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Works by the same Author.

PROBLEMS OF LIFE AND MIND. The Foundations of a Creed. Two Volumes. Octavo. Per volume, $3.00.

Contents: The Method of Science and its Applications to Metaphysics—The Rules of Philosophizing—Psychological Principles—The Limitations of Knowledge—The Principles of Certitude—From the Known to the Unknown—Matter and Force—Force and Cause—The Absolute in the Correlations of Feeling and Motion.

THE STORY OF GOETHE’S LIFE. New Edition. One volume. 16mo. With Portrait. $1.50.

*_** For sale by all Booksellers. Sent, post-paid, on receipt of price by the Publishers,

HOUGHTON, MIFFLIN & CO., BOSTON.

THE
PHYSICAL BASIS OF MIND.

With Illustrations.

BEING THE SECOND SERIES
OF
PROBLEMS OF LIFE AND MIND.

BY
GEORGE HENRY LEWES.

BOSTON AND NEW YORK:
HOUGHTON, MIFFLIN AND COMPANY.
The Riverside Press, Cambridge.
1891.

AUTHOR’S EDITION.
From Advance Sheets.

The Riverside Press, Cambridge, Mass., U. S. A.
Printed by H. O. Houghton & Company.

PREFACE.

The title indicates that this volume is restricted to the group of material conditions which constitute the organism in relation to the physical world—a group which furnishes the data for one half of the psychologist’s quest; the other half being furnished by historical and social conditions.

The Human Mind, so far as it is accessible to scientific inquiry, has a twofold root, man being not only an animal organism but an unit in the social organism; and hence the complete theory of its functions and faculties must be sought in this twofold direction. This conception (which has been declared “to amount to a revolution in Psychology”), although slowly prepared by the growing conviction that Man could not be isolated from Humanity, was first expounded in the opening volume of these Problems of Life and Mind; at least, I am not aware that any predecessor had seen how the specially human faculties of Intellect and Conscience were products of social factors co-operating with the animal factors.

In considering the Physical Basis a large place must be assigned to the mechanical and chemical relations which are involved in organic functions; yet we have to recognize that this procedure of Analysis is artificial and preparatory, that none of its results are final, none represent the synthetic reality of vital facts. Hence one leading object of the following pages has been everywhere to substitute the biological point of view for the metaphysical and mechanical points of view which too often obstruct research—the one finding its expression in spiritualist theories, the other in materialist theories; both disregarding the plain principle that the first requisite in a theory of biological phenomena must be to view them in the light of biological conditions: in other words, to fix our gaze upon what passes in the organism, and not on what may pass in the laboratory, where the conditions are different. Analysis is a potent instrument, but is too often relied on in forgetfulness of what constitutes its real aid, and thus leads to a disregard of all those conditions which it has artificially set aside. We see this in the tendency of anatomists and physiologists to assign to one element, in a complex cluster of co-operants, the significance which properly belongs to that cluster: as when the property of a tissue is placed exclusively in a single element of that tissue, the function of an organ assigned to its chief tissue, and a function of the organism to a single organ.

Another object has been to furnish the reader uninstructed in physiology with such a general outline of the structure and functions of the organism, and such details respecting the sentient mechanism, as may awaken an interest in the study, and enable him to understand the application of Physiology to Psychology. If he comes upon details which can only interest specially educated students, or perhaps only by them be really understood, he can pass over these details, for their omission will not seriously affect the bearing of the general principles. I have given the best I had to give; and must leave each reader to find in it whatever may interest him. The uses of books are first to stimulate inquiry by awakening an interest; secondly, to clarify and classify the knowledge already gained from direct contemplation of the phenomena. They are stimuli and aids to observation and thought. They should never be allowed to see for us, nor to think for us.

The volume contains four essays. The first, on the Nature of Life, deals with the speciality of organic phenomena, as distinguished from the inorganic. It sets forth the physiological principles which Psychology must incessantly invoke. In the course of the exposition I have incorporated several passages from four articles on Mr. Darwin’s hypotheses, contributed to the Fortnightly Review during the year 1868. I have also suggested a modification of the hypothesis of Natural Selection, by extending to the tissues and organs that principle of competition which Mr. Darwin has so luminously applied to organisms. Should this generalization of the “struggle for existence” be accepted, it will answer many of the hitherto unanswerable objections.

The second essay is on the Nervous Mechanism, setting forth what is known and what is inferred respecting the structure and properties of that all-important system. If the sceptical and revolutionary attitude, in presence of opinions currently held to be established truths, surprises or pains the reader unprepared for such doubts, I can only ask him to submit my statements to a similar scepticism, and confront them with the ascertained evidence. After many years of laborious investigation and meditation, the conclusion has slowly forced itself upon me, that on this subject there is a “false persuasion of knowledge” very fatal in its influence, because unhesitatingly adopted as the ground of speculation both in Pathology and Psychology. This persuasion is sustained because few are aware how much of what passes for observation is in reality sheer hypothesis. I have had to point out the great extent to which Imaginary Anatomy has been unsuspectingly accepted; and hope to have done something towards raising a rational misgiving in the student’s mind respecting “the superstition of the nerve-cell”—a superstition which I freely confess to have shared in for many years.

The third essay treats of Animal Automatism. Here the constant insistance on the biological point of view, while it causes a rejection of the mechanical theory, admits the fullest recognition of all the mechanical relations involved in animal movements, and thus endeavors to reconcile the contending schools. In this essay I have also attempted a psychological solution of that much-debated question—the relation between Body and Mind. This solution explains why physical and mental phenomena must necessarily present to our apprehension such profoundly diverse characters; and shows that Materialism, in attempting to deduce the mental from the physical, puts into the conclusion what the very terms have excluded from the premises; whereas, on the hypothesis of a physical process being only the objective aspect of a mental process, the attempt to interpret the one by the other is as legitimate as the solution of a geometrical problem by algebra.

In the final essay the Reflex Theory is discussed; and here once more the biological point of view rectifies the error of an analysis which has led to the denial of Sensibility in reflex actions, because that analysis has overlooked the necessary presence of the conditions which determine Sensibility. In these chapters are reproduced several passages from the Physiology of Common Life.

According to my original intention, this volume was to have included an exposition of the part I conceive the brain to play in physiological and psychological processes, but that must be postponed until it can be accompanied by a survey of psychological processes which would render the exposition more intelligible.

The Priory, March, 1877.

CONTENTS.

PROBLEM I.
THE NATURE OF LIFE.

“La Physiologie a pour but d’exposer les phénomènes de la vie humaine et les conditions d’où ils dépendant. Pour y arriver d’une manière sûre, il faut nécessairement avant tout déterminer quels sont les phénomènes qu’on désigne sous le nom de vie en général. C’est pourquoi la première chose à faire est d’étudier les propriétés générales du corps qu’on appelle organiques ou vivans.”—Tiedemann, Traité de Physiologie de l’Homme, I. 2.

“Some weak and inexperienced persons vainly seek by dialectics and far-fetched arguments either to upset or establish things that are only to be founded on anatomical demonstration and believed on the evidence of the senses. He who truly desires to be informed of the question in hand must be held bound either to look for himself, or to take on trust the conclusions to which they who have looked have come.”—Harvey, Second Dissertation to Riolan.

THE NATURE OF LIFE.

CHAPTER I.
THE PROBLEM STATED.

1. Although for convenience we use the terms Life and Mind as representing distinct orders of phenomena, the one objective and the other subjective, and although for centuries they have designated distinct entities, or forces having different substrata, we may now consider it sufficiently acknowledged among scientific thinkers that every problem of Mind is necessarily a problem of Life, referring to one special group of vital activities. It is enough that Mind is never manifested except in a living organism to make us seek in an analysis of organic phenomena for the material conditions of every mental fact. Mental phenomena when observed in others, although interpretable by our consciousness of what is passing in ourselves, can only be objective phenomena of the vital organism.

2. On this ground, if on this alone, an acquaintance with the general principles of structure and function is indispensable to the psychologist; although only of late years has this been fully recognized, so that men profoundly ignorant of the organism have had no hesitation in theorizing on its highest functions. In saying that such knowledge is indispensable, I do not mean that in the absence of such knowledge a man is debarred from understanding much of the results reached by investigators, nor that he may not himself make useful observations and classifications of psychological facts. It is possible to read books on Natural History with intelligence and profit, and even to make good observations, without a scientific groundwork of biological instruction; and it is possible to arrive at empirical facts of hygiene and medical treatment without any physiological instruction. But in all three cases the absence of a scientific basis will render the knowledge fragmentary and incomplete; and this ought to deter every one from offering an opinion on debatable questions which pass beyond the limit of subjective observations. The psychologist who has not prepared himself by a study of the organism has no more right to be heard on the genesis of the psychical states, or of the relations between body and mind, than one of the laity has a right to be heard on a question of medical treatment.

THE POSITION OF BIOLOGY.

3. Science is the systematic classification of Experience. It postulates unity of Existence with great varieties in the Modes of Existence; assuming that there is one Matter everywhere the same, under great diversities in the complications of its elements. The distinction of Modes is not less indispensable than the identification of the elements. These Modes range themselves under three supreme heads: Force, Life, Mind. Under the first, range the general properties exhibited by all substances; under the second, the general properties exhibited by organized substances; under the third, the general properties exhibited by organized animal substances. The first class is subdivided into Physics, celestial and terrestrial, and Chemistry. Physics treats of substances which move as masses, or which vibrate and rotate as molecules, without undergoing any appreciable change of structural integrity; they show changes of position and state, without corresponding changes in their elements. Chemistry treats of substances which undergo molecular changes of composition destructive of their integrity. Thus the blow which simply moves one body, or makes it vibrate, explodes another. The friction which alters the temperature and electrical state of a bit of glass, ignites a bit of phosphorus, and so destroys its integrity of structure, converting phosphorus into phosphoric acid.

4. The second class, while exhibiting both physical and chemical properties, is markedly distinguished by the addition of properties called vital. Their peculiarity consists in this: they undergo molecular changes of composition and decomposition which are simultaneous, and by this simultaneity preserve their integrity of structure. They change their state, and their elements, yet preserve their unity, and even when differentiating continue specific. Unlike all other bodies, the organized are born, grow, develop, and decay, through a prescribed series of graduated evolutions, each stage being the indispensable condition of its successor, no stage ever appearing except in its serial order.

5. The third class, while exhibiting all the characteristics of the two preceding classes, is specialized by the addition of a totally new property, called Sensibility, which subjectively is Feeling. Here organized substance has become animal substance, and Vegetality has been developed into Animality by the addition of new factors,—new complexities of the elementary forces. Many, if not most, philosophers postulate an entirely new Existence, and not simply a new Mode, to account for the manifestations of Mind; they refuse to acknowledge it to be a vital manifestation, they demand that to Life be added a separate substratum, the Soul. This is not a point to be discussed here. We may be content with the assertion that however great the phenomenal difference between Humanity and Animality (a difference we shall hereafter see to be the expression of a new factor, namely, the social factor), nevertheless the distinctive attribute of Sensibility, out of which rise Emotion and Cognition, marks the inseparable kinship of mental with vital phenomena.

Thus all the various Modes of Existence may, at least in their objective aspect, be ranged under the two divisions of Inorganic and Organic,—Non-living and Living,—and these are respectively the objects of the cosmological and the biological sciences.

6. The various sciences in their serial development develop the whole art of Method. Mathematics develops abstraction, deduction, and definition; Astronomy abstraction, deduction, and observation; Physics adds experiment; Chemistry adds nomenclature; Biology adds classification, and for the first time brings into prominence the important notion of conditions of existence, and the variation of phenomena under varying conditions: so that the relation of the organism to its medium is one never to be left out of sight. In Biology also clearly emerges for the first time what I regard as the true notion of causality, namely, the procession of causes,—the combination of factors in the product, and not an ab extra determination of the product. In Vitality and Sensibility we are made aware that the causes are in and not outside the organism; that the organic effect is the organic cause in operation; that there is autonomy but no autocracy; the effect issues as a resultant of the co-operating conditions. In Sociology, finally, we see brought into prominence the historical conditions of existence. From the due appreciation of the conditions of existence, material and historical, we seize the true significance of the principle of Relativity.

7. Having thus indicated the series of the abstract sciences we have now to consider more closely the character of Biology. The term was proposed independently yet simultaneously in Germany and France, in the year 1802, by Treviranus and Lamarck, to express “the study of the forms and phenomena of Life, the conditions and laws by which these exist, and the causes which produce them.” Yet only of late years has it gained general acceptance in France and England. The term Cosmology, for what are usually called the Physical Sciences, has not yet come into general use, although its appropriateness must eventually secure its recognition.

Biology,—the abstract science of Life,—embracing the whole organic world, includes Vegetality, Animality, and Humanity; the biological sciences are Phytology, Zoölogy, and Anthropology. Each of the sciences has its cardinal divisions, statical and dynamical, namely, Morphology—the science of form,—and Physiology—the science of function.

Morphology embraces—1°, Anatomy, i. e. the description of the parts then and there present in the organism; and these parts, or organs, are further described by the enumeration of their constituent tissues and elements; and of these again the proximate principles, so far as they can be isolated without chemical decomposition. 2°, Organogeny, i. e. the history of the evolution of organs and tissues.

Physiology embraces the properties and functions of the tissues and organs—the primary conditions of Growth and Development out of which rise the higher functions bringing the organism into active relation with the surrounding medium. The first group of properties and functions are called those of vegetal, or organic life; the second those of animal, or relative life.

ORGANISMS.

8. It will be needful to fix with precision the terms, Organism, Life, Property, and Function.

An organism, although usually signifying a more or less complex unity of organs, because the structures which first attracted scientific attention were all thus markedly distinguished from inorganic bodies, has by the gradual extensions of research been necessarily generalized, till it now stands for any organized substance capable of independent vitality: in other words, any substance having the specific combination of elements which manifests the serial phenomena of growth, development, and decay. There are organisms that have no differentiated organs. Thus a microscopic formless lump of semifluid jelly-like substance (Protoplasm) is called an organism, because it feeds itself, and reproduces itself. There are advantages and disadvantages in such extensions of terms. These are notable in the parallel extension of the term Life, which originally expressing only the complex activities of complex organisms, has come to express the simplest activities of protoplasm. Thus a Monad is an organism; a Cell is an organism; a Plant is an organism; a Man is an organism. And each of these organisms is said to have its Life, because

“Through all the mighty commonwealth of things
Up from the creeping worm to sovereign man”[1]

there is one fundamental group of conditions, one organized substance, one vitality.

Obviously this unity is an abstraction. In reality, the life manifested in the Man is not the life manifested in the Monad: he has Functions and Faculties which the Monad has no trace of; and if the two organisms have certain vital characteristics in common, this unity is only recognized in an ideal construction which lets drop all concrete differences. The Life is different when the organism is different. Hence any definition of Life would be manifestly insufficient which while it expressed the activities of the Monad left unexpressed the conspicuous and important activities of higher organisms. A sundial and a repeater will each record the successive positions of the sun in the heavens; but although both are instruments for marking time, the sundial will not do the work of the repeater; the complexity and delicacy of the watch mechanism are necessary for its more varied and delicate uses. A semifluid bit of protoplasm will feed itself; but it will not feed and sustain a complex animal; nor will it feel and think.

9. Neglect of this point has caused frequent confusion in the attempts to give satisfactory definitions. Biologists ought to have been warned by the fact that some of the most widely accepted definitions exclude the most conspicuous phenomena of Life, and are only applicable to the vegetable world, or to the vegetal processes in the animal world. A definition, however abstract, should not exclude essential characters. The general consent of mankind has made Life synonymous with Mode of Existence. By the life of an animal is meant the existence of that animal; when dead the animal no longer exists; the substances of which the organism was composed exist, but under another mode; their connexus is altered, and the organism vanishes in the alteration. It is a serious mistake to call the corpse an organism; for that special combination which constituted the organism is not present in the corpse. This misconception misleads some speculative minds into assigning life to the universe. The universe assuredly exists, but it does not live; its existence can only be identified with life, such as we observe in organisms, by a complete obliteration of the speciality which the term Life is meant to designate. Yet many have not only pleased themselves with such a conception, but have conceived the universe to be an organism fashioned, directed, and sustained by a soul like that of man—the anima mundi. This is to violate all scientific canons. The life of a plant-organism is not the same as the life of an animal-organism; the life of an animal-organism is not the same as the life of a human-organism; nor can the life of a human-organism be the same as the life of the world-organism. The unity of Existences does not obliterate the variety of Modes; yet it is the speciality of each Mode which Science investigates; to some of these Modes the term Life is consistently applied, to others not; and if we merge them all in a common term, we must then invent a new term to designate the Modes now included under Life.

10. In resisting this unwarrantable extension of the term I am not only pointing to a speculative error, but also to a serious biological error common in both spiritualist and materialist schools, namely that of assigning Life to other than organic agencies. Instead of recognizing the speciality of this Mode of Existence as dependent on a speciality of the organic conditions, the spiritualist assigns Life to some extra-organic Vital Principle, the materialist assigns it to some inorganic agent—physical or chemical. Waiving for the present all discussion of Vitalism, let us consider in what sense we must separate organic from all inorganic phenomena.

11. There is a distinction between inorganic and organic which may fitly be called radical: it lies at the root of the phenomena, and must be accepted as an ultimate fact, although the synthesis on which it depends is analytically reducible to a complication of more primitive conditions. It has been already indicated in § [5]. All organisms above the very simplest are syntheses Of three terms: Structure, Aliment, and Instrument. Crystals, like all other anorganisms have structure, and in a certain sense they may be said to grow (Mineralia crescunt), though the growth is by increase and not by modification:[2] the motherlye, which is the food of the crystal, is never brought to the crystal, nor prepared for it, by any instrumental agency of the crystal. Organisms are exclusively instrumental; the organ is an instrument. The structural integrity of an organism is thus preserved through an alimentation which is effected through special instruments. Nothing like this is visible in anorganisms.

The increase of a crystal is further distinguishable from the growth of an organism, in the fact Of its being simple accretion without development; and the structure of the crystal is distinguishable from that of an organism in the fact that its integrity is preserved by the exclusion of all molecular change, and not by the simultaneous changes of molecular decomposition and recomposition. Inorganic substances are sometimes as unstable as organic, sometimes even more unstable; but their instability is the source of their structural destruction—they change into other species; whereas the instability of organized substances (not of organic) is the source of their structural integrity: the tissue is renovated, and its renovation is a consequence of its waste.

12. But while the distinction is thus radical, when we view the organism from the real—that is, from the synthetic point of view—we must also urge the validity of the analytical point of view, which seizes on the conditions here complicated in a special group, and declares these conditions to be severally recognizable equally in anorganisms and in organisms. All the fundamental properties of Matter are recognizable in organized Matter. The elementary substances and forces familiar to physicists and chemists are the materials of the biologist; nor has there been found a single organic substance, however special, that is not reducible to inorganic elements. We see, then, that organized Matter is only a special combination of that which in other combinations presents chemical and physical phenomena; and we are prepared to find Chemistry and Physics indispensable aids in our analysis of organic phenomena. Aids, but only aids; indispensable, but insufficient.

13. There is therefore an ambiguity in the common statement that organized matter is not ordinary matter. Indisputable in one sense, this is eminently disputable when it is interpreted as evidence of a peculiar Vital Force “wholly unallied with the primary energy of Motion.” If by “ordinary matter” be meant earths, crystals, gases, vapors, then assuredly organized matter is not ordinary. “Between the living state of matter and its non-living state,” says Dr. Beale, “there is an absolute and irreconcilable difference; so far from our being able to demonstrate that the non-living passes by gradations into or gradually assumes the scale or condition of the living, the transition is sudden and abrupt, and matter already in the living state may pass into the non-living condition in the same sudden and complete manner.”[3] The ambiguity here is sensible in the parallel case of the difference between crystallizable and coagulable matter, or between one crystal and another. If we can decompose the organic into the inorganic, this shows that the elements of the one are elements of the other; and if we are not yet able to recompose the inorganic elements into organic matter (not at least in its more complex forms), may this not be due to the fact that we are ignorant of the proximate synthesis, ignorant of the precise way in which the elements are combined? I may have every individual part of a machine before me, but unless I know the proper position of each, I cannot with the parts reconstruct the machine. Indeed the very common argument on which so much stress is laid in favor of some mysterious Principle as the source of organic phenomena, namely, that human skill is hopelessly baffled in the attempt to make organic substances, still more a living cell, is futile. Men can make machines, it is said, but not organisms, ergo organisms must have a spiritual origin. But the fact is that no man can make a machine, unless he take advantage of the immense traditions of our race, and apply the skill of millions who have worked and thought before him, slowly and tentatively discovering the necessary means of mechanical effect. The greatest thinker, or the deepest scholar, who did not place himself in the line of the tradition, and learn the principles of mechanism, and the properties of the materials, would be as incapable of making a watch, as the physiologist now is of making a cell. But the skill of man has already succeeded in making many organic substances, and will perhaps eventually succeed in making a cell, certainly will, if ever the special synthesis which binds the elements together should be discovered. Not that such a discovery would alter the position of Biology in relation to Chemistry. The making of albumen, nay, the construction of an organism in the laboratory, would not in the least affect the foundation of Biology, would not obliterate the radical difference between organisms and anorganisms. It is the speciality of organic phenomena which gives them a special place, although the speciality may only be due to a complication of general agencies.

VITAL FORCE.

14. A similar ambiguity to that of the phrase “ordinary matter” lies in the equally common phrase “Vital Force,” which is used to designate a special group of agencies, and is then made to designate an agent which has no kinship with the general group; that is to say, instead of being employed in its real signification—that which alone represents our knowledge—as the abstract statical expression of the complex conditions necessary to the manifestation of vital phenomena, or as the abstract dynamical expression of the phenomena themselves, it is employed as an expression of their unknown Cause, which, because unknown, is dissociated from the known conditions, and erected into a mysterious Principle, having no kinship with Matter. In the first sense the term is a shorthand symbol of what is known and inferred. The known conditions are the relations of an organism and its medium, the organism being the union of various substances all of which have their peculiar properties when isolated; properties that disappear in the union, and are replaced by others, which result from the combination—as the properties of chlorine and sodium all disappear in the sea-salt which results from their union; or as the properties of oxygen and the properties of hydrogen disappear and are replaced by the properties of water. When therefore Vital Force is said to be exalted or depressed, the phrase has rational interpretation in the alteration which has taken place in one or more of the conditions, internal and external: a change in the tissues, the plasma, or the environment, exalts or depresses the energy of the vital manifestations; and to suppose that this is effected through the agency of some extra-organic Principle is a purely gratuitous fiction.

15. That we are ignorant of one or more of the indispensable conditions symbolized in the abstract term Vitality or Vital Force, is no reason for quitting the secure though difficult path of Observation, and rushing into the facile but delusive path of Fiction, which proposes metempirical Agents (in the shape of Vital and Psychical Principles) to solve the problems of Life and Mind. We may employ the term Vital Force to label our observations, together with all that still remains unobserved; and we are bound to recognize the line which separates observation from inference, what is proved from what is inferred; but while marking the limits of the known, we are not to displace the known in favor of the unknown. It is said that because of our ignorance we must assume these causes of Life and Mind to be unallied with known material causes, and belonging to a different order of existences. This is to convert ignorance into a proof; and not only so, but to allow what we do not know to displace what we do know. The organicist is ready to admit that much has still to be discovered; the vitalist, taking his stand upon this unknown, denies that what has been discovered is really important, and declares that the real agent is wholly unallied to it. How can he know this?

He does not know it; he assumes it; and the chief evidence he adduces is that the ordinary laws of inorganic matter are incapable of explaining the phenomena of organized matter; and that physical and chemical forces are controlled by vital force. I accept both these positions, stripping them, however, of their ambiguities. The laws of ordinary matter are clearly incompetent in the case of matter which is not ordinary, but specialized in organisms; and when we come to treat of Materialism we shall see how unscientific have been the hypotheses which disregard the distinction. The question of control is too interesting and important to be passed over here.

VITAL FORCE CONTROLLING PHYSICAL AND CHEMICAL FORCES.

16. The facts relied on by the vitalists are facts which every organicist will emphasize, though he will interpret them differently. When, for example, it is said that “Life resists the effect of mechanical friction,” and the proof adduced is the fact that the friction which will thin and wear away a dead body is actually the cause of the thickening of a living—the skin of a laborer’s hand being thickened by his labor; the explanation is not that Life, an extra-organic agent, “resists mechanical friction”—for the mechanical effect is not resisted (the skin is rubbed off the rower’s hand sooner than the wood is rubbed off the oar)—but that Life, i. e. organic activity repairs the waste of tissue.

17. Again, although many of the physical and chemical processes which invariably take place under the influences to which the substances are subjected out of the organism, will not take place at all, or will take place in different degrees, when the substances are in the organism, this is important as an argument against the notion of vital phenomena being deducible from physical and chemical laws, but is valueless as evidence in favor of an extra-organic agent. Let us glance at one or two striking examples.

18. No experimental inquirer can have failed to observe the often contradictory results which seemingly unimportant variations in the conditions bring about; no one can have failed to observe what are called chemical affinities wholly frustrated by vital conditions. Even the ordinary laws of Diffusion are not always followed in the organism. The Amœba, though semifluid, resists diffusion when alive; but when it dies it swells and bursts by osmosis. The exchange of gases does not take place in the tissues, precisely as in our retorts. The living muscle respires, that is, takes up oxygen and gives out carbonic acid, not on the principle of simple diffusion, but by two separable physiological processes. The carbonic acid is given out, even when there is no oxygen whatever present in the atmosphere, and its place may then be supplied by hydrogen; and this physiological process is so different from the physical process which goes on in the dead muscle (the result of putrefaction), that it has been proved by Ranke to go on when the temperature is so low that all putrefaction is arrested. The same experimenter finds[4] that whereas living nerve will take up, by imbibition, 10 per cent of potash salts, it will not take up 1 per cent of soda salts, presented in equal concentration; and he points to the general fact that the absorption of inorganic substances does not take place according to the simple laws of diffusion, but that living tissues have special laws, the nerve, for instance, having a greater affinity for neutral potash salts than for neutral soda salts. Let me add, by way of anticipating the probable argument that may urge this in favor of Vital Principle which is lightly credited with the prescience of final causes, that so far from this “elective affinity” of the tissues being intelligent and always favorable, Ranke’s experiments unequivocally show that it is more active towards destructive, poisonous substances, than towards the reparative, alimentary substances; which is indeed consistent with the familiar experience that poisons are more readily absorbed than foods, when both are brought to the tissues. Thus it is well known that of all the salts the sulphate of copper is that which plants most readily absorb—and it kills them. The special affinities disappear as the vitality disappears, and dying plants absorb all salts equally.

19. The more the organism is studied, the more evident it will become that the simple laws of diffusion, as presented in anorganisms rarely if ever take effect in tissues; in other words, what is called Imbibition in Physics is the somewhat different process of Absorption in Physiology.[5] The difference is notable in this capital fact, that whereas the physical diffusion of liquids and gases is determined by differences of density, the physiological absorption of liquids and gases is determined by the molecular organization of the tissue, which is perfectly indifferent to, and resists the entrance of, all substances incapable of entering into organic combination, either as aliment or poison. A curious example of the indifference of organized substances to some external influences and their reaction upon others, is the impossibility of provoking ciliary movement in an epithelial cell, during repose, by any electrical, mechanical, or chemical stimuli except potash and soda. Virchow discovered that a minute quantity of either of these, added to the water in which the cell floated, at once called forth the ciliary movements.

20. The true meaning of the resistance of Vitality to ordinary chemical affinity is, that the conditions involved in the phenomena of Vitality are not the conditions involved in the phenomena of Chemistry; in other words, that in the living organism the substances are placed under conditions different from those in which we observe these substances when their chemical affinities are displayed in anorganisms. But we need not go beyond the laboratory to see abundant examples of this so-called resistance to chemical affinity, when the conditions are altered. The decomposition of carbonates by tartaric acid is a chemical process which is wholly resisted if alcohol instead of water be the solvent employed. The union of sulphur with lead is said to be due to the affinity of the one for the other; but no one supposes this affinity to be irrespective of conditions, or that the union will take place when any one of these conditions is absent. If we fuse a compound of lead and iron in a crucible containing sulphur, we find it is the iron, and not the lead, which unites with the sulphur; yet we do not conclude that there is a Crucible Principle which frustrates chemical affinity and resists the union of sulphur and lead; we simply conclude that the presence of the iron is a condition which prevents the combination of the sulphur with the lead: not until all the iron has taken up its definite proportion of sulphur will the affinity of the lead come into play. This is but another illustration of the law that effects are processions of their causes, summations of the conditions of their existence. If the fire burns no hole in the teakettle so long as there is water to conduct the heat away, this is not due to any principle more mysterious than the presence of a readily conducting water.[6]

21. In accordance with the law of Causation just mentioned, which has been expounded in detail in our First Series (Vol. II. p. 335), the special combinations of Matter in organisms must present special phenomena. Therefore since the province of Biology is that of explaining organic phenomena by means of their organic conditions, it must be radically distinguished from the provinces of Physics and Chemistry, which treat not of organized but of inorganic matter. It is idle, it is worse, for it is misleading, to personify the organic conditions, known and inferred, in a Vital Principle; idle, because we might with equal propriety personify the conditions of crystallization in a Crystal Principle; misleading, because the artifice is quickly dropped out of sight, and the abstract term then becomes accepted as an entity, supposed to create or rule the phenomena it was invented to express.

22. Inquirers are but too apt to misconceive the value of Analysis, which is an artifice of Method indispensable to research, though needing the complementary rectification by Synthesis before a real explanation can be reached. Analysis decomposes the actual fact into ideal factors, separates the group into its components, and considers each of these, not as it exists in the group, in the reality, but as it exists when theoretically detached from the others. The oxygen and hydrogen into which water is decomposed did not exist as these gases in the water; the albumen and phosphate we extract from a nerve did not exist as isolated albumen and phosphate in the nerve, they were molecularly combined. In like manner the physical and chemical processes which may analytically be inferred in vital processes do not really take place in the same way as out of the organism. The real process is always a vital process, and must be explained by the synthesis of all the co-operant conditions. The laws of Physics and Chemistry formulate abstract expressions of phenomena, wherever and whenever these appear, without reference to the modes of production; and in this sense the movement of a limb is no less a case of Dynamics than the movement of a pulley—the decomposition of a tissue is a case of Chemistry no less than the decomposition of a carbonate; the electromotor phenomena observed in muscle are as purely physical as those observed in a telegraph. But when a biologist has to explain the movements of the limbs, or the decompositions of tissues, he has to deal with the phenomena and their modes of production, he has a particular group before him, and must leave out nothing that is characteristic of it. The movements of the pulley do not depend on Contractility and Sensibility, which in turn depend on Nutrition. The decomposition of the carbonate does not depend on conditions resembling those of a living tissue. Vaucanson’s duck was surprisingly like a living duck in many of its movements; but in none of its actions was there any real similarity to the actions of a bird, because the machine was unlike an organism in action. The antithesis of mechanism and organism will be treated of in § [78].

23. We conclude, then, that defining physical phenomena as the movements which take place without change of structure, and chemical phenomena as the movements with change of structure, although both classes may be said to take place in the organism, and to be the primary conditions on which organic phenomena depend, they do not embrace the whole of the conditions, nor are the sciences which formulate them capable of formulating either the special phenomena characteristic of organisms or their special modes of production. The biologist will employ chemical and physical analysis as an essential part of his method; but he will always rectify what is artificial in this procedure, by subordinating the laws of Physics and Chemistry to the laws of Biology revealed in the synthetic observation of the organism as a whole. The rectification, here insisted on, will be recognized as peculiarly urgent in Psychology, which has greatly suffered from the misdirection of Analysis.

24. No one will misunderstand this specialization of Biology to mean a separation of Life from the series of objective phenomena, and the introduction of a new entity; the specialization points to a Mode of Existence. All classifications are artifices, but they have their objective grounds; the ground of difference on which Biology is separated from Chemistry and Physics, though all three may be merged in a common identity, is such as to justify the term radical. A vital process is no more to be considered physico-chemical, because physico-chemical conditions are presupposed in it, than a feeling is to be considered a nutritive process, because Nutrition is presupposed in all Feeling. Organic substances have been made by chemists, and inorganic “cells” have also been made; but these substances were not organized, these “cells” would not live. The germ-cell is the workshop of generation, the secreting-cell the workshop of secretion, the muscle-cell the workshop of contraction. What is required over and above organic substances and cell-forms, is that special state called organization. See § [49].

Those who contemplate the manifestations without also taking into account their modes of production may see nothing but physico-chemical facts in vital facts. It is by a similar limitation of the point of view that Vitality is often confounded with Movement, and portions of organic matter are said to live, simply on the evidence of their movements.[7]

CHAPTER II.
DEFINITIONS OF LIFE.

25. Biology, the science of Life, being thus assigned its place in the hierarchy of objective laws, we now proceed to consider what the term Life symbolizes.

By a large preliminary simplification, Life may be defined as the mode of existence of an organism in relation to its medium. To render this of any value, however, a clear conception of the organism is first indispensable; and this must be preceded by an examination of the various attempts to define life in anticipation of such a clear conception.

26. Every phenomenon, or group of phenomena, may be viewed under two aspects—the statical, which considers the conditions of existence; and the dynamical, which considers these conditions in their resultant,—in their action. The statical definition of Life will express the connexus of the properties of organized substance, all those conditions, of matter, form, and texture, and of relation to external forces, on which the organism depends. These various conditions, condensed into a single symbol, constitute Vitality or Vital Force, and are hence taken as the Cause of vital phenomena. The dynamical definition will express the connexus of Functions and Faculties of the organism, which are the statical properties of organized substance in action, under definite relations.

It is obvious that the term Life must vary with the varying significates it condenses,—every variation in the complexity of the organism will bring a corresponding fulness in the signification of the term. The life of a plant is less significant than the life of an animal; and the life of a mollusc less than that of a fish. But not only is the term one of varying significance, it is always an abstract term which drops out of sight particular concrete differences, registering only the universal resemblances.

* * * * *

27. It would be a profitless labor to search out, and a wearisome infliction to set down, the various definitions which have been proposed and accepted; but certain characteristic examples may be selected. All that I am acquainted with belong to two classes: 1°, the meta-physiological hypothesis of an extra-organic agent, animating lifeless matter by unknown powers; 2°, the physiological hypothesis which seeks the cause of the phenomena (i. e. the conditions) within the organism itself,—a group of conditions akin to those manifested elsewhere, but differently combined. The first hypotheses are known under the names of Animism and Vitalism,—more commonly the latter. The second are known as Organicism and Materialism,—but the latter term only applies to some of the definitions.

28. Under Vitalism are included all the hypotheses of a soul, a spirit, an archæus, a vital principle, a vital force, a nisus formativus, a plan or divine idea, which have from time to time represented the metaphysical stage of Biology. The characteristic of that stage is the personification of a mystery, accompanied by the persuasion that to name a mystery is to explain it. In all sciences when processes are imperfectly observed, the theory of the processes (which is a systematic survey of the available evidence marshalled in the order of causal dependence) is supplemented by hypothesis, which fills up with a guess the gap left by observation. The difference between the metaphysical and the positive stages of a science lies in the kind of guess thus introduced to supplement theory, and the degree of reliance accorded to it. I have more than once insisted on the scientific canon that “to be valid, an explanation must be expressed in terms of phenomena already observed”; now it is quite clear that most of the extra-organic hypotheses do not fulfil this condition; no one having ever observed a spirit, an archæus, or a vital principle; but only imagined these agents to explain the facts observed. As an example of the difference, and a proof that the value of an hypothesis does not rest on the facility with which it connects observations, and seems to explain them, take the three hypotheses of animal spirits, nervous fluid, and electricity, by which neural processes have been explained. The animal spirits are imaginary; the nervous fluid is without a basis in observation, no evidence of such a fluid having been detected; but electricity (or, speaking rigorously, the movements classed as electrical), although not proved to be the agent in nerve-action, is proved to exist in nerves as elsewhere, and its modes of operation are verifiable. It, therefore, and it alone of the three hypotheses, is in conformity with the scientific canon. It may not, on full investigation, meet all requirements; it may be rejected as imperfect; but it is the kind of guess which scientific theory demands.

The second difference noticeable between the metaphysical and the positive stages is the degree of reliance accorded to hypothesis; which is very much the same as that noticeable in the uncritical and critical attitudes of untrained and trained intellects. The one accepts a guess as if it were a proof; is fascinated by the facility of linking together isolated observations, and, relying on the guess as truth, proceeds to deduce conclusions from it; the other accepts a guess as an aid in research, trying by its aid to come upon some observation which will reveal the hidden process; but careful never to allow the guess to supersede observation, or to form a basis of deductions not immediately verified.

29. A glance at the metaphysiological definitions will detect both the kind of guess and the kind of reliance which prevailed. The mystery was not simply recognized, it was personified as an entity: Will and Intelligence were liberally accorded to it, for it was supposed to shape matter, and direct force into predestined paths by prescience of a distant end. The observed facts of the egg passing through successive changes into a complex organism were so marvellous, so unlike any facts observable in the inorganic world, that they seemed to demand a cause drawn from higher sources. The mystery of life obtruded itself at every turn. It was named, and men fancied it explained. But in truth no mystery is got rid of by explanation, however valid; it is only shifted farther back. Explanation is the resolution of a complex phenomenon into its conditions of existence—the product is reduced to its factors; the explanation is final when this resolution has been so complete that a reconstruction of the product is possible from the factors. The vast majority of explanations—especially in the organic region—are no more than what mathematicians call “a first approximation.” It is through successive approximations that science advances; but even when the final stage is reached a mystery remains. We may know that certain elements combine in certain proportions to produce certain substances; but why they produce these, and not different substances, is no clearer than why muscles contract or organisms die. This Why is, however, an idle question. That alone which truly concerns us is the How, and not the Why.

30. Biology is still a long way off the How. But it can boast of many approximations; and its theories are to be tested by the degree of approximation they effect. In this light the physiological, intra-organic, hypotheses manifestly have the advantage. Many of them are indeed very unacceptable; they are guided by a mistaken conception of the truths reached by Analysis. For when men first began to discard the extra-organic hypotheses, and to look into the organism itself, they were so much impressed by the mechanical facts observed, that they endeavored to reduce all the phenomena to Mechanics. The circulation became simply a question of hydraulics. Digestion was explained as trituration. The chemists then appeared, and their shibboleths were “affinities” and “oxidations.” With Bichat arose the anatomical school, which decomposing the organism into organs, the organs into tissues, and these tissues into their elements, sought the analytical conditions of existence of the organism in the properties of these tissues, and the functions of these organs. The extra-organic agent was thus finally shown to be not only a fiction, but a needless fiction.

Every student of the history of the science will note how from the very necessities of the case the metaphysiologists, without relinquishing their Vital Principle, have been led more and more to enter on the track of the physiologists, pursuing their researches more and more into the processes going on in the organism, and assigning more and more causal efficiency to these, with a corresponding restriction of the province of their extra-organic cause. Hence in the ranks of the vitalists have been found some of the very best observers and theorists; but they were such in despite of, and not in consequence of, their hypothesis, which was only invoked by them when evidence was at fault. Nor, unscientific as vitalism is, can we deny that it has been so far serviceable to the science, that it has corrected the materialist error of endeavoring to explain organic phenomena by physico-chemical laws; and has persistently kept in view the radical difference between organic and inorganic.

31. These remarks may justify a selection of definitions, classified under the two heads. The selection is fitly opened by the Aristotelian definition which prevailed for centuries.

Aristotle distinguishes Life, which he says means “the faculties of self-nourishment, self-development, and self-decay,” from the Vital Principle. Every natural body manifesting life may be regarded as an essential existence (οὐσία); but then it is an existence only as a synthesis (ὡς συθέτη); and since an organism is such a synthesis, being possessed of Life, it cannot be the Vital Principle (ψυχή). Therefore it follows that the Vital Principle must be an essence, as being the Form of a natural body holding life in potentiality. The Vital Principle is the primary reality of an organism. “It is therefore as idle to ask whether the Vital Principle and Organism are one, as whether the wax and the impress on it are one.... Thus if an eye were an animal, Vision would be its Vital Principle: for Vision is, abstractedly considered, the essence of the eye; but the eye is the body of Vision, and if Vision be wanting, then, save in name, it is no longer an eye.”

Apart from certain metaphysical implications, inevitable at that period, there is profound insight in this passage. His adversary Telesio quite misconceives the meaning here assigned to the Vital Principle.[8]

32. Let us pass over all the intermediate forms of the hypothesis, and descend to Kant, who defines Life “an internal principle of action” (this does not distinguish it from fermentation); an organism he says is “that in which every part is at once means and end.” “Each part of the living body has its cause of existence in the whole organism; whereas in non-living bodies each part has its cause in itself.” Johannes Müller adopts a similar view: “The harmonious action of the essential parts of the individual subsist only by the influence of a force, the operation of which is extended to all parts of the body, and does not depend on any single parts; this force must exist before the parts, which are in fact formed by it during the development of the embryo.... The vital force inherent in them generates from the organic matter the essential organs which constitute the whole being. This rational creative force is exerted in every animal strictly in accordance with what the nature of each requires.”

33. This is decidedly inferior to Aristotle, who did not confound the vegetative with the rational principle. It rests on the old metaphysical error of a vis medicatrix, an error which cannot sustain itself against the striking facts which constantly point to a vis destructrix, a destructive tendency quite as inexorable as the curative tendency. And the experimental biologist soon becomes impressed with the fact that the tissues have indeed a selective action, by which from out the nutrient material only these substances are assimilated which will enter into combination with them; but this selective action is fatal, no less than reparative: substances which poison the tissue are taken up as readily as those which nourish it. The idea of prescience, therefore, cannot be sustained; it is indeed seldom met with now in the writings of any but the Montpellier school, who continue the traditions of Stahl’s teaching. It has been so long exploded elsewhere that one is surprised to find an English physiologist clinging to a modification of it—I mean Dr. Lionel Beale, who repeatedly insists on Life as “a peculiar Force, temporarily associated with matter,” a “power capable of controlling and directing both matter and force,” an “undiscovered form of force having no connection with primary energy or motion.” “The higher phenomena of the nervous system are probably due primarily to the movements of the germinal matter due to vital power, which vital power of this the highest form of germinal matter is in fact the living I.”

34. Apart from the primary objection to all these definitions, namely, that they seek to express organic phenomena in terms of an extra-organic principle, to formulate the facts observed in terms of a cause inferred, there is the fatal objection that they speak confidently on what is avowedly unknown. If the force be, as Dr. Beale says, “undiscovered,” on what grounds can he assert that it has no connection with the forces which are known? All that the observed facts warrant is the assertion that organic phenomena are special (which no one denies), and must therefore depend on special combinations of matter and force. But on this ground we might assume a crystallizing Force, and a coagulating Force, having no connection with the molecular forces manifested elsewhere: these also are special phenomena, not to be confounded with each other.

35. Schelling defines Life as “a principle of individuation” and a “cycle of successive changes determined and fixed by this internal principle.” Which is so vague that it may be applied in very different senses. Bichat’s celebrated definition (which is only a paraphrase of a sentence in Stahl), “the sum of the functions which resist Death,” although an endeavor to express the facts from the Intra-organic point of view, is not only vague, but misrepresents one of the cardinal conditions, by treating the External Medium as antagonistic to Life, whereas Life is only possible in the relation to a Medium.

36. Were it not so vague, the definition proposed by Dugès and Béclard would be unexceptionable: the former says it is “the special activity of organized beings”; the latter, “the sum of the phenomena proper to organized bodies.” When supplemented by a description of organized bodies, these formulæ are compendious and exact. The same remark applies to the definition of Lamarck: “that state of things which permits organic movements; and these movements, which constitute active life, result from a stimulus which excites them.”

37. De Blainville, and after him Comte and Charles Robin, define it thus: “Life is the twofold internal movement of composition and decomposition at once general and continuous.” This, excellent as regards what is called vegetal life, is very properly objected to by Mr. Herbert Spencer in that it excludes those nervous and muscular functions which are the most conspicuous and distinctive of vital phenomena. The same objection must be urged against Professor Owen’s definition: “Life is a centre of intussusceptive assimilative force capable of reproduction by spontaneous fission.”

38. In 1853, after reviewing the various attempts to express in a sentence what a volume could only approximately expound, I proposed the following: “Life is a series of definite and successive changes, both of structure and composition, which take place within an individual without destroying its identity.” This has been criticised by Mr. Herbert Spencer and by Dr. Lionel Beale, and if I had not withdrawn it before their criticisms appeared, I should certainly have modified and enlarged it afterwards. I mention it, however, because it is an approach to a more satisfactory formula in so far as it specifies two cardinal characteristics distinguishing organisms from all anorganisms, namely, the incessant evolution through definite stages, and the preservation of specific integrity throughout the changes; not only the organism as a whole is preserved amidst incessant molecular change, but each tissue lives only so long as the reciprocal molecular composition and decomposition persist. On both of these points I shall have to speak hereafter. The definition, however, is not only defective in its restriction to the molecular changes of Nutrition, taking no account of the Properties and Functions of the organism; but defective also in giving no expression to equally important relations of the organism to the medium.

39. This last point is distinctly expressed in Mr. Spencer’s definition: “Life is the continuous adjustment of internal relations to external relations.” Considered as a formula of the most general significance, embracing therefore what is common to all orders of vital phenomena, this is the best yet proposed.[9] If I propose another it will not be to displace but to run alongside with Mr. Spencer’s; and this only for more ready convenience. Before doing so I must say a few words by way of clearing the ground.

40. What does the term Life stand for? What are the concrete significates of this abstract symbol? As before stated, it is sometimes a compendious shorthand for the special phenomena distinguishing living from non-living bodies; and sometimes it expresses not these observed phenomena, but their conditions of existence, which are by one school personified in an abstract and extra-organic cause. Thus the life of an animal, a man, or a nation, means—1°, the special manifestations of these organisms, and groups of organisms; or 2°, the causes which produce these manifestations. We are often misunderstood by others, and sometimes vague to ourselves, when we do not bear these two different meanings in view. It was probably some sense of this which made Aristotle distinguish Vitality from Life, as that of the one uniform cause separated from its multiple effects; it was certainly the motive of Fletcher, who thus expressly limits the meanings: “Vitality or Irritability, the property which characterizes organized beings of being acted on by certain powers otherwise than either strictly mechanically or strictly chemically; Life, the sum of the actions of organized beings resulting directly from their vitality so acted on.”[10]

Vitality and Life being thus discriminated as the statical and the dynamical aspects of the organism, we find in relation to the former two radically opposed conceptions: the metaphysiological or extra-organic, and the physiological or intra-organic. The first conceives Vitality to be a Vital Principle, or extra-organic agent, sometimes a soul, spirit, archæus, idea, and sometimes a force, which easily becomes translated into a property.

The conception of an entity must be rejected, because it is metempirical and unverifiable, § [34]. The conception of a force must be rejected, because it is irreconcilable with any definite idea we have of force. What the term Force signifies in Physics and Chemistry, namely, mass animated by velocity, or directed pressure, which is the activity of the agent,—is precisely that which these vitalists pertinaciously exclude. They assume a force which has nothing in common with mass and velocity; which is not a resultant, but a principle; which instead of being a directed quantity, is itself autonomous and directive, shaping matter into organization, and endowing it with powers not assignable to matter. If this vital force has any mass at its back, it is a spiritual mass; if it is directed, the direction issues from a “Mind somewhere.” Now this conception is purely metempirical. Not only is it inexact to speak of Vitality as a force, it is almost equally inexact to speak of it as a property; since it is a term which includes a variety of properties; and when Fletcher assigns the synonym of Irritability, this at once reveals the inexactness; for beside this property, we must place Assimilation, Evolution, Disintegration, Reproduction, Contractility, and Sensibility,—all characteristic properties included in Vitality.

41. Having thus rejected the conceptions of entity, force, and property, we are left in presence of—1°, the organic conditions as the elements, and 2°, of their synthesis (in the state called organization) as the personified principle. Vital forces, or the vital force, if we adopt the term for brevity’s sake, is a symbol of the conditions of existence of organized matter; and since organisms are specially distinguishable from anorganisms by this speciality of their synthesis, and not by any difference in the nature of the elements combined, this state of organization is the “force” or “principle” of which we are in quest. To determine what Life means, we must observe and classify the phenomena presented by living beings. To determine what Vitality—or organization—means, we must observe and classify the processes which go on in organized substances. These will occupy us in the succeeding chapters; here I may so far anticipate as to propose the following definitions:—

42. Life is the functional activity of an organism in relation to its medium, as a synthesis of three terms: Structure, Aliment, and Instrument; it is the sum of functions which are the resultants of Vitality; Vitality being the sum of the properties of matter in the state of organization.

43. Vital phenomena are the phenomena manifested in organisms when external agencies disturb their molecular equilibrium; and by organisms when they react on external objects. Thus everything done in an organism, or by an organism, is a vital act, although physical and chemical agencies may form essential components of the act. If I shrink when struck, or if I whip a horse, the blow is in each case physical, but the shrinking and the striking are vital.

Every part of a living organism is therefore vital, as pertaining to Life; but no part has this Life when isolated; for Life is the synthesis of all the parts: a federation of the organs when the organism is complex, a federation of the organic substances when the organism is a simple cell.

44. All definitions, although didactically placed at the introduction of a treatise, are properly the final expression of the facts which the treatise has established, and they cannot therefore be fully apprehended until the mind is familiarized with the details they express. Much, therefore, which to the reader may seem unintelligible or questionable in the foregoing definition, must be allowed to pass until he has gone through the chapters which follow.

CHAPTER III.
ORGANISM, ORGANIZATION, AND ORGANIC SUBSTANCE.

45. There is a marked difference between organic and organised substances. The organic are non-living, though capable of living when incorporated in organized tissue (albumen is such a substance); or they may be incapable of living because they have lived, and are products of waste, e. g. urea. The organized substance is a specific combination of organic substances of various kinds, a combination which is organization. Any organized substance is therefore either an independent organism, or part of a more complex organism. Protoplasm, either as a separate organism or as a constituent of a tissue, is organized substance.

Organic substances are numerous and specific. They are various combinations of proximate principles familiar to the chemist, which may conveniently be ranged under three classes: The first class of organic substances comprises those composed of principles having what is called a mineral origin; these generally quit the organism unchanged as they entered it. The second class comprises those which are crystallizable, and are formed in the organism, and generally quit it in this state as excretions. The third class comprises the colloids, i. e. substances which are coagulable and not crystallizable, and are formed in and decomposed in the organism, thus furnishing the principles of the second class. All the principles are in a state of solution. Water is the chief vehicle of the materials which enter and the materials which quit the organism; and bodies in solution are solvents of others, so that the water thus acquires new solvent properties.

45a. Two points must be noted respecting organic substances: they are mostly combinations of higher multiples of the elements; and their combinations are not definite in quantity. Albumen, for example, has (according to one of the many formulas which have been given) an elementary composition of 216 atoms of Carbon, 169 of Hydrogen, 27 of Nitrogen, 3 of Sulphur, and 68 of Oxygen; whereas in its final state, in which it quits the organism as Urea, it is composed of 2 atoms of Carbon, 4 of Hydrogen, 2 of Nitrogen, and 2 of Oxygen, all the Sulphur having disappeared in other combinations. In like manner in the organism Stearin falls from C₁₁₄, H₁₁₀, O₁₂, to Oxalic Acid, which is C₄, H₂, O₈. It is obvious that the necessary modifiability of organic substance is due to this multiplicity of its elementary parts and the variety of its molecular structure.

45b. Nor is the indefiniteness of the quantitative composition less important, though seldom adequately appreciated, or even suspected. Robin and Verdeil[11] are the only writers I can remember who have distinctly brought the fact into prominence. That all inorganic substances are definite in composition, every one knows. Quicklime, for example, may be got from marble, limestone, oyster-shells, or chalk; but however produced, it always contains exactly 250 ounces of calcium to 100 ounces of oxygen; just as water is always OH₂. Not so the pre-eminently vital substances, those which are coagulable and not crystallizable: no precise formula will express one of these; for the same specific substance is found to vary from time to time, and elementary analyses do not give uniform results. Thus, if after causing an acid to combine with one of these substances, we remove the acid, we are not certain of finding the substance as it was before—as we are, for example, after urea is combined with nitric acid and then decomposed. The same want of definiteness is of course even more apparent in the combinations of these proximate principles into organized substance. Protoplasm differs greatly in different places. Epithelial cells differ. Muscular and nervous fibres are never absolutely the same in different regions. A striped and unstriped muscular fibre, the muscular fibre of a sphincter or of a limb, a nerve-fibre in a centre, in a trunk, or in a gland, will present variations of composition. The elastic fibres of the ligaments are larger in the horse than in man; and in other animals they are smaller. These differences are sometimes due to the constituents, and sometimes to the arrangement of the constituents; the conversion of Albumen into Fibrine without elementary loss or addition, is a good example of the latter. That the tissues of one man are not absolutely the same as the tissues of another, in the sense in which it is true to say that the chalk of one hill is the same as that of another, or as gold in Australia is the same as gold in Mexico, is apparent in their very different reactions under similar external conditions: the substance which poisons the one leaves the other unaffected. The man who has once had the small-pox, or scarlet fever, is never the same afterwards, since his organism has now become insusceptible of these poisons. And Sir James Paget has called attention to the striking fact revealed in disease, namely, that in the same tissue—say the bone or the skin—a morbid substance fastens only on certain small portions leaving all the rest unaltered, but fastens on exactly corresponding spots of the opposite sides of the body; so that on both arms, or both legs, only the corresponding bits of tissue will be diseased. “Manifestly when two substances display different relations to a third their composition cannot be identical; so that though we may speak of all bone or of all skin as if it were all alike, yet there are differences of intimate composition. No power of artificial chemistry can detect the difference; but a morbid material can.”[12] It is to this variability of composition that we must refer individual peculiarities, and those striking forms of variety known as idiosyncrasies, which cause some organisms to be affected by what seem inexplicable influences—physical and moral.

In spite of all these variations, however, there are certain specific resemblances dependent of course on similarity of composition and structure, so that the muscle of a crustacean is classed beside the muscle of a vertebrate, although the elementary analysis of the two yields different results. Nerve-tissue, according to my experience, is the most variable of all, except the blood; variable not only from individual to individual, and from genus to genus, but even in the same individual it never contains the same quantities of water, phosphates, etc. Hence it is that different nerves manifest different degrees of excitability, and the same nerve differs at different times. Thus the fifth pair, in a poisoned animal, retains its excitability long after the others are paralyzed; and the patient under chloroform feels a prick on the brow or at the temples, when insensible at any other spot. The pneumogastric which is excitable during digestion is—in dogs at least—inexcitable when the animal is fasting.

46. The organic substances are what analysis discovers in organized substances, but none of them, not even the highest, is living, except as organized. Albumen alone, or Stearin alone, is as incapable of Vitality, as Plumbago, or Soda; but all organic substances are capable of playing a part in vital actions; and this part is the more important in proportion to their greater molecular variety. Organization is a special synthesis of substances belonging to all three classes; and the organized substance, thus formed, alone merits the epithet living. We see how organized substances, being constituted by principles derived from the inorganic world, and principles derived from the organic world, have at once a dependence on the external Medium, and an independence of it, which is peculiar to living beings. An analogous dependence and independence is noticeable with respect to the parts; and this is a character not found in inorganic compounds. The organism, even in its simplest forms, is a structure of different substances, each of which is complex. While one part of a crystal is atomically and morphologically identical with every other, and is the whole crystal “writ small,” one part of an organism is unlike another, and no part is like the whole. Hence the dependence of one organ and one tissue on another, and each on all. Yet, while every part is, so to speak, a condition of existence of every other, and the unity of the organism is but the expression of this solidarity,—wherever organized substance has been differentiated into morphological elements (cells, etc.), each of these has its own course of evolution independently of the others,—is born, nourished, developed, and dies.

47. The interdependence of nerve and muscle is seen in this, that the more the muscle is excited the feebler its contractions become; this decrease in contractility is compensated by an increased excitability in its nerve; so that while the muscle demands a more powerful stimulus, the nerve acquires a more energetic activity. Ranke’s curious and careful experiments seem to prove that this depends on the wearied muscle absorbing more water, owing to the acids developed by its activity, and on the nerve losing this water—a nerve being always more irritable when its quantity of water diminishes.

48. Herein we see illustrated the great law of organized activity, that it is a simultaneity of opposite tendencies, as organized matter is a synthesis of compositions and decompositions, always tending towards equilibrium and disturbance, storing up energy and liberating it. Unlike what is observed in unorganized matter, the conditions of waste bring with them conditions of repair, and thus—within certain limits—every loss in one direction is compensated by gain in another. There is a greater flow of nutrient material, or, more properly speaking, a greater assimilation of it by the tissue, where there has been made a greater opening for it by previous disintegration. The alkaline state of the nutrient material, and the acid state of the material that has been used,—the alkaline state which characterizes repose and assimilation, and the acid state which characterizes activity and deassimilation, are but cases of this general law; on the synthesis of these opposite tendencies depends the restless change, together with the continued specific integrity, of organized matter.

49. The state of organization may therefore be defined as the molecular union of the proximate principles of the three classes in reciprocal dissolution. An organism is formed of matter thus organized, which exists in two states—the amorphous and the figured. The amorphous substances are liquid, semi-liquid, and solid; the figured are the cells, fibres, and tubes, called “anatomical elements.” For these I prefer the term suggested, I believe, by Milne Edwards, namely, organites, because they are the individual elements which mainly constitute the organs, and are indeed by many biologists considered as elementary organisms. These organites, which go to form the tissues, and by the tissues the organs, have their specific form, volume, structure, and chemical reactions. They exist in textures or tissues, or separately (e. g. blood corpuscles), and are in many respects like the simplest organisms known, such as Monads, Vibrios, Amœbæ, etc.

50. The simplest form of life is not—as commonly stated—a cell, but a microscopic lump of jelly-like substance, or protoplasm, which has been named sarcode by Dujardin, cytode by Haeckel, and germinal matter by Lionel Beale. This protoplasm, although entirely destitute of texture, and consequently destitute of organs, is nevertheless considered to be living, because it manifests the cardinal phenomena of Life: Assimilation, Evolution, Reproduction, Mobility, and Decay. Examples of this simplest organism are Monads, Protamœbæ, and Polythalamia.[13] Few things are more surprising than the vital activity of these organites, which puzzle naturalists as to whether they should be called plants or animals. All microscopists are familiar with the spectacle of a formless lump of albuminous matter (a Rhizopod) putting forth a process of its body as a temporary arm or leg, or else slowly wrapping itself round a microscopic plant, or morsel of animal substance, thus converting its whole body into a mouth and a stomach; but these phenomena are surpassed by those described by Cienkowski,[14] who narrates how one Monad fastens on to a plant and sucks the chlorophyll first from one cell and then from another; another Monad, unable to make a hole in the cell-wall, thrusts long processes of its body into the opening already made, and drags out the remains of the chlorophyll left there by its predecessor; while a third Monad leads a predatory life, falling upon other Monads that have filled themselves with food. Here, as he says, we stand on the threshold of that dark region where Animal Will begins; and yet there is here only the simplest form of organization.[15]

51. Now let our glance pass on to the second stage—the Cell. Here we have a recognized differentiation in the appearance of a nucleus amid the protoplasm. The nucleus is chemically different from the substance which surrounds it; and although perhaps exaggerated importance has been attributed to this nucleus, and mysterious powers have been ascribed to it, yet as an essential constituent of the cell it commands attention. Indeed, according to the most recent investigations, the definition of a cell is “a nucleus with surrounding protoplasm.” The cell-wall, or delicate investing membrane—that which makes the cell a closed sac—is no longer to be regarded as a necessary constituent, but only as an accessory.[16]

52. The cell may be either an organism or an organite. It may lead an isolated life as plant or animal, or it may be united with others and lead a more or less corporate existence; but always, even as an element of a higher organism, it preserves its own individuality. At first we see that the corporate union is very slight, merely the contact of one cell with another of its own kind, as in the filament of a Conferva. Rising higher, we see the cell united with others different from it; plants and animals appear, having structures composed of masses of various cells. Rising still higher, we see animal forms of which the web is woven out of myriads upon myriads of cells, with various cell-products, processes, fibres, tubes.

ORGANISM AND MEDIUM.

53. But we have only one half of the great problem of life, when we have the organism; and it is to this half that the chief researches have been devoted, the other falling into neglect. What is that other? The Medium in which the organism lives. Every individual object, organic or inorganic, is the product of two factors:—first, the relation of its constituent molecules to each other; secondly, the relation of its substance to all surrounding objects. Its properties, as an object or an organism, are the results of its constituent molecules, and of its relation to external conditions. Organisms are the results of a peculiar group of forces, exhibiting a peculiar group of phenomena. Viewing these in the abstract, we may say that there are three regulative laws of life:—(1) The Lex Formationis—the so-called nisus formativus, or “organizing force”; (2) the Lex Adaptationis, or adaptive tendency; (3) the Lex Hereditatis, or tendency to reproduce both the original form and its acquired modifications. We have always to consider the organizing force in relation to all surrounding forces—a relation succinctly expressed in the word Adaptation. Just as water is water only under a certain relation of its constituent molecules to the temperature and atmospheric pressure—just as it passes into other forms (ice or steam) in adapting itself to other conditions; so, likewise, the organism only preserves its individuality by the adjustment of its forces with the forces which environ it.

54. This relation of Organism and Medium, the most fundamental of biological data, has had a peculiar fortune: never wholly unrecognized, for it obtrudes itself incessantly in the facts of daily experience, it was very late in gaining recognition as a principle of supreme importance; and is even now often so imperfectly apprehended that one school of philosophers indignantly rejects the idea of the Organism and Medium being the two factors of which Life is the product. Not only is there a school of vitalists maintaining the doctrine of Life as an entity independent both of Organism and Medium, and using these as its instruments; but there is also a majority among other biologists, who betray by their arguments that they fail to keep steadily before them the fundamental nature of the relation. Something of this is doubtless due to the imperfect conception they have formed of what constitutes the Medium; instead of recognizing in it the sum of external conditions affecting the organism—i. e. the sum of the relations which the organism maintains with external agencies,—they restrict, or enlarge it, so as to misapprehend its significance—restrict it to only a few of the conditions, such as climate, soil, temperature, etc., or enlarge it to embrace a vast array of conditions which stand in no directly appreciable relation to the organism. Every one understands that an organism is dependent on proper food, on oxygen, etc., and will perish if these are withheld, or be affected by every variation in such conditions. Every one understands that an animal which can devour or be devoured by another, will flourish or perish according to the presence of its prey or its enemy. But it is often forgotten that among external existences, all those which stand in no appreciable relation to the organism are not properly to be included in its Medium. In consequence of this oversight we frequently hear it urged as an objection to the Evolution Hypothesis, that manifold organisms exist under the same external conditions, and that organisms persist unchanged amid a great variety of conditions. The objection is beside the question. In the general sum of external forces there are certain items which are nearly related to particular organisms, and constitute their Medium; those items which are so distantly related to these organisms as to cause no reactions in them, are, for them, as if non-existent.[17] Of the manifold vibrations which the ether is supposed to be incessantly undergoing, only certain vibrations affect the eye as light; these constitute the Medium of Sight; the others are as if they were not. Only certain vibrations of the air affect the ear as Sound; to all other vibrations we are deaf; though ears of finer sensibility may detect them and be deaf to those which affect us.

55. “The external conditions of existence” is therefore the correct definition of the Medium. An animal may be surrounded with various foods and poisons, but if its organism is not directly affected by them they cannot be food or poison to it. An animal may be surrounded with carnivorous rivals, but if it is not adapted to serve them as food, or is too powerful to be attacked by them, they only indirectly enter into its Medium, by eating the food it would eat. The analogy is similar with anorganisms and their relation to their media. Every physical or chemical phenomenon depends on the concurrence of definite conditions: namely, the substance which manifests the change, and the medium in which the change is manifested. Alter the medium, solid, liquid, or gaseous, change its thermal or electrical state, and the phenomenon is altered. But although similar alterations in the medium notoriously influence the organism, yet, because a great many variations in external conditions are unaccompanied by appreciable changes in the organism, there are biologists who regard this as a proof of Life being independent of physical and chemical laws; an error arising from their not recognizing the precise nature of organic conditions.

56. To give greater precision to the conception of a Medium it will be desirable to adopt the distinction much insisted on by Claude Bernard, namely, 1°, an External or Cosmical Medium, embracing the whole of the circumstances outside the organism, capable of directly affecting it, and 2°, an Internal or Physiological Medium, embracing the conditions inside the organism, and in direct relation with it—that is to say, the plasma in which its tissues are bathed, by which they are nourished. To these add its temperature and electrical conditions. Bernard only includes the nutritive fluid; but inasmuch as each organism possesses a temperature and electrical state of its own, and these are only indirectly dependent on the external temperature and electricity, and as it is with these internal conditions that the organism is in direct relation, I include them with the plasma among the constituents of the Physiological Medium. Any change in the External Medium, whether of temperature or electricity, of food or light, which does not disturb the Internal Medium, will of course leave the organism undisturbed; and for the most part all the changes in the External Medium which do affect the organism, affect it by first changing the Internal Medium. External heat or cold raises or depresses the internal temperature indirectly by affecting the organic processes on which the internal temperature depends. We see here the rationale of acclimatization. Unless the organism can adapt itself to the new External Medium by the readjustment of its Internal Medium, it perishes.

57. We are now enabled to furnish an answer to the very common objection respecting the apparent absence of any direct influence of external conditions. Let the objection first be stated in the words of a celebrated naturalist, Agassiz: “It is a fact which seems to be entirely overlooked by those who assume an extensive influence of physical causes upon the very existence of organized beings, that the most diversified types of animals and plants are everywhere found under identical circumstances. The smallest sheet of fresh water, every point of the sea-shore, every acre of dry land, teems with a variety of animals and plants. The narrower the boundaries which are assigned as the primitive home of all these beings, the more uniform must be the conditions under which they must be assumed to have originated; so uniform indeed that in the end the inference would be that the same physical causes can produce the most diversified effects.”

Obviously there is a complete misstatement of the argument here; and the excess of the misstatement appears in the following passage: “The action of physical agents upon organized beings presupposes the very existence of those beings.” Who ever doubted it? “The simple fact that there has been a period in the history of our earth when none of these organized beings as yet existed, and when, nevertheless, the material constitution of our globe and the physical forces acting upon it were essentially the same as they are now, shows that these influences are insufficient to call into existence any living being.”[18] Although most readers will demur to the statement that because the material constitution of our globe was “essentially the same” before and after animal life appeared, therefore there could have been no special conditions determining the appearance of Life, the hypothesis of Evolution entirely rejects the notion of organic forms having been diversified by diversities in the few physical conditions commonly understood as representing the Medium. Mr. Darwin has the incomparable merit of having enlarged our conception of the conditions of existence so as to embrace all the factors which conduce to the result. In his luminous principle of the Struggle for Existence, and the Natural Selection which such a struggle determines, we have the key to most of the problems presented by the diversities of organisms; and the Law of Adaptation, rightly conceived, furnishes the key to all organic change.

58. In consequence of the defective precision with which the phrase “Medium,” or its usual equivalent “physical conditions,” is employed, several biological errors pass undetected. Haeckel[19] calls attention to the common mistake of supposing the organism to be passive under the influence of external conditions, whereas every action, be it of light or heat, of water or food, necessarily calls forth a corresponding reaction, which manifests itself in a modification of the nutritive process. He points out the obverse of this error in the current notion that Habit is solely due to the spontaneous action of the organism, in opposition to the influence of external agency,—as if every action were not the response to a stimulus. Corresponding with the fluctuations in the Medium there must necessarily be fluctuations of Adaptation, and I think we may safely assume that it is only when these fluctuations cease that the Adaptation becomes Habit. This is the interpretation of the phrase “Habit is second Nature,” and is very different from the common interpretation which attributes it to the use or disuse of organs; as if use or disuse were a spontaneous uncaused activity.

59. The organism, simple or complex, is, we have already seen, built up from materials originally derived from the External Medium, but proximately from the Internal Medium. This statement, however, requires some qualification, especially in view of the hypothesis that organized substance was originally created such as we now find it, and not evolved from inorganic materials. Whether this hypothesis be adopted, or rejected, we have the fact that the immense majority of organisms now existing—if not all—are products of pre-existing organisms; and therefore organized matter is now mainly, if not solely, formed by organized matter.

We take, therefore, as our point of departure, the protoplasm; this is the first of the three terms of the vital synthesis: Structure, Aliment, and Instrument. The evolution of this is proximately dependent on the pabulum afforded it in the Internal Medium, which is the true nutrient material, and to which what is usually called food stands in an external relation: for between the reception of food and its assimilation by the organite, there is an indispensable intermediary stage, through which matter passes from the unorganized to the organized state. This intermediate is now recognized in plants as in animals. The old belief that plants were nourished directly from the soil and atmosphere can no longer be sustained. The process of Nutrition is alike in both: in both the materials drawn from the External Medium are formed into proximate principles and organic substances. It is daily becoming more and more probable that the inorganic materials, water and oxygen, so freely entering into the organism, never pass directly from the External Medium to the tissues, but have to pass through the Internal Medium where they are changed, so that the water is no longer free, but exists in a fixed state which has no analogue out of the living substance. Only a part of the water can be pressed out mechanically; the rest—that which is already incorporated with the other elements—can only be got rid of in a vacuum and at a high temperature. Oxygen, also, comports itself differently in the tissue; as is proved by the fact that its physiological absorption is markedly different from any chemical oxidation in a dead or decomposing tissue.[20] Be this as it may, we know that organic substances have to be unbuilt and rebuilt in the organism; that the albumen of our food never passes directly into the albumen of our tissues; any more than the milk drunk by a nursing mother will pass into her breasts, and increase her supply, except by nourishing her.

60. In the First Series of these Problems the term Bioplasm was employed to designate this organized part of the Internal Medium. I was led to adopt it as a corresponding term to that of Psychoplasm, by which I wished to designate the sentient material of the psychological medium. There can be little doubt that the term Bioplasm was an unconscious reproduction of the title of Dr. Beale’s work, which I must have seen advertised. I withdraw it now that I have read Dr. Beale’s work, and see that the signification he attaches to the term is almost identical with Protoplasm. In lieu thereof, the term Plasmode (from plasma, anything formed, and odos, a pathway) may be substituted: it represents the nutrient material on its way to form Protoplasm, which is formative material; while the materials formed may be termed Organites and Products: the organite being the cell or cell-derivative (fibre, tube); the products being the gaseous liquid and solid derivatives of vital processes, which are secretions when they form intercellular substance or return into the plasmode and re-enter the vital circle; excretions when they are rejected, as incapable of further assimilation. The liver-cell will furnish an example of each kind of product. The bile, though containing principles serviceable in the chemical transformations, is for the most part excreted; but besides bile, the liver-cell produces starchy and saccharine principles which are true secretions, and re-enter the plasmode.

61. The organite is thus composed of sap, substance, and product; the organism, of plasmode, tissue, and product. A glance at the vegetable-cell shows it to be constituted by the primordial utricle, or protoplasm, the outermost layer of which is condensed into a membrane, or cell-wall, and the cavity thus enclosed is filled with sap. The cell-wall grows as the protoplasm grows, and the protoplasm draws its material from the plasmode. A glance at the blood, the great reservoir of the river of life, shows us plasmode in the serum, and organites in the corpuscles; the one distinguished by sodic salts, the other by potassic salts. The plasmode, or serum, is in a constant change of composition and decomposition, giving up to the various tissue-organites and intercellular plasmodes the requisite materials, and receiving from organites and plasmodes the products of their changes. The serum is fed from the food and the tissues; and it feeds the several plasmodes which bathe the several tissues. Passing into the capillaries, it becomes transformed as it passes through their walls into the intercellular spaces, saturating the acid products of the cell-activities with its alkalies, and furnishing the protoplasms with their needed materials.

62. It will be understood that, although in appearance these stages are sharply defined, in reality they are insensible. But from the analytical point of view we may regard Nutrition as the office of the plasmode, and Evolution as the office of the protoplasm. Although evolution or genesis of form depends on assimilation, it is not a necessary consequence: the plasmode or the protoplasm might preserve such perfect equality in the waste and repair, such complete equilibrium, as not to undergo any development. The ova, for example, which exist in the ovaries at birth are not all subsequently developed; and if with modern embryologists we conclude that there is no replacement of these by proliferation we shall in them have examples of organites remaining unchanged through a period of fifty years.[21] But such an equilibrium is perhaps only possible in complete inactivity.

63. Again, although the office of the plasmode is primarily that of forming protoplasm, I think there is evidence to suggest that it not only does this, but that some of it is used in the direct development of energy, especially heat and electricity. The various forms of starch and sugar taken in with the food or formed in the liver, certainly do not as such enter into protoplasm. The same with alcohol.

64. It is perhaps in forgetfulness of the artificial nature of analytical distinctions that controversies rage respecting what are called intercellular substances and cell-walls. Now that the wall is no longer regarded as an essential constituent of the cell, but as a secondary formation, two opinions are maintained: first, that it is merely a concentration of the external layer of protoplasm; secondly, that it is a product of secretion from the protoplasm. Both positions may be correct. Certainly in some cases there is no other appreciable difference between wall and protoplasm than that of a greater consistence; whereas in many other cases there exists a decided difference in their chemical reactions, showing a difference of composition. Taking both orders of fact, we may conclude that the cell-wall is sometimes part of the organite, and sometimes product: a blood-cell and a cartilage-cell may be cited as examples of each. And this argument applies to the intercellular substance also.

65. The terms plasmode and protoplasm are general, and include many species. There are different plasmodes for the different tissues, so that we find phosphates of soda in the blood-serum, phosphates of potash in the nerve-plasma, phosphates of magnesia in the muscle-plasma, and phosphates of lime in the bone-plasma; having severally to form the specifically different protoplasms of these tissues. Observe, moreover, the gradations of these in respect of their physical state: the blood being the most liquid, the nerve a degree more solid, the muscle still more solid, and the bone almost entirely solid; and since solubility of material is a necessary condition of the chemical changes, we can understand how the blood, the nerve, the muscle, and the bone represent degrees of vital activity: the greater the instability of organized substance, the more active its molecular renovation. Many serious errors result from overlooking the specific differences of protoplasms; among them may be mentioned that very common one of asserting that the ovum of a man is not distinguishable from the ovum of any other mammal, nor the ovum of a mammal from that of a reptile; nay, we sometimes see it stated that the protoplasm from which a mammal may be developed is the same as that which is the germ of an oak. So long as this simply asserts that we have at present no means of distinguishing them by any chemical or physical tests, there can be no objection raised; but it is a serious misconception, which any embryological investigation ought to rectify, to suppose that the ovum is not specific from the first.

66. Between the organites and their plasmodes there is the necessary relation, which corresponds with the relation between organisms and their mediums. Once formed, the organites are arranged side by side, or end on end, into textures or tissues, and these are grouped into organs, every organ being constituted by a collection of tissues, as every apparatus is by a collection of organs, and the organism by the federation of all the parts. We have more than once insisted on the necessity of synthetic interpretation to complete the indications of analysis: which means that no account of vital phenomena is real unless it takes in all the co-operant factors, both those of the organism and the medium. Neglect of this canon vitiates Dr. Beale’s otherwise remarkable labors.

THE HYPOTHESIS OF GERMINAL MATTER.

67. It may help to elucidate certain important points if I here examine the hypothesis which Dr. Beale has worked out with such patient skill, but with what seem to me such unphysiological results. He deserves, I think, more applause than has been awarded to him, not only for the admirable patience with which he has pursued the idea, but also for the striking definiteness of the idea itself—always a great advantage in an hypothesis, since it gives precision to research. If biologists have paid but little attention to it, this is no doubt due to the theoretical, still more than to the observational contradictions it presents. Histologists dispute his facts, or his interpretations; while other biologists do not see their way in the application of his hypothesis. Respecting all disputed points of observation I shall be silent, for I have myself made no systematic researches in this direction, such as would entitle me to form an estimate of the evidence. But my dissent from the hypothesis is founded on biological principles so fundamental that I should be willing to take my stand entirely on the facts he himself puts forward.[22]

68. The hypothesis is that nothing in the organism has any claim to vitality except the minute masses of protoplasm (by him called bioplasm), which in the egg represent, he thinks, about the one-thousandth part of the whole mass, the rest being lifeless matter, namely, pabulum, and formed material. This bioplasm is the germinal matter out of which, by a process of dying, arise the tissues and humors constituting the formed material—these, with the pabulum which feeds the germinal matter, being all dead material. The germinal matter itself, though living, only lives because there is temporarily associated with it that Vital Force of which we have already spoken (§ [14]). In virtue of this association, a particle of matter not exceeding the one hundred-thousandth of an inch in diameter is said to be alive; and, presumably, to contain within it all those manifold powers which the term Life condenses. The pabulum brought under the influence of this Vital Force is transformed into germinal matter which, escaping from this mysterious influence, dies into tissue. Muscle-fibres and nerve-fibres are thus not living parts, nor are their actions vital. So that, to be consistent, we must not speak of the organism as living, but as a dead structure produced by the Vital Force, and set in action by the aid of scattered bits of germinal matter. He has not, I think, stated whether each of these bioplasms has its own Vital Force, so that the organism is the theatre of millions of Vital Forces; or whether it is one Vital Force which animates the whole organic world of plants and animals. But nothing can be less equivocal than his position respecting the lifelessness of every part of the organism except the germinal matter.

69. The germinal matter may be selected as the primary stage of the formed material, the initial point of growth, and thus stand for the pre-eminently distinctive centre of Nutrition; but were we to limit all Nutrition to the germinal matter, as defined by Dr. Beale, and deny the co-operation of all the formed material, we should still not be justified in restricting Life to simple Nutrition. We cannot exclude such phenomena as those of Sensation and Motion, nor can we assign these to the germinal matter.[23] To suppose this, would be equivalent to saying that the steam which issues from a teakettle is capable of the actions of a locomotive engine. The steam from the kettle is like the steam from the boiler, it has molecular energy, and by this will co-operate in the production of mechanical work, if the mechanism be adjusted to it. The molecular energy of the protoplasm in muscular fibre may be indispensable to the movements of the muscles, but these, and not the protoplasmic movements alone, are muscular contractions. An hypothesis, therefore, which is obliged to declare that muscle-fibre and nerve-fibre are not living, even when active in the organism, seems to me defective at its base. If we view these apart from the organism, they may, like all the other formed materials, be regarded as dead; and no one doubts that epidermis, nail, horn, hair, and bone are dead in this sense, that they cannot live independently, and do not reproduce themselves. But so long as even these form constituents of the living organism, they also are living (§ [42]).[24] It is only by a misconception of the analytical artifice that so simple a truth could have been missed.

70. But this misconception meets us at many a turn. The Vitalist hypothesis of an extra-organic agent of course refuses to regard Life as the expression of all the co-operant conditions; and even opponents of that hypothesis often fall into the same error of principle, when they attempt to explain Life by localizing it in the cells; which is simply a morphological substitution for the once popular doctrine that only the vascular parts were organized, and every part destitute of blood-vessels was dead. This idea seemed supported by the facts of the most highly vascular parts being the most vital, and of a parallelism existing between the vital activity of those organs which when injected seemed almost entirely composed of blood-vessels, as the liver and brain, and those which showed scarcely a trace of vessels, as cartilage and bone; it seemed supported also by the appearance of blood-vessels in all new formations, and by the idea of the blood as the nutrient fluid. Then came the cell-doctrine, and the belief that the cell was the really ultimate morphological element—which may be true—and that “here alone there is any manifestation of life to be found, so that we must not transfer the seat of vital action anywhere beyond the cell,”[25]—which is very questionable.

71. We have already seen that the cell is an anatomical element, or organite; the organism is but an aggregate of organites and their plasmodes. But Biology, which deals with the organism as a whole, and with functions which are the resultants of all the vital properties, must not be restricted to any single factor, however important. It would assuredly be deemed absurd to say that diamond rings and lead-pencils were the same, because the diamond and the plumbago, which are the specific elements of each, are both the same chemical element,—carbon. The substance is really different in diamond and plumbago, is different in properties, and is, in rings and pencils, united with different substances into objects having very different properties. Whatever analysis may discover as to the identities of organic structures, we cannot explain a single vital phenomenon without taking into account the three terms, Structure, Aliment, and Instrument; and whenever a cell is said to be the seat of vital action, these three terms must be implied. In Dr. Beale’s hypothesis the restriction is carried to its extreme; not content with the cell, he withdraws vital action from the cell as a whole, assigning it to the protoplasm and nucleus—cell-contents and cell-wall being, in his view, dead. If it be true that the protoplasm is alone concerned in Nutrition, yet Nutrition is not Life. Occupied mainly with formative processes, it leaves other indispensable processes to other parts. He instances the removal of all the tissues during the metamorphoses of insects:—“new organs and textures are laid down afresh and developed ab initio, instead of being built up upon those first formed.” But to show how he restricts the idea of Life, he adds: “Such complete change, however, necessitates a state of existence during which action or function remains in complete abeyance.”[26]

The muscles and nerves which are instrumental in this functional life are said to be dead. It is true that the muscle-fibre does not develop fresh fibres. But it is equally true that the protoplasm of muscle does not alone execute muscular contraction. Each has its special office. Hence I reject the idea that formed material is dead. He further says “formed material may be changed, it cannot change itself.” The antithesis is doubly inexact: 1°, nothing changes itself, but only yields to pressure, or reacts on being stimulated; and 2°, all the evidence at hand is against the notion that the formed material is not the seat of incessant molecular change; it is wasted and repaired molecule by molecule. Kölliker properly protests against the growing tendency of histologists to deify protoplasm, and to make it the sole seat of vital changes, the cell-wall and cell-products having also, he says, their physiological importance. It is manifestly erroneous to deny vital changes to the red blood-corpuscles on the ground of their no longer containing germinal matter.[27]

72. The analytical view may separate certain parts as active, and other parts as passive, and thus regard the cells as the seats of vital activity, the intercellular substance as merely accessory and instrumental; but the real or synthetical view must recognize both parts as equally indispensable, equally vital. Take cartilage, for instance, with its enormous preponderance of intercellular substance (formed material), and consider how absolutely impossible any of its uses would be were it reduced to the germinal matter of its corpuscles! And so of all the tissues.

73. If formed material is not to be excluded from the living parts of the organism, neither is the plasmode, out of which the germinal matter arises, since here we have the nutritive changes in their highest activity; and because the property of Nutrition is here most active, the other property of Development is in abeyance. Dr. Beale holds that pabulum necessarily becomes germinal matter; but when we come to treat of Nutrition it will appear that this is not more true than that Food necessarily becomes Tissue: some of it does; but much of it is used up for heat and other purposes.

74. What is true and important in the distinction between germinal matter and formed material is, that from the former onwards there is a gradual process of devitalization, the older parts of every organite and tissue approaching more and more to the state of inorganic matter. But to show how vain is the attempt to restrict Vitality to any one out of a complex of co-operant factors, we might set up a chemical hypothesis to the effect that Vitality depends on phosphates, and with it explain the phenomena quite as well as with the hypothesis of germinal matter. For not only is it found that the productive quality of a soil depends on its richness in phosphates, but, as Lehmann has shown, wherever cells and fibres make their appearance phosphates are found, even in the lowest organisms, which, however, contain but little. Phosphates abound in seeds and ova, in muscles and ganglia, and are deficient in the woody parts of plants and the elastic fibres of animals. The infant absorbs phosphates in large quantities and excretes them in small quantities. Nervous activity is accompanied by the consumption of a third more phosphorus than accompanies muscular activity. Phosphates are among the most energetic of organic stimulants. But who would endow the phosphates with Vitality, on the ground of their indispensable presence in all vital processes?

75. Life, as we saw, is the expression of the whole organism. Many of the parts are incapable of manifesting any vital phenomena except in connection with all the rest; and of those parts which may be separated from the organism and continue to manifest some vital phenomena, none are capable of manifesting all. When the connexus of the parts is destroyed the organism is dead. Long after that cessation which we call Death, there are still evidences of Vitality in some of the parts: the heart will continue to beat, the glands will secrete, the hair will grow, the temperature will still be above that of the surrounding medium, the muscles will be excitable; these vital properties are the activities of organized substances, and so long as the state of organization is preserved they are preserved; but the Life, which is the synthesis of all the vital properties, vanishes with the destruction of that synthesis.

76. May we not generalize this, and say that every special form of existence, organic or inorganic, is determined by the synthesis of its elements? Atoms are grouped into molecules, molecules into masses, masses into systems. Out of the textureless germinal membrane and the yolk, with no additions from without except oxygen and heat, are developed all the textures and organs of the chick; and this chick weighs no more than the egg out of which it was evolved. The development has been a succession of syntheses—epigenesis upon epigenesis. We may, if we please, regard each organite, as it appears, living its separate life, and each tissue its separate life; but we must not confound under the same symbol modes of existence so widely different as the activities of an organite, and the activities of an organism constituted by millions of organites.

77. If therefore we cannot restrict Life to the processes of Nutrition, Dr. Beale’s hypothesis, whatever value it may have as explaining histogenesis, is quite unacceptable. Neither Vital Force nor Bioplasm covers the whole ground. For the former there is no better evidence than our ignorance of the real synthesis; for the latter the evidence is positive in its nature, but its interpretation is questionable. Dr. Beale selects as the germinal matter those portions of tissue which are susceptible of being deeply stained by the carmine solution, the formed material being only stained in a faint degree; the nucleus and nucleolus are the portions of germinal matter which are most deeply stained; and hence he concludes that the older the matter the fainter will be its coloration. There is no dispute as to the value of the staining process, invented by Gerlach, for the discrimination of chemically different parts of a tissue; and Dr. Beale has made excellent use of it in his researches.[28] But I altogether dispute the conclusion that the staining process reveals the parts which are exclusively vital; and for this reason: it depends solely on the acid reaction of those parts; and we cannot divorce the acid from the alkaline agencies, both being indispensable. Nay, it has been proved that in the living animal no organized substance can be stained. Lord Godolphin Osborne first discovered, in 1856, that the protoplasm of growing wheat was susceptible of coloration;[29] but Gerlach, in 1858, found that this never took place in the animal during life. He kept tadpoles and intestinal worms for weeks in colored fluids, without a single spot becoming stained; although no sooner did these animals die than the staining began. Nor even when he injected the colored fluids under the skin and into the stomach, was the slightest coloration produced.[30]

To Gerlach’s testimony may be added that of Stein, who, in his magnificent work on Infusoria, says that not only has no foreign substance ever been found in the protoplasm of the Opalina, but in the Acineta, and all the embryos of the higher Infusoria known to him, he has been unable to color the living substance.[31] This resistance of the living protoplasm is surely a serious objection to the hypothesis that only those parts of the dead organism which are stained were the truly vital parts. Ranke sums up the results of his experiments thus: “They all show that the living cell resists the imbibition of every substance which it cannot assimilate. It is precisely the impossibility of staining the cell that proves this conclusively, since every particle of carmine absorbed would have revealed its presence.”

It is not to be supposed that Dr. Beale was unacquainted with Gerlach’s experiments. He has at any rate so far qualified the statement of his hypothesis as to admit that it is only after death that the germinal matter is stained. “The living matter” (he says, How to Work with the Microscope, p. 107) “possesses an acid reaction, or to speak more correctly, an acid reaction is always developed immediately after its death.” Now, since this acid reaction only presents itself after death, and it is this which is revealed by the carmine, we have no right to conclude that the carmine singles out the vital parts. Every one knows that the living muscle and nerve, when in repose, present an alkaline or faintly neutral reaction, and after excitation this is changed into an acid reaction, which increases with the exhaustion of the tissue. In strict logic, therefore—if we could logically apply such a test—it is the unstained parts that ought to be called vital. But, in truth, alkalinity and acidity are equally indispensable.

78. The main object of my bringing this question forward was to illustrate the danger of being misled by analysis: a danger we shall see to be very serious in psychological inquiries. The aid derived from analysis need never be undervalued; all that we have to bear in mind is that it is only a logical artifice, and that our real explanation must always be synthetic. Because of the tendency to rely on analysis there has been an imperfect discrimination of the profound difference between

ORGANISMS AND MACHINES;

and while on the one hand the legitimate striving of the biologist to display the mechanism of organic actions has been denounced by a certain school as Materialism and a hateful attempt to “rob Life of its mystery,” there has been on the other hand a misconception of this mechanism, as if its dependent actions were of the nature of machines, that is to say, as if organized mechanisms were strictly comparable with machines constructed of inorganic parts. No doubt the laws of Mechanics are the same in both, for these are abstract laws which take no account of concrete differences. But when elaborate parallels are drawn up between steam-engines and animal organisms, the coal consumed in the one likened to the food in the other, and the force evolved in the combustion in both being the same, there is a complete obliteration of all that specially distinguishes vital activity.

79. Between an organism and a machine there is the superficial resemblance that both have a complex structure, and are constructed of different and dependent parts. But underneath this resemblance there is a radical diversity.[32] The arrangement of parts in the organism is more than a juxtaposition, it is a solidarity, arising from the fact of their being all differentiations from a common substance which is a special combination of the three classes of proximate principles. Thus they are not parts which have been put together, but which have been evolved, each out of a pre-existing part, and each co-operating in the very existence of the other. The machine is made of independent and primarily unrelated parts; its integrity depends on the continued preservation of the substance of each part; waste is here destruction. The organism is constituted by interdependent and primarily related parts; its integrity depends on the continued destruction and renovation of their substance; waste is a condition of vitality. The actions of the machine are subordinated; the actions of an organism are co-ordinated. The lever moves a wheel, and the wheel in moving liberates a spring, each transmitting a communicated impulse, but otherwise each acts independently—no slight modification in the structure or movement of the wheel will modify the structure or the movements of the lever, no alteration in the tension of the spring will affect the structure of the wheel. But in the organism all are parts of one sympathetic whole; each reacts on each; each is altered by the other. Not a nerve is stimulated, nor a muscle moved, but the entire organism is affected. A condensation here is the cause of a greater imbibition there. The injection of salt or sugar under the skin of the frog’s leg will produce cataract in its eye. The activity of a secreting cell in the ovary, or liver, alters the condition of the brain; the activity of the brain will check the secretion of a gland, or relax the sphincters of the bladder. When we observe the growth of horns, or the appearance of the beard, concomitant with the secretion of spermatic cells—and especially when we observe with these a surprising change in the physical and moral capabilities and tendencies of the organism—we understand how the remotest parts of this mechanism are bound together by one subtle yet all-powerful tie. Nothing of this is visible in a machine. In a machine the material is so far of secondary importance that it may be replaced by materials of various kinds: a pulley may be worked with a hempen cord, a silken cord, or an iron chain; a wheel may be wood, iron, copper, brass, or steel; the actions will in each case be similar. Not so the organic mechanism: the slightest variation, either in composition or intimate structure, will affect, and may frustrate the organic activity. It is only in the skeleton that the specific character of the materials may be changed; and here only in the substitution of one phosphate for another in the solid masonry.[33]

80. Another marked characteristic of the organism is that it has a connexus of actions, the simultaneous effect of a continuous evolution, appearing in stages and ages. And in the animal organism there is a consensus as well as a connexus, through which there is evolution of Mind; and in the Social Organism an evolution of Civilization. This consensus forms an intermediate stage through which the animal actions are sensitive as well as nutritive, and the nutritive are regulated by the sensitive. It is obvious that nothing like this is to be found in a machine; and we conclude, therefore, that any view of the organism which regards its mechanism without taking in these cardinal characteristics must be radically defective. We no more deny the existence of mechanical phenomena in denying that the organism is like a machine, than we deny the existence of chemical phenomena in denying that Vitality is chemical.

CHAPTER IV.
THE PROPERTIES AND FUNCTIONS.

81. The terms Property and Function are not always used with desirable precision. There is, however, a marked distinction between the property which characterizes a tissue in whatever organ the tissue may be found, and the function which is exhibited by an organ composed of several tissues. We ought never to speak of a function unless we imply the existence of a correlative organ; and it is therefore incorrect to speak of the function of Nutrition, since all the tissues nourish themselves; but we may speak of certain organs as special instruments in facilitating Nutrition. Thus also with respiration, usually, but not accurately, spoken of as the function of the lungs; the lungs being simply the most effective of the instruments by which the interchange of gases (which also takes place in every tissue) is facilitated. If by Respiration we mean Breathing, then, indeed, Respiration is the function of the lungs; if we mean the absorption of oxygen and the exhalation of carbonic acid, Respiration is a general property of vital tissue. A fragment of muscle removed from the body respires, so long as its organization is intact; but it does not breathe—it has no accessory instruments, nor does it need them. The co-operation of nerve centres, diaphragm, ribs, circulating system, etc., necessary in the complex organism to bring the due amount of oxygen to the tissues, and convey away the carbonic acid, is here needless. In the ascending animal series we find this necessity growing with the complexity of the organism. The whole skin respires in the amphibia, and to some extent in man also: a frog will live for ten or fourteen days after extirpation of its lungs, the skin respiring sufficiently to keep up a feeble vitality. But the skin does not suffice; and, very early, certain portions are specialized into organs (at first in the shape of external gills, and finally as internal lungs), for the more energetic, because more specialized, performance of this office. In the simpler organisms the blood is easily reached by the air; therefore no instrument is needed. In primitive societies the transport of goods is effected by men and women carrying them; in civilized societies by the aid of horses and camels, and wagons drawn by oxen; till finally these are insufficient, and railways are created, whose power of transport transcends the earlier methods, as the breathing of a mammal transcends the respiration of a mollusc. Breathing is the special function of an organ—the lungs (or more strictly, the thoracic apparatus)—as Railway Transport is a special social function. Although each of the tissues forming this organ can, and does, exhale carbonic acid and absorb oxygen—and each of the railway servants can, and does, transport objects to and from the locomotive—yet the main work is thrown upon the special apparatus.

82. What is meant by properties of tissue and functions of organs may be thus illustrated. Let us suppose ourselves investigating the structure of a ship. We find it composed of various materials—wood, iron, copper, hemp, canvas, etc.; and these under various configurations are formed into particular parts serving particular purposes, such as deck, masts, anchor, windlass, chains, ropes, sails, etc. In all these parts the materials preserve their properties; and wherever wood or iron may be placed, whatever purpose the part may serve, the properties of wood and iron are unaffected; and it is through a combination of these properties that the part is effective; while through the connection of one part with another the purpose becomes realized. The purposes to which masts, ropes, or sails are subservient may be called their functions; and these of course only exist, as such, in the ship. It is the same with the organism. We find it composed of various Tissues, and these are combined into various Organs or Instruments.[34] The properties of Tissues remain the same, no matter into what Organs they may be combined; they preserve and exert their physical, chemical, and vital properties, as wood and iron preserve their properties. Each Tissue has its characteristic quality; and the Organ which is constructed out of a combination of several Tissues, more or less modified, is effective solely in virtue of these properties,[35] while the Function of that organ comes into play through its combination with other organs. For example, muscular tissue has a vital property which is characteristic of it, Contractility; and muscles are organs constituted by this tissue and several others;[36] such organs have the general function of Contraction, but whether this shall be specially manifested in the beating of the heart, the winking of the eyelid, the movement of the chest, or the varied movements of the limbs, will depend on the anatomical connections. The reader unfamiliar with Biology is requested to pay very particular attention to this point; he will find many obscurities dissipated if he once lays hold of the “principal connections.”

82a. Although Bichat’s conception was of great value, it was not sufficiently disengaged from the metaphysical mode of viewing biological phenomena. Both he and his disciples will be found treating Properties as entities, and invoking them as causes of the phenomena instead of recognizing them simply as abstract expressions of the phenomena. Readers of my First Series will remember how often I have had occasion to point out this common error: men having baptized observed facts with a comprehensive name, forget the process of baptism, and suppose the name to represent a mysterious agency. The fact that gases combine is expressed in the term affinity; and then Affinity is understood to be the cause of the combinations. The fact that bodies tend towards each other is called their gravitation, and Gravitation is then said to cause the tendency. The doctrine of vital properties has been thus misunderstood. While no one imagines that he can operate on affinity otherwise than by operating on the known conditions under which gases combine, many a biologist and physician speaks as if he could operate on the Irritability of a tissue, or the Co-ordination of muscles, by direct action on these abstractions.

Let it be therefore once for all expressly stated that by the property of a tissue is simply meant the constant mode of reaction of that tissue under definite conditions. The property is not a cause, otherwise than the conditions it expresses are a cause. And these conditions are first those of the organized structure itself, and secondly those of the medium in which it lives. Oxygen unites with Hydrogen to form water, but only under certain pressures; so likewise muscles manifest Contractility on being stimulated (that is their mode of reaction), but only under certain degrees of temperature, humidity, and a certain chemical composition of the plasmode. The property is so truly an expression of the co-operant conditions, that it is found to vary with those conditions, and to vanish when they vary beyond a certain limit.

An attempt has been made to restrict the notion of a property to an ultimate fact. Whatever is not reducible to known conditions is to be accepted as a property. Combustion, for example, is reducible to the molecular combination of oxygen and some other gas; but this combination itself is not reducible, and it is therefore christened affinity. I cannot accept this view. Admitting our inability to say why gases combine under certain conditions (and in this sense all facts are inexplicable and ultimate, unless we take the how as ample explanation of the why), I must still say that since affinity itself depends on the co-operation of known conditions, it is not less explicable than combustion. But the point is unimportant: what we have here to settle is the meaning of a property of tissue,—and that is the mode of reaction which that tissue manifests under constant conditions, internal and external.

83. The evolution of Life is the evolution of special properties and functions from general properties and functions. The organism rises in power as it ramifies into variety. Out of a seemingly structureless germinal membrane, by successive differentiations certain portions are set apart for the dominant, or exclusive, performance of certain processes; just as in the social organism there is a setting apart of certain classes of men for the dominant or exclusive performance of offices, which by their co-operation constitute Society. The soldier fights, but ceases to build or reap, weave or teach; the mason builds; the agriculturist sows and reaps; the priest and thinker teach; the statesman governs. In simple societies each does all, or nearly all; but the social life thus manifested is markedly inferior to the energetic life of a complex society. So with organisms. An amœba manifests the general properties of Nutrition, Reproduction, Sensibility, and Movement. But it has no special organs, consequently no special functions. The polype has a certain rudimentary specialization of parts: it has a simple alimentary cavity, and prehensile tentacles; and although by these it can seize and digest its prey, it can only do so in a limited way—all the manifold varieties and power of prehension and digestion observed in more complex organisms are impossible with such organs as the polype possesses.

84. Differences of structure and connection necessarily bring about corresponding differences in Function, since Function is the directed energy of the Properties of tissues. One organ will differ from another in structure, as the liver from the pancreas, or the kidney from the spleen; or one organ may closely resemble another but differ from it only in connections, as a sensory and a motor nerve, or an extensor and a flexor muscle. We must therefore always bear both points in mind. Every modification, structural or connectional, is translated by a corresponding modification in the office. The hand and the foot show this well. The tissues are the same in both, the properties are the same, and both have the same general function of Prehension; but their morphological differences carry corresponding differences in their uses.

Suppose we have a galvanic battery, we know that its electric force may be variously applied. Two pieces of charcoal fixed to the ends of its conducting wires give us the electric light; replacing the charcoal by a telegraphic apparatus we can transmit a message from one continent to the other; the wires dipped in a solution effect a chemical decomposition, dipped into a mixture of gases they effect a chemical composition. In these, and many other applications, the property of the battery is constant; but the functions it subserves have varied with the varying co-operants. So with the properties of tissue.[37] Not only have we to bear in mind the organic connections of the tissues, but also the relation of the organs to their media. Swimming and Walking, for example, are both functions of the locomotive apparatus, but they are specially differenced by the media in which the animal moves.

85. The properties of tissues are their peculiar modes of reaction, and each tissue has its dominant characteristic, such as the Contractility of the muscle, and the Neurility of the nerve. But there has of late years sprung up a misleading conception, partly a consequence of the cell-theory, and partly of the almost inevitable tendency of analysis to disregard whatever elements it provisionally sets aside; this conception is the removal of the property from its tissue, and the localization of it in one of the organites—cell or fibre. This has been conspicuously mischievous in the case of the nerve-cell, which has been endowed with mysterious powers, and may be said to have usurped the place of nerve-tissue. I shall have to speak of this in the next problem. Here I only warn the student against the common error. The properties of a tissue depend on the structure and composition of that tissue, together with its plasmode and products; they vary as these vary. To select any one element in this complex, and ascribe the reaction of the tissue to that, is only permissible as a shorthand expression.

86. What has just been expounded may be condensed in the following biological law:—

Identity of tissue everywhere implies identity of property; and similarity of tissue corresponding similarity of property. Identity of organic connection everywhere implies identity of function; and similarity of organic connection similarity of function.

87. This law, first formulated by me in 1859, and then applied to the interpretation of nervous functions, was so little understood that for the most part it met with either decided denial or silent neglect; no doubt because of the general disinclination to admit that the properties and functions of the spinal cord could be similar to those of the brain, in correspondence with the similarity of their tissues and organic connections. Even Professor Vulpian, who adopted it, as well as my principal interpretations, hesitated, and relapsed into the orthodox view in assigning three different properties to one and the same tissue in cord, medulla oblongata, and cerebrum.[38] In the course of our inquiries we shall so frequently have to invoke this law that I earnestly beg the reader to meditate upon it, and ask himself upon what other grounds, save those of structure and connection, the properties and functions can possibly rest? If on no other, then similarity in structure and connection by logical necessity involves similarity in property and function.

DOES THE FUNCTION DETERMINE THE ORGAN?

88. Closely connected with this law, which simply formulates the self-evident principle that every action is rigorously determined by the nature of the agent, and the conditions under which the act takes place, is the surprising question whether functions are dependent upon organs, or organs dependent on functions?—a question which sometimes takes this shape: Is Life the result of organization, or is organization the result of Life?

The vitalist, who holds that Life is an extra-organic agent, is logical in declaring organization to be the consequence of Life;[39] but there are many organicists who conclude from certain facts that organs are developed by functions, and that organization is a result of Life. There seems, however, to be some equivoque here. I cannot otherwise understand how Mr. Spencer should have written: “There is one fact implying that Function must be regarded as taking the precedence of Structure. Of the lowest rhizopods which present no distinctions of parts, and nevertheless feed and grow and move about, Professor Huxley has remarked that they exhibit Life without Organization.”[40] The equivoque here arises from the practice of calling all living bodies “organisms,” even those destitute of the differentiations called organs; but if we substitute the term “living body” in lieu of “organism,” the equivoque will disappear, and Function no longer seem to precede Structure. Neither Mr. Spencer nor Mr. Huxley would affirm that Life can be manifested without a living body; and every living body must have a structure of some sort—unless by structure be meant a special configuration of parts. The properties of a body, whether it be simple or complex in structure, result from the properties of its components; and the vital phenomena vary with these varying components. The substance of a Rhizopod is indeed simple as compared with that of higher organisms, but is complex as compared with anorganisms; and corresponding with this simplicity of structure there is simplicity of vital function.[41]

89. The properties of steam are exhibited by the kettle on the fire, no less than by the gigantic engine which animates a manufactory; but the uses of steam (the functions of the engine) vary with the varying structure, and the applications of that structure to other structures. Precisely analogous is the case of the organ and its function, in relation to the living substance of which it is a peculiar modification. Vital actions are manifested by a lump of protoplasm; but these actions are as sharply demarcated from the actions of more highly organized animals, as the phenomena of a steam-engine are from those of a teakettle.

90. Mr. Spencer has nowhere defined what he means by Structure, nor given a definition of Organ, and this neglect makes it difficult rightly to appreciate his view. But whether we take structure to signify the substance of the living body, or the differentiations of that substance into separate tissues and organs, in either case the actions (functions) of which this structure is the agent must be rigorously determined by it. Mr. Spencer has avowed this in declaring that the “general physiologist may consider functions in their widest sense as the correlatives of tissue.” Is this true in the widest sense and not true in the narrowest? I am puzzled to find him insisting that “function from beginning to end is the determining cause of structure. Not only is this manifestly true where the modification of structure arises by reaction from modification of function; but it is also true where a modification of structure otherwise produced apparently initiates a modification of function.” Such language would be consistent were he a vitalist who believed in a Principle independent of Matter which shapes matter into organic forms; but as a positive thinker he can scarcely escape the admission that since Function is the activity of the Agent (Function in the widest sense being the action of the whole Organism, and in its narrowest sense the action of the special Organ) there cannot be an activity preceding the agent. I suspect that he does not always bear in mind the distinction between Property and Function, and consequently is led into statements at variance with the principles he professes. As far as I understand the course of his thought, it runs somewhat thus: With the increased use of an organ its volume may be increased, its structure altered; this alteration will, by reaction, cause alterations in other organs, and thus the result of a change in the habitual activities of an animal will be an alteration in the arrangement of its parts.

91. We speak loosely of an organ being developed by increased activity; but this is loose speech, and investigation shows that the organ is not developed by, but accompanies the increased activity, every increment of activity being necessarily preceded by a corresponding increment of structure. This is evident à priori: the force manifested is inherent in the structure manifesting it. Thus we ought not to say “the vascular system furnishes good instances of the increased growth that follows increased function”; we ought to say, “that permits increased function.” The muscle having a contractile power represented by 10, expends, we will suppose, 7 units of force in its normal activity, and these are replaced by its normal nutrition. If from an extra demand upon it 9 units are expended, the muscle becomes fatigued, if 10, exhausted, and it will no longer contract, the whole disposable sum of its contractility being dissipated. During all these stages the structure of the muscle—or to prevent all equivoque, let us say the substance of the muscle—has been changing, not indeed in any degree appreciable to the eye, but appreciable by the more decisive tests of chemical and physiological reactions. Yet inasmuch as in the ordinary course of things the waste is quickly repaired, the muscle in repose once more regains its original state, once more represents 10 units of contractility. Now let us consider what takes place when extra labor is thrown upon the muscle, when exercise causes growth. At the outset of a walking tour we may not be able to compass more than twenty miles a day, at its close we manage thirty. Is it the increased activity of the function which has caused this increase of structure? In one sense, yes; but let us understand it. Had the increase of activity been temporary, there would have been only a temporary increase of structure. But when the ordinary expenditure of 7 units rises to 9, on several successive days, this extra expenditure of tissue has had to be met by an extra nutrition—i. e. more plasmode has been formed and more protoplasm. It is a physiological law, easily explained, that, within due limits, extra waste brings about extra repair: as the channels are widened and multiplied, the derived currents become stronger, and the increased flow of nutrition which was temporary becomes permanent, because this increase is no longer dependent on an extra stimulus, but on an enlarged channel.[42] When the channels have not become multiplied or enlarged, which must be the case whenever the extra stimulus is fluctuating and temporary, the extra expenditure is not followed by increased size of the muscle: the currents resume their old directions, no longer being diverted.

92. Let the social organism furnish us with an illustration. At the present moment there is a movement against the retail shopkeepers of London in favor of Co-operative Stores. The stimulus of getting better goods and cheaper, attracts the flow of custom from its old channels; and if this continue a certain time the new arrangements will be so thoroughly organized, and will work so easily, that Co-operative Stores will to a great extent supplant the retail shops. But if from any causes the stimulus slackens before this reorganization has passed from the oscillating into the permanent stage—if the goods are not found to be superior, or the cheapness not worth the extra trouble—the old influences (aiding our indolence) which have been long and continuously at work, will cause the social organism to resume its old aspect, and the co-operative “varieties” will disappear, or exist beside the ancient “species.”

In the one case as in the other a glance at the process is enough to detect that the increase in the activity has been preceded by a corresponding increase in the structure. The muscle has not been enlarged by extra activity, but with it. The co-operative action has grown with each additional co-operator. Looking at the cases from afar we may justly say that development has been due to function; but looking to the process we see that each increment of activity was necessarily dependent on an increment of substance. When changes of habit or adaptation are said to produce modifications in structures, this is true in as far as one modification of structure necessarily brings with it correlative modifications, the growth of one part affecting the growth of all more or less; but we must remember that to render the structure capable of new adaptations corresponding modifications must have been going on. The retail shopkeepers might securely laugh at the co-operative movement if the respectable families would not or could not become co-operant. When Mr. Spencer urges that “not only may leaf-stalks assume to a great degree the character of stems when they have to discharge the functions of stems by supporting many leaves, and very large leaves, but they may assume the characters of leaves when they have to undertake the functions of leaves,” I would ask if he is not reversing the actual process? The stem cannot assume the functions of a leaf until it has first assumed the character of a leaf. The assumptions of both must be gradual, and pari passu.

93. The hand is an organ, its function is prehension. The performance of this function in any of its numerous applications is rigorously limited by the structure of the hand—the bones, muscles, nerves, circulating and absorbent vessels, connective tissue, fat, etc. Fatigue the nerve, and the function will be feebly performed; exhaust it, and the function ceases; diminish the action of the heart, tie an artery, or vitiate the structure of the blood, and the function will be correspondingly affected; stiffen the tendons, soften the bones, diminish the synovial fluid, or increase the fat—in short, make any alteration whatever in the structure of the hand, and an alteration is necessarily produced in its function. So rigorously is function dependent upon structure, that the hand of one man will execute actions which are impossible to another. The hand of a baby is said to be the same in structure as the hand of a man; and since the powers (functions) of the two are notoriously different, we might rashly conclude that here function was dissociated from structure. The case is illustrative. In baby and man the structure is similar, not the same; the resemblance is of kind, not of degree; and the function likewise varies with the degree. The penny cannon which delights the child is similar in structure to the ten-pounder which batters down walls; and though, speaking generally, we may say that the function of both is to fire gunpowder for human ends, no one expects the penny cannon to be employed in warfare. In physiology, as in mechanics, the effect varies with the forces involved.

There can be no doubt that an exaggerated activity will produce a modification in the active organ, for this is only the familiar case of increased growth with increased exercise, and this is the biological meaning in which Function can be said not, indeed, to create, but to modify an existing Organ. Preceding the activity there must be the agent. Every organ although having its special function has also the properties of all the tissues which constitute it. The function is only the synthesis of these properties to which a dominant tissue gives a special character. The eye, for example, though specially characterized by its retinal sensibility to light, is largely endowed with muscles, and its movements are essential to Vision. The intestinal canal, again, though specially characterized by its secretions for the decomposition of food, has muscles which are essential to Digestion. In many animals, especially vegetable-feeders, there is an exaggeration of the muscular activity in certain parts of the intestinal canal which is only possible through a corresponding development of the muscular tissue, so that in some birds, crustaceans, and molluscs we find a gizzard, which is wholly without a mucous membrane to secrete fluids, and which aids Digestion solely by trituration.

94. Mr. Spencer, as I have already suggested, seems to have been led into his view by not keeping distinctly present to his mind the differences between Properties of tissue and Function, the activity of an organ. “That function takes precedence of structure,” he says, “seems implied in the definition of Life. If Life consist of inner actions so adjusted as to balance outer actions—if the actions are the substance of Life, while the adjustment constitutes its form; then may we not say that the actions formed must come before that which forms them—that the continuous change which is the basis of function must come before the structure which brings the function into shape?” The separation of “actions formed” from “that which forms them” is inadmissible. An action cannot come before the agent: it is the agent in act. The continuous change, which is the basis of Vitality, is a change of molecular arrangements; and the organ which gives a special direction to the vital activity, e. g. which shapes the property of Contractility into the function of Prehension, this organ must itself be formed before it can manifest this function. It is true that in one sense the organs are formed by, or are differentiated in, a pre-existent organism; true that the general activity of living substance must precede the special activity of any organ, as the expansions of steam must precede any steam-engine action; but the general activity depends on the general structure; and the special actions on the special structures. If by Organization we are to understand not simply organized substance, but a more or less complex arrangement of that substance into separate organs, the question is tantamount to asking whether the simplest animals and plants have life? And to ask the question, whether Life precedes organic substance? is tantamount to asking whether the convex aspect of a curve precedes the concave! or whether the motions of a body precede the body! To disengage ourselves from the complicated suggestions of such a word as Life, let us consider one of the vital phenomena, Contraction. This is a phenomenon manifested by simple protoplasm, and by the highly differentiated form of protoplasm known as muscle. In one sense it would be correct to say that Contractility as a general property of tissue precedes Contraction, which is specialized in muscle. But it would be absurd to say that muscular contraction preceded the existence of muscle, and formed it. The contractions of the protoplasm are not the same as muscular contractions any more than the hand of a baby is the same as a man’s; the general property which both have in common depends on the substance both have in common; the special property which belongs to the muscle depends on its special structure. An infinite activity of the contractile protoplasm would be incompetent to form a muscle, unless it were accompanied by that peculiar change in structure which constitutes muscle. The teakettle might boil forever without producing a steam-engine or the actions of a steam-engine. That which is true of one function is true of all functions, and true of Life, which is the sum of vital activities.

95. It is this haziness which made Agassiz “regret to observe that it has almost become an axiom that identical functions presuppose identical organs. There never was a more incorrect principle leading to more injurious consequences.”[43] And elsewhere he argues that organs can exist without functions. But this is obviously to pervert the fundamental idea of an organ. “The teeth of the whale which never eat through the gums, and the breasts of the males of all classes of mammalia,” are cited by him as examples of such organs without functions; but in the physiological significance of the term these are not organs at all. It is no more to be expected that the breasts of the male should act in lactation, than that the slackened string of a violin should yield musical tones; but the breasts of the male may be easily stimulated into yielding milk, and the slackened string of the violin may be tightened so as to yield tone. Even the breasts of the female do not yield milk except under certain conditions, and in the absence of these are on a par with those of the male.

96. Organized substance has the general properties of Assimilation, Evolution, Sensibility, and Contractility; each of the special tissues into which organized substance is differentiated manifests a predominance of one of these properties. Thus although the embryo-cells all manifest contractility, it is only the specialized muscle-cell which continues throughout its existence to manifest this property, and in a dominant form; the muscle-cell also assimilates and develops, but besides having these properties in common with all other cells, it has the special property of contracting with an energy not found in the others. All cells respire; but the blood-cells have this property of absorbing oxygen to a degree so far surpassing that of any other cell that physiologists have been led to speak of their containing a peculiar respiratory substance. In like manner all, or nearly all, the tissues contain myeline—which indeed is one of the chief constituents of the yolk of eggs—but only in the white sheath of the nerves is it detached and specialized as a tissue.

97. But while Sensibility and Contractility are general properties of organized substance, specialized in special tissues; Sensation and Contraction are functions of the organs formed by such tissues; and these organs are only found in animal organisms. It is a serious error, which we shall hereafter have to insist on, to suppose that Sensation can be the property of ganglionic cells, or, as it is more often stated, the property of the central gray matter. Sensation is the function of the organism; it varies with the varying organ; the sensation of Touch not being the same as the sensation of Sight, or of Sound.

98. We may consider the organism under two aspects—that of Structure and that of Function. The latter has two broad divisions corresponding with the vegetal and animal lives; the one is Nutrient, the other Efficient. The one prepares and distributes Food, the other distributes Motion. Of course this separation is analytical. In reality the two are interblended; and although the neuro-muscular system is developed out of the nutritive system, it is no sooner developed than it plays its part as Instrument in the preparation and distribution of Aliment.

This not being a treatise on Physiology, there can be no necessity for our here considering the properties and functions in detail. What is necessary to be said on Sensibility and Contractility will find its place in the course of future chapters; for the present we will confine ourselves to Evolution on account of its psychological, no less than its physiological, interest.

CHAPTER V.
EVOLUTION.

99. That organized substance has the property of nourishing itself by assimilating from its internal medium substances there present in an unorganized state, and that this is followed by a development or differentiation of structure, is familiar to every inquirer.

Every one who has pursued embryological researches, and in a lesser degree every one who has merely read about them, must have been impressed by this marvel of marvels: an exceedingly minute portion of living matter, so simple in aspect that a line will define it, passes by successive modifications into an organism so complex that a treatise is needed to describe it; not only do the cells in which the ovum and the spermatozoon originate, pass into a complex organism, reproducing the forms and features of the parents, and with these the constitutional peculiarities of the parents (their longevity, their diseases, their mental dispositions, nay, their very tricks and habits), but they may reproduce the form and features, the dispositions and diseases, of a grandfather or great-grandfather, which had lain dormant in the father or mother. Consider for an instant what this implies. A microscopic cell of albuminous compounds, wholly without trace of organs, not appreciably distinguishable from millions of other cells, does nevertheless contain within it the “possibilities” of an organism so complex and so special as that of a Newton or a Napoleon. If ever there was a case when the famous Aristotelian notion of a “potential existence” seemed justified, assuredly it is this. And although we can only by a fallacy maintain the oak to be contained in the acorn, or the animal contained in the ovum, the fallacy is so natural, and indeed so difficult of escape, that there is no ground for surprise when physiologists, on first learning something of development, were found maintaining that the perfect organism existed already in the ovum, having all its lineaments in miniature, and only growing into visible dimensions through the successive stages of evolution.[44] The preformation of the organism seemed an inevitable deduction from the opinions once universal. It led to many strange, and some absurd conclusions; among them, to the assertion that the original germ of every species contained within it all the countless individuals which in process of time might issue from it; and this in no metaphysical “potential” guise, but as actual boxed-up existences (emboîtés); so that Adam and Eve were in the most literal sense progenitors of the whole human race, and contained their progeny already shaped within them, awaiting the great accoucheur, time.

100. This was the celebrated “emboîtement” theory. In spite of obvious objections it gained scientific acceptance, because physiologists could not bring themselves to believe that so marvellous a structure as that of a human organism arose by a series of successive modifications, or because they could not comprehend how it was built up, part by part, into forms so closely resembling the parent-forms. That many and plausible reasons pleaded in favor of this opinion is evident in the fact that illustrious men like Haller, Bonnet, Vallisneri, Swammerdamm, Réaumur, and Cuvier, were its advocates; and if there is not a sigle physiologist of our day who accepts it, or who finds any peculiar difficulty in following the demonstrations of embryologists, how from the common starting-point of a self-multiplying epithelial cell parts so diverse as hairs, nails, hoofs, scales, feathers, crystalline lens, and secreting glands may be evolved, or how from the homogeneous germinal membrane the complex organism will arise, there are very few among the scorners of the dead hypothesis who seem capable of generalizing the principles which have destroyed it, or can conceive that the laws of Evolution apply as rigorously to the animal and vegetable kingdoms as to the individual organisms. The illustrious names of those who advocated the preformation hypothesis may serve to check our servile submission to the authorities so loudly proclaimed as advocates of the fixity of species. The more because the two doctrines have a common parentage. The one falls with the other, and no array of authorities can arrest the fall. That the manifold differentiations noticeable in a complex organism should have been evolved from a membrane wholly destitute of differences is a marvel, but a marvel which Science has made intelligible. Yet the majority of those to whom this has been made intelligible still find an impossibility in admitting that the manifold forms of plant and animal were successively evolved from equally simple origins. They relinquish the hypothesis of preformation in the one case, and cling to it in the other. Evolution, demonstrable in the individual history, seems preposterous in the history of the class. And thus is presented the instructive spectacle of philosophers laughing at the absurdities of “preformation,” and yet exerting all their logic and rhetoric in defence of “creative fiats”—which is simply the preformation hypothesis “writ large.”

101. It would not be difficult to show that the doctrine of Epigenesis, with which Wolff forever displaced the doctrine of Preformation, leads by an inevitable logic to the doctrine of universal Evolution; and that we can no more understand the appearance of a new organism which is not the modification of some already existing organism, than we can understand the sudden appearance of a new organ which is not the modification of some existing structure. In the one case as in the other we may disguise the process under such terms as creative fiat and preformation; but these terms are no explanations; they re-state the results, they do not describe the process; whereas Epigenesis describes the process as it passes under the eye of science.

102. If any reader of these pages who, from theological or zoölogical suspicion of the Development Hypothesis, clings to the hypothesis of a creative Plan which once for all arranged the organic world in Types that could not change, will ask what rational interpretation can be given to the succession of phases each embryo is forced to pass through, it may help to give him pause. He will observe that none of these phases have any adaptation to the future state of the animal, but are in positive contradiction to it, or are simply purposeless; whereas all show stamped on them the unmistakable characters of ancestral adaptations and the progressions of Organic Evolution. What does the fact imply? There is not a single known example of a complex organism which is not developed out of simpler forms. Before it can attain the complex structure which distinguishes it, there must be an evolution of forms similar to those which distinguish the structures of organisms lower in the series. On the hypothesis of a Plan which prearranged the organic world, nothing could be more unworthy of a supreme intelligence than this inability to construct an organism at once, without previously making several tentative efforts, undoing to-day what was so carefully done yesterday, and repeating for centuries the same tentatives, and the same corrections, in the same succession. Do not let us blink this consideration. There is a traditional phrase much in vogue among the anthropomorphists, which arose naturally enough from the tendency to take human methods as an explanation of the divine—a phrase which becomes a sort of argument—“The Great Architect.” But if we are to admit the human point of view, a glance at the facts of embryology must produce very uncomfortable reflections. For what should we say to an architect who was unable, or being able was obstinately unwilling, to erect a palace except by first using his materials in the shape of a hut, then pulling it down and rebuilding them as a cottage, then adding story to story and room to room, not with any reference to the ultimate purposes of the palace, but wholly with reference to the way in which houses were constructed in ancient times? What should we say to the architect who could not form a museum out of bricks and mortar, but was forced to begin as if going to build a mansion: and after proceeding some way in this direction, altered his plan into a palace, and that again into a museum? Yet this is the sort of succession on which organisms are constructed. The fact has long been familiar; how has it been reconciled with Infinite Wisdom? Let the following passage answer for a thousand:—“The embryo is nothing like the miniature of the adult. For a long while the body in its entirety and its details presents the strangest of spectacles. Day by day and hour by hour the aspect of the scene changes, and this instability is exhibited by the most essential parts no less than by the accessory parts. One would say that Nature feels her way, and only reaches the goal after many times missing the path,—on dirait que la nature tâtonne et ne conduit son œuvre à bon fin qu’après s’être souvent trompée.”[45] Writers have no compunction in speaking of Nature feeling her way and blundering; but if in lieu of Nature, which may mean anything, the Great Architect be substituted, it is probable that the repugnance to using such language of evasion may cause men to revise their conceptions altogether; they dare not attribute ignorance and incompetence to the Creator.

103. Obviously the architectural hypothesis is incompetent to explain the phenomena of organic development. Evolution is the universal process; not creation of a direct kind. Von Baer, who very properly corrected the exaggerations which had been put forth respecting the identity of the embryonic forms with adult forms lower in the scale, who showed that the mammalian embryo never was a bird, a reptile, or a fish, nevertheless emphasized the fact that the mammalian embryo passes through all the lower typical forms; so much so that, except by their size, it is impossible to distinguish the embryos of mammal, bird, lizard, or snake. “In my collection,” he says, “there are two little embryos which I have omitted to label, so that I am now quite incompetent to say to what class they belong. They may be lizards, they may be small birds, or very young mammals; so complete is the similarity in the mode of formation of the head and trunk. The extremities have not yet made their appearance. But even if they existed in the earliest stage we should learn nothing from them, for the feet of lizards, mammals, and the wings of birds, all arise from the same common form.” He sums up with his formula: “The special type is always evolved from a more general type.”[46]

Such reminiscences of earlier forms are intelligible on the supposition that originally the later form was a modification of the earlier form, and that this modification is repeated; or on the supposition that there was a similarity in the organic conditions, which similarity ceased at the point where the new form emerged. But on no hypothesis of creative Plan are they intelligible. They are useless structures, failing even to subserve a temporary purpose. Sometimes, as Mr. Darwin remarks, a trace of the embryonic resemblance lasts till a late age: “Thus birds of the same genus, and of closely allied genera, often resemble each other in their first and second plumage: as we see in the spotted feathers in the thrush group. In the cat tribe most of the species are striped and spotted in lines; and stripes or spots can plainly be distinguished in the whelp of the lion and the puma. We occasionally, though rarely, see something of this kind in plants.... The points of structure in which the embryos of widely different animals of the same class resemble each other often have no direct relation to their conditions of existence. We cannot, for instance, suppose that in the embryos of the vertebrata the peculiar loop-like courses of the arteries near the bronchial slits are related to similar conditions in the young mammal which is nourished in the womb of its mother, in the egg of a bird which is hatched in a nest, and in the spawn of a frog under water.”

104. It would be easy to multiply examples, but I will content myself with three. The tadpole of the Salamander has gills, and passes his existence in the water; but the Salamandra atra, which lives high up among the mountains, brings forth its young full-formed. This animal never lives in the water. Yet if we open a gravid female, we find tadpoles inside her with exquisitely feathered gills, and (as I have witnessed) these tadpoles “when from the mother’s womb untimely ripped,” if placed in water, swim about like the tadpoles of water newts. Obviously this aquatic organization has no reference to the future life of the animal, nor has it any adaptation to its embryonic condition; it has solely reference to ancestral forms, it repeats a phase in the development of its progenitors. Again, in the embryo of the naked Nudibranch, we always observe a shell, although the animal is without a shell, and there can be no purpose served by the shell in embryonic life.[47] Finally, the human embryo has a tail, which is of course utterly purposeless, and which, although to be explained as a result of organic laws, is on the creative hypothesis only explained as an adherence to the general plan of structure—a specimen of pedantic trifling “worthy of no intellect above the pongo’s.”[48]

105. Humanly appreciated, not only is it difficult to justify the successive stages of development, the incessant building up of structures immediately to be taken down, but also to explain why development was necessary at all. Why are not plants and animals formed at once, as Eve was mythically affirmed to be taken from Adam’s rib, and Minerva from Jupiter’s head? The theory of Evolution answers this question very simply; the theory of Creation can only answer it by affirming that such was the ordained plan. But the theory of Evolution not only gives the simpler and more intelligible answer to this question, it gives an answer to the further question which leaves the theory of Creation no loophole except a sophism—namely, why the formation of organisms is constantly being frustrated or perverted? And, further, it gives an explanation of the law noticed by Milne Edwards, that Nature is as economical in her means as she is prodigal in her variation of them: “On dirait qu’avant de recourir à des ressources nouvelles elle a voulu épuiser, en quelque sorte, chacun des procédés qu’elle avait mis en jeu.”[49] The applause bestowed on Nature for being economical is a curious transference to Nature of human necessities. Why, with a whole universe at her disposal, should Nature be economical? Why must she always be working in the same groove, and using but a few out of the many substances at her command? Economy is a virtue only in the poor. If Nature, in organic evolutions, is restricted to a very few substances, and a very few modes of combination, always creating new forms by modification of the old, and apparently incapable of creating an organism at once, this must imply an inherent necessity which is very unlike the free choice that can render economy a merit.

106. There may indeed be raised an objection to the Development Hypothesis on the ground that if the complex forms were all developed from the simpler forms, we ought to trace the identities through all their stages. If the fish developed into the reptile, the reptile into the bird, and the bird into the mammal (which I, for one, think questionable), we ought to find, it is urged, evidence of this passage. And at one time it was asserted that the evidence existed; but this has been disproved, and on the disproof the opponents of Evolution take their stand. Although I cannot feel much confidence in the idea of such a passage from Type to Type, and although the passage, if ever it occurred, must have occurred at so remote a period as to leave no evidence more positive than inference, I cannot but think the teaching of Embryology far more favorable to it than to our opponents. Supposing, for the sake of argument, that the passage did take place, ought we to find the embryonic stages accurately reproducing the permanent forms of lower types? Von Baer thinks we ought; and lesser men may follow him without reproach. But it seems to me that he starts from an inadmissible assumption, namely, that the development must necessarily be in a straight line rather than in a multiplicity of divergent lines. “When we find the embryonic condition,” he says, “differing from the adult, we ought to find a corresponding condition somewhere in the lower animals.”[50] Not necessarily. We know that the mental development of a civilized man passes through the stages which the race passed through in the course of its long history, and the psychology of the child reproduces the psychology of the savage. But as this development takes place under conditions in many respects different, and as certain phases are hurried over, we do not expect to find a complete parallel. It is enough if we can trace general resemblances. Von Baer adds, “That certain correspondences should occur between the embryonic states of some animals and the adult states of others seems inevitable and of no significance(?). They could not fail, since the embryos lie within the animal sphere, and the variations of which the animal body is capable are determined for each type by the internal connection and mutual reaction of its organs, so that particular repetitions are inevitable.” A profound remark, to which I shall hereafter have occasion to return, but its bearing on the present question is inconclusive. The fact that the embryonic stages of the higher animals resemble in general characters the permanent stages of the lower animals, and very closely resemble the embryonic stages of those animals, is all that the Development Hypothesis requires. Nor is its value lessened by the fact that many of the details and intermediate stages seem passed over in the development of the higher forms, for the recapitulation can only be of outlines, not of details; since there are differences in the forms, there must be differences in their histories.

107. In the preceding observations the object has simply been to show that the phenomena to be explained can be rationally conceived as resulting from gradual Evolution, whereas they cannot be so rationally interpreted on any other hypothesis. And here it may be needful to say a word respecting Epigenesis.

The Preformation hypothesis, which regarded every organism as a simple educt and not the product of a germ, was called by its advocates an evolution hypothesis—meaning that the adult form was an outgrowth of the germ, the miniature magnified. Wolff, who replaced that conception by a truer one, called his, by contrast, Epigenesis, meaning that there was not simply out-growth but new growth. “The various parts,” he says, “arise one after the other, so that always one is secreted from (excernirt), or deposited (deponirt) on the other; and then it is either a free and independent part, or is only fixed to that which gave it existence, or else is contained within it. So that every part is the effect of a pre-existing part, and in turn the cause of a succeeding part.”[51] The last sentence expresses the conception of Epigenesis which embryologists now adopt; and having said this, we may admit that Wolff, in combating the error of preformation, replacing it with the truer notion of gradual and successive formation, was occasionally open to the criticism made by Von Baer, that he missed the true sense of Evolution, since the new parts are not added on to the old parts as new formations, but evolved from them as transformations. “The word Evolution, therefore, seems to me more descriptive of the process than Epigenesis. It is true that the organism is not preformed, but the course of its development is precisely the course which its parents formerly passed through. Thus it is the Invisible—the course of development—which is predetermined.”[52] When the word Epigenesis is used, therefore, the reader will understand it to signify that necessary succession which determines the existence of new forms. Just as the formation of chalk is not the indifferent product of any combination of its elements, carbon, oxygen, and calcium, but is the product of only one series of combinations, an evolution through necessary successions, the carbon uniting with oxygen to form carbonic acid, and this combining with the oxide of calcium to form chalk, so likewise the formation of a muscle, a bone, a limb, or a joint has its successive stages, each of which is necessary, none of which can be transposed. The formation of bone is peculiarly instructive, because the large proportion of inorganic matter in its substance, and seemingly deposited in the organic tissue, would lead one to suppose that it was almost an accidental formation, which might take place anywhere; yet although what is called connective tissue will ossify under certain conditions, true bone is the product of a very peculiar modification, which almost always needs to be preceded by cartilage. That the formation of bone has its special history may be seen in the fact that it is the last to appear in the animal series, many highly organized fishes being without it, and all the other systems appearing before it in the development of the embryo. Thus although the mother’s blood furnishes all the requisite material, the fœtus is incapable of assimilating this material and of forming bone, until its own development has reached a certain stage. Moreover, when ossification does begin, it generally begins in the skull (in man in the clavicle); and the only approach to an internal skeleton in the Invertebrates is the so-called skull of the Cephalopoda. Not only is bone a late development, but cartilage is also; and although it is an error to maintain that the Invertebrates are wholly destitute of cartilage, its occasional presence having been fully proved by Claparède and Gegenbaur, the rarity of its presence is very significant. The animals which can form shells of chalk and chitine are yet incapable of forming even an approach to bone.

108. Epigenesis depends on the laws of succession, which may be likened to the laws of crystallization, if we bear in mind the essential differences between a crystal and an organism, the latter retaining its individuality through an incessant molecular change, the former only by the exclusion of all change. When a crystalline solution takes shape, it will always take a definite shape, which represents what may be called the direction of its forces, the polarity of its constituent molecules. In like manner, when an organic plasmode takes shape—crystallizes, so to speak—it always assumes a specific shape dependent on the polarity of its molecules. Crystallographers have determined the several forms possible to crystals; histologists have recorded the several forms of Organites, Tissues, and Organs. Owing to the greater variety in elementary composition, there is in organic substance a more various polar distribution than in crystals; nevertheless, there are sharply defined limits never overstepped, and these constitute what may be called the specific forms of Organites, Tissues, Organs, Organisms. An epithelial cell, for example, may be ciliated or columnar, a muscle-fibre striated or non-striated, a nerve-fibre naked or enveloped in a sheath, but the kind is always sharply defined. An intestinal tube may be a uniform canal, or a canal differentiated into several unlike compartments, with several unlike glandular appendages. A spinal column may be a uniform solid axis, or a highly diversified segmented axis. A limb may be an arm, or a leg, a wing, or a paddle. In every case the anatomist recognizes a specific type. He assigns the uniformities to the uniformity of the substance thus variously shaped, under a history which has been similar; the diversities he assigns to the various conditions under which the processes of growth have been determined. He never expects a muscular tissue to develop into a skeleton, a nervous tissue into a gland, an osseous tissue into a sensory organ. He never expects a tail to become a hand or a foot, though he sees it in monkeys and marsupials serving the offices of prehension and locomotion. He never expects to find fingers growing anywhere except from metacarpal bones, or an arm developed from a skull. The well-known generalization of Geoffroy St. Hilaire that an organ is more easily annihilated than transposed, points to the fundamental law of Epigenesis. In the same direction point all the facts of growth. Out of a formless germinal membrane we see an immense variety of forms evolved; and out of a common nutritive fluid this variety of organs is sustained, repaired, replaced; and this not indifferently, not casually, but according to rigorous laws of succession; that which precedes determining that which succeeds as inevitably as youth precedes maturity, and maturity decay. The nourishment of various organs from plasmodes derived from a common fluid, each selecting from that fluid only those molecules that are like its own, rejecting all the rest, is very similar to the formation of various crystals in a solution of different salts, each salt separating from the solution only those molecules that are like itself. Reil long ago called attention to this analogy. He observed that if in a solution of nitre and sulphate of soda a crystal of nitre be dropped, all the dissolved nitre crystallizes, the sulphate remaining in solution; whereas on reversing the experiment, a crystal of sulphate of soda is found to crystallize all the dissolved sulphate, leaving the nitre undisturbed. In like manner muscle selects from the blood its own materials which are there in solution, rejecting those which the nerve will select.

109. Nay, so definite is the course of growth, that when a limb or part of a limb is cut off from a crab or salamander, a new limb or new part is reproduced in the old spot, exactly like the one removed. Bonnet startled the world by the announcement that the Naïs, a worm common in ponds, spontaneously divided itself into two worms; and that when he cut it into several pieces, each piece reproduced head and tail, and grew into a perfect worm. This had been accepted by all naturalists without demur, until Dr. Williams, in his “Report on British Annelida, 1851,” declared it to be a fable. In 1858, under the impulse of Dr. Williams’s very emphatic denial, I repeated experiments similar to those of Bonnet, with similar results. I cut two worms in half, and threw away the head-bearing segments, placing the others in two separate vessels, with nothing but water and a little mud, which was first carefully inspected to see that no worm lay concealed therein. In a few days the heads were completely reformed, and I had the pleasure of watching them during their reconstruction. When the worms were quite perfect, I again cut away their heads, and again saw these reformed. This was repeated, till I had seen four heads reproduced; after which the worms succumbed.

110. The question naturally arises, Why does the nutritive fluid furnish only material which is formed into a part like the old one, instead of reproducing another part, or one having a somewhat different structure? The answer to this question is the key to the chief problem of organic life. That a limb in situ should replace its molecular waste by molecules derived from the blood, seems intelligible enough (because we are familiar with it), and may be likened to the formation of crystals in a solution; but how is it that the limb which is not in existence can assimilate materials from the blood? How is it that the blood, which elsewhere in the organism will form other parts, here will only form this particular part? There is, probably, no one who has turned his attention to these subjects who has not paused to consider this mystery. The most accredited answer at present before the world is one so metaphysiological that I should pass it by, were it not intimately allied with that conception of Species, which it is the object of these pages to root out. It is this:

111. The organism is determined by its Type, or, as the Germans say, its Idea. All its parts take shape according to this ruling plan; consequently, when any part is removed, it is reproduced according to the Idea of the whole of which it forms a part. Milne Edwards, in a very interesting and suggestive work, concludes his survey of organic phenomena in these words: “Dans l’organisme tout semble calculé en vue d’un résultat déterminé, et l’harmonie des parties ne résulte pas de l’influence qu’elles peuvent exercer les unes sur les autres, mais de leur co-ordination sous l’empire d’une puissance commune, d’un plan préconçu, d’une force pré-existante.”[53] This is eminently metaphysiological. It refuses to acknowledge the operation of immanent properties, refuses to admit that the harmony of a complex structure results from the mutual relations of its parts, and seeks outside the organism for some mysterious force, some plan, not otherwise specified, which regulates and shapes the parts. Von Baer, in his great work, has a section entitled, “The nature of the animal determines its development”; and he thus explains himself: “Although every stage in development is only made possible by the pre-existing condition [which is another mode of expressing Epigenesis], nevertheless the entire development is ruled and guided by the Nature of the animal which is about to be (von der gesammten Wesenheit des Thieres welches werden soll), and it is not the momentary condition which alone and absolutely determines the future, but more general and higher relations.”[54] One must always be slow in rejecting the thoughts of a master, and feel sure that one sees the source of the error before regarding it as an error; but in the present case I think the positive biologist will be at no loss to assign Von Baer’s error to its metaphysical origin. Without pausing here to accumulate examples both of anomalies and slighter deviations which are demonstrably due to the “momentary conditions” that preceded them, let us simply note the logical inconsistency of a position which, while assuming that every separate stage in development is the necessary sequence of its predecessor, declares the whole of the stages independent of such relations! Such a position is indeed reconcilable on the assumption that animal forms are moulded “like clay in the hands of the potter.” But this is a theological dogma, which leads to very preposterous and impious conclusions; and whether it leads to these conclusions or to others, positive Biology declines theological explanations altogether. Von Baer, although he held the doctrine of Epigenesis, coupled it, as many others have done, with metaphysical doctrines to which it is radically opposed. He believed in Types as realities; he was therefore consistent in saying, “It is not the Matter and its arrangements which determine the product, but the nature of the parent form—the Idea, according to the new school.” How are we to understand this Idea? If it mean an independent Entity, an agency external to the organism, we refuse to acknowledge its existence. If it mean only an a posteriori abstraction expressing the totality of the conditions, then, indeed, we acknowledge that it determines the animal form; but this is only an abbreviated way of expressing the law of Evolution, by which each stage determines its successor. The Type does not dominate the conditions, it emerges from them; the animal organism is not cast in a mould, but the imaginary mould is the form which the polarities of the organic substance assume. It would seem very absurd to suppose that crystals assumed their definite shapes (when the liquid which held their molecules in solution is evaporated) under the determining impulse of phantom-crystals, or Ideas; yet it has not been thought absurd to assume phantom forms of organisms.

112. The conception of Type as a determining influence arises from that fallacy of taking a resultant for a principle, which has played so conspicuous a part in the history of philosophy. Like many others of its class it exhibits an interesting evolution from the crude metaphysical to the subtle metaphysical point of view, which at last insensibly blends into the positive point of view. At first the Type or Idea was regarded as an objective reality, external to the organism it was supposed to rule. Then this notion was replaced by an approach to the more rational interpretation, the idea was made an internal not an external force, and was incorporated with the material elements of the organism, which were said to “endeavor” to arrange themselves according to the Type. Thus Treviranus declares that the seed “dreams of the future flower”; and “Henle, when he affirms that hair and nails grow in virtue of the Idea, is forced to add that the parts endeavor to arrange themselves according to this Idea.”[55] Even Lotze, who has argued so victoriously against the vitalists, and has made it clear that an organism is a vital mechanism, cannot relinquish this conception of legislative Ideas, though he significantly adds, “these have no power in themselves, but only in as far as they are grounded in mechanical conditions.” Why then superfluously add them to the conditions? If every part of a watch, in virtue of the properties inherent in its substance, and of the mutual reactions of these and other parts, has a mechanical value, and if the sum of all these parts is the time-indicating mechanism, do we add to our knowledge of the watch, and our means of repairing or improving it, by assuming that the parts have over and above their physical properties the metaphysical “tendency” or “desire” to arrange themselves into this specific form? When we see that an organism is constructed of various parts, each of which has its own properties inalienable from its structure, and its uses dependent on its relation to other parts, do we gain any larger insight by crediting these parts with desires or “dreams” of a future result which their union will effect? That which is true in this conception of legislative Ideas is that when the parts come together there is mutual reaction, and the resultant of the whole is something very unlike the mere addition of the items, just as water is very unlike oxygen or hydrogen; further, the connexus of the whole impresses a peculiar direction on the development of the parts, and the law of Epigenesis necessitates a serial development, which may easily be interpreted as due to a preordained plan.

113. In a word, this conception of Type only adds a new name to the old difficulty, adding mist to darkness. The law of Epigenesis, which is simply the expression of the material process determined by the polarity of molecules, explains as much of the phenomena as is explicable. A lost limb is replaced by the very processes, and through the same progressive stages as those which originally produced it. We have a demonstration of its not being reformed according to any Idea or Type which exists apart from the immanent properties of the organic molecules, in the fact that it is not reformed at once, but by gradual evolution; the mass of cells at the stump are cells of embryonic character, cells such as those which originally “crystallized” into muscles, nerves, vessels, and integument, and each cell passes through all its ordinary stages of development. It is to be remembered that so intimately dependent is the result on the determining conditions, that any external influence which disturbs the normal course of development will either produce an anomaly, or frustrate the formation of a new limb altogether. One of my tritons bit off the leg of his female;[56] the leg which replaced it was much malformed, and curled over the back so as to be useless; was this according to the Idea? I cut it off, and examined it; all the bones were present, but the humerus was twisted, and of small size. In a few weeks a new leg was developed, and this leg was normal. If the Idea, as a ruling power, determined the growth of this third leg, what determined the second, which was malformed? Are we to suppose that in normal growth the Idea prevails, in abnormal the conditions? That it is the polarity of the molecules which at each moment determines the group those molecules will assume, is well seen in the experiment of Lavalle mentioned by Bronn.[57] He showed that if when an octohedral crystal is forming, an angle be cut away, so as to produce an artificial surface, a similar surface is produced spontaneously on the corresponding angle, whereas all the other angles are sharply defined. “Valentin,” says Mr. Darwin, “injured the caudal extremity of an embryo, and three days afterwards it produced rudiments of a double pelvis, and of double hind limbs. Hunter and others have observed lizards with their tails reproduced and doubled. When Bonnet divided longitudinally the foot of the salamander, several additional digits were occasionally formed.”[58] Where is the evidence of the Idea in these cases?

114. I repeat, the reproduction of lost limbs is due to a process which is in all essential respects the same as that which originally produced them; the genesis of one group of cells is the necessary condition for the genesis of its successor, nor can this order be transposed. But—and the point is very important—it is not every part that can be reproduced, nor is it every animal that has reproductive powers. The worm, or the mollusk, seems capable of reproducing every part; the crab will reproduce its claws, but not its head or tail; the perfect insect of the higher orders will reproduce no part (indeed the amputation of its antennae only is fatal), the salamander will reproduce its leg, the frog not. In human beings a muscle is said never to be reproduced; but this is not the case in the rare examples of supplementary fingers and toes, which have been known to grow again after amputation. The explanation of this difference in the reproductive powers of different animals is usually assigned to the degree in which their organisms retain the embryonic condition; and this explanation is made plausible by the fact that the animals which when adult have no power of replacing lost limbs, have the power when in the larval state. But although this may in some cases be the true explanation, there are many in which it fails, as will be acknowledged after a survey of the extremely various organisms at widely different parts of the animal series which possess the reproductive power. Even animals in the same class, and at the same stage of development, differ in this respect. I do not attach much importance to the fact that all my experiments on marine annelids failed to furnish evidence of their power of reproducing lost segments; because it is difficult to keep them under conditions similar to those in which they live. But it is significant that, among the hundreds which have passed under my observation, not one should have been found with a head-segment in the process of development, replacing one that had been destroyed; and this is all the more remarkable from the great tenacity of life which the mutilated segments manifest. Quatrefages had observed portions of a worm, after gangrene had destroyed its head and several segments, move about in the water and avoid the light![59]

115. A final argument to show that the reproduction is not determined by any ruling Idea, but by the organic conditions and the necessary stages of evolution, is seen in the reappearance of a tumor or cancer after it has been removed. We find the new tissue appear with all the characters of the normal tissue of the gland, then rapidly assume one by one the characters of the diseased tissue which had been removed; and there as on is, that the regeneration of the tissue is accompanied by the same abnormal conditions which formerly gave rise to the tumor: the directions of “crystallization” are similar because the conditions are similar. In every case of growth or regrowth the conditions being the same, the result must be the same.

116. It seems a truism to insist that similarity in the results must be due to similarity in the conditions; yet it is one which many theorists disregard; and especially do we need to bear it in mind when arguing about Species. I will here only touch on the suggestive topic of the analogies observed not simply among animals at the extreme ends of the scale, but also between animals and plants where the idea of a direct kinship is out of the question.

My very imperfect zoölogical knowledge will not allow me to adduce a long array of instances, but such an array will assuredly occur to every well-stored mind. It is enough to point to the many analogies of Function, more especially in the reproductive processes—to the existence of burrowers, waders, flyers, swimmers in various classes—to the existence of predatory mammals, predatory birds, predatory reptiles, predatory insects by the side of herbivorous congeners,—to the nest-building and incubating fishes; and in the matter of Structure the analogies are even more illustrative when we consider the widely diffused spicula, setæ, spines, hooks, tentacles, beaks, feathery forms, nettling-organs, poison-sacs, luminous organs, etc.; because these have the obvious impress of being due to a community of substance under similar conditions rather than to a community of kinship. The beak of the tadpole, the cephalopod, the male salmon, and the bird, are no doubt in many respects unlike; but there is a significant likeness among them, which constitutes a true analogy. I think there is such an analogy between the air-bladder of fishes and the tracheal rudiment which is found in the gnat-larva (Corethra plumicornis).[60] Very remarkable also is the resemblance of the avicularium, or “bird’s-head process,” on the polyzoon known popularly as the Corkscrew Coralline (Bugula avicularia), which presents us in miniature with a vulture’s head—two mandibles, one fixed, the other moved by muscles visible within the head. No one can watch this organ snapping incessantly, without being reminded of a vulture, yet no one would suppose for a moment that the resemblance has anything to do with kinship.

117. Such cases are commonly robbed of their due significance by being dismissed as coincidences. But what determines the coincidence? If we assume, as we are justified in assuming, that the possible directions of Organic Combination, and the resultant forms, are limited, there must inevitably occur such coincident lines: the hooks on a Climbing Plant will resemble the hooks on a Crustacean or the claws of a Bird, as the one form in which under similar external forces the more solid but not massive portions of the integument tend to develop. I am too ill acquainted with the anatomy of plants to say how the hooks so common among them arise; but from examination of the Blackberry, and comparison of its thorns with the hooks and spines of the Crustacea, I am led to infer that in each case the mode of development is identical—namely, the secretion of chitine from the cellular matrix of the integument.

Another mode of evading the real significance of such resemblances is to call them analogies, not homologies. There is an advantage in having two such terms, but we ought to be very clear as to their meaning and their point of separation. Analogy is used to designate similarity in Function with dissimilarity in Structure. The wing of an insect, the wing of a bird, and the wing of a bat are called analogous, but not homologous, because their anatomical structure is different: they are not constructed out of similar anatomical parts. The fore-leg of a mammal, the wing of a bird, or the paddle of a whale, are called homologous, because in spite of their diverse uses they are constructed out of corresponding anatomical parts. To the anatomist such distinctions are eminently serviceable. But they have led to some misconceptions, because they are connected with a profound misconception of the relation between Function and Organ. Embryology teaches that the wing of the bird and the paddle of the whale are developed out of corresponding parts, and that these are not like the parts from which the wing of an insect or the flying-fish will be developed; nevertheless, the most cursory inspection reveals that the wing of a bird and the paddle of a whale are very unlike in structure no less than in function, and that their diversities in function correspond with their diversities in structure; whereas the wing of the insect, of the bird, and of the bat, are in certain characters very similar, and correspondingly there are similarities in their function. It is, however, obvious that the resemblance in function is strictly limited to the resemblance in anatomical structure; only in loose ordinary speech can the flight of an insect, a bird, or a bat be said to be “the same”: it is different in each—the weight to be moved, the rapidity of the movement, the precision of the movements, and their endurance, all differ.

NATURAL SELECTION AND ORGANIC AFFINITY.

118. It is impossible to treat of Evolution without taking notice of that luminous hypothesis by which Mr. Darwin has revolutionized Zoölogy. There are two points needful to be clearly apprehended before the question is entered upon. The first point relates to the lax use of the phrase “conditions,” sometimes more instructively replaced by “conditions of existence.” Inasmuch as Life is only possible under definite relations of the organism and its medium, the “conditions of existence” will be those physical, chemical, and physiological changes, which in the organism, and out of it, co-operate to produce the result. There are myriads of changes in the external medium which have no corresponding changes in the organism, not being in any direct relation to it (see § [54]). These, not being co-operant conditions, must be left out of the account; they are not conditions of existence for the organism, and therefore the organism does not vary with their variations. On the other hand, what seem very slight changes in the medium are often responded to by important changes in the vital chemistry, and consequently in the structure of the organism. Now the nature of the organism at the time being, that is to say, its structure and the physico-chemical state of its tissues and plasmodes, is the main condition of this response; the same external agent will be powerful, or powerless, over slightly different organisms, or over the same organism at different times. Usually, and for convenience, when biologists speak of conditions, they only refer to external changes. This usage has been the source of no little confusion in discussing the Development Hypothesis. Mr. Darwin, however, while following the established usage, is careful in several places to declare that of the two factors in Variation—the nature of the organism and the nature of the conditions—the former is by far the more important.

118a. A still greater modification of terms must now be made. Instead of confining the “struggle for existence” to the competition of rivals and the antagonism of foes, we must extend it to the competition and antagonism of tissues and organs. The existence of an organism is not only dependent on the external existence of others, and is the outcome of a struggle; but also on the internal conditions which co-operate in the formation of its structure, this structure being the outcome of a struggle. The organism is this particular organism, differing from others, because of the particular conditions which have co-operated. The primary and fundamental struggle must be that of the organic forces at work in creating a structure capable of pushing its way amid external forces. The organism must find a footing in the world, before it can compete with rivals, and defend itself against foes. Owing to the power of reproduction, every organism has a potential indefiniteness of multiplication; that potential indefiniteness is, however, in reality restricted by the supply of food, and by the competition of rivals for that supply. The multiplication of any one species is thus kept down by the presence of rivals and foes: a balance is reached, which permits of the restricted quantities of various species. This balance is the result of a struggle.

Now let me call attention to a similar process in the formation of the organism itself. Every organite, and every tissue, has a potential growth of indefinite extent, but its real growth is rigorously limited by the competition and antagonism of the others, each of which has its potential indefiniteness, and its real limits. Something, in the food assimilated, slightly alters the part which assimilates it. This change may be the origin of other changes in the part itself, or in neighboring parts, stimulating or arresting the vital processes. A modification of structure results. Or there may be no new substance assimilated, but external forces may call a part into increased activity—which means increased waste and repair; and this increase here is the cause of a corresponding decrease somewhere else. Whatever the nature of the change, it finds its place amid a complex of changes, and its results are compounded with theirs. When organites and tissues are said to have a potential indefiniteness of growth, there is assumed a potential indefiniteness in the pabulum supplied: if the pabulum were supplied, and if there were no antagonism thwarting its assimilation, growth would of course continue without pause, or end; but in reality this cannot be so. For, take the blood as the vehicle of the pabulum—not only is its quantity limited, and partly limited by the very action of the tissues it feeds, but even in any given quantity there is a limit to its composition—it will only take up a limited quantity of salts, iron, albumen, etc.; no matter how abundant these may be in the food. So again with the plasmodes of the various tissues—they have each their definite capacities of assimilation. What has already been stated respecting chemical affinity (§ [20]) is equally applicable to organic affinity; as the presence of fused iron in the crucible partially obstructs the combination of sulphur and lead, so the presence of connective tissue partially obstructs the combination of muscle protoplasm with its pabulum.

118 b. Owing to the action and reaction of blood and plasmode, of tissues on tissues, and organs on organs, and their mutual limitations, the growth of each organism has a limit, and the growth of each organ has a limit. Beyond this limit, no extra supply of food will increase the size of the organism; no increase of activity will increase the organ. “Man cannot add a cubit to his stature.” The blacksmith’s arm will not grow larger by twenty years of daily exercise, after it has once attained a certain size. Increase of activity caused it to enlarge up to this limit; but no increase of activity will cause it to pass this limit. Why? Because here a balance of the co-operating formative forces has been reached. Larger muscles, or more muscle-fibres, demand arteries of larger calibre, and these a heart of larger size; with the increase of muscle would come increase of connective tissue; and this tissue would not only compete with the muscle for pabulum, but by mechanical pressure would diminish the flow of that pabulum. And why would connective tissue increase? Because, in the first place, there is a formative association between the two, so that owing to a law, not yet understood, the one always accompanies the other; and, in the second place, there is a functional association between the two, a muscle-fibre being inoperative unless it be attached to a tendon, or connective tissue; it will contract out of the body although separated from its tendon or other attachment; but in the body its contraction would be useless without this attachment. We must bear in mind that muscle-fibres are very much shorter than ordinary muscles; according to the measurements of W. Krause they never exceed 4 cm in length, and usually range between 2 and 3 cm; their fine points being fixed to the interstitial connective tissue, as the whole muscle is fixed to its tendon. The function of the muscle is thus dependent on a due balance of its component tissues; if that balance is disturbed the function is disturbed. Should, from any cause, an excess of muscle-fibre arise, the balance would be disturbed; should an encroachment of connective tissue, or of fat, take place, there would be also a defect of function.

Here we have the co-operation and limitation of the tissues illustrated; let us extend our glance, and we shall see how the co-operation and limitation of the organs come into play, so that the resulting function depends on the balance of their forces. The contractile power of each individual muscle is always limited by the resistance of antagonists, which prevent the muscle being contracted more than about a third of its possible extent, i. e. possible when there are no resistances to be overcome. Not only the increasing tension of antagonist muscles, but the resistance of tendons, bones, and softer parts must be taken into account. Thus, the increase of the blacksmith’s muscular power would involve a considerable increase in all the tissues of the arm; but such an increase would involve a reconstruction of his whole organism.

Whenever there is an encroachment of one tissue on another, there is a disturbance of the normal balance, which readily passes into a pathological state. If the brain is overrun with connective tissue, or the heart with fatty tissue, we know the consequences. If connective tissue is deficient, epithelial runs to excess, no longer limited by its normal antagonist, and pus, or cancer, result.

118c. It is unnecessary here to enlarge on this point. I have adduced it to show that we must extend our conception of the struggle for existence beyond that of the competition and antagonism of organisms—the external struggle; and include under it the competition and antagonism of tissues and organs—the internal struggle. Variability is inherent in organic substances, as the result of their indefiniteness of composition (§ [45b]). This variability is indefinite, and is rendered definite by the competition and antagonism, so that every particular variation is the resultant of a composition of forces. The forces in operation are the internal and external conditions of existence—i. e. the nature of the organism, and its response to the actions of its medium. A change may take place in the medium without a corresponding response from the organism; or the change may find a response and the organism become modified. Every modification is a selection, determined by laws of growth; it is the resultant of a struggle between what, for want of a better term, may be called the organic affinities—which represent in organized substances what chemical affinities are in the anorganized. Just as an organism which has been modified and thereby gained a superiority over others, has by this modification been selected for survival—the selection being only another aspect of this modification—so one tissue, or one organ, which has surpassed another in the struggle of growth, will thereby have become selected. Natural Selection, or survival of the fittest, therefore, is simply the metaphorical expression of the fact that any balance of the forces which is best adapted for survival will survive. Unless we interpret it as a shorthand expression of all the internal and external conditions of existence, it is not acceptable as the origin of species.

118d. Mr. Darwin has so patiently and profoundly meditated on the whole subject, that we must be very slow in presuming him to have overlooked any important point. I know that he has not altogether overlooked this which we are now considering; but he is so preoccupied with the tracing out of his splendid discovery in all its bearings, that he has thrown the emphasis mainly on the external struggle, neglecting the internal struggle; and has thus in many passages employed language which implies a radical distinction where—as I conceive—no such distinction can be recognized. “Natural Selection,” he says, “depends on the survival under various and complex circumstances of the best-fitted individuals, but has no relation whatever to the primary cause of any modification of structure.”[61] On this we may remark, first, that selection does not depend on the survival, but is that survival; secondly, that the best-fitted individual survives because of that modification of its structure which has given it the superiority; therefore if the primary cause of this modification is not due to selection, then selection cannot be the cause of species. He separates Natural Selection from all the primary causes of variation, either internal or external—either as results of the laws of growth, of the correlations of variation, of use and disuse, etc., and limits it to the slow accumulations of such variations as are profitable in the struggle with competitors. And for his purpose this separation is necessary. But biological philosophy must, I think, regard the distinction as artificial, referring only to one of the great factors in the production of species. And for this reason: Selection only comes into existence in the modifications produced either by external or internal changes; and the selected change cannot be developed further by mere inheritance, unless the successive progeny have such a disposition of the organic affinities as will repeat the primary change. Inherited superiority will not by mere transmission become greater. The facts which are relied on in support of the idea of “fixity of species” show at any rate that a given superiority will remain stationary for thousands of years; and no one supposes that the progeny of an organism will vary unless some external or internal cause of variation accompanies the inheritance. Mr. Darwin agrees with Mr. Spencer in admitting the difficulty of distinguishing between the effects of some definite action of external conditions, and the accumulation through natural selection of inherited variations serviceable to the organism. But even in cases where the distinction could be clearly established, I think we should only see an historical distinction, that is to say, one between effects produced by particular causes now in operation, and effects produced by very complex and obscure causes in operation during ancestral development.

118e. The reader will understand that my criticism does not pretend to invalidate Mr. Darwin’s discovery, but rather to enlarge its terms, so as to make it include all the biological conditions, and thus explain many of the variations which Natural Selection—in the restricted acceptation—leaves out of account. Mr. Darwin draws a broad line of distinction between Variation and Selection, regarding only those variations that are favorable as selected. I conceive that all variations which survive are by that fact of survival, selections, whether favorable or indifferent. A variety is a species in formation; now Selection itself is not a cause, or condition, of variation, it is the expression of variation. Mr. Darwin is at times explicit enough on this head: “It may metaphorically be said that Natural Selection is daily and hourly scrutinizing throughout the world the slightest variations; rejecting those that are bad, preserving and adding up all that are good; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life.”[62] But the metaphorical nature of the term is not always borne in mind, so that elsewhere Natural Selection is said to “act on and modify organic beings,” as if it were a positive condition and not the expression of the modifying processes. Because grouse are largely destroyed by birds of prey, any change in their color which would render them less conspicuous would enable more birds to escape; but it is obvious that this change of color will be due to Organic Affinity; and only when the change is effected will there have been that selection which expresses it. Mr. Darwin’s language, however, is misleading. He says: “Hence Natural Selection might be most effective in giving the proper color to each kind of grouse, and in keeping that color when once acquired.” This is to make Selection an agent, a condition of the development of color; which may be accepted if we extend the term so as to include the organic changes themselves. Again: “Some writers have imagined that Natural Selection induces variability, whereas it only implies the preservation of such variations as are beneficial to the being under its conditions of life.” It, however, is made to imply more than this, namely, the accumulation and further modification of such variations. “The mere existence of individual variability and of some well-marked varieties, though necessary as the foundation, helps us but little in understanding how species arise in nature. How have all those exquisite adaptations of one part of the organization to another part, and to the conditions of life, and of one organic being to another being, been perfected?” My answer to this question would be: By Organic Affinity, and the resulting struggle of the tissues and organs, the consequences of which are that very adaptation of the organism to external conditions, which is expressed as the selection of the structures best adapted. The selections are the results of the struggle, according to my proposed extension of the term “struggle.” Mr. Darwin defines the struggle: “The dependence of one being on another, and including (what is more important) not only the life of the individual but success in leaving progeny.” This definition seems defective, since it omits the primary and more important struggle which takes place between the organic affinities in operation. To succeed in the struggle with competitors, the organism must have first acquired—by selection—a superiority in one or more of its organs.

118f. A little reflection will disclose the importance of keeping our eyes fixed on the internal causes of variation, as well as on the external conditions of the struggle. Mr. Darwin seems to imply that the external conditions which cause a variation are to be distinguished from the conditions which accumulate and perfect such variation, that is to say, he implies a radical difference between the process of variation and the process of selection. This, I have already said, does not seem to me acceptable; the selection, I conceive, to be simply the variation which has survived.[63]

If it be true that a Variety is an incipient Species and shows us Species in formation, it is in the same sense true that a variation is an incipient organ. A species is the result of a slowly accumulating divergence of structure; an organ is the result of a slowly accumulating differentiation. At each stage of differentiation there has been a selection, but we cannot by any means say that this selection was determined by the fact of its giving the organism a superiority over rivals, inasmuch as during all the early stages, while the organ was still in formation, there could be no advantage accruing from it. One animal having teeth and claws developed will have a decided superiority in the struggle over another animal that has no teeth and claws; but so long as the teeth and claws are in an undeveloped state of mere preparation they confer no superiority.

118g. Natural Selection is only the expression of the results of obscure physiological processes; and for a satisfactory theory of such results we must understand the nature of the processes. In other words, to understand Natural Selection we must recognize not only the facts thus expressed, but the factors of these facts,—we must analyze the “conditions of existence.” As a preliminary analysis we find external conditions, among which are included not only the dependence of the organism on the inorganic medium, but also the dependence of one organism on another,—the competition and antagonism of the whole organic world; and internal conditions, among which are included not only the dependence of the organism on the laws of composition and decomposition whereby each organite and each tissue is formed, but also the dependence of one organite and one tissue on all the others—the competition and antagonism of all the elements.

The changes wrought in an organism by these two kinds of conditions determine Varieties and Species. Although many of the changes are due to the process of natural selection brought about in the struggle with competitors and foes, many other changes have no such relation to the external struggle, but are simply the results of the organic affinities. They may or they may not give the organism a greater stability, or a greater advantage over rivals; it is enough that they are no disadvantage to the organism, they will then survive by virtue of the forces which produced them.

119. The position thus reached will be important in our examination of the Theory of Descent by which Mr. Darwin tentatively, and his followers boldly, explain the observed resemblances in structure and function as due to blood-relationship. The doctrine of Evolution affirms that all complex organisms are evolved by differentiation from simpler organisms, as we see the complex organ evolved from simpler forms. But it does not necessarily affirm that the vast variety of organisms had one starting-point—one ancestor; on the contrary, I conceive that the principles of Evolution are adverse to such a view, and insist rather on the necessity of innumerable starting-points. Let us consider the question.

That the Theory of Descent explains many of the facts must be admitted; but there are many which it leaves obscure; and Mr. Darwin, with that noble calmness which distinguishes him, admits the numerous difficulties. Whether these will hereafter be cleared away by an improvement in the Geological Record, now confessedly imperfect, or by more exhaustive exploration of distant countries, none can say; but, to my mind, the probability is, that we shall have to seek our explanation by enlarging the idea of Natural Selection, subordinating it to the laws of Organic Affinity. It does not seem to me, at present, warrantable to assume Descent as the sole principle of morphological uniformities; there are other grounds of resemblance beyond those of blood-relationship; and these have been too much overlooked; yet a brief consideration will disclose that similarity in the physiological laws and the conditions of Organic Affinity must produce similarity in organisms, independently of relationship; just as similarity in the laws and conditions of inorganic affinity will produce identity in chemical species. We do not suppose the carbonates and phosphates found in various parts of the globe, or the families of alkaloids and salts, to have any nearer kinship than that which consists in the similarity of their elements and the conditions of their combination. Hence, in organisms, as in salts, morphological identity may be due to a community of conditions, rather than community of descent. Mr. Darwin justly holds it to be “incredible that individuals identically the same should have been produced through Natural Selection from parents specifically distinct,” but he, since he admits analogous variations, will not deny that identical forms might issue from parents having widely different origins, provided that these parent forms and the conditions of their reproduction were identical, as in the case of vegetable and animal resemblances. To deny this would be to deny the law of causation. And that which is true of identical forms under identical conditions is true of similar forms under similar conditions. When History and Ethnology reveal a striking uniformity in the progression of social phases, we do not thence conclude that the nations are directly related, or that the social forms have a common parentage; we conclude that the social phases are alike because they have had common causes. When chemists point out the uniformity of type which exists in compounds so diverse in many of their properties as water and sulphuretted or selenetted hydrogen, and when they declare phosphoretted hydrogen to be the congener of ammonia, they do not mean that the one is descended from the other, or that any closer link connects them than that of resemblance in their elements.

In the case of vegetal and animal organisms, we observe such a community of elementary substance as of itself to imply a community in their laws of combination; and under similar conditions the evolved forms must be similar. With this community of elementary substance, there are also diversities of substance and of co-operant conditions; corresponding with these diversities there must be differences of form. Thus, although observation reveals that the bond of kinship does really unite many widely divergent forms, and the principle of Descent with Natural Selection will account for many of the resemblances and differences, there is at present no warrant for assuming that all resemblances and differences are due to this one cause, but, on the contrary, we are justified in assuming a deeper principle which may be thus formulated: All the complex organisms are evolved from organisms less complex, as these were evolved from simpler forms; the link which unites all organisms is not always the common bond of heritage, but the uniformity of organized substance acting under similar conditions.

It is therefore consistent with the hypothesis of Evolution to admit a variety of origins or starting-points, though not consistent to admit the sudden appearance of complex Types, such as is implied in the hypothesis of specific creations.

119 a. The analogies of organic forms and functions demand a more exhaustive scrutiny than has yet been given them. Why is it that vessels, nerves, and bones ramify like branches, and why do these branches take on the aspect of many crystalline forms? Why is it that cavities are constantly prolonged in ducts, e. g. the mouth succeeded by the œsophagus, the stomach by the intestines, the bladder by the urethra, the heart by the aorta, the ovary by the oviduct, and so on? Why are there never more than four limbs attached to a vertebral column, and these always attached to particular vertebræ? Why is there a tendency in certain tissues to form tubes, and in these tubes commonly to assume a muscular coat?[64] To some of these queries an answer might be suggested which would bring them under known physical laws. I merely notice them here for the sake of emphasizing the fact that such analogies lie deeply imbedded in the laws of evolution, and that what has been metaphorically called organic crystallization will account for many similarities in form, without forcing us to have recourse to kinship. To take a very simple case. No one will maintain that the crystalline forms of snow have any kinship with the plants which they often resemble. Mr. Spencer has noticed the development of a wing-bearing branch from a wing of the Ptilota plumosa, when its nutrition is in excess. “This form, so strikingly like that of the feathery crystallizations of many inorganic substances, proves to us that in such crystallizations the simplicity or complexity of structure at any place depends on the quantity of matter that has to be polarized at that place in a given time. How the element of time modifies the result, is shown by the familiar fact that crystals rapidly formed are small, and that they become larger when they are formed more slowly.”[65]

It may be objected, and justly, that in the resemblance between crystals and organisms the analogy is purely that of form, and usually confined to one element, whereas between organisms there is resemblance of substance no less than of form, and usually the organisms are alike in several respects. The answer to this objection is, that wherever there is a similarity in the causal conditions (substance and history) there must be a corresponding similarity in the results; if this similarity extends to only a few of the conditions, the analogy will be slight; if to several, deep. But whether slight or deep we are not justified, simply on the ground of resemblance, in assuming, short of evidence, that because they are alike, two organisms are related by descent from a common ancestor.

120. Let us glance at a few illustrations. It has been urged as a serious objection to Mr. Darwin’s hypothesis,[66] that it fails to explain the existence of phosphorescent organs in a few insects; and certainly, when one considers the widely different orders in which these organs appear, and their absence in nearly related forms, it is a difficulty. In noctilucæ, earthworms, molluscs, scolopendra, and fireflies, we may easily suppose the presence of similar organic conditions producing the luminosity; but it requires a strong faith to assign Descent as the cause.[67] We may say the same of the electric organs possessed by seven species of fish, belonging to five widely separated genera. Although each species appears to have a limited geographical range, one or the other is found in almost every part of the globe. These organs occupy different positions, being now on each side of the head, now along the body, and now along the tail; and in different species they are innervated from different sources. Their intimate structure also varies; as appears from the remarkable investigations of Max Schultze.[68] They cannot, therefore, be homologous. How could they have arisen? Not by the slow accumulations of Natural Selection, because, until the organs were fully formed, they could be of no advantage in the struggle; hence the slow growth of the organ must have proceeded without the aid of an advantage in the struggle—in each case from some analogous conditions which produced a differentiation in certain muscles. The fundamental resemblance to muscles was pointed out by Carus long ago. It has been insisted on by Leydig:[69] and Owen says, “The row of compressed cells constituting the electric prism of the Torpedo offers some analogy to the row of microscopic discs of which the elementary muscle fibre appears to consist.”[70] We must not, however, forget that these resemblances are merely such as suggest that the electric organ is a differentiation of the substance which elsewhere becomes muscular, and that Dr. Davy was justified in denying the organ to be muscular.[71] That it is substituted for muscle cannot be doubted. Now, although we are entirely ignorant of the conditions which cause this differentiation of substance which elsewhere becomes muscular, but here becomes electric organs, we can understand that, when once such a development had taken place, if it in any way profited the fish in its struggle for existence, Natural Selection would tend to its further increase and propagation. So far Mr. Darwin carries us with him; but we decline proceeding further. The development of these organs in fishes so widely removed, does not imply an ancestral community. It is interpretable as mere growth on a basis once laid; and therefore would occur with or without any advantage in the struggle with rivals. The similarity in concurrent conditions is quite enough to account for the resemblance in structure. This, with his accustomed candor, Mr. Darwin admits. “If the electric organs,” he says, “had been inherited from one ancient progenitor thus provided, we might have expected that all electric fishes would be specially related to each other. Nor does Geology at all lead to the belief that formerly most fishes had electric organs which most of their modified descendants have lost.”

121. It may seem strange that he should urge a difficulty against his hypothesis when it could be avoided by the simple admission that even among nearly allied animals great differences in development are observable, and the electric organs might be ranged under such diversities. But Mr. Darwin has so thoroughly wrought out his scheme, that he foresees most objections, and rightly suspects that if this principle of divergent development be admitted, it will cut the ground from under a vast array of facts which his hypothesis of Descent requires.

The sudden appearance of new organs, not a trace of which is discernible in the embryo or adult form of organisms lower in the scale,—for instance, the phosphorescent and electric organs,—is like the sudden appearance of new instruments in the social organism, such as the printing-press and the railway, wholly inexplicable on the theory of Descent,[72] but is explicable on the theory of Organic Affinity. For observe: if we admit that differentiations of structure, and the sudden appearance of organs, can have arisen spontaneously—i. e. not hereditarily—as the outcome of certain changed physical conditions, we can hardly refuse to extend to the whole organism what we admit of a particular organ. If, again, we admit that organs very similar in structure and function spontaneously appear in organisms of widely different kinds—e. g. the phosphorescent and electric organs—we must also admit that similar resemblances may present themselves in organisms having a widely different parentage; and thus the admission of the spontaneous evolution of closely resembling organs carries with it the admission of the spontaneous evolution of closely resembling organisms: that the protoplasm of muscular tissue should, under certain changed conditions, develop into the tissue of electric organs, is but one case of the law that organized substance will develop into organisms closely resembling each other when the conditions have been similar.

122. It is to be remarked that Mr. Darwin fixes his attention somewhat too exclusively on the adaptations which arise during the external struggle for existence, and to that extent neglects the laws of organic affinity; just as Lamarck too exclusively fixed his attention on the influence of external conditions and of wants. Not that Mr. Darwin can be said to overlook the organic laws; he simply underestimates the part they play. Occasionally he seems arrested by them, as when instancing the “trailing palm in the Malay Archipelago, which climbs the loftiest trees by the aid of exquisitely constructed hooks, clustered around the ends of the branches, and this contrivance no doubt is of the highest service to the plant; but as there are nearly similar hooks on many trees which are not climbers, the hooks on the palm may have arisen from unknown laws of growth, and have been subsequently taken advantage of by the plant undergoing further modification and becoming a climber.”

123. I come round to the position from which I started, that the resemblances traceable among animals are no proof of kinship; even a resemblance so close as to defy discrimination would not, in itself, be such a proof. The absolute identity of chalk in Australia and in Europe is a proof that there was absolute identity in the formative conditions and the constituent elements, but no proof whatever that the two substances were originally connected by genesis. In like manner the similarity of a plant or animal in Africa and Europe may be due to a common kinship, but it may also be due to a common history. It is indeed barely conceivable that the history, from first to last, would ever be so rigorously identical in two parts of the globe as to produce complex identical forms in both; because any diversity, either in structure or external conditions, may be the starting-point of a wide diversity in subsequent development; and the case of organic combinations is so far unlike the inorganic, that while only one form is possible to the latter (chalk is either formed or not formed), many forms are possible to organic elements owing to the complexity and indefiniteness of organic composition. But although forms so allied as those of Species are not readily assignable to an identical history in different quarters of the globe, it is not only conceivable, but is eminently probable, that Orders and Classes have no nearer link of relationship than is implied in their community of organized substance and their common history. The fact that there is not a single mammal common to Europe and Australia is explicable, as Mr. Darwin explains it, on the ground that migration has been impossible to them; but it is also explicable on the laws of Evolution—to have had mammals of the same species and genera would imply a minute coincidence in their history, which is against the probabilities. Again, in the Oceanic Islands there are no Batrachians; but there are Reptiles, and these conform to the reptilian type. Mr. Darwin suggests that the absence of Batrachia is due to the impossibility of migration, their ova being destroyed by salt water. But may it not be due to the divergence from the reptilian type, which was effected elsewhere, not having taken place in these regions? When we find the metal Tin in Prussia and Cornwall, and nowhere else in Europe, must we not conclude that in these two countries, and nowhere else, a peculiar conjunction of conditions caused this peculiar evolution?

124. The question at issue is, Are the resemblances observable among organic forms due to remote kinship, and their diversities to the divergences caused by adaptation to new conditions? or are the resemblances due to similarities, and the diversities to dissimilarities in the substance and history of organic beings? Are we to assume one starting-point and one centre of creation, or many similar starting-points at many centres? So far from believing that all plants and animals had their origin in one primordial cell, at one particular spot, from which descendants migrated and became diversified under the diverse conditions of their migration, it seems to me more consistent with the principle of Evolution to admit a vast variety of origins more or less resembling each other; and this initial resemblance will account for the similarities still traceable under the various forms; while the early differences, becoming intensified by development under different conditions, will yield the diversities. The evolution of organisms, like the evolution of crystals, or the evolution of islands and continents, is determined, 1st, by laws inherent in the substances evolved, and, 2d, by relations to the medium in which the evolution takes place. This being so, we may à priori affirm that the resultant forms will have a community strictly corresponding with the resemblance of the substances and their conditions of evolution, together with a diversity corresponding with their differences in substance and conditions. It is usually supposed that the admission of separate “centres of creation” is tantamount to an admission of “successive creations” as interpreted by the majority of those who invoke “creative fiats.” But the doctrine of Evolution, which regards Life as making its appearance consequent upon a concurrence of definite conditions, and regards the specific forms of Life as the necessary consequences of special circumstances, must also accept the probability of similar conditions occurring at different times and in different places. Upon what grounds, cosmical or biological, are we to assume that on only one microscopic spot of this developing planet such a group of conditions was found—on only one spot a particle of protein substance was formed out of the abundant elements, and under conditions which caused it to grow and multiply, till in time its descendants overran the globe? The hypothesis that all organic forms are the descendants of a single germ, or of even a few germs, and are therefore united by links of kinship more or less remote, is not more acceptable than the hypothesis that all the carbonates and phosphates, all the crystals, and all the strata found in different parts of the globe, are the descendants of a single molecule, or a few molecules; or,—since this may seem too extravagant,—than that the various maladies which afflict organic beings are, in a literal sense, members of families having a nearer relationship than that of being the phenomena manifested by similar organs under similar conditions—a conception which might have been accepted by those metaphysical pathologists who regarded Disease as an entity. Few philosophers have any hesitation in supposing that other planets besides our own are peopled with organic forms, though, from the great differences in the conditions, these forms must be extremely unlike those of our own planet. If separate worlds, why not separate centres? The conclusion seems inevitable that wherever and whenever the state of things permitted that peculiar combination of elements known as organized substance, there and then a centre was established—Life had a root. From roots closely resembling each other in all essential characters, but all more or less different, there have been developed the various stems of the great tree. Myriads of roots have probably perished without issue; myriads have developed into forms so ill-adapted to sustain the fluctuations of the medium, so ill-fitted for the struggle of existence, that they became extinct before even our organic record begins; myriads have become extinct since then; and the descendants of those which now survive are like the shattered regiments and companies after some terrific battle.

125. There seems to me only one alternative logically permissible to the Evolution Hypothesis, namely, that all organic forms have had either a single origin, or else numerous origins; in other words, that a primordial cell was the starting-point from which all organisms have been successively developed; or that the development issued from many independent starting-points, more or less varied. This is apparently not the aspect presented by the hypothesis to many of its advocates; they seem to consider that if all organic forms are not the lineal descendants of one progenitor, they must at any rate be the descendants of not more than four or five. The common belief inclines to one. Mr. Darwin, whose caution is as remarkable as his courage, and whose candor is delightful, hesitates as to which conclusion should be adopted: “I cannot doubt,” he says, “that the theory of descent, with modifications, embraces all the members of the same class. I believe that animals have descended from, at most, only four or five progenitors, and plants from an equal or lesser number. Analogy would lead me one step further, namely, to the belief that all animals and plants have descended from some one prototype. But analogy may be a deceitful guide.”

126. I cannot see the evidence which would warrant the belief that Life originated solely in one microscopic lump of protoplasm on one single point of our earth’s surface; on the contrary, it is more probable that from innumerable and separate points of this teeming earth, myriads of protoplast sprang into existence, whenever and wherever the conditions of the formation of organized substance were present. It is probable that this has been incessantly going on, and that every day new protoplasts appear, struggle for existence, and serve as food for more highly organized rivals; but whether an evolution of the lower forms is, or is not, still going on, there can be no reluctance on the part of every believer in Evolution to admit that when organized substance was first evolved, it was evolved at many points. If this be so, the community observable in organized substance, wherever found, may as often be due to the fact of a common elementary composition as to the fact of inheritance. If this be so, we have a simple explanation both of the fundamental resemblances which link all organisms together, and of the characteristic diversities which separate them into kingdoms, classes, and orders. The resemblances are many, and close, because the forms evolved had a similar elementary composition, and their stages of evolution were determined by similar conditions. The diversities are many, because the forms evolved had from the first some diversities in elementary composition, and their stages of evolution were determined under conditions which, though similar in general, have varied in particulars. Indeed, there is no other ground for the resemblances and differences among organic beings than the similarities and dissimilarities in their Substance and History; and, whether the similarities are due to blood-relationship, or to other causes, the results are the same. There is something seductive in the supposition that Life radiated from a single centre in ever-increasing circles, its forms becoming more and more various as they came under more various conditions, until at last the whole earth was crowded with diversified existences. “From one cell to myriads of complex organisms, through countless æons of development,” is a formula of speculative grandeur, but I cannot bring myself to accept it; and I think that a lingering influence of the tradition of a “creative fiat” may be traced in its conception. May we not rather assume that the earth at the dawn of Life was a vast germinal membrane, every slightly diversified point producing its own vital form; and these myriads upon myriads of forms—all alike and all unlike—urged by the indwelling tendencies of development, struggled with each other for existence, many failing, many victorious, the victors carrying their tents into the camping ground of the vanquished. The point raised is the immense improbability of organized substance having been evolved only in one microscopic spot; if it were evolved at more than one spot, and under slightly varying conditions, there would necessarily have arisen in these earliest formations the initial diversities which afterwards determined the essential independence and difference of organisms.

129. Let us for a moment glance at the resemblances and diversities observable in all organisms. All have a common basis, all being constructed out of the same fundamental elements: carbon, hydrogen, nitrogen, and oxygen; these (the organogens, as they are named), with varying additions of some other elements, make up what we know as Organic Substance, vegetal and animal. Another peculiarity all organisms have in common, namely, that their matter is neither solid nor liquid, but viscid. Beside this community of Substance we must now place a community of History. All organisms grow and multiply by the same process; all pass through metamorphic stages ending in death; all, except the very simplest, differentiate parts of their substance for special uses, and these parts (cilia, membranes, tubes, glands, muscles, nerves) have similar characters in whatever organism they appear, and their development is always similar, so that the muscles or nerves of an intestinal worm, a lobster, or a man, are in structure and history fundamentally alike. When, therefore, we see that there is no biological character of fundamental importance which is not universal throughout the organic world, when we see that in Structure and History all organisms have a community pervading every variety, it is difficult not to draw the conclusion that some hidden link connects all organisms into one; and when, further, it is seen that the most divergent forms may be so arranged by the help of intermediate forms only slightly varying one from the other, that the extreme ends—the monad and the man—may be connected, and a genealogical tree constructed, which will group all forms as modified descendants from a single form, the hypothesis that kinship is the bidden link of which we are in search becomes more and more cogent.

130. But now let the other aspect be considered. If there is an unmistakable uniformity, there is also a diversity no less unmistakable. The chemical composition of organic substances is various. Unlike inorganic substances, the composition of which is rigorously definite, organic substances are, within narrow limits, variable in composition (§ [45]).

I pass over the resemblances and differences observed in the earliest stages of development, marked as they are, and direct attention to the fact, that down at what must be considered the very lowest organic region, we meet with differences not less striking than those met with in the highest, we find structures (if structures they may be called), which cannot be affiliated, so widely divergent is their composition. The structureless vibrio, for example, is not only capable of living in a medium destitute of Oxygen, but is, according to M. Pasteur, actually killed by oxygen; whereas the equally simple bacteria can no more dispense with Oxygen than other animals can. Consider for a moment the differences implied in the fact that one organism cannot even form an enveloping membrane to contain its protoplasm, whereas another contrives to secrete an exquisite shell; yet between the naked Rhizopod and the shelled Rhizopod our lenses and reagents fail to detect a difference. One Monad can assimilate food of only one kind, another Monad assimilates various kinds.[73] What a revelation of chemical differences appears in the observations of M. Pasteur respecting the vibrio and bacteria, in a fermentescible liquid—the former beginning the putrid fermentation which the latter completes! We cannot doubt that some marked difference must exist between the single-celled organism which produces alcoholic fermentation, and that which produces acetic fermentation, and that again which produces butyric fermentation; and if we find distinctions thus established at the lowest region of the organic series, we need not marvel if the distinctions become wider and more numerous as the series becomes more diversified. The structure and development of an organism are dependent on the affinities of its constituent molecules, and it is a biological principle of great importance which Sir James Paget insists on, when he shows how “the existence of certain materials in the blood may determine the formation of structures in which they may be incorporated.”[74] Any initial diversity may thus become the starting-point of a considerable variation in subsequent evolution.[75] Thus, supposing that on a given spot there are a dozen protoplasts closely resembling each other, yet each in some one detail slightly varying; if this variation is one which, by its relations to the external medium, admits of a difference in the assimilation of materials present in the medium, it may be the origin of some new direction in development, and the ultimate consequence may be the formation of a shell, an internal skeleton, a muscle, or a nerve. Were this not so, it would be impossible to explain such facts as that chitine is peculiar to the Articulata, cellulose to Molluscoida, carbonates of lime to Mollusca and Crustacea, and phosphates to Vertebrata—all assimilated from the same external medium. But we see that from this medium one organism selects the materials which another rejects; and this selection is determined by the nature of the structure: which assimilates only those materials it is fitted to assimilate. We hear a great deal of Adaptation determining changes of structure and function, and are too apt to regard this process as if it were not intimately dependent on a corresponding structural change. By no amount of external influence which left the elementary composition of the structure unchanged, could an organism with only two tissues be developed into an organism with three or four. By no supply or stimulus, could an animal incapable of assimilating peroxide of iron acquire red blood corpuscles, although it might have the iron without the corpuscles; nor could an oyster form its shell unless capable of assimilating carbonate of lime. For myriads of years, in seas and ponds, under endless varieties of external conditions, the amœbæ have lived and died without forming a solid envelope, although the materials were abundant, and other organisms equally simple have formed envelopes of infinite variety. In all the seas, and from the earliest ages, zoophytes have lived, and assumed a marvellous variety of shapes and specialization of functions; but although some of them have acquired muscles, none have acquired true nerves, none bone. Ages upon ages rolled on before fishes were capable of forming bone; and thousands are still incapable of forming it, though living in the same waters as the osseous fishes.

131. “Looking to the dawn of life,” says Mr. Darwin (repeating an objection urged against his hypothesis), “when all organic beings, as we imagine, presented the simplest structure, how could the first steps in advancement, or in the differentiation and specialization of parts have arisen? I can make no sufficient answer; and can only say that, as we have no facts to guide us, all speculation would be baseless and useless.”

Where Mr. Darwin hesitates, lesser men need extra caution; but I must risk the danger of presumption, at least so far as to suggest that while an answer to this question is difficult on that dynamical view of Evolution which regards Function as determining Structure, it is less difficult on the statico-dynamical view propounded in these pages; the difficulty which besets the explanation when all the manifold varieties of organic forms are conceived as the successive divergences from an original starting-point, is lessened when a variety of different starting-points is assumed, in each of which some initial diversity prepared the way for subsequent differentiations; just as we know that between the ovum of a vertebrate and the ovum of an invertebrate, similar as they are, there is a diversity which manifests itself in their subsequent evolution. If Function is determined by Structure, and Evolution is the product of the two, it is clear that the different directions in the lines of development will have their origin in structural differences, and not in the action of external circumstances, unless these previously bring about a structural change. The action of the medium on the organism is assuredly a potent factor which Biology cannot ignore: but the organism itself is a factor, and according to its nature the influence of the medium is defined. (§ [118].)

132. Quitting for a moment the track of this argument, let us glance at the resemblances and differences observable in Plants and Animals, because most people admit that these have separate origins. The resemblances are scarcely less significant than those existing among animals. Both have a similar basis of elementary composition; not only are both formed out of protoplasts with similar properties, but in both the first step from the protoplasm to definite structure is the Cell. And the life of this Cell is remarkably alike in both, its phases of development being in many respects identical; nay, even such variations as obtain in the cell-membranes are curiously linked together by a community in the formative process.[76] In both Plants and Animals we find individuals constituted—1st, by single cells; 2d, by groups of cells undistinguishable among each other; and 3d, by groups of differentiated cells. In both we find colonies of individuals leading a common life. In both the processes of Nutrition and Reproduction are essentially similar; both propagate sexually and asexually; both exhibit the surprising phenomena of parthenogenesis and alternate generations. In both there are examples of a free-roving embryo which in maturity becomes fixed to one spot, losing its locomotive organs and developing its reproductive organs. In both the development of the reproductive organs is the climax which carries Death. So close is the analogy between plant-life and animal-life, that it even reaches the properties usually held to be exclusively animal; I mean that even should we hesitate to accept Cohn’s discovery of the muscles in certain plants,[77] we cannot deny that plants exhibit Contractility; and should we refuse to interpret as Sensibility the phenomena exhibited by the Sensitive Plants, we cannot deny that they present a very striking analogy to the phenomena of Sensibility exhibited by animals.

133. It is unnecessary to continue this enumeration, which might easily be carried into minute detail. A chapter of such resemblances would only burden the reader’s mind, without adding force to the conclusion that a surprising community in Substance and Life-history must be admitted between Plants and Animals. This granted, we turn to the differences, and find them no less fundamental and detailed. Chemistry tells us nothing of the differences in the protoplasms from which animals and plants arise; but that initial differences must exist is proved by the divergence of the products. The vegetable cell is not the animal cell; and although both plants and animals have albumen, fibrine, and caseine, the derivatives of these are unlike. Horny substance, connective tissue, nerve tissue, chitine, biliverdine, creatine, urea, hippuric acid, and a variety of other products of evolution or of waste, never appear in plants; while the hydrocarbons so abundant in plants are, with two or three exceptions, absent from animals. Such facts imply differences in elementary composition; and this result is further enforced by the fact that where the two seem to resemble, they are still different: the plant protoplasm forms various cells, but never forms a cartilage-cell or nerve-cell; fibres, but never a fibre of elastic tissue; tubes, but never a nerve tube; vessels, but never a vessel with muscular coatings; solid “skeletons,” but always from an organic substance (cellulose), not from phosphates and carbonates. In no one character can we say that the plant and the animal are identical; we can only point throughout the two kingdoms to a great similarity accompanying a radical diversity.

134. Having brought together the manifold resemblances, and the no less marked diversities, we must ask what is their significance? Do the resemblances imply a community of origin, an universal kinship? If so, the diversities will be nothing more than the divergences which have been produced by variations in the Life-history of the several groups. Or—taking the alternative view—do the diversities imply radical differences of origin? If so, the resemblances will be nothing more than the inevitable analogies resulting from Organized Substance being everywhere somewhat similar in composition, and similar in certain phases of evolution. To state the former position in the simplest way, we may assume that of two masses of protoplasm having a common parentage, one, by the accident of assimilating a certain element not brought within the range of the other, thereby becomes so differentiated as to form the starting-point of a series of evolutions widely divergent from those possible to its congener; and at each stage of evolution the introduction of a new element (made possible by that stage) will form the origin of a new variation. It is thus feasible to reduce all organic forms to a primordial protoplasm, in the evolutions of which successive differentiations have been established. On the other hand, it is equally feasible to assume that the existence of radical differences must be invoked to account for the possibility of the successive differentiations.

135. The hunt after resemblances has led to much mistaken speculation; and with reference to the topic now before us, it may be urged, that although by attaching ourselves to the points of community, in disregard of the diversities, we may make it appear that all animals have a common parentage, and that plants and animals are merely divergent groups of the same prototype, a rigorous logic will force us onwards, and compel us to admit that a kinship no less real unites the organic with the inorganic world. For upon what principle are we to pause at the cell or protoplasm? If by a successive elimination of differences we reduce all organisms to the cell, we must go on and reduce the cell itself to the chemical elements out of which it is constructed; and inasmuch as these elements are all common to the inorganic world, the only difference being one of synthesis, we reach a result which is the stultification of all classification, namely, the assertion of a kinship which is universal. We must bear in mind that all things may be reduced to a common root by simply disregarding their differences. All things are alike when we set aside their unlikeness.

136. Suppose, for the sake of illustration, we regard an Orchestra in the light of the Development Hypothesis. The various instruments of which it is composed have general resemblances and particular differences, not unlike those observable in various organisms; and as we proceed in the work of classification we quickly discover that they may be arranged in groups analogous to the Sub-kingdoms, Classes, Orders, Genera, and Species of the organic world. Each group has its cardinal distinction, its initial point of divergence. All musical instruments resemble each other in the fundamental character of producing Tone by the vibrations of their substance. This may be called their organic basis. The first marked difference which determines the character of two sub-kingdoms (namely, instruments of Percussion and Wind instruments) arises from a difference in the method of impressing the vibrations; and the grand divisions of these sub-kingdoms arise from the nature of the vibrating substances. Each type admits of many modifications, but the primary distinction is ineffaceable. We can conceive the Pipe modified into a Flute, a Flageolet, a Clarionet, a Hautbois, a Bassoon, or a Fife, by simple accessory changes; to modify the Pipe into a Trumpet, and thus produce the peculiar timbre of the trumpet, would be impossible except by the substitution of a new material; by replacing the wood with metal we may adhere to the old Type, but we have created a new Class. (Attention is requested to this point, because the current views respecting the transmutation of tissues, which seem to lend a decisive support to the hypothesis of the transmutation of species are very commonly vitiated by the confusion of transformation with substitution. No anatomical element is transformed into another specifically different—an epithelial-cell into a nerve-cell, for instance—but one anatomical element is frequently substituted for another.) To convert the Pipe or the Trumpet into a Violin or a Drum would be impossible. We can follow the modifications of a Tambourine into a Drum or Kettle-drum, but no modifications of these will yield the Cymbals. That is to say, the vibrating materials—wood, metal, parchment, and the combination of wood and strings—have peculiar properties, and the instruments formed of such materials must necessarily from the very first belong to different groups, each subdivision of the groups being dependent on some characteristic difference in methods of impressing the vibrations, or in the materials. Although all musical instruments have a common property and a common purpose, we do not regard them as transformations of one primitive instrument; their kindred nature is a subjective conception; the analogies are numerous and close, but we know their origin. It is obvious that men being pleased by musical tones, have been led by their delight to construct instruments whenever they have discovered substances capable of musical vibrations, or methods of impressing such vibrations. By substituting the bow for the plectrum or the fingers, they may have changed the Lyre into the Violin, Viola, Violoncello, and Bass. (It seems historically probable that the real origin of the Violin class was an instrument with one string played on by a bow.) By grouping together Pipes of various sizes they got the Panpipes; by substituting metal and enlarging the blowing apparatus they got the Organ. By beating on stretched parchment with the finger, they got the Tambourine and Tom-Tom; by doubling this and using a stick they got the Drum. By beating metal with metal they got the Cymbals; by beating wood they got the Castanets.

137. The application of this illustration is plain. Just as a wind-instrument is incapable of becoming a stringed instrument, so a Mollusc, with all its muscles unstriped, and its nervous system unsymmetrical, is incapable of becoming a Crustacean, with all its muscles striped and its nervous system symmetrical. Indeed there are probably few biologists of the present day who imagine the transmutation of one kind into the other to be possible; but many biologists assume that both may have been evolved from a common root. The point is beyond proof; yet I think there is a greater probability in the assumption that both were evolved from different roots. At any rate, one thing is certain; a divergence could only have been effected by a series of substitutions; and the question when and how these substitutions took place is unanswerable: one school believes them to have been creative fiats, the other school believes them to have been transmutations.

138. When we see an annelid and a vertebrate resembling each other in some special point which is not common either to their classes or to any intermediate classes—as when we see the wood-louse (Oniscus) and the hedgehog defend themselves in the same strange way by rolling up into a ball—we cannot interpret this as a trace of distant kinship. When we see a breed of pigeons and a breed of canaries turning somersaults, and one of the Bear family (Ratel) given to the same singular habit, we can hardly suppose that this is in each case inherited from a common progenitor. When we see one savage race tipping arrows with iron, and another, ignorant of iron, using poison, there is a community of object effected by diversity of means; but the analogy does not necessarily imply any closer connection between the two races than the fact that men with similar faculties and similar wants find out similar methods of supplying their wants. Even those who admit that the human race is one family, and that the various peoples carried with them a common fund of knowledge when they separated from the parent stock, may still point to a variety of new inventions and new social developments which occurred quite independently of each other, yet are strikingly alike. Their resemblance will be due to resemblance in the conditions. The existence, for example, of a religious worship, or a social institution, in two nations widely separated both in time and space, and under great historical diversities, is no absolute proof that these two nations are from the same stock, and that the ideas have the same parentage. It may be so; it may be otherwise. It may be an analogy no more implying kinship than the fact of ants making slaves of other ants (and these the black ants!) implies a kinship with men. Given an organization which in the two nations is alike, and a history which is in certain characteristics analogous, there must inevitably result religious and social institutions having a corresponding resemblance. I do not wish to imply that the researches of philologists and ethnologists are misdirected, or that their conclusions respecting the kinship of mankind are to be rejected; I only urge the consideration that perhaps too much stress is laid on community of blood, and not enough on community of conditions.

RECAPITULATION.

139. The various lines of argument may here be recapitulated. The organic world presents a spectacle of endless diversity, accompanied by a pervading uniformity. The general resemblances in forms and functions are more or less masked by particular differences. The resemblances, it is said, may be all due to kinship, all the living individuals having descended from a primordial cell; and at each stage of the descent the adaptations to new conditions may have issued in deviations from the ancestral form, while the process of Natural Selection giving stability to those variations which best fitted the organism in the struggle of existence, has made greater and greater gaps, and produced more marked diversities among the descendants. This is the Darwinian Theory: “On my theory unity of Type is explained by unity of Descent.”

140. By the general consent of biologists, this theory is held to explain many if not all the observed facts. It is a very luminous suggestion; but it requires an enlargement so as to include Organic Affinity; and when once this fundamental principle is admitted, it brings with it very serious doubts as to the theory of Descent. We are then entitled to assume that many of the most striking resemblances, instead of being due to kinship, are due simply to the general principle that similar causes must have similar effects, and that organic substances having a very close resemblance, organized substances must have similar stages of evolution under similar conditions; and thus organs will necessarily take on very similar forms in very different organisms (for example, the eye of the cephalopod and the eye of the vertebrate), and organisms having widely different parentage may closely resemble each other. If we are entitled to assume that protoplasm appeared not in one microscopic spot alone, but in many places and in vast quantities—and this is surely the more justifiable assumption—then we must also admit that these germinal starting-points were from the first, or very shortly afterwards, differentiated by variations in their elementary composition. Now we know that a very minute change in composition may lead to immense differences in evolution. Thus the descendants of two slightly different progenitors may, by continual differentiation, become very markedly unlike; yet, because of the original resemblance of their substances, they will reveal a pervading similarity.

While it is thus conceivable that all organisms may resemble each other, and all differ, owing to the similarities and diversities in the “conditions of existence” (and among those conditions that of descent is of wide range), it is not very readily conceivable how advantage in the external struggle could have determined the varieties of form and function, because many differentiations give no superiority in the struggle. As Mr. St. George Mivart urges, “Natural Selection utterly fails to account for the conservation and development of the minute and rudimentary beginnings, the slight and infinitesimal commencements of structures, however useful those structures may afterwards become.”[78] And this is undeniable on the supposition that Natural Selection is an agency not identical with the variations of growth, but exclusively confined to the accumulation of favorable variations.

141. In estimating the two hypotheses—First, of Descent from one primordial germ, and the modifications due to Natural Selection, or, as I should say, expressed in Selection; and Secondly, of Descent from innumerable germs having initial differences, which differences radiated into the marked modifications, there is this superiority to be claimed for the first, that it is more easily handled as an aid to research, and is therefore more decidedly useful. The laws of Organic Affinity are at present too obscure for any successful application. I only wish to point out that the theory of Descent is an imaginary construction of what may have been the process of species-formation, not a transcription of the process observed. It constructs an imaginary Type as progenitor of a long line of widely different descendants. The annelid which is taken as the ancestor of the vertebrates is not any annelid known either to zoölogists or geologists, but a generalized and imaginary type. So daringly liberal is the imagination in endowing the ancestor with whatever may be required for the descendants, that Mr. Darwin thinks it probable, from what we know of the embryos of vertebrates, that these animals “are the modified descendants of some ancient progenitor which was furnished in its adult state with branchiæ, a swim-bladder, four simple limbs, and a long tail, all fitted for an organic life,” (p. 533); and Dr. Dohrn conceives the original type to have contained within itself all that has been subsequently evolved in the highest vertebrate, the other and less elaborate organisms being mere degradations from this type.[79] This use of the imagination, although not without advantages, is also not without dangers. It may direct research, it must not be suffered to replace research.

PROBLEM II.
THE NERVOUS MECHANISM.

“All the functions of the nervous system are as dependent upon its structure and nature, as the accurate indication of time upon the construction of the chronometer.”—Prochaska.

“Unser Wissen wird nie vollendet, ist und bleibt Stückwerk; dessen Ergänzung das Streben und Hoffen der forschenden Denker bleiben wird für alle Zeit.”—Radenhausen, Osiris.

“Our nimble souls
Can spin an insubstantial universe
Suiting our mood, and call it possible,
Sooner than see one grain with eye exact,
And give strict record of it.”

George Eliot, The Spanish Gypsy.

“If we compare the teachings of our books with what Nature is constantly showing, we find there is no agreement between those two sources of learning.”—Brown Séquard.

THE NERVOUS MECHANISM.

CHAPTER I.
SURVEY OF THE SYSTEM.

1. Our knowledge of mental processes is derived from reflection on our personal experiences, combined with inferences from our observation of other men and animals, under similar conditions. The processes are complex and variable; so complex and variable, that knowledge of their component factors can only be gained through long tentative study, aided by fortunate circumstances which present these factors separately, or at any rate in such marked predominance as to fix attention. This subjective analysis of the processes has to be supplemented by, and confirmed by an objective analysis of, the conditions, external and internal: the facts of Feeling have to be traced to facts of Physiology, which will exhibit that Physical Basis of Mind so earnestly sought by the inquirer.

Both the subjective and the objective analysis are at present in a very imperfect state. Although there is much confident assertion and “false persuasion of knowledge” in both regions, there is, unhappily, little that can be seriously accepted as demonstrated. In the present volume we shall concern ourselves almost exclusively with the objective analysis, and do our utmost to mark what is mere inference from what is verified observation. It is only by Observation that facts can be settled; however Analogy and Inference may suggest where the truth may lie, they are finger-posts, not goals. At the best they only tell us what Observation would reveal could the processes be submitted to Sense.

In a loose and general way every one knows that the Nervous System is a dominant agent in all sentient processes; although not by any means the only agent, yet, because of its predominance, it is artificially accepted as the only one. With the greater complexity of this system, there is observed a corresponding increase in the variety of sentient phenomena. The labors of anatomists have secured a tolerably exact plan of the topographical distribution of this system; a somewhat chaotic mass of observation and inference passes as a description of its elementary structure. The labors of physiologists have succeeded to a small extent in localizing certain functions in certain organs of this system. But imperfect as our knowledge of the elementary structures is, our knowledge of the functions is still more so. I wish I could say otherwise, and that I could ask my readers to accept with confidence what teachers confidently propound. The attitude of scepticism is always repulsive; the sceptic is seldom received without disfavor, because he throws on us the labor of investigation there where we wish for the confidence of knowledge. Yet it is only by facing the facts that we can hope one day to solve the great questions.

2. The nervous system has, in our artificial view of it, two divisions: the Peripheral, which connects the organism with the external world; and the Central, which connects each part of the organism with all the other parts. Although the system is constituted by various tissues—neural, connective, vascular, and elastic—it receives its characteristic designation from nerve-fibrils, nerve-fibres, and nerve-cells; just as the muscular system receives its designation from contractile cells and fibres. This neural tissue assumes three well-marked forms: 1°, nerves, which are bundles of fibres and fibrils, enclosed in a membranous sheath; 2°, ganglia, which are clusters of cells, fibres, and fibrils, sometimes enclosed in a sheath, sometimes not; 3°, centres, which are artificial divisions of the neural axis, serving as points of union for different organs.

In the Invertebrata the neural axis is the chain of ganglionic masses running along the ventral side, and giving off the nerves to organs of sense, and to the muscles. It may be seen represented in [Fig. 1].

Fig. 1.—Nervous system of a beetle. The small round masses, or ganglia, are seen to be connected by longitudinal fibres, and from the ganglia issue fibres to the limbs, organs of sense, and viscera.

In the Vertebrata the axis is dorsal, and is called the cerebro-spinal axis, including brain and spinal cord. When we look at this structure superficially we see various nerves radiating from it to skin, glands, and muscles; but a closer examination, enlightened by knowledge of function, shows that some of these nerves pass into it from the various surfaces and sense-organs, and are therefore called afferent or sensory; whereas another set passes out of it to glands and muscles, and these nerves are therefore called efferent or motory. There are also fibres which, passing from one part of the great centre to another, are called commissural.

To this brief account of the cerebro-spinal system may be added a word on the connected chain of ganglia and nerves known as the Sympathetic, because it was formerly supposed to be the organ through which the various “sympathies” were effected. It is now held to be the system devoted to the viscera and blood-vessels; but there is still great want of agreement among physiologists as to whether it is an independent system, having a special structure somewhat different from that of the cerebro-spinal, or whether it is simply a great plexus of nerves and ganglia, only topographically distinguishable from the rest of the nervous system. Into this point it is unnecessary for me to enter here. Enough to say, that I entirely agree with Sigmund Mayer in adopting the second view.[80] In no histological character, yet specified, are the sympathetic nerves and ganglia demarcated from the others. There are, indeed, more non-medullary fibres (the gray fibres of Remak) in the sympathetic; but the same fibres are also abundant in the cerebro-spinal system; and the sympathetic has also its large medullary fibres.

3. The Centres are composed of two substances: the gray and the white. The gray substance is often called the vesicular because of its abundant cells; but it has even more fibres than cells, and the white substance has also a few cells.[81] The gray substance is distributed over the surface of the brain—in the convolutions; and in various other parts of the encephalon. It surrounds the central canal which forms the ventricles of the brain and is continued as a very small cavity all down the spinal cord. Besides entering into the important and conspicuous masses known as the cerebral ganglia—(the optic thalami, and corpora striata)—the gray substance is massed in the corpora quadrigemina, crura cerebri pons varolii, and medulla oblongata. We shall have occasion to refer to each of those parts. Until modern times all the masses included in the skull under the familiar term Brain (or the technical term Encephalon) were regarded as the only centre, and also as the origin of all the nerves. Nor has this notion even yet entirely disappeared, although the spinal cord is known not to be a large nerve trunk, but a centre or connected chain of centres, structurally and functionally similar to the cranial centres. The shadow of the ancient error still obscures interpretation of the part this spinal cord plays in the sentient mechanism; and thus although the cord is universally admitted to be a centre for “sensitive impressions,” it is usually excluded from Sensation. This widespread and misleading notion will be critically examined in a future problem.

4. Beginning our survey of the cerebro-spinal axis with the Spinal Cord, we observe it to consist: 1°, of central gray substance surrounding the scarcely visible canal, which is all that remains of the primitive groove in the germinal membrane (§ [9]); 2°, irregular gray masses, called the anterior and posterior horns,[82] connected with the anterior and posterior roots of the spinal nerves; and 3°, strands of white fibres enclosing this central substance, and called the anterior lateral and posterior columns.

Like the Cerebrum, it is a double organ formed by two symmetrical halves, as the cerebrum is of two hemispheres. Each half innervates the corresponding half of the body. The cord is unlike the cerebrum in external form, though very like it in internal structure. The gray structure is mainly external in the cerebrum, and is internal in the cord.

From the anterior side of the cord (that which in animals is the under side) the motor nerves issue; from the posterior (in animals the upper) side, issue the sensory nerves. On each of the sensory nerves there is a ganglion. The roots of each nerve, formed of several rootlets issuing from the anterior and posterior columns, subsequently unite together, and proceed in a single sheath to muscles and skin, separating again, however, before they reach muscles and skin. [Fig. 2] represents this arrangement.

Fig. 2.—A portion of the spinal cord with its nerves (after Bernard). The left-hand figure shows the anterior side; the right-hand the posterior. A the anterior, and P, the posterior root, they meet at g, the ganglion; c and d are filaments connecting two posterior roots.

5. There are thirty-one pairs (sometimes thirty-two) of such nerves—namely, eight cervical, twelve thoracic, five lumbar, five sacral, and one (or two) coccygeal. [Figs. 3] to [6] represent transverse sections, which display the entrance of the roots of the nerves into the anterior and posterior horns.

6. Similar masses of gray substance in the Medulla Oblongata (which is the name given to the cord when it passes into the skull)[83] are supposed to be the origins of some other nerves (the cranial).

Fig. 3.—Transverse section of one half of the spinal cord in the lumbar region (after Kölliker). a, anterior root entering the anterior gray horns, m and l, where cells are clustered; c, central canal; d and e, the anterior and posterior commissures uniting the two halves of the cord; b, posterior root entering the posterior gray horn.

Fig. 4.—Transverse section of both halves of the cord, cervical region. a, Fissure separating the anterior columns; b, fissure of the posterior.

Fig. 5.—Transverse section of the cord in the dorsal region.

Fig. 6.—Transverse section in the lumbar region.

Although the Medulla Spinalis is unquestionably continued as the Medulla Oblongata, the arrangement of its tissues here becomes gradually changed, and so complicated that it baffles the scalpel. Anatomists are, however, agreed on the one point of fundamental importance to us here—namely, that there is only a rearrangement, not a new tissue. Accepting the artificial division into two organs, we may say that their functions are different, inasmuch as they are different in their anatomical connections—they innervate different parts; but as nerve-centres they have one and the same property.

On its posterior surface the Medulla Oblongata opens as the fourth ventricle. It is then no longer a closed canal, but an expansion of the spinal canal, which is covered by the Cerebellum. On its anterior surface projects the pons varolii. [Figs. 7] and [8] represent these.

Fig. 7.—Back, or upper view of the Medulla Oblongata as it continues the Med. Spinalis. 1, Section of the thalami; 2, corpora quadrigemina (the two lower bodies are imperfectly represented in the engraving); 3, section of the crura cerebelli; 4, the fourth ventricle; 5, the restiform bodies; 6, the calamus scriptorius.