700 cubic feet are required for each individual to keep the air within the given limit, and five times this amount will be required for five persons = 8,500 cubic feet.

A room has been occupied for one hour, at the end of which the total carbonic acid present was found to be 1·1 per 1,000 parts. The carbonic acid in the open air amounting to ·0004 per cubic foot, find the quantity of air supplied per hour.

• Here x = ·0011.
• p = ·0004 and P = ·6.
• Hence ·0011 = ·0004 + ·6 ∕ A.
• Therefore A = 857 cubic feet.

If six persons are in a room containing 3,000 cubic feet, and there is a supply of 2,000 cubic feet of air per head per hour; how much carbonic acid is there in the air of the room at the end of 4 hours?

• Here p = ·0004.
• P = ·6 × 6 × 4 = 14·4.
• A = 2,000 × 6 × 4 + 3,000 = 51,000.
• x = ·004 + 14·4  ∕  51,000 = ·000682 = 6·82 parts CO₂ in 10,000 of air.

The air of a room occupied by 6 persons and containing 5,000 cubic feet of space, yields 7·5 parts of CO₂ per 10,000 parts of air. How much air is being supplied per hour?

A = P ∕ (x - p) = ·6 x 6/(·00075 - ·0004) = 10,280 cubic feet.

In the same room what would be the condition of the air at the end of 4 hours?

x = ·0001 + ·6 × 6 × 4/(10280 × 4 + 5,000)
= ·0004 + 14·4  ∕  46,120 = ·000712 = 7·12 of CO₂ in 10,000 of air.

Given two sleeping rooms, Y 10 ft. by 15 ft. and 10 ft. high, Z 15 ft. by 20 ft. and 12 ft. high, with three adults in each; how much fresh air would you supply in each? What would be the condition of the air of each of the rooms after, ¼;, ½, 1, and 2 hours respectively?

Amount of fresh air to be supplied in Y—
A = P ∕ (x - p) = ·6 × 3/(·0005 - ·0004) = 9,000 cubic feet per hour.

Condition of air in Y after ¼ hour—

Here p = ·0004.
P = ·6 × 3  ∕  4= ·45.
A = 9,000  ∕  4 + 1,500 = 3,750.
x = ·0004 + ·45  ∕  3,750 = ·00052.

At the end of 2 hours—
x = ·0004 + 3·6∕(18,000 + 1,500) = ·000584.

And similarly for Z.

Suppose two rooms, one 10 feet cube, the other 50 feet by 20 feet and 15 feet high, have continuously admitted into each of them a volume of fresh air containing ·04 parts carbonic acid per 100 parts, amounting to 2,000 cubic feet per hour, so as to replace to that extent the air of the room; suppose also that an average adult be placed in each room: show by detailed calculation what would be the condition of impurity of air in each room, as measured by carbonic acid, at the end of 4 hours and 12 hours respectively.

In the case of the first room—

• P = ·6 × 4 = 2·4.
• A = 2,000 × 4 + 1,000 = 9,000.
• p = ·0004.
• x = ·0004 + 2·4  ∕  9,000 = ·000667.

The amount of impurity at the end of 12 hours, and in the second room may be similarly ascertained.

Ventilation in relation to Temperature.—The temperature of a given atmosphere is a most important factor in determining the ease with which it is replenished from the external air. Speaking generally, the greater the difference between the temperature of two masses of air the more rapidly an interchange occurs.

Air has weight. A column of it one inch square and extending to the uppermost limit of the atmosphere weighs about 14·6 lbs., and exerts this pressure on all substances at the surface of the earth. This pressure is exerted uniformly in all directions; but for this fact our chests would be crushed in by the external pressure on them, which amounts to over four tons. If the atmospheric pressure is diminished at any point, it is evident that the surrounding air will tend to press in this direction. Now, when air is heated it expands, and consequently the heavier fresh air flows in from all sides and pushes the lighter air upwards.

The expansion of air for every increase of 1° Cent. is ·003665 (¹ ∕ ₂₇₃), for every increase of 1° Fahr. is ·00203 (¹ ∕ ₄₉₂). Thus if the air in a room is 20° F. warmer than that outside, it will be expanded to ¹ ∕ ₂₅ additional bulk.

Thus if M = volume of a given air at 32°, with the barometer at 30 inches, and

M₁ = volume at temperature t° above 32°, while a = co-efficient of expansion for each degree of elevation of temperature, then the dilatation effected by heat will be expressed by the formula—

M₁ = M (1 + at).

When the temperature is decreasing

M₁ = M (1-at).

If the air in a chimney flue is cooler than the air of the room with which it communicates, it will flow down into the room. It is the object of an economical fire-place to cause the chimney to act as an outlet for the products of combustion and for the impurities of the air of the room with the smallest possible waste of heat. Short of producing a down draught of cold air and smoke, the smaller the difference between the temperature of the air of a room and of the air escaping near the top of the chimney, the greater the economy of fuel.

The movement of air in flues and other outlets is governed by general laws, like those governing the general movements of fluids, but allowances require to be made for friction in the channels of entrance and outlet.

The theoretical velocity, when friction is not taken into account, may be calculated by a formula based on what is known as the law of Montgolfier, or the law of spouting fluids. According to this law, fluids pass through an opening in a partition with the same velocity as a body would attain in falling through a height equal to the difference in depth of the fluid on the two sides of the partition, i.e. to the difference of pressure on the two sides. Thus, if AB equals the height of a column of air at, say, 50° F., and AC is the height of the same quantity of air heated to 60°, then the velocity with which the warmer air ascends will be that which a body would acquire in falling from C to B.