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THE PHILOSOPHY OF BIOLOGY

CAMBRIDGE UNIVERSITY PRESS
London: FETTER LANE, E.C.
C. F. CLAY, Manager

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THE PHILOSOPHY OF BIOLOGY

BY

JAMES JOHNSTONE, D.Sc.

Cambridge:

at the University Press

1914

INTRODUCTION

It has been suggested that some reference, of an apologetic nature, to the title of this book may be desirable, so I wish to point out that it can really be justified. Science, says Driesch, is the attempt to describe Givenness, and Philosophy is the attempt to understand it. It is our task, as investigators of nature, to describe what seems to us to happen there, and the knowledge that we so attain—that is, our perceptions, thinned out, so to speak, modified by our mental organisation, related to each other, classified and remembered—constitutes our Givenness. This is only a description of what seems to us to be nature. But few of us remain content with it, and the impulse to go beyond our mere descriptions is at times an irresistible one. Fettered by our habits of thought, and by the limitations of sensation, we seem to look out into the dark and to see only the shadows of things. Then we attempt to turn round in order that we might discover what it is that casts the shadows, and what it is in ourselves that gives shape to them. We seek for the Reality that we feel is behind the shadows. That is Philosophy.

The Physics of a generation earlier than our own thought that it had discovered Reality in its conception of an Universe consisting of atoms and molecules in ceaseless motion. What it described were only motions and transformations, but it understood these motions and transformations as matter and energy. Yet more subtle minds than the great physicists of the beginning of the nineteenth century had already seen that sensation might mislead us. There was something in us that continually changed—that was our consciousness, and it was all that we knew. If external things did exist they existed only because we thought them. But we ourselves exist, for we are not only a stream of consciousness that continually changes, but there is in us a personality, or identity, which has remained the same throughout all the vicissitudes of our consciousness. If the things that exist for us exist only because we think them, and if we also exist, then we must exist in the thought of an Absolute Mind that thinks us. Physical Science, studying only motions and transformations, understood that there was something that moved and transformed—this was matter and energy. Mental Science, studying only thought, understood that nature was only the thought of an Universal Mind. Either conclusion was equally valid Philosophy (or metaphysics), and neither could be proved or disproved by the methods of Science. The speculative game is drawn, said Huxley, let us get to practical work!

Both Physics and Biology did get to work, with the results that we know. But Physics advanced far beyond the acquirement of the results that stimulated Biology to formulate our present hypotheses of evolution and heredity. As its knowledge accumulated, it began to doubt whether matter and energy, atoms and molecules, mass and inertia—all those things which it thought at first were so real—were anything else after all than ways in which our mental organisation dealt with crude sensations. They might, as Bergson said later on, be the moulds into which we pour our perceptions. Physics set up a test of Reality, the law of the conservation of matter and energy. There are existences which may or may not persist. Visions and phantasms and dreams are existences while they last. They are true for the mind in which they occur. But they seem to arise out of nothing, and to disappear into nothing, and physical Science cannot investigate them. They are existences which are not conserved. On the other hand those images which we call moving matter and transforming energy can be investigated by the methods of physics. Molecules change, but something in them, the atoms, remain constant. Energy becomes transformed, and it may even seem to cease to exist, but if it disappears, then something is changed so that the lost energy can be traced in the nature of the change. Matter and energy are conserved and therefore they are the only Realities. But the test is obviously one that has an a priori basis, and we may doubt whether it is a test of Reality.

Thus Physics constructed a dynamical Universe, that is, one which consisted of atoms which attracted or repelled each other with forces which were functions of the distances between them. Even now this conception of a dynamical, Newtonian Universe is a useful one, though we recognise that it is only symbolism. But it was not a conception with which Physics could long remain content. How could atoms separated from each other by empty space act on each other, that is, how could a thing act where it was not? There must be something between the atoms. The Universe could not be a discontinuous one, and so Physics invented an Universe that was full. It was an immaterial, homogeneous, imponderable, continuous Universe. That which existed behind the appearances of atoms and molecules and energy was the ether of space. It must be admitted that the conception appears to the layman to involve only contradictions: heterogeneous, discontinuous, ponderable atoms are only singularities in a homogeneous, continuous, imponderable medium, or ether. Yet it is easy to see that this contradiction arises in our mind only because we had previously thought of the Universe in terms of matter and energy, and in spite of ourselves we attempt to think of the new Reality in terms of the old one. In its attempt to understand all its later results Physics had therefore to invent a new Philosophy—that of the ether of space.

It is only in our own times that Biology has become sceptical and has begun to doubt whether its earlier Philosophy is a sound one. That which it describes—the object-matter of its Science—is not that which Physics describes. There are two domains of Givenness, the organic and the inorganic. Biology, leaning on Physics, studied motions and transformations, just as Physics did, though the motions which it studied were more complex and the transformations more mysterious. But borrowing the methods of investigation of Physics it borrowed also its Philosophy, and so it placed behind its Givenness the Reality that Physics at first postulated and then abandoned. The organism was therefore a material system actuated by energy. The notion, it should be noted, is not a deduction from the results of Biology, but only from its methods.

Did Physiology, that is, the Physiology of the Schools, ever really investigate the organism? A muscle-nerve preparation, an excised kidney through which blood is perfused, an exposed salivary gland which is stimulated, even a frog deprived of its cerebral hemispheres—these things are not organisms. They are not permanent centres of action, autonomous physico-chemical constellations capable of independent existence, and capable of indefinite growth by dissociation. They are parts of the organism, which, having received the impulse of life, an impulse which soon becomes exhausted, exhibit for a time some of the phenomena of the organism. What Physiology did attain in such investigations was an analytical description of some of the activities of the organism. It did not describe life, but rather the physico-chemical reactions in which life is manifested. The description, it should be noted, is all-important for the human race in its effort to acquire mastery over its environment; and there is no other way in which it may be carried further but by the methods of physical Science. Givenness is one, though we arbitrarily divide it into the domains of the organic and the inorganic, and there can be only one way of describing it. That is the mechanistic method.

Nevertheless all this is only a description, and our Philosophy must be the attempt to understand our description. The mechanistic biologist, in the attempt to identify his Philosophy with that of a former generation of physicists, says that he is describing a physico-chemical aggregate—an assemblage of molecules of a high degree of complexity—actuated by energy, and undergoing transformations. But our scepticism as to the validity of this conclusion is aroused by reflecting on its origin. If it was borrowed from the Philosophy of a past Physics, and if the more penetrating analysis of the Physics of our own time has made a new Philosophy desirable, should not Biology also revise its understanding of its descriptions? For Biology has not stood still any more than Physics, and the Physiology of our own day has become different from that of the times when the mechanistic Philosophy of life took origin. The embryologists and the naturalists of our own generation have studied the whole organism in its normal functioning and behaviour, and have obtained results which cannot easily be understood as physico-chemical mechanism. Life is not the activities of the organism, but the integration of the activities of the organism, just as Reality for Physics is not the atoms and molecules of gross matter, but the integration of these in the ether of space.

This, then, is all that we mean by the philosophy of Biology—the attempt to understand the descriptions of the Science in the light of its later investigations. Philosophy, in the academic sense, we have not considered in relation to the subject-matter of our science, though there is much in the classic systems that is of absorbing interest, even to the working investigator of the nineteenth century. The biological education is not, however, such as to predispose one towards these studies. The reader will recognise that the point of view, and the methods of treatment, adopted in this book are those suggested by Driesch and Bergson, even if no references are given. He may, perhaps, appreciate this limitation; for, influenced by the modern scientific training, he may be inclined to regard Philosophy as Mark Twain regarded his Egyptian mummy: if he is to have a corpse it might as well be a real fresh one.

J. J.

Liverpool
November 1913

CONTENTS

CHAPTER I

PAGE

THE CONCEPTUAL WORLD[1]

Argument.—The conscious organism is one that acts. Its consciousness of an external world is not simply the result of the stimuli made by that world on its organs of sense, for it becomes fully aware only of those stimuli which result in deliberated bodily activity. This awareness of an outer world on which it acts is the perception of the organism. Its consciousness is an intensive multiplicity. This multiplicity is arbitrarily dissociated, for convenience’ sake, by the mental organisation, which confers extension and magnitude and succession on those aspects of consciousness which it arbitrarily dissociates from each other. Our notion of space is an intuitive one and depends on our modes of bodily exertion. Our notions of motion and continuity are also intuitive ones, and they cannot be represented intellectually, but we can approximate to them by the methods of the infinitesimal calculus. Mathematical time is only a series of standard events which punctuate our duration. Duration is the accumulated existence and experience of the organism. We cannot prove intellectually that there is a world external to our consciousness, but that this world exists is a conviction intuitively held.

CHAPTER II

THE ORGANISM AS A MECHANISM[49]

Argument.—If the organism is a physico-chemical mechanism its activities must conform to the two principles of energetics: the law of conservation of energy and matter, and the law of entropy-increase. They conform strictly to the law of conservation. The law of the degradation of energy is true of our experience of inorganic nature, but we can show that it cannot be universally true. Inorganic processes are irreversible ones, and they proceed in one direction only, and in them energy is degraded. Organic processes, that is, the processes carried on in the generalised organism, are irreversible; or, at least, there is a tendency for them to be carried on without necessary dissipation of energy.

CHAPTER III

THE ACTIVITIES OF THE ORGANISM[83]

Argument.—If the organism is investigated by the methods of physical and chemical science, nothing but physico-chemical activities can be discovered. This is necessarily the case, since methods which yield physico-chemical results only are employed. The physiologist makes an analysis of the activities of the organism, and he reduces these activities to certain categories; although all attempts completely to describe the functioning of the organism solely in terms of physical and chemical reactions fail. In addition to the reactions which make up the functioning of an organ or organ-system, there is direction and co-ordination of these reactions. The individual physico-chemical reactions which occur in the functioning of the organism are integrated, and life is not merely these reactions, but also their integration.

CHAPTER IV

THE VITAL IMPETUS[120]

Argument.—The notion of the organism as a physico-chemical mechanism is a deduction from the methods of physiology, and not from its results. The notion of vitalism is a natural or intuitive one. The historic systems of vitalism assumed the existence of a spiritual agency in the organism, or of a form of energy which was peculiar to the activities of the organism. Modern investigation lends no support to either belief. But the study of the organism as a whole, that is, the study of developmental processes, or that of the organism acting as a whole, afford a logical disproof of pure mechanism. It shows that there cannot be a functionality, in the mathematical sense, between the inorganic agencies that affect the whole organism and the behaviour or functioning of the whole organism. Mechanism is only suggested in the study of isolated parts of the organism. We are compelled toward the belief that there is an agency operative in the activities of the organism which does not operate in purely inorganic becoming. This is the Vital Impetus of Bergson, or the Entelechy of Driesch.

CHAPTER V

THE INDIVIDUAL AND THE SPECIES[162]

Argument.—The concept of the organic individual is one which is arbitrary, and is convenient only for purposes of description. Life on the earth is integrally one. Personality is the intuition of the conscious organism that it is a centre of action, and that all the rest of the universe is relative to it. The individual organism, regarded objectively, is an isolated, autonomous constellation, capable of indefinite growth by dissociation, differentiation, and re-integration. This growth is reproduction. The dissociated part reproduces the form and manner of functioning of the individual organism from which it has proceeded. The offspring varies from the parent organism, but it resembles it much more than it varies from it. There are therefore categories of organisms in nature the individuals of which resemble each other more than they resemble the individuals belonging to other categories: these are the elementary species. Hypotheses of heredity are corpuscular ones, and are based on the physical analogy of molecules and atoms. The concept of the species is a logical one. The organism is a phase in an evolutionary or a developmental flux, and the idea of the species is attained by arresting this flux.

CHAPTER VI

TRANSFORMISM[208]

Argument.—A reasoned classification of organisms suggests that a process of evolution has taken place. It suggests logical relationships between organisms, while the results of embryology and palæontology suggest chronological relationships. Yet this kinship of organisms might only be a logical, and not a material one. Evolution may have occurred somewhere, but it might be argued that the ideas of species have generated each other in a Creative Thought. But transformism may be produced experimentally, and so science has adopted a mechanistic hypothesis of the nature of the process. Transformism of species depends on the occurrence of variations, but these arise spontaneously and independently of each other, and they must be co-ordinated. This co-ordination of variations cannot be the work of the environment. Variations are cumulative, and they exhibit direction, and this direction is either an accidental one, or it is the expression of an impetus or directing agency in the varying organism itself. The problem of the cause of variation is only a pseudo-problem.

CHAPTER VII

THE MEANING OF EVOLUTION[245]

Argument.—If we assume the existence of an evolutionary process, the results of morphology, embryology, and palæontology ought to enable us to trace the directions followed during this process. But these results are still so uncertain that they indicate only a few main lines of transformism. Phylogenetic trees are largely conjectural in matters of detail. Evolution has resulted in the establishment of several dominant groups of organisms—the metatrophic bacteria, the chlorophyllian organisms, the arthropods, and the vertebrates. Each of these groups displays certain characters of morphology, energy-transformation, and behaviour; and a certain combination of characters is concentrated in each of the groups. But there is a community of character in all organisms which have arisen during the evolutionary process. The transformation of kinetic into potential energy is characteristic of the chlorophyllian organisms. The utilisation of potential energy, and its conversion into the kinetic energy of regulated bodily activity, by means of a sensori-motor system, is characteristic of the animal. The bacteria carry to the limit the energy-transformations begun in the tissues of the plants and animals. Immobility and unconsciousness characterise the plant, mobility and consciousness the animal. Animals indicate two types of actions—intelligent actions and instinctive actions. Instinctive activity involves the habitual exercise of modes of action that have been inherited. Intelligent activities involve the exercise of modes of action that are not inherited, but which are acquired by the animal during its own lifetime, and are the results of perceptions which show the animal that its activity is relative to an outer environment.

CHAPTER VIII

THE ORGANIC AND THE INORGANIC[289]

Argument.—A strictly mechanistic hypothesis of evolution compels us to regard the organic world, and the inorganic environment with which it interacts, as a physico-chemical system. All the stages of an evolutionary process must therefore be equally complex: they are simply phases, or rearrangements, of the elements of a transforming system. The physics on which these mechanistic hypotheses were based was that of a discontinuous, granular, Newtonian universe, that is, one consisting of discrete particles, or mass-points, attracting or repelling each other with forces which are functions of the distances between them. It was a spatially extended system of parts. Therefore at all stages in an evolutionary process, or one of individual development, the elements of the system constitute an extensive manifoldness, and the obligation of mechanistic hypotheses of evolution and development to accept this view has shaped modern theories of heredity. Life is an intensive manifoldness, but in individual or racial evolution this intensive manifoldness becomes an extensive manifoldness. Life is a bundle of tendencies which can co-exist, but which cannot all be fully manifested, in the same material constellation, therefore these tendencies become dissociated in the evolutionary process. In this dissociation there is direction and co-ordination, which are the Vital Impetus of Bergson, or the Entelechy of Driesch.

Entelechy is an elemental agency in nature which we are compelled to postulate because of the failure of mechanism. It is not spirit, nor a form of energy, but the direction and co-ordination of energies. There is a sign, or direction of inorganic happening which absolutely characterises the processes which are capable of analysis by physico-chemical methods of investigation, and the result of this direction of inorganic happening is material inertia. Yet this direction cannot be universal: it must be evaded somewhere in the universe. It is evaded by the organism.

The problem of the nature of life is only a pseudo-problem.

APPENDIX

MATHEMATICAL AND PHYSICAL NOTIONS[342]

Infinity and the notion of the limit. Functionality. Frequency distributions and probability. Matter, force, mass, and inertia. Energy-transformations. Isothermal and adiabetic transformations. The Carnot engine and cycle. Entropy. Inert matter.

INDEX[377]

THE PHILOSOPHY OF BIOLOGY

CHAPTER I THE CONCEPTUAL WORLD

Let us suppose that we are walking along a street in a busy town; that we are familiar with it, and all the things that are usually to be seen in it, so that our attention is not likely to be arrested by anything unusual; and let us further suppose that we are thinking about something interesting but not intellectually difficult. In these circumstances all the sights of the town, and all the turmoil of the traffic fail to impress us, though we are, in a vague sort of way, conscious of it all. Electric trams approach and recede with a grinding noise; a taxicab passes and we hear the throb of the engine and the hooting of the horn, and smell the burnt oil; a hansom comes down the street and we hear the rhythmic tread of the horse’s feet and the jingle of the bells; we pass a florist’s shop and become aware of the colour of the flowers and of their odour; in a café a band is playing “ragtime.” There are policemen, hawkers, idlers, ladies with gaily coloured dresses and hats, newsboys, a crowd of people of many characteristics. It is all a flux of experience of which we are generally conscious without analysis or attention, and it is a flux which is never for a moment quite the same, for everything in it melts and flows into everything else. The noise of the tram-cars is incessant, but now and then it becomes louder; the music of the orchestra steals imperceptibly on our ears and as imperceptibly fades away; the smell of the flowers lingers after we pass the shop, and we do not notice just when we cease to be conscious of it; the rhythm of the ragtime continues to irritate after we have ceased to hear the band—all the sense-impressions that we receive melt and flow over into each other and constitute our stream of consciousness, and this changes from moment to moment without gap or discontinuity. It is not a condition of “pure sensation,” but it is as nearly such as we can experience in our adult intellectual life.

It is easy to discover that many things must have occurred in the street which did not affect our full consciousness. We may learn afterwards that we have passed several friends without recognising them; we may read in the newspapers about things that happened that we might have seen, but which we did not see; we may think we know the street fairly well, but we find that we have difficulty in recalling the names of three contiguous shops in it; if we happen to see a photograph which was taken at the time we passed through the street we are usually surprised to find that there were many things there that we did not see. Why is it, then, that so much that might have been perceived by us was not really perceived? We cannot doubt that everything that came into the visual fields of our eyes must have affected the terminations of the optic nerves in the retinas; the complex disturbances of the air in the street must have set our tympanic membranes in motion; and all the odoriferous particles inhaled into our nostrils must have stimulated the olfactory mucous membranes. In all these cases the stimulation of the receptor organs must have initiated nervous impulses, and these must have been propagated along the sensory nerves, and must have reached the brain, affecting masses of nerve cells there. Nothing in physiology seems to indicate that we can inhibit or repress the activity of the distance sense-receptors, visual, auditory, and olfactory, with their central connections in the brain; they must have functioned, and must have been physically affected by the events that took place outside ourselves, and yet we were unconscious, in the fullest sense of this term, of all this activity. Why is it, then, that our perception was so much less than the actual physical reception of external stimuli that we must postulate as having occurred? Sherlock Holmes would have said that we really saw and heard all these things although we did not observe them, but the full explanation involves a much more careful consideration of the phenomena of perception than this saying indicates.

There is, of course, no doubt that we did see and hear and smell all the things that occurred in the street during our aimless peregrination, that is, all the things which so happened that they were capable of affecting our organs of sense. This is true if we mean by seeing and hearing and smelling merely the stimulation of the nerve-endings of the visual, auditory, and olfactory organs, and the conduction into the brain of the nervous impulses so set up. But merely to be stimulated is only a part of the full activity of the brain; the stimulus transmitted from the receptor organs must result in some kind of bodily activity if it is to affect our stream of consciousness. Two main kinds of activity are induced by the stimulation of a receptor organ and a central ganglion, (1) those which we call reflex actions, and (2) those actions which we recognise as resulting from deliberation. We must now consider what are the processes that are involved in these kinds of neuro-muscular activity.

The term “reflex action” is one that denotes rather a scheme of sensori-motor activity than anything that actually happens in the animal body; it is a concept that is useful as a means of analysis of complex phenomena. In a reflex three things happen, (1) the stimulation of a receptor organ and of the nerve connecting this with the brain, (2) the reflection, or shunting, of the nervous impulse so initiated from the terminus ad quem of the afferent or sensory nerve, to the terminus a quo of the efferent or motor nerve, and (3) the stimulation of some effector organ, say a motor organ or muscle, by the nervous impulse so set up. The simplest case, perhaps, of a reflex is the rapid closure of the eyelids when something, say a few drops of water, is flicked into the face. Stated in the way we have stated it the simple reflex does not exist. In the first place, it is a concept based on the structural analysis of the complex animal where the body is differentiated to form tissues—receptor organs, nerves, muscles, glands, and so on. But a protozoan animal, a Paramœcium for instance, responds to an external stimulus by some kind of bodily activity, and yet it is a homogeneous, or nearly homogeneous, piece of protoplasm, and this simple protoplasm acts at the same time as receptor organ, conducting tissue or nerve, and effector organ. In the higher animal certain parts of the integument are differentiated so as to form visual organs, and the threshold of these for light stimuli is raised while it is lowered for other kinds of physical stimuli. Similarly other parts of the integument are modified for the reception of auditory stimuli, becoming more susceptible for these but less susceptible for other kinds of stimuli than the adjacent parts of the body. Within the body itself certain tracts of protoplasm are differentiated so that they can conduct molecular disturbances set up in the receptor organs in the integument better than can the general protoplasm; these are the nerves. Other parts are modified so that they can contract or secrete the more easily; these are the muscles and glands. The conception of a reflex action, as it is usually stated in books on physiology, therefore includes this idea of the differentiation of the tissues, but all the processes that are included in the typical reflex are processes which can be carried on by undifferentiated protoplasm.

It is also a schematic description that assumes a simplicity that does not really exist. As a rule a reflex is initiated by the stimulation of more than one receptor organ, and the impulses initiated may thus reach the central nervous system by more than one path. There is no simple shunting of the afferent impulse from the cell in which it terminates into another nerve, when it becomes an efferent impulse; but, instead of this, the impulse may “zigzag” through a maze of paths in the brain or spinal cord connecting together afferent and efferent nerves and ganglia. Further, the final part of the reflex, the muscular contraction, is far from being a simple thing, for usually a series of muscles are stimulated to contract, each of them at the right time and with the right amount of force, and every contraction of a muscle is accompanied by the relaxation of the antagonistic muscle. There are muscles which open the eyelids and others which close them, and the cerebral impulse which causes the levators to contract at the same time causes the depressors to relax.

It is quite necessary to remember that the simple reflex is really a process of much complexity and may involve many other parts and structures than those to which we immediately direct our attention. But leaving aside these qualifications we may usefully consider the general characters of the reflex, regarding it as a common, automatically performed, restricted bodily action, involving receptor organ, central nervous organ, and effector organ. There are certain kinds of external stimuli that continually affect our organs of sense, and there are certain kinds of muscular and glandular activity that occur “as a matter of course,” when these stimuli fall on our organs of sense. The emanation from onions or the vapour of ammonia causes our eyes to water; the smell of savoury food causes a flow of saliva; and anything that approaches the face very rapidly causes us to close the eyes. Reflexes are, in a way, commonly occurring, purposeful and useful actions, and their object is the maintenance of a normal condition of bodily functioning.

We dare hardly say that the simple reflex is an unconsciously performed action, although we are not conscious, in the fullest sense of the term, of the reflexes that habitually take place in ourselves. But even in the decapitated frog, which moves its limbs when a drop of acid is placed on its back, something, it has been said, akin to consciousness may flash out and light up the automatic activity of the spinal cord. We must not think of consciousness as that state of acute mentality which we experience in the performance of some difficult task, or in some keenly appreciated pleasure, or in some condition of mental or bodily distress; it is also that dimly felt condition of normality that accompanies the satisfactory functioning of the parts of the bodily organism. But this dim and obscure feeling of the awareness of our actions is easily inhibited whenever what we call intellectual activity proceeds.

Much of the stimulation of our receptor organs is of this generally occurring nature, and we are not aware of it although the stimuli received are such as to induce useful and purposeful bodily activity. In walking along the street we automatically avoid the people, and the other obstacles that we encounter, by means of regulated movements of the body and limbs, but this is activity that has become so habitual and easy that we are hardly aware of it, and not at all, perhaps, of the physical stimuli which induce it. But not only do we receive stimuli which are reflected into bodily actions without our being keenly aware of this reception, but we also receive stimuli which do not become reflected into bodily activity. It is, Bergson suggests, as if we were to look out into the street through a sheet of glass held perpendicularly to our line of sight; held in this way we see perfectly all that happens in front of us, but when we incline the glass at a certain angle it becomes a perfect reflector and throws back again the rays of light that it receives. This is, of course, a physical analogy, and no comparison of material things with psychical processes can go very far, but in a way it is more than an analogy. In our indolent absorbed state of mind we do not as a rule see the objects which we are not compelled to avoid, and which do not, in any way, influence our immediate condition of bodily activity. The optical images of all these things are thrown upon our retinas and are, in some way, thrown or projected upon the central ganglia, but there the series of events comes to an end, for the images are not reflected out towards the periphery of the body as muscular actions. We cannot doubt that this is why we do not perceive all the stimulation of our organs of sense that we are sure that take place. These stimuli pass through us, as it were, unless they are reflected out again as actions. In this reflection, or translation of neutral into muscular activity, perceptions arise.

But even then perception need not arise. It does not, as a rule, accompany the automatically performed reflex action, because the latter is the result of intra-cerebral activities that have become so habitual that they proceed without friction. There are innumerable paths in the brain along which impulses from the receptor organs may pass into the motor ganglia, but in the habitually performed reflex actions these paths have been worn smooth, so to speak. The images of objects which are perceived over and over again by the receptor organs glide easily through the brain and as easily translate themselves into muscular, or some other kind of activity. The things that matter in the life of an animal which lives “according to nature” are cyclically recurrent events in which, after a time, there is nothing new. Most of them proceed just as well in the animal deprived of its cerebral hemispheres by operation as in the intact cerebrate animal. In the performance of actions of this kind the organism becomes very much of an automaton.

Let something unusual happen in the street while we are walking through it—a runaway horse, or the fall of an overhead “live” wire, for instance, something that has seldom or never formed part of our experience, and something that may have an immediate effect on us as living organisms. Then perception arises at once because the stimulation of our organs of sense presents us with something which is unfamiliar, and yet not so unfamiliar that it does not recall from memory, or from derived experience, reminiscences of the images of somewhat similar things, and of the effects of these. The train of events that now proceeds in our central nervous system becomes radically different from that which proceeded in our former, rather aimless, series of actions. The stimuli no longer pass easily through the “lower” ganglia of the brain, but flash upwards into the cortical regions, where they become confronted with the possibility of innumerable alternative paths and connections with all the parts of the body. They waver, so to speak, before adopting one or other, or a combination of these paths; there is hesitation, deliberation, and finally choice of a path, with the result that a series of muscular organs become inervated and motor actions, of a type more or less competent to the situation in which we find ourselves, are set up. In this hesitation and deliberation perception arises. It is when the animal may act in a certain way as the result of a stimulus which is not a continually recurrent one, but at the same time may refrain from acting, or may act in one of several different ways, that perception of external things and their relations arises.

That is to say, we perceive and think because we act. We do not look out on the environment in which we are placed in a speculative kind of way, merely receiving the images of things, and classifying and remembering them, while all the time we are passive in so far as our bodily activities are concerned. If the results of modern physiology teach us anything in an unequivocal way they teach us this—that the organs of activity, muscles, glands, and so on, and the organs of sense and communication, are integrally one series of parts, and that apart from motor activity nervous activity is an aimless kind of thing. It is because we act that we think and disentangle the images of things presented to us by our organs of sense, and subject all that is in the stream of consciousness to conceptual analysis.[1]

That is to say, in thinking about the flux of consciousness we decompose it into what we regard as its constituent parts, and we confer upon these parts separate existence in space and time. But it is clear that none of the things which we thus regard as the elements of our consciousness has any real existence apart from the others. The smell of the flowers and that of the burnt oil interpenetrate in our consciousness of the stimulation of our olfactory organs just as do the jingle of the cab bells, the music of the orchestra, and the throb of the motor car in the impressions transmitted by our auditory organs. It is difficult to see that all these things, with the multitude of other things which we perceive, constitute a “multiplicity in unity,” that is an assemblage of things which are separate things, but which do not lie alongside each other in space and mutually exclude each other, but which are all jammed into each other, so to speak. It is easy to see that we are conscious of a heterogeneity, and whenever we think of this multitude of things it seems natural that we should separate them from each other. The stream of our consciousness is so complex that we cannot attend to it all at once, not even to the few things that we have picked out in our example. If we concentrate our attention on any part, or rather aspect of it, all the rest ceases to exist, or rather we agree to ignore it, and this very concentration of thought upon one part of our experience isolates it from all the rest. To a certain extent the analysis of the complex of sensation is the result of the work of different receptor organs; certain fields of energy, which we call light, radiation, etc., affect the nerve-endings in the retina; chemically active particles in the atmosphere affect the nerve-endings in the olfactory membranes; and rapidly repeated changes of pressure in the atmosphere (sound vibrations) affect the auditory organs in the internal ear, and so on. But this reception of different stimuli by different receptor organs exists only in the higher animal; there are no specialised sense organs in a Paramœcium, for instance, and the whole periphery of the animal must receive all these different kinds of external stimuli at once. The specialisation of its receptor organs in the higher animal is rather the means whereby the organism becomes more receptive of its environment, than the means whereby it analyses that environment. This analysis is the work of the consciousness of the animal.

Fig. 1.

Suppose that we draw a curve AB freehand with a single undivided sweep of the pencil. By making a certain assumption—that the curve which we drew was one that might be regarded as cyclical, that is, might be repeated over and over again—we can subject it to harmonic analysis. We can decompose it into a number of other curves (CD, EF, etc.), each of which is a separate “wave” rising above and falling below the axis OX in a symmetrical manner. If we draw any vertical line MN cutting these curves, we shall find that the distance between the axis OX and the main curve AB is always equal to the algebraic sum of the distances between the axis and the other curves. These latter we call the harmonic constituents of the curve AB, supposing them to “add up” so as to form it. But AB was something quite simple and elemental and its constituents cannot be said to have existed in it when we drew it freehand; it was only by an artifice of practical utility in mathematical computations that we constructed them. It may be, of course, that the harmonic constituents of a curve had actual existence apart from the curve itself, but, in the case that we take, they certainly had not. Now we must think of our stream of consciousness in much the same way. It is something immediately experienced and elementary; it is the concomitant, if we choose so to regard it, of the external processes that go on outside our bodies. We can investigate it by thinking about it, and attending to one aspect of it after another, thus arbitrarily detaching one “part” of it from all the rest, but immediately we do this we rise above the flux of experience into the region of intellectual concepts. We have converted a multiplicity of states of consciousness, all of which co-exist along with each other, and in each other, and which have no spatial existence, into a multiplicity of states, visual, auditory, olfactory, etc., which have become separated from each other and have therefore acquired extension. This dissociation of the flux of experience is the process of conceptual analysis carried out by thought.

If we dissociate the stream of consciousness in this way, breaking it up into states which we choose to regard as separate from each other, we shall see that of the elements which we thus isolate many are like each other and can be associated. Obviously there is a greater resemblance between different smells than between smells and sounds. Different musical sounds are more like each other than are sounds, and feelings of heat and cold. There is a greater likeness between the states of consciousness which arise from the stimulation of the same receptor organ, than between those that arise from the stimulation of different receptors. Those differences of sensation accompanying the stimulation of different sense organs we regard as different in kind; there is absolutely no resemblance between a colour and a sound, we say, however much the modern annotator of concert programmes may suggest the analogy. But we say that there may be different degrees of stimulation of the same sense organ, and that the sensations that we thus receive are of the same kind though they differ in intensity. The whistle of a railway engine becomes louder as the train approaches, that is to say, more intense, and if we study the physical conditions that are concomitant with the stimulation of our tympanic membranes we shall see that waves of alternate rarefaction and compression are set up in the atmosphere outside our ears. All the time that the train approaches the frequency of these waves remains the same, that is, just as many occur in a second when the train is distant as when it is near. But the amplitude of the waves has been increasing, and the velocity with which the molecules of air strike against the tympanic membranes becomes greater the nearer is the source of sound.

Fig. 2. We can represent this by means of a diagram which shows that the amplitude of the waves—which represents the loudness of the sound—increases while the frequency—which represents the pitch—remains the same. The amplitude is represented by the straight vertical lines, 11, 22, 33, etc., which are of increasing magnitude. Thus we represent the physical cause of the increasing loudness of the sound by space-magnitudes, and then we transfer these magnitudes to the states of consciousness concomitant with the vibrating molecules of air. Suppose that we knew nothing at all about the cause of the differences of pitch of musical sounds and that we listen to the notes of the octave, C, D, E,——C, sounded by an organ; all that we should experience would be that the sounds were different. If we were to sing the notes we might attain the intuition that the notes G, A, B were “higher” than the notes C, D, E, because a greater effort was required in order to produce these sounds, but obviously this is a different thing from saying that the notes themselves were “higher” or “lower.” But let us match the notes by striking tuning-forks, and then having selected forks which give the notes of the octave let us fix them so that they will make a tracing, while still vibrating, on a revolving strip of paper. We shall then find that the fork emitting the note C makes (say) 256 vibrations per second, the fork D  9/8 256 vibrations, the fork E  5/4 256 vibrations, and so on. Thus we associate the notes of the octave together and we say that their quality was the same but that their pitch differed, and since the pitch depends on the frequency of vibration of the fork, or of the air in its vicinity, we say that pitch differences are quantitative ones, and that the states of consciousness which accompany these physical events are also quantitatively different.

So also with colour. If we had no such apparatus as prisms or diffraction gratings, which enable us to find what is the wave length of light, should we have any idea of the spectral hues, red, yellow, orange, green, etc., as differing from each other quantitatively? It is certain that we should not. But observation and experiment have shown that the nerve-endings of the optic nerve in the retina are stimulated by vibrations of something which we agree to call the ether of space, and that the frequency of vibration of light which we call red is less than that which we call orange, while the frequency of vibration of orange light is less again than that of blue light, and so on. To our consciousness red, orange, yellow, and blue light are absolutely different, but we disregard this intuition and we say that our perceptions of light are similar in kind but differ, in some of them are more intense than are some others. Again, have we any intuitive knowledge of increasing temperature? If we dip our hands into ice-cold water the sensation is one of pain, if the water has a temperature of 5° C. it feels cold, if it is at 15° C. we have no particular appreciation of temperature, if at 25° C. it feels very warm, if it is at 60° it is very hot, and if it is at 90° we are probably scalded and the feeling is again one of pain. If we place a thermometer in the water we notice that each sensation in turn is associated with a progressive lengthening of the mercury thread, and if we investigate the physical condition of the water we find that at each stage the velocity of movement of the molecules was greater than that at the preceding stage. We say, then, that our different perceptions were those of heat of different degrees of intensity, so transferring to the perceptions themselves the notions of space-magnitudes acquired by a study of the expansion of the mercury in the thermometer, or by the adoption of the physical theory of the kinetic structure of the water. Yet it is quite certain that what we experienced were quite different things or conditions, cold, warmth, heat, and pain, and indeed, in this series of perceptions different receptor organs are involved.

Suppose we listen to the note emitted by a syren which is sounding with slowly increasing loudness but with a pitch which remains constant. We do not notice at first that the sound is becoming louder, but after a little time we do notice a difference. Let us call the amplitude of vibration of the air when the syren first sounds E, and then, when we notice a difference, let us call the amplitude ΔE + E, ΔE being the increment of amplitude. Let us call our sensation when the syren first sounds S, and our sensations when the sound has become louder S + ΔS, ΔS being the “increment of sensation.” Then the relation holds:—

Fig. 3.

If we plot these equal increments of loudness as the dependent variable S in a graph, and the amplitude of the vibrations of the atmosphere as the independent variable E, we can obtain the following curve. If we investigate this we shall find that a certain relation exists between the “values” of the sensation and the values of the stimuli that correspond to them; a regular increase in the loudness of the sensation corresponds to a regular increase in the logarithms of the strength of the stimuli. Let S = the sensation, E the stimulus, and C and Q constants; then

Thus we decompose our stream of consciousness into a series of quantitatively different and qualitatively different things, upon each of which we confer independent existence. We attribute to these different aspects of our consciousness extension, but the extension is due only to our analysis; for the qualities of pitch, loudness, colour, odour, etc., which we disentangle from each other, did not exist apart from each other, any more than do the sine and cosine curves into which we decompose an arbitrarily drawn curved line. The multiplicity of our consciousness is intensive, like the multiplicity that we see to exist in the abstract number ten. This number stands for a group of things, but its multiplicity is intensive and only exists because we are able to subdivide anything in thought to an indefinite extent. Now, so far we have only separated what we agree to regard as the elemental parts of our general perception of the environment, but it is to be noted that we have not given to these elements anything like spatial extension.

We may, if we like, regard our intuition of space as that of an indefinitely large, homogeneous, empty medium which surrounds us and in which we may, in imagination, place things. So regarded it is difficult to see in what way our notion of space differs from our idea of “nothing,” a pseudo-idea incapable of analysis, except into the idea of something which might be somewhere else. The more we think about it the more we shall become convinced that space, that is the “form” of space, represents our actual or potential modes of motion, that is, our powers of exertional activity. Space, we say, has three dimensions; in all our analysis of the universe, and of the activities that we can perceive in it, this idea of movement in three dimensions, forward and backward, up and down, and right and left, occurs; and we have to recognise that in it there is something fundamental, as fundamental as the intuitive knowledge that we possess of the direction of right and left. It is because we can move in such a way that any of our motions, no matter how complex, can be resolved into the components of backward and forward, right and left, and up and down, these directions all being at right angles to each other, that we speak of our movements as three-dimensional ones. Our geometry is founded, therefore, on concepts derived from our modes of activity; and there is nothing in the universe, apart from our own activity, that makes this the only geometry possible to us. Euclidean geometry does not depend on the constitution of the external universe, but on the nature of the organism itself.

There is a little Infusorian which lives, in its adult phase, on the surface of the spherical ova of fishes. These ova float freely in sea water, and the Infusorian crawls on their surfaces, moving about by means of ciliary appendages. It does not swim about in the water, but adheres closely to the surface of the ovum on which it lives. Let us suppose that it is an intelligent animal and that it is able to construct a geometry of its own; if so, this geometry would be very different from our own.

It would be a two-dimensional geometry, for the animal can move backward and forward, and right and left, but not up and down; it is a stereotropic organism, as Jacques Loeb would say, that is, it is compelled by its organisation to apply its body closely to the surface on which it lives. But its two-dimensional geometry would, on this account, be different from ours. Our straight lines are really the directions in which we move from one point to another point in such a way as to involve the least exertion; they are the shortest distances between two points, and if we deviate from them we exert a greater degree of activity than if we had moved along them. For us there is only one straight line that can be drawn between two points, but this is not necessarily true for our Infusorian, and its straight line need not be the shortest distance between two points. It might be either the longest or the shortest distance between the points, for the latter can always be placed on a great circle passing through the two points and the poles of the egg, and in moving from a point on which it is placed the animal could reach the other point by moving in two directions, just as we could go round the earth along the equator by moving to the east or to the west. Therefore the straight line of the Infusorian would be not only a scalar quantity but a vector quantity, that is, it would represent, not only a quantity of energy, but a quantity of energy that has direction. For us only one straight line can be drawn between two given points, but this limitation would not exist in the two-dimensional geometry of a curved surface. Suppose that the two points are situated on a great circle and that they are exactly 180° apart; then the Infusorian could move from one pole to another pole along an infinite number of straight lines or meridians all of which had a different direction, but all of which were of the same length; that is to say, in this geometry an infinite number of straight lines can be drawn between the same two points. Again, its triangles might be different from ours; our triangles are figures formed by drawing straight lines between three points, and on a plane surface the sum of the angles of the triangle are together equal to two right angles, though on a curved surface they may be greater or less than two right angles. But our Infusorian could not imagine a triangle in which the sum of the angles was not greater than two right angles, for all its figures would be drawn on a convex surface.

Our three-dimensional geometry depends, therefore, on our modes of activity and the concepts with which it operates; points, straight lines, etc. are conceptual limits to those modes of activity. We can imagine a straight line only as a direction along which we can move without deviating to the right or the left, or up or down. But even if we draw such a line on paper with a fine pencil the trace would still have some width, and we can imagine ourselves small enough to be able to deviate to the right or the left within the width of the line drawn on the paper. We might make a very small mark on the paper, but no matter how small this mark is it would still have some magnitude; otherwise we should be unable to see it. If the straight line had no width and the point no magnitude they would have no perceptual existence. Our perceptual triangles are not figures, the angles of which are necessarily equal to two right angles. If we drive three walking sticks into a field and then measure the angles between them by means of a sextant we shall find that the sum is nearly 180°, but in general not that amount. If we stick a darning needle into the heads of each of the walking sticks and then remeasure the angles by means of a theodolite we shall obtain values which are nearer to that of two right angles, but we should not, except by “accident,” obtain exactly this value. We do not, therefore, get the “theoretical” result, and we say this is because of the errors of our methods of observation; but why do we suppose that there is such a theoretical result from which our observations deviate, if our observations themselves do not in general give this ideal result? We might accumulate a great series of measurements of the angles of our triangle, and we should then find that these results would tend to group themselves symmetrically round a certain value which would be 180°. Some of the results would be considerably less than the ideal, and some of them would be considerably more; but these relatively great deviations would be small in number and most of the results would be a very little less than 180° or a very little more, and there would be as many which would be a little less as those that were a little more. We should have formed a “frequency distribution”[2] with its “mode” at 180°.

But by “reasoning” about the “properties” of these lines and triangles in plane two-dimensional space, we should arrive at the conclusion that the angles of a triangle were equal to 180°, and neither more nor less. We should then think of a straight line as still a path along which we move in imagination, and a path which still has some width. But we imagine the width of the path to become less and less, so that, even if we imagine ourselves to become thinner and thinner, we should be unable to deviate either to the right or left in moving along the path, because the thinner we make ourselves the thinner becomes also the path. We imagine our intuition of a deviation to the right or left becoming keener and keener, so that, no matter how small the deviation we should still be able to appreciate it by the extra exertion which it would involve. We think of a point as a little spot, and we think of ourselves as being very small indeed, so that we can move about on this spot. But we can reduce the area of the spot more and more, until it becomes “infinitesimally” small; and at the same time we think of ourselves as becoming smaller and smaller, so that we can still move about on the spot. But we think of the area of the spot as becoming so small that no matter how small we make ourselves we are unable to move on it.

This means that we substitute conceptual lines and points and triangles for the perceptual ones of our experience, and then we operate in imagination with these concepts. That is to say, we carry our modes of exertional activity to their limits,[3] in the way which we have tried to indicate above—a process of thought which is the foundation of the reasoning of the infinitesimal calculus.

What we call space, therefore, depends on our intuition of bodily exertion. This intuition includes the knowledge that a certain change has occurred as the consequence of the expenditure of a certain amount of bodily energy, and that, as the result of this change, the relation of the rest of the universe to our body has become different. We think of our body as the origin, or centre, of a system of co-ordinates:—

Fig. 4.

We imagine three lines at right angles to each other to extend indefinitely out into space, and we think of ourselves as being situated at the point of intersection of these three straight lines. If anything moves in the universe outside ourselves we can resolve this motion into three components, each of which is to be measured along one of the axes of our system of co-ordinates. But any motion whatever in the universe outside ourselves can be represented equally well by supposing that the origin of the system of co-ordinates has been changed; that is, by supposing that we have changed our position relative to the rest of the universe. Therefore motion outside ourselves is not to be distinguished from a contrary motion of our own body—a statement of the “principle of relativity”—except that any change outside ourselves may be distinguished from that compensatory change in the position of our body which appears to be the same thing, by the absence of the intuition that we have expended a certain quantity of energy in producing the change. Conscious motion of our own body is something absolute; all other motion is relative.

So far we have been speaking of our crude bodily motion, but a very little consideration will show that our knowledge of space attained by scientific measurements depends just as much on our intuition of our bodily activity, and its direction; the measurement of a stellar parallax, or that of the meridian altitude of the sun, for instance, by astronomical instruments, involves bodily exertion, though of a refined kind. Three-dimensional space, that is our space, therefore represents the manner of our activity, just as convex two-dimensional space represents the manner of the activity of the Infusorian, and one-dimensional space would represent the manner of activity of an animal which was compelled to live in a tube, the sides of which it fitted closely, so that it could move only in one direction—up and down. A parasite, living attached to some fixed object, and the movements of which were represented only by the growth of its tissues, could not form any idea of space; and the “higher” forms of geometry, that is, space of four or more dimensions, present no clear notion to our minds, even although we regard the operations included in mathematics of this kind as pure symbolism, because we cannot relate this imaginary space to any form of bodily exertion. Geometry, then, represents the manner in which our bodily exertion cuts up the homogeneous medium in which we live.

Motion, whether it be that of our own body in controlled muscular activity, or that imaginary motion of the environment which we call giddiness, or a sensibly perceived motion of some part of the environment, that is, a motion which we can compensate by some actual or imaginary change in the position of our own body produced by our own exertion, is an intuitively felt change, and is incapable of intellectual representation. It is not clearly conceived either in ancient or in modern geometry. Euclidean geometry is, as we have seen, based directly on our intuition of bodily exertion, but it is essentially static in treatment. Let it be admitted that we can draw a straight line of any length and in any direction, and so on; then we regard these straight lines, etc., as motionless, abstract things, and we proceed to discuss their relationships. Cartesian geometry, and the methods of the infinitesimal calculus, do not treat of real motion, and the concept, if it is introduced at all, is introduced illegitimately and surreptitiously. Consider what we do when we “plot a curve.” Let the latter be a parabola having the equation y =  1/2 x. Now a parabola is defined as “the locus of a point which moves, so that its distance from a fixed point is in a constant relation to its distance from a fixed straight line.” How do we construct such a curve?

Fig. 5.

We proceed to fix the positions of a series of points in this way: there are two straight lines, OX and OY, at right angles to each other, and we measure off certain steps along the line OX; these steps are OX_0·5, OX₁, OX_1·5, OX₂, and so on, the small numerals indicating the distance of each point (OX_0·5, etc.) from the origin O. We then draw lines perpendicular to the X-axis through these points. We have now to calculate one-half of the square of each of these lengths OX_0·5, OX₁, etc., and then we mark off these calculated lengths along the perpendicular lines. The point A, for instance, is  1/2(0·5)² from the point X_0·5, B is  1/2(1)² from X₁, and so on. In this way we obtain a series of points, A, B, C, D, E, etc., and these are points on the locus of the “moving” point.

Fig. 6.

There is nothing at all about motion here. All that we have done is to measure lengths. We have made a kind of counterpoint, X-points against Y-points, but we have not even made a curve. We connect the points A, B, C, D, E, etc., by means of short, straight lines, and then we may connect together these short lines, and, if we plot a number of intermediate points between those that we have already obtained and join these, the points may be so close together that they may seem to be indistinguishable from a curve. Yet, no matter how numerous they may be, they can never be connected together so as to form a curve; we therefore draw a curved line freehand through them, and at once, in so doing, we abandon our intellectual methods, for our curve depends on our intuition of continuously changing direction. But if we think about it we shall find that we can form no clear intellectual notion of continuity and we can only measure the curvature of a line at a point in the line by drawing a tangent to the curve at this point, and then by measuring the slope of the tangent. The curve itself we obviously leave out of consideration.

We cannot conceive of the point moving along the locus OD. We can think of it only as at the places O, A, B, C, D, E, etc., but we must neglect the intervals OA, AB, BC, CD, DE, and so on, or we can divide them into smaller intervals by supposing the point to have occupied the positions f, g, i, j, between the points A and B, for instance. Yet, no matter how many these intervals may be, we can only think of the point as being at the places O, A, B, C, D, E, or at f, g, i, j, and so on. We never think of the intervals themselves, and, if all we think about is the position of the point, we do not really think of it as in motion at all. We can see it in motion, but we cannot form an intellectual concept of its motion. It is not really necessary that we should in the affairs of everyday life, but for the adequate treatment of problems involving rates of change science had to wait for the invention of the methods of the infinitesimal calculus before this disability of the human mind could be circumvented.

But the moving point occupies successively a number of different positions in space. If it is a material point that we observe to move from one place to another, we perceive that a certain interval of our duration corresponds with the change of position of the point. Duration was not used up in the occupancy of the different positions O, A, B, C, D, E, and so on, nor in that of the occupancy of the indefinitely numerous other positions in which we may place the moving point, but in the intervals themselves. We have said “duration” and not “time,” using Bergson’s term. By duration and time we understand different things.

Time is, for us, only a series of standard events which punctuate, so to speak, our experienced duration. The unit of time is the sidereal day, that is, the interval of time between two successive transits of a fixed star across the arbitrary meridian. But if we try to conceptualise this interval we find that we can do so only by breaking it up into smaller intervals, and this we do by using a pendulum of a certain length which makes a certain number of swings (86,400) during the interval between the two transits of the star. Thus we obtain a smaller interval of duration and we call this a second of time. But for many purposes this interval is too long, and we can again sub-divide it by making use of a tuning-fork which makes, say, 1000 complete vibrations in a second; in this way we obtain still smaller intervals of duration—the sigmata of the physiologists. A sigma, therefore, represents the interval between the beginning and end of one complete vibration of a certain kind of tuning-fork; a second, that between the beginning and end of one complete swing of a pendulum of a certain length, placed at certain parts of the earth’s surface; and a day, that between two successive transits of a fixed star across a selected meridian, after all the necessary corrections have been made to the observation. These actual occurrences, the positions of the prongs of the tuning-fork, or those of the bob of the pendulum, or those of the fixed star do not involve duration. We consider the meridian of Greenwich as an imaginary line drawn across the celestial sphere, and the star as a point of light, so that the actual transit is, in the limit, an occurrence which occupies only an “infinitesimal” interval of duration. So also with the pendulum and the tuning-fork; the positions of these things do not “use up” time, and even if the intervals into which we divide astronomical time are indefinitely numerous no real quantity of duration is taken up by their occurrence. We know that the interval between two successive transits of a fixed star are not really constant, that is, the astronomical day is lengthening by an incredibly small part of a second each year, but how do we know this? It is not that we can feel the increments of duration, but just that we assume that Newton’s laws of motion are true; and hence that the tidal friction due to the motions of the earth, sun, and moon must retard the period of rotation of the earth so that the intervals between two successive transits of a star must become greater.

Thus we do not conceptualise the actual intervals of duration of which we are able to mark the end-points; they are lived by us, and they are real absolute things independent of our wills. Suppose we come in from a long walk, tired and thirsty, and ask the maid to get tea ready at once. She puts the kettle on the gas stove and then sits down to read. The water takes, say, five minutes to boil. What do we mean by this?

This is what we mean:—

What we call time here is only a series of simultaneously occurring events. The standard events are the positions of the hands of the clock on the clock face, that is, lengths of arc recording the number of swings of the pendulum that have occurred since the beginning of the operation of the boiling of the kettle. When this began, the hands of the clock were at, say, 4.30, and the temperature of the water was then, say, 17° C.; and, when it ended, the hands of the clock were at 4.35 and the temperature of the water was 100° C. It is only the simultaneities of these events that we have recorded and not the interval of duration that they mark. It does not matter how many times we might have looked at the hands of the clock and the thermometer, we should still have observed only simultaneities.

But we had to wait for the kettle to boil, and the temperature 100° was attained after the temperature 90°, and so on. What does this mean? While we were waiting, the water seemed to take an intolerably long time to boil. But the maid was reading one of Mr Charles Garvice’s novels, and “before she knew where she was” the kettle boiled over. There was a certain interval of duration experienced by her, and another, but different, interval of duration experienced by us. In each case there was a stream of consciousness. We felt fatigue, thirst, a lack of satisfaction, wandering attention, and irritation—all that was our duration. But the maid was identifying herself with Lady Mary, who had sprained an ankle and was being helped along by the new, young gamekeeper, and that was her duration.

There need not be any succession of events in the conceptual representation of a physical process. There is, for instance, no succession in such a conception as is represented by the following diagram—a conception well worth analysis:—

Fig. 7.

The figure represents a tracing made by a muscle-nerve preparation. A living muscle taken from an animal has been attached to a light lever, the end of which makes a scratch on a piece of smoked paper. The paper is fastened on a revolving cylinder and so long as the muscle is motionless the end of the lever marks a horizontal line on the paper. But if the muscle is stimulated so that it contracts and then relaxes again the lever is pulled up and is then lowered, and so its point makes a curve on the paper. The nerve going to the muscle can be stimulated electrically and the moment of the stimulation can be recorded by another lever, which makes a mark on the paper below the trace made by the lever which is attached to the muscle. Two such shocks have been applied to the nerve and they have elicited two contractions of the muscle and these two contractions have fused together.

In the actual experiment the operators could see that the muscle moved, and they could feel that a certain interval of their own duration coincided with the interval between the first and second depressions of the key that made the electric shocks. But the extent of motion of the muscle was too small, and the depressions of the key succeeded each other too rapidly to be easily observed, and therefore all these events were made to record themselves on the myogram. The series of little notches at the base of the figure represent the movements of the time-lever, that is, they are scratches made on the paper by a little lever which moves up and down at a rate fixed beforehand. Now when this time lever had made ten notches on the paper the first shock was applied to the nerve, and at the eleventh the muscle began to contract. At the seventeenth notch the second shock was applied and the muscle continued to contract. At the twenty-fifth notch the muscle ceased to contract and began to relax, and at the forty-second notch the muscle had ceased to contract. Everything now becomes clear and easy to represent mentally; the time-lever makes 100 notches on the paper in a second, so that there was an interval of 0.07 seconds between the two stimuli, and these two stimuli produced a compound contraction of the muscle lasting for 0.1 second. This is what the experimenters might have perceived, had human unaided senses been sufficiently acute. But they are not, and so the crude perception of the results of the experiment is replaced by a conception of the train of events involved in the operation. Duration and succession disappear and the myogram represents only a series of simultaneous events of this nature; the first stimulus occurs simultaneously with the tenth movement of the time-lever; the second stimulus with the seventeenth, and so on. In seeing the experiment the operators had to wait for one phase to be completed before they could observe another one, but in reasoning about it all the phases are spread out and are present in the conception at once. The duration was in the operators but not in the experiment: it was experienced, but it disappears when the results of the experiment are conceptualised.

A succession of events is in ourselves and not in the events observed. If a point is said to move along the locus OD through the positions A, B, C, it is we that have the feeling of succession, and the whole trajectory, or locus, or path of the point corresponds with a portion of our duration. The operation of boiling the kettle corresponds with a portion of our duration, which in its turn corresponds with that part of our duration which was marked by the positions of the hands of the clock. Thus we perceive a simultaneity in these two trains of events, and this enables us to assign a certain period of astronomical time to the operation of raising the temperature of the water, in the conditions of the experiment, from 17° C. to 100° C. But there is nothing absolute in this interval of astronomical time: what is absolute is that certain successions of events always correspond with other successions of events. A certain number of swings of a seconds-pendulum always corresponds with a certain rise in temperature of a definite mass of water which is in thermal contact with an indefinitely large reservoir of heat at a certain temperature, and, no matter how often we repeat this experience, the same simultaneity is always to be observed. Thus what the physicist considers is not intervals of his own duration but series of correspondences—that is, correspondences of certain standard events with the events which he is studying.

In reality time, in the sense of the astronomer’s time, does not enter into the methods of the mathematical physicist. Let us suppose that he is investigating the change that occurs in a material system between the two moments of time t₁ and t₂, these moments being separated from each other by a period of duration that we can feel. Let the system be, say, the earth and moon; the first body being supposed to be motionless, and the second being supposed to have a certain tangential velocity of movement. If the interval t₁ to t₂ is really an interval of astronomical time, the problem, what is the difference of position of the moon owing to the gravitation of the earth, is incapable of solution, and even if we reduce the interval of time indefinitely while still supposing that it is a finite interval, the mathematical difficulty remains. We then replace the finite interval t₁ to t₂ by the differential dt, which means that the two phases of the system, motionless earth and moving moon at the time t₁, and motionless earth and moving moon at the time t₂, are separated by an interval of time dt, which is smaller than any finite interval that we can conceive. We must then integrate the differential of the position difference so as to obtain the real difference in the condition of the system after the finite interval of time t₁ to t₂ has elapsed. Thus mathematics, incapable of dealing with real intervals of time, evades this difficulty by considering tendencies, not real occurrences.

Things that happen in a part of inorganic nature arbitrarily detached from the rest, and investigated by the methods of mathematical physics, do not endure. Let us suppose that we take some silver and add nitric acid to it: the metal dissolves. We can then add hydrochloric acid to the solution and precipitate the metal in the form of chloride; and we can then fuse this chloride with carbonate of soda, or some other substance, and so obtain the metal again. If we work carefully enough we can repeat this series of operations again and again and the original portion of silver will remain unchanged both in nature and in mass. All the chemical reactions into which it has entered have not affected it in any way; that is to say, these reactions have not endured.

If we inject a serum, containing a toxin, into the blood stream of a susceptible animal, certain things happen. The animal will become ill, but, provided that the amount of serum which has been injected was not too great, it will recover. If the toxin be again injected a reaction occurs, but the animal does not become so ill as on the first occasion, and after a number of injections the dose administered may be so great as to kill a susceptible animal but may yet produce no effect on the animal which is the subject of the process of immunisation: immunity has been conferred on it. Now can we compare the two operations, that of the solution and precipitation of the metal and that of the immunisation of the animal? We can to some extent, but the analogy soon fails, and indeed we should not attempt to formulate a theory of immunity on a physico-chemical basis if we did not start with the assumption that the series of operations was one in which only physico-chemical reactions were involved, that is to say, there is nothing in the phenomena of immunisation that suggests that what occurs in the animal body is similar to what we can cause to occur in inorganic materials outside the tissues of the living organism. We start with the assumption that the administration of the toxin causes the formation of an antitoxin in very much the same sort of way as the administration of hydrochloric acid to a solution of nitrate of silver causes the formation of chloride of silver. This antitoxin then neutralises the dose of toxin which may be administered after the process of immunisation has been effected, very much in the same sort of way as a certain amount of some acid can be neutralised by an equivalent amount of some base with which the acid can combine. If the reader will analyse any of the theories of immunisation current at the present day he will find that these are the physical ideas that are involved in it.[4] But physiological science has the much more formidable task of explaining the persistence of the immunity. The animal rendered immune to the toxins produced by certain species of bacteria may remain so for many years, that is, for a very long time after the antitoxins originally produced by the reaction of the tissues to the toxins first administered have disappeared. We must imagine, therefore, that the anti-substances produced originally by the reaction of the toxin are produced again and again by the tissues of the susceptible animal, for the latter may resist repeated infections, that is, repeated doses of toxin, without illness. But then the tissues of the animal body are transitory substances and they do not persist unchanged. Muscles, glands, connective tissues, even nerve-fibres and nerve-cells undergo metabolism, and the chemical substances of which they are composed break down into the excretory products, pass out into the blood stream, and are eliminated from the body; while at the same time these tissues are continually being renewed from the nutritive substances in the blood and lymph. It is the organisation of the tissues—their form and modes of reaction—that endure, but the material substances of which they are composed are in a state of continual flux. Yet the organisation of these tissues does not persist unchanged, for it is continually responding to new conditions experienced by it. The reactions that occur when a toxin is administered to a susceptible animal affect the organisation of its tissues in such a way that the latter acquire the capability of producing antitoxins which may—if we like to say so—neutralise the toxins that enter into them when they become infected. The reaction endures. But this is a different thing from saying that the process is a physico-chemical one alone.

This is what we must understand by the duration of the organism. Everything that it experiences for the first time persists in its organisation. It acquires the ability of responding to some stimulus by a definite, purposeful reaction, the effect of which is to aid it in its struggle for existence; and this reaction, once carried out, becomes a “motor habit” or the basis of a reflex, or in some other way, as in the process of immunisation, remains a part of the modes of functioning of the animal. In our behaviour certain cerebral nerve tracts become laid down and continue to exist throughout life, modifying all our future experience. Our past experience accumulates. There must be direct continuity in our flux of consciousness, for no perception seems ever to fade absolutely from memory. This continual addition of perceptions to those that already exist makes our consciousness ever become more complex, so that a perception experienced for the first time is never quite the same when it is again experienced. The first time that we go up and down in an elevator, or sit on a “joy-wheel,” or ascend in a balloon or an aeroplane, or become intoxicated, constitutes an unique event in our lives, and we experience a “new sensation.” What the blasé man of the world complains of is this accumulation, or rather persistence, of his experiences. A repetition of the same stimulus never again begets the same perception. The first hearing of a modern drawing-room song may be enjoyable, but the next time we hear it we are not interested, and by-and-bye it becomes very tiresome. The first hearing of a great symphony usually perplexes us, and we are perhaps repelled by unusual harmonies, or progressions, or strange modulations, but subsequent hearings afford increasing pleasure. We say that there was “so much in it” that we did not understand it, yet precisely the same series of external stimuli affected our auditory membranes on each occasion, and the same molecular disturbances were transmitted along our afferent nerves to the central nervous system, where the same physical effects must have been produced. The difference in all these cases between the repetitions of the same stimuli was that the later ones became added to the earlier ones, so that the state of consciousness produced by, or which was concomitant with, these external stimuli was a different state in each case.

This is the duration of the intelligently acting animal: it is not merely memory, but memory and the accumulation of all its past modes of responding to changes in its environment, whether these modes of response were conscious ones (as in the case of an intelligently performed or “learned” action), or unconscious ones (as, for instance, in the case of the acquirement of immunity by an animal which had become able to resist disease). It is not merely the experience of the individual organism, but also all the experience of those things which were done or experienced by the ancestry of the organism, and which were transmitted by heredity to the progeny. Motor habits are formed, so that much the same series of muscular actions are carried out when a stimulus formerly experienced is again experienced. Pure memory remains, so that the images of past things and actions somehow persist in our consciousness. Physical analogy suggests that these images are inscribed on the substance of the brain or are stored away in some manner; but, apart from the incredible difficulty of imagining a mechanism competent for this purpose, it is obvious that we thus apply to the investigation of our consciousness (which is an intensive multiplicity), the concept of extension which can only apply in all its strictness to the things outside ourselves on which we are able to act. All these motor habits, functional reactions, and memory images are our duration or accumulated experience. The motor habits and those functional habitual reactions of other parts of the body than the sensori-motor system are the basis of our actions, but the memory images are, so to speak, pressed back into that part of our organisation which does not emerge into consciousness. Only so much of them as bear on the situation in which we, for the moment, find ourselves and which may therefore influence our actions, flash out into consciousness. As “dreamers” we indulge ourselves in the luxury of becoming conscious of these memory images, but as “men of action” we sternly repress them, or so much of them as do not assist us in the actions that we are performing. Yet it is in the experience of each of us that, in spite of this continual inhibition, parts of our memories slip through the barriers of utility and surreptitiously remind us of all that we have been and thought.

Thus we simplify the stream of our consciousness. That of which we are conscious at any time is never more than a part of our crude sensation: we never perceive more than a small part of all that our organs of sense transmit to our central nervous system. But even these chosen perceptions of the external world are so rich, so chaotic and confused, that we are unable to attend to them all at once and we therefore “skeletonise” the contents of our consciousness. We think about it a bit at a time. It is an unitary thing, unable to be broken up, but we look at it from a great number of different points of view, so to speak; and then, fixing our attention on some aspect of it, we agree to ignore all the rest. We thus detach parts of it from the rest and, having thus arbitrarily decomposed it, we call these separate aspects the elements of our perceptions, and confer upon them separate existence in space and time. We remember and classify things and group together all those that seem to resemble each other. We form genera, agreeing to ignore all but the most general characteristics of the things which we try to conceptualise. We do not think separately about all the dogs or horses or fishes that we have ever seen, but we group all these animals into species, and it is usually the species that we think about when the idea of a dog or a horse or a herring emerges into our consciousness. When we think about a tramcar we do not think about all the separate vehicles that we have seen, nor about their colours, nor the advertisements on the boards outside, nor the people hanging on to the straps inside. Just so much of the experience of what is relevant to the purpose of our thought enters into our idea of the tramcar: it is a conceptual vehicle that we think about. Such is the nature of the concepts that form the basis of our reasoning: they are generalised aspects of our experience of nature, usually poorer in content than were the actually perceived things, except when it is necessary that some individual thing seen or otherwise experienced should be investigated or reasoned about. All our descriptions of nature are conceptual schemes. The world of perception, says William James, is too rich to be attended to all at once, but in conceptualising it we spread it out and make it thinner, and we mark out boundaries and division lines in it that do not really exist. It is this generalised nature that is the subject matter of our reasoning of pure science; and it is these concepts that form the matter of all our descriptions. We do not describe nature “as we see it,” it is our conceptions that we write about. Genera and species and varieties do not really exist in the animate world: all these are logical categories generated by our thought, concepts that facilitate our descriptions. When an anatomist gives an account of the structure of an animal he does not say what it looks like, nor as a rule does he content himself by making a photograph of his dissections. For him the animal is a complex of muscles, skeleton, nerves, glands, and so on, and in his drawings all these things are given an individuality that they do not really possess. In the living creature there were no such sharply-distinguished organs as a good drawing represents: all are bound together and are continuous. But for practical convenience in description—that is, in the long run, that we may act upon these things, we isolate from each other aspects that are in reality one unitary whole.

The universe, that is, all that is given to us, presents itself as immediately perceived phenomena which are then conceptually transformed. It is an aggregate of things—gross matter, particles, molecules, atoms, and electrons. These things have separate existence and shape, so that each of them lies outside all other things—we apply to them the category of extension. They possess properties—that is, they are hard, or heavy, or hot, or cold, or they are coloured, or they smell, and so on—we thus apply to them the category of inherence. They are not things that are immutable, for they change in place, or are transformed in other ways, that is, they are acted upon by energies. But beneath the properties of the things, or the transformations that they undergo, we imagine something that has properties and which transforms: it is not convenient that we speak solely of attributes or transformations as entities in themselves, for we think of things as having properties and being subject to transformations. Thus we apply the category of substance.

Has this universe that we construct from the data of sensation objective reality? We are led quite naturally by our study of physiology to the notion of idealism. We see that our perception of things, that is, our knowledge of the universe, depends on the integrity of functioning of certain bodily structures, and upon the condition that in men in general this integrity of functioning is normal, that is, common to the great majority of mankind.

To say that a thing exists is to say that it is perceived in some way; that immediately or remotely it affects our state of consciousness. To say that the star Sirius exists is to say that the stimulation of the retina by a minute spot of light transmits certain molecular disturbances along the optic nerve, and that other molecular disturbances are set up in the tissues of the central nervous system. Even if we do not see those dark stars that we know to exist, there are still evidences of their being that in some way affect the instruments of the astronomer and lead to their being perceived. Even if we do not actually see the emanations from a radio-active substance, we can cause these emanations to produce changes in something that we can see. We speak of the star as a minute spot of coloured light. But if we are short-sighted the spot becomes a little flare, and if we are colour-blind the hue of the star is different from what it is to normal persons. If we put a drop of atropine into one eye and then close the other, objects appear to lose their distinctness, but if we close this eye and then open the other, the original sharpness of vision returns. When we are bilious, wisps and spots may appear on a sheet of white paper that at other times was blank. If we take an overdose of quinine, rustlings and singing noises become apparent even in conditions that ought to preclude all sensation of sound. If we have a bad cold, we do not smell substances which at other times strongly affect our olfactory membranes. When we become intoxicated, a host of aberrations of sense displace our normal perceptions of things.

Our perception of the universe, therefore, depends on the normal functioning of our organs of sense, that is, such modes of functioning as we can describe and communicate to others, and which are thus common to the majority of other men and women. These perceptions resulting from the normal functioning of the organs of sense constitute givenness, and we enlarge, or conceptualise this givenness and call it the subject matter of science. But what is this reality that we say is external to us? It is, we see, our inner consciousness. If we walk along a road in the dark we can feel what is the nature of the path on which we tread, whether stones or gravel, or sand or grass. But this feeling is obviously not in the soles of our boots, and neither is it in the skin of the feet, for we should feel nothing if the afferent nerves in the legs were severed. Is it then in the brain? It would appear to be there, but it disappears if certain tracts in the brain are injured.

All that we can say is that the appearance of reality of things outside ourselves is only the ever-changing condition of our consciousness. This is all that we immediately know, and if we say that there is an universe external to ourselves we thus project outside our own minds what is in them; and we construct an environment which may or may not exist, but which we have no right to say does exist. A philosophy based on the science of the organism would appear to be restricted to this idealistic view of the universe. When we come across it for the first time when we are young it appeals to us with all the force of exact reasoning, and yet it has all the charm of paradox. There is no part of our intuitive knowledge which appears to us to be more certain than this distinction between ourselves and an outer environment: we know that our conscious Ego is something different from our body—and we know that outside our body there is something else. Yet the idealistic view so appeals to the intellect that we cannot think speculatively about it without, at times, almost convincing ourselves of the unreality and shadowiness of all that at other times seems most real and tangible; and we indulge in these speculations all the more readily because we know that whenever we begin to act, the intuitively felt body and outer world will return to us with all their original conviction of reality.

Some such system of idealism must generally characterise a system of philosophy founded on pure reasoning. We cannot but feel that the universe that we construct is one that depends on our perceptions: it is our perceptions. The essence of a thing is that it is perceived. If there were no mind to perceive it, would it exist? The universe is our thought, and we, that is our thought, exist only in the Thought of an absolute Mind which we call God. Such is the metaphysics to which the study of sensation led Berkeley.

The metaphysics of science has taken another turn. It is true that men and women see something outside themselves which differs slightly in different individuals—these differences are due to what we call the “personal equation.” The image of the universe seen by some individuals may differ profoundly from the image seen by some others, or most others; but a well-marked gap separates these slight individual deviations in the images seen by normal individuals from the large deviations seen by those whose perceptions are what we call pathological ones. The normal universe common to the majority of men and women is an aggregate of molecules in motion. But this is a conclusion with which modern physics has been unable to remain content, for molecules must be able to act on each other across empty space, and this is inconceivable. The universe therefore consists of a homogeneous immaterial medium, the ether of space, and this is the true substantia physica. Molecules and radiation are conditions of the ether, and for the physicist it is the only reality. The “materialism” of our own time is therefore the belief in the existence, unconditioned by time or anything else, of the ether, or physical continuum; a homogeneous medium, of which matter and energy, and the consciousness of the organism, are only states or conditions.

The materialism of the twentieth century, like the idealism of Berkeley, thus finds that there is something outside our own consciousness that possesses absolute existence. To the materialist it is the ether of space, and to Berkeley it is the existence of absolute Mind. But if our desire to avoid metaphysics is a genuine one, we must reject the notion of the universal ether no less than we must reject the notion of an absolute Mind, and we must rest content with pure phenomenalism. For each of us there can be no existence except that which is perceived or conceptualised. There is nothing but our own consciousness; there cannot even be an Ego which perceives; there is only perception. We never do really believe this in spite of our professions of reason. We find on strict self-analysis that we believe that there is an Ego that perceives and that there are other Egos that perceive, and that the universe which our Ego perceives is also the same universe that other Egos perceive. If we did not believe that there were other men and women that perceived—other consciousnesses like our own, all that part of our own behaviour that we call morality would be meaningless. In a philosophy of pure idealism other men and women are only phenomena; only bodies moving in nature. Why, then, should these elements of our consciousness influence the rest of our consciousness as if they were men and women like ourselves. All this amounts to saying that while our speculative thought suggests to us that all that exists is our stream of consciousness, our actions must convince us that there are other thinking individuals like ourselves.[5]

Even if we do surrender ourselves to phenomenalism and try to believe that all that exists is our own consciousness, the fact of our duration would suggest to us that this present consciousness is not all. Our reality is not only that which is present in our minds now, but all that was ever present in our mind. All that we have ever thought and done persists and forms our conscious and unconscious experience. This past of ours is something that is ever being added to, or becoming incorporated with, our present state of consciousness; and if it is something other than that which we now perceive and conceptualise, it is something that has an existence of its own.

We must believe that there is something that we perceive, and not that we merely perceive. For the phases of our immediate givenness, that is, those things which were present in our minds from moment to moment of the past were connected together and had direction, and this direction was something that could not be influenced by our will, and may even have been contrary to our will. Something that is very hot always cools, a wheel that is revolving of itself always comes to a stop, a pendulum ceases to swing, a stone that is rolling down a hill continues to roll. Let us look back at a fire that was going out: it is now nearly dead; let us start a pendulum to swing and then go away: when we come back the pendulum is still swinging but the amplitude of its vibrations is now less than it was; let us look away from the stone that was falling: when we look again it is still falling but it is not where it was. In all our givenness, in all the phenomena that we perceive, there is something that is determined and unequivocal, something that goes its own way apart from our consciousness of it.

Above all, we have the conviction of absoluteness in our sense of personal identity. We, that is our Ego, are something that endures, and we can trace no beginning to our identity, and we have no intuition that it will cease to exist. Our Ego is now the same Ego that it was in the past, and round it something has accumulated—the memories of our former perceptions, and the habits that these have engendered. Did our Ego create this from itself? Was it not rather a centre of action which, residing in an existence other than itself—the absolute which we call the universe—modified that existence and continually acquired new relationships to it?

CHAPTER II THE ORGANISM AS A MECHANISM

We propose now to consider the organism purely as a physico-chemical mechanism, but before doing so it may be useful to summarise the results of the discussions of the last chapter. Let us, for the moment, cease to regard the organism as a structure—a “constellation of parts”—and think of it as the physiologist does: it is a machine; it is essentially “something happening.” What, then, is the object of its activity? Whatever else the study of natural history shows us, it shows us this, that the immediate object of the activity of the organism is to adapt itself to its surroundings. It must master its environment, and subdue, or at least avoid whatever in the latter is inimical. It must avoid accident, disease, and death, it must find food and shelter; it must seek for those conditions of the environment which are most favourable to its prolonged existence. Ultimate aims—the preservation of its race, ethical ideals—do not concern us in the meantime. The main object of the functioning of the individual organism is that it may dominate its environment, and obtain mastery over inert matter. Consciously or unconsciously it acts towards this end.

All those actions which we call reflex, or automatic, or instinctive, have this in common, that the organism in performing them comes into relation with only a very limited region of its environment. But knowing that region intuitively, its actions have a completeness that an intelligent action does not exhibit until it has become so habitual as to approach to automatic acting. The relations between the organism and that part of its world on which it acts, intuitively or instinctively, is something like that between a key and the lock to which it is fitted: it opens this lock, perhaps one or two others which resemble it, but no more. Now just because of this perfect, but restricted, adjustment of the instinctive or automatically acting organism to the objects on which it operates, knowledge of all else in the environment becomes of little consequence.

It is clear that intelligent acting involves deliberation. The almost inevitable motor response to a stimulus, which is characteristic of the reflex or instinct, does not occur in the intelligent action: instead of this we find that we choose between two or more responses to the same stimulus. We reply to the latter by doing this now, and that another time; and we see at once what results flow from acting differently upon the same part of our environment, or acting in the same way upon different parts. Perception, that is, knowledge of the world, arises from acting; and as our actions, when carried out intelligently, become almost infinitely varied, the environment appears to us in very many aspects. In every action we modify that part of our surroundings on which we operate. We can produce many modifications that are of no use to us: these we do not attend to. We produce others that are useful, and then we note the sequences of events involved in our actions. Thus we discover or invent natural law—an environment which is an orderly one. We can calculate and predict what will happen: we produce, for instance, a Nautical Almanac, at once the type of useful knowledge and of knowledge of sequences of events rigidly determined—knowledge in short that is mechanistic; and which has been engendered by the necessity for acting on our environment in our own interests.

All this, the reader may note, is Bergson’s theory of intellectual knowledge, a theory which, new and paradoxical at first, becomes more and more convincing the longer we think about it, until at last it seems so obvious that we wonder that it ever seemed new. Our modes of thinking become constrained into certain grooves, just because these modes of thinking have been those that were generated by our modes of acting. So long as our thinking relates only to our acting, its exercise is legitimate. But if its object is pure speculation its results may be illusory, for a method has been applied to objects other than those for which it was evolved. Let us now extend our intellectual methods to the investigation of the organism. Necessarily we must reason about the latter as a mechanism if we reason about it at all.

If it is a mechanism it must conform to the laws of energetics, for science, so far as it is quantitative, whether its results are expressed in the form of equations or inequalities, is based on these principles.

The first principle of energetics,[6] or the first law of thermodynamics, is that of the conservation of energy. Let us think of an isolated system of parts such as the sun with its assemblage of planets, satellites, and other bodies: in reality these do not form an isolated system, but we can regard them as such by supposing that just as much energy is received by them from the rest of the universe as is radiated off by them to the rest of the universe. In this system, then, the sum of a certain entity remains constant, and no conceivable process can diminish or increase its quantity. We call this entity energy, and we usually extend the principle of its absolute conservation to matter, though this extension is unnecessary, for we must think of matter in terms of energy. Stated more generally the principle is that whatever exists must continue to exist, if we are to regard this existence as a real one.[7]

It is not at all self-evident to the mind that energy must be conserved, for we see that, to all appearance, it may disappear. A golf-ball driven up the side of a hill possesses energy while in flight, kinetic energy or the energy of motion; but this apparently is lost when the ball alights on the hill-top and comes to rest. We say, however, that it now possesses potential energy in virtue of its position; for if the hill is a steep one a little push will start the ball rolling down with increasing velocity, and when it reaches the spot from which it was originally impelled it possesses kinetic energy. This is described as one-half of the mass of the ball multiplied by the square of its velocity. Now the kinetic energy of the ball at the instant when it left the head of the driver ought to be equal to its kinetic energy when it reached the same horizontal level on its downward roll. Yet it can easily be shown that this is not the case, and we account for the lost kinetic energy by saying that it has been dissipated by the friction of the ball against the atmosphere in its flight, and against the side of the hill on its roll back. We cannot verify this quantitatively, but we are quite certain that it is the case. If we take a clock-spring and wind it up, the energy expended becomes potential in the spring, and when the latter is released most of it is recovered. But we may dissolve the spring in weak acid without allowing it to uncoil. What then becomes of the energy imparted to it? We are compelled to say that it has changed the physical condition of the solution into which it passes, either becoming potential in this solution, or becoming dissipated in some way. Yet again we cannot trace this transformation experimentally though we may be quite sure that all the energy potential in the coiled spring is conceivably traceable. Suppose, again, we burn some hundredweights of coal in a steam-boiler furnace. Heat is evolved which raises steam in the boiler, and the steam actuates an engine, and the latter exhibits measurable kinetic energy. Where did this come from? It was potential in the coal, we say, though no method known to physics enables us to prove this by mere inspection of the coal. We must cause the latter to undergo some transformation. But by rigid methods we can estimate very exactly the potential energy of the coal, and we can calculate the kinetic energy equivalent to this. Yet again we find that the kinetic energy of the steam-engine is only a fraction of that which calculation shows us is the equivalent of the kinetic energy of the coal. What becomes of the balance? We can be quite certain that it has been dissipated in friction, radiation, loss of heat by conduction, loss of heat in the condenser, and so on, although we cannot prove this rigidly by experimental methods.

Think of the universe as an isolated system. It contains an invariable quantity of energy. This energy may be that of bodies in motion—suns, planets, cosmic dust, molecules, etc.—when it is kinetic energy; or it may be the energy of electric charges at rest or in motion; or any one of the many kinds of potential energy. It may pass through numerous transformations—the chemical potential energy of coal may be transformed into the kinetic energy of water molecules (steam at high temperature), and this into the kinetic energy of the revolving armature of a dynamo, and this again into the energy of moving electrons (the current of electricity in the circuit of the dynamo), and then again into the energy of ethereal vibration (light, heat, X-rays, or other electro-magnetic waves), and these again into mechanical or kinetic energy, and so on. When we say that we can control energy we say that we can produce these transformations; we can cause things to happen, we bring becoming into being. In this sense energy is causality. But while the sum-total of energy in the universe remains constant, the sum of causality continually diminishes. Energy is the power, or condition, of producing diversity, but while energy can suffer no diminution of quantity, diversity tends continually to decrease.

In the last two sentences we state, in one way, the second law of thermodynamics—in some respects the most fundamental result of our experience in the physical investigation of the universe. In its most technical form, as enunciated by Clausius, this law states that the value of a certain mathematical function, called entropy,[8] tends continually towards a maximum, when it is applied to the universe as a whole. When we say the “universe,” we mean all that comes within our power of physical investigation. Let us now see what this statement means.

The energy of the solar system is in part the kinetic energy of those parts of it which are in motion—planets, planetesimals,[9] and satellites. This quantity of energy is enormously great. In the case of our earth it is  1/2(mv²), m being the mass of the earth, and v its velocity. Translated into numerical symbols we find this quantity almost inconceivable. The greater part of this energy is unavailable, that is, it can undergo no transformations. But because the earth is in rotation at the same time as it revolves round the sun, and because the moon revolves round the earth, there are tides in the watery and atmospheric envelopes of the earth. The energy of the tides is the kinetic energy of water or air in motion, and we can employ this energy in the production of transformations, and it is therefore available. But well-known investigations have shown that the tides produce friction, and that the period of rotation of the earth is slowly becoming greater. Ultimately the earth will rotate on its own axis in the same time that it revolves round the sun—then a year and day will be of the same length. When that occurs, the sun, earth, and moon will be in equilibrium, and tidal phenomena due to the sun will cease. The kinetic energy of the earth, rotating once in 24 hours is obviously greater than its kinetic energy when rotating in the period which will then be its year. What has become of the balance? It has been transformed into the mechanical friction of the tides against the surface of the earth,[10] and this friction has been transformed into low-temperature heat, and this heat has been radiated off into space.

The solar system also contains energy in the form of the heated sun and planets, and in the form of chemical potential energy of the substances of which those bodies are composed. Let us think of the system, sun and earth. The sun contains enormous heat energy, its temperature being some 6000° C. absolute.[11] It contains enormous chemical energy in the shape of compounds existing beneath its outer envelopes, and it contains energy in the form of its own gravity—its contraction together produces heat. But this heat is being continually radiated away: chemical reactions must occur in which the potential chemical energy of its substances must become transformed into heat, and this heat is also radiated away; contraction of its mass must occur up to a point when the materials are as closely packed together as possible; heat is developed during the contraction, and this also passes away by radiation. Suppose that modern speculations are well founded and that radio-active substances are present in the sun: in the atomic disintegration of these substances heat is produced and again radiated. Therefore in whatever form energy exists in the sun, it transforms into heat and this radiates. The ultimate fate of the sun is to cool down and solidify. It will then move through space as a body having a cool, solid crust, and an intensely heated interior. Slowly, very slowly, this heated interior will cool down by the conduction of its heat from the core to the outer shell, and by the radiation of this heat from the shell into space. For incredibly long periods radio-active substances in the interior must generate heat, but even this process must reach an end.

The energy received by the earth is that of solar and stellar radiation. Stellar radiation is minute, the absolute temperature of cosmic space (or ether) being about −263° C. The absolute temperature of the earth is about +17° C., so that it radiates off more heat into space (other than that represented by the sun) than it receives. All energy-transformations on the earth (except tidal effects, and energy-conduction from the heated core, and possibly radio-active effects) are transformations of this solar energy received by radiation. We see these in oceanic and atmospheric circulations (currents, winds, rainfall, etc.). We see them also in the transformations of the chemical potential energy of coal and other products of life—products in which the contained potential energy has been absorbed from solar radiation.

Let us follow the transformations of this energy. Oceanic currents transport heat from the equatorial sea-areas to the colder temperate and polar areas, and compensatory polar currents flow towards the equator, absorbing heat from the waters of temperate and equatorial areas. Winds act in an analogous way. Water is evaporated where the solar radiation is intense, and heat is absorbed in the transformation of water into aqueous vapour. Then this water vapour is transported in the winds into regions where it becomes condensed and precipitated as rain or snow, heat being emitted in this condensation. In all these movements there is friction, and this friction transforms to heat. In all the effect is the general distribution over the earth of the heat which the equatorial regions receive in excess of that which the polar regions receive. Other mechanical effects are also produced by oceanic and atmospheric circulations—the denudation of the coasts by tides and storms, the erosion of the land by rivers, rains, snow, and ice, the transport of dust in winds, etc. In all these friction is produced, and this friction passes into heat.

The potential chemical energy which results from absorption of solar radiation by plants is principally accumulated as coal. Apart from the interference of man, this coal would slowly accumulate, perhaps it would more slowly disappear by bacterial action, or by physical transformations. In these transformations the energy of the coal would become heat energy and the potential energy of the gas produced by bacterial activity. By man’s agency the coal suffers other transformations, and in the present phase of civilisation it is his chief source of energy. It is available for doing work of many kinds, and in all these forms of work it becomes transformed by chemical action (burning) into high temperature heat.

We can cause this potential energy of coal to transform into mechanical energy of machines, vehicles, and ships in motion by causing it to pass into heat. In the steam-engine, or gas-engine, a highly heated gas (steam, or the mixture resulting from the explosion of coal gas and air in the cylinder of the engine) expands and propels a piston or rotates a turbine. (Obviously in the petrol engine the same essential process takes place.) We employ this kinetic energy directly in transport, or we cause it to undergo other transformations. In the dynamo, kinetic energy of machinery in motion transforms to electrical energy; and this may transform to radiant energy (light, heat in electric radiators, wireless telegraphy radiations), or it may transform to chemical energy (the manufacture of carborundum in the electric furnace, for instance), or it may transform again to the kinetic energy of bodies in motion (electric traction). In innumerable ways the human power of direction causes transformation of this accumulated potential energy, and the reader will notice the analogy of all this with the essential, unconsciously expressed activity of the animal organism in its own metabolism—a point to which we return later.

Notice now that all the energy-transformations we have noticed are irreversible. This is a matter of deep philosophical importance, and we must devote some time to it. Consider first of all the working of the steam-engine; what occurs is this—coal is burned in the boiler-furnace, that is to say, potential chemical energy passes into heat and this vaporises water in the boiler, producing a gas at high temperature (steam). This gas expands in the high-pressure cylinder of the engine, driving forward a piston; it expands further in the intermediate cylinder, propelling its piston also, and again in the low-pressure cylinder. It is then cooled by passing through the condenser, and in the contraction further mechanical energy is obtained. The train of events thus begins with a gas at a high temperature and ends with the same gas at the temperature of the water in the condenser. The heat lost is transformed into the mechanical energy of the engine. But not all of it. A certain quantity is lost by radiation from the boiler walls, the walls of the steam-pipes, the cylinders, and other parts of the engine; also some of the energy is transformed to friction, and this again to heat. In this way a very considerable part of the energy contained in the coal is frittered away in unavoidable heat-conduction and radiation, and a last residue of it goes down the drain, so to speak, with the condenser water. This loss is inherent in the nature of the mechanism of the engine.

Suppose that the energy of the engine is employed to drive a dynamo. The armature of the latter rotates against the constraint of powerful electro-magnets, and in so doing a current of electricity is generated. By the law of conservation this current should contain as much energy as was put into the rotation of the armature; as a matter of fact it does not, and the deficiency is represented by the friction of the parts of the machine against each other, by imperfect conductivity of electricity in the wires, and by imperfect insulation of the current. Friction, imperfect conductivity, and imperfect insulation all transform to heat, and this radiates away. Suppose now that the current is used for lighting purposes: to do this it must heat the metallic filaments in the lamps, or the points of the carbons in an arc. This heat then transforms to light, but along with the light, which was the object of the transformation, heat is produced, and this heat radiates away.

The actual process in which the particular form of energy required is generated may or may not be reversible in theory. That employed in the steam-engine is not, for if we start with a cold boiler and then work the engine backwards we could not raise steam. The process in the dynamo is theoretically reversible: if we send a current of electricity into a dynamo the machine will begin to rotate, and become a motor, so that we can obtain mechanical work from it. Now in theory all forms of energy are mutually convertible, and all can be expressed in terms of a common unit. The unit of mechanical energy is called the erg: let a current, the energy of which is equal to N ergs, be sent into the dynamo, then we ought to obtain from the latter mechanical energy equal to N ergs. Conversely, if N ergs of mechanical energy be employed to rotate the dynamo, we should obtain electrical energy equal to this amount. Now as a matter of fact we do not obtain these theoretical conversions, for some of the electrical energy is dissipated when we employ the machine as a motor, and some of the mechanical energy is likewise dissipated when we employ it as a dynamo.

The entity that we call energy is the product of two factors, a capacity-factor and an intensity-factor. Thus:—

What is it that determines whether or not an energy-transformation will occur? It is the condition that a difference of the intensity-factors of the energy in different parts of a system exists. Water will flow from a higher to a lower level, doing work as it flows, if it is directed through a motor. Electricity will flow if there is a difference of electrical potential. A chemical reaction will occur if two substances before interacting possess greater chemical potential than do the products which may possibly be formed during the interaction. Coal and oxygen possess greater chemical potential than do carbon dioxide and water, therefore they will combine, forming carbon dioxide and water. Energy-transformations will therefore occur wherever it is possible that differences of intensity or potential can become abolished. The energy that may thus flow from a condition of high to a condition of low potential, undergoing a transformation as it flows, is the available energy of the system of bodies in which it is contained. A closed vessel surrounded by an envelope impervious to heat, and containing a mixture of oxygen and hydrogen, is an isolated system containing available energy. Let the mixture be fired by an electric spark, and heat is evolved. The total energy of the system is unaltered in amount, but the available energy has disappeared, since the heated water vapour is incapable of undergoing further transformations while it forms part of its isolated system.[12]

All physical processes are therefore irreversible, that is to say, proceed in one direction only. Either a process is irreversible in the sense that it cannot proceed both in the positive and negative directions (a steam-engine, for instance), or it is irreversible in the sense that while it proceeds the energy involved in it becomes less capable of being transformed into other conditions. (In the theoretically reversible dynamo, energy becomes dissipated in the form of heat.) The following statements may be regarded as axioms[13]:—

(1) “If a system can undergo an irreversible change, it will do so.”

(2) “A perfectly reversible change cannot take place by itself.”

In the phenomena studied by physics we see only irreversible changes. In all these processes energy descends the incline, and some (considerable) fraction of the amount involved passes into conditions in which it is incapable of further transformation; in all, energy becomes less and less available. Expressed in its most technical form, the second law of thermodynamics states that entropy tends continually to increase. Every such process as we can study in physics “leaves an indelible imprint somewhere or other on the progress of events in the universe considered as a whole.”[14]

We cannot observe a truly isolated system. The earth itself is part of the solar system, and the latter receives energy from, and radiates it to the rest of, the universe. Our only isolated system is the whole universe. We must think of it, in so far as we regard it as physical, as a finite system: if it is infinite, our speculations become meaningless. The universe therefore is a system in which energy tends continually towards degradation. In every process that occurs in it—that is to say every purely physical process—heat is evolved, and this heat is distributed by conduction and radiation, and tends to become universally diffused throughout all its parts. When this ultimate, uniform distribution of energy will have been attained, all physical phenomena will have ceased. It is useless to argue that universal phenomena are cyclical. We vainly invoke the speculations (founded on rather prematurely developed cosmical physics) of stellar collisions, light-radiation pressure, the distribution of cosmic dust, etc. to support our notions of alternate phases of dissipation and concentration of energy; close analysis will show that all these processes must be irreversible. The picture physics exhibits to us is that of the universe as a clock running down; of an ultimate extinction of all becoming; an universal physical death.

In this conclusion there is nothing that is speculative. It is the least metaphysical of the great generalisations of science. It represents simply our experience of the direction in which physical changes are proceeding. Based upon the most exact methods of science known to us, nothing seems more certain and more capable of rigorous mathematical investigation.

And yet we are certain that it is not universally true. For there must always have been an universe—at least our intellect is incapable of conceiving beginning. If we suppose a beginning, an unconditioned creation, at once we leap from science into the rankest of metaphysics. Holding, then, that the duration of our physical universe is an infinite one, we see that the ultimate attainment of energy—dissipation—must have occurred if our physics is true. It does not matter what new sources of energy modern investigation has shown to us; nor do the incredibly great lapses of duration necessary for the depletion of these sources matter. We have eternity to draw upon. Everywhere in the universe we see diversity and becoming. Is then the whole problem a transcendental one, or is the second law untrue? We refuse to regard the problem as insoluble, and we must think of the second law as true of our physical experience only. But our conception of the universe shows that it cannot be true, and so we have to seek for an influence compensatory to it.

If the organism is a mechanism of the physico-chemical kind, it should therefore conform to the two great principles of energetics established by the physicists. Now there can be no doubt that the law of energy-conservation does apply to all the processes observed in animals and plants. Let us consider the “calorimetric experiments.” An animal, together with the food and oxygen supplied to it, and the various substances excreted by it, constitutes a physical system. This system can be approximately isolated so that no heat enters it from outside, while the heat that leaves it can be determined quantitatively. The animal is made to perform mechanical work, and this is measured. The energy-value of the food ingested by it, and that of the excreta, can be estimated. All the physical conditions can thus be controlled, and the results of such experiments show that energy is conserved. The energy contained in the food is greatly in excess of the energy contained in the excreta, but the deficit is quantitatively represented by the work done by the animal, and by the heat lost in conduction and radiation from its body. The difference between the observed results and the theoretical ones are within the limits of error of the experiment. The metabolism of the animal as a whole, then, conforms to the law of conservation, and the general results of physiology all go to show that this is also true of chemico-physical changes considered in detail.

It cannot be shown that the second law, that of the dissipation of energy, applies to the organism with all the strictness in which it applies to purely physical systems. If we consider only the warm-blooded animal we do indeed find that its general metabolism does proceed in one direction, and that irreversible changes occur. In the mammal and bird we have organisms which present a superficial resemblance to the heat-engine, with respect to their chemico-physical processes, a resemblance, however, which is rather an analogy than an identity of processes. In the heat-engine we have (1) a mechanism of parts which do not change in material and relationships to each other (boiler, cylinder, pistons, cranks, slide-valves, etc.); and (2) a working substance (the steam).

Energy in the form of the chemical potential of coal and oxygen is supplied to the mechanism. The coal is oxidised, producing heat. The heat then expands the working substance (the water in the boiler), and this working substance—now a gas at high temperature and pressure—propels the piston and confers kinetic energy on the engine. Note the essential steps in this process: substances of high chemical potential (coal and oxygen) suffer transformation into substances of low chemical potential (carbon dioxide and water), and the difference of energy appears as high-temperature heat (increased kinetic energy of water molecules, to be more precise). This heat is then transformed into mechanical work (the kinetic energy of the molecules of steam is imparted to the piston of the engine). But in this transformation only a relatively small proportion (10% to 20%) of the energy available is transformed into mechanical work: the rest is dissipated as irrecoverable low-temperature heat, by radiation from boiler, steam-pipes, engine, and as the heat which passes into the condenser water.

In the organism in general there is no distinction between the fixed parts of the mechanism and the working substance. The organism itself (its muscles, nerves, glands, etc.) is the working substance. Further, it is not quite certain that there is a necessary transformation of chemical energy into heat. The source of energy in the case of the warm-blooded animal is the chemical energy of the food substances and oxygen taken into its body. These chemical substances undergo transformations in the alimentary canal and in the metabolic tissues. The proteids of the food are broken down into amino-substances in the alimentary canal, and these amino-substances are synthesised into the specific proteids of the animal’s body. Corresponding changes occur with the carbohydrates and fats ingested. These rearrangements of the molecular structure of the foodstuffs are the object of the processes of digestion and assimilation; and when they are concluded, a certain proportion of the food taken into the body has become incorporated with, or has actually become a part of, the living tissues (muscles, nerves, etc.) of the animal body. This living substance, compounds of high chemical potential (proteids, carbohydrates, and fats) undergoes transformation into compounds of low chemical potential (water, carbon dioxide, and urea). There is a difference of energy, and this appears as mechanical energy, as the chemical energy required for glandular activity, and as heat.

We must not, however, conclude that this heat of the warm-blooded animal is comparable with the waste heat of the steam-engine. The homoiothermic animal maintains its body at a constant temperature, which is usually higher than that of the medium in which it lives, and this constancy of temperature obviously confers many advantages. Chemical reactions proceed with a velocity which varies with the temperature, so that in the warm-blooded animal the processes of life go on almost unaffected by changes in the medium. The animal exhibits complete activity throughout all the seasons of the year. It does not, or need not, hibernate, and it can live in climates which are widely different. We therefore find that the most widely-distributed groups of land-animals are the warm-blooded mammals and birds, while the largest and most cosmopolitan marine animals are the warm-blooded whales. Heat-production in the mammals and birds is therefore a direct object of the metabolism of the animal; it is a means whereby the latter acquires a more complete mastery over its environment. That it is not necessarily a step in the transformation of chemical into mechanical energy we see by considering the metabolism of the cold-blooded animals. In these poikilothermic organisms the body preserves the temperature of the medium. The temperature in such animals may be a degree, or a fraction of a degree, higher than that of the environment, but, in the absence of exact calorimetric experiments, we cannot say what proportion of the energy of the food of these animals passes into unavailable food energy. Probably it is a very small fraction of the whole, and we are thus justified in saying that in the cold-blooded animal chemical energy does not, to a significant extent, become transformed into heat. The result is, of course, that the vital processes in these organisms keep pace, so to speak, with the temperature of the environment, since the chemical reactions of their metabolism are affected by the external temperature. We find therefore that hibernation, the formation of resting stages, and a general slowing down of metabolic processes are more characteristic of the cold-blooded animal during the colder seasons than of the warm-blooded animal. The former has not that mastery over the environment attained by the mammal or bird.

The metabolism of the animal therefore resembles the energy process of the heat-engine only in the general way, that in both series of transformations chemical energy descends from a condition of high potential to a condition of low potential, transforming into mechanical energy in so doing, and thus performing work. In the heat-engine chemical energy transforms to heat, and then to mechanical energy, and of the total quantity transformed a certain large proportion suffers dissipation by conversion into low-temperature heat. In the animal organism chemical energy transforms directly to mechanical energy without passing through the phase of heat. If heat is produced it is because it is, in a way, available energy, inasmuch as it permits of the continuance of chemical reactions at a normal rate. The analogy of the animal with the heat-engine is therefore a false one. It suggests oxidation of the food-stuffs and heat production, whereas it is not at all certain that any significant proportion of the energy of the organism is the result of oxidation: many animal organisms indeed function in the entire absence of free oxygen. Further, the proportion of energy dissipated is always small compared with the heat-engine, and tends to vanish. The second law of thermodynamics does not, then, restrict the energy-transformations of the animal organism to the same extent that it restricts the energy-transformations of the physico-chemical mechanism.

The processes involved in the plant organism differ still more in their direction from those of a “purely physical” train. To see this clearly we must consider the imaginary mechanism known as a Carnot heat-engine.[15] This is a system in which we have (1) a heat-reservoir at a constant high temperature, (2) a refrigerator at a constant low temperature, and (3) a working substance which is a gas. Energy is drawn from the reservoir in the form of heat, and this heat expands the gas, doing work. The gas contracts, and its heat is then given up to the refrigerator. The work done is equal to the difference between the amount of heat taken from the reservoir and the amount given to the refrigerator.

This series of operations is called a direct Carnot cycle. But the mechanism can be worked backwards. In this case heat passes from the refrigerator into the working substance, which was at a lower temperature. The working substance, or gas, is then compressed, as the result of which operation it is heated to just above the temperature of the reservoir. The heat it thus acquires is then given up to the reservoir.

In the direct Carnot cycle, therefore, energy passes from a state of high potential to a state of low potential and work is done by the mechanism. In the reversed Carnot cycle energy passes from a state of low potential to a state of high potential and work is done on the mechanism. The Carnot engine is thus perfectly reversible. No energy is dissipated in its working. It is, of course, a purely imaginary mechanism.

In the metabolism of the green plant carbon dioxide and water are taken into the tissues of the leaf and are transformed into starch. But the energy of the compounds, carbon dioxide and water, is much less than that of the same compounds when built up into starch. Energy must therefore be derived from some source, and this source is said to be the ether. Solar radiation is absorbed by the green leaf, and this energy is employed to produce the chemical transformation. Just how this is effected we do not positively know, in spite of much investigation. It is possible that formaldehyde is formed from carbon dioxide and water, polymerized, and then converted into starch. It is possible that the absorbed electro-magnetic vibrations are converted into electricity in the chlorophyll bodies of the leaf, though when radiation is absorbed in physical experiments it is converted into heat. We do not know just what are the steps in the transformation, though it is clear that solar radiation is absorbed and that the chlorophyll of the leaf is instrumental in converting this energy of radiation into chemical potential energy. But the important thing to notice is, that we have here a process closely analogous to that of a reversed Carnot engine. Energy (that of the carbon dioxide and water) passes from a state of low potential to a state of high potential (that of the energy of starch), and work is done on the plant in producing this transformation.

Work is not done by the green plant. This statement is not, of course, quite rigidly true, for a certain amount of mechanical work is done by the plant. Flowers open and close; tendrils may move and clasp other objects; there is a circulation of protoplasm in the plant cells, and a circulation of sap in the vessels of stems, etc. Also work is done against gravity in raising the tissues of the plant above the soil, while work is also done by the roots in penetrating the soil. But when compared with the work done by radiation in producing the chemical transformations referred to above, these other expenditures of energy must be insignificant. Speaking generally, then, we may describe the green plant as a system in which available energy is accumulated in the form of chemical compounds of high potential. It is, further, a system in which energy becomes transformed without doing mechanical work, except to a trifling extent, and in which there is no formation of heat, or at least in which the quantity of heat dissipated is only perceptible during very restricted phases, is relatively small during the other phases, and tends to vanish.

Let us now combine the processes of plant and animal; we start with the latter. In it we have a mechanism which does work. The source of its energy is the potential chemical energy of its foodstuffs, which latter reduce down to those substances known as proteids, fats, and carbohydrates. The energy-value of these compounds is considerable, that is to say, if they are burned in a stream of oxygen a large quantity of heat is obtained from their combustion. They are ingested by the animal, broken down chemically, and rearranged. The proteids eaten by the animal (say those of beef or mutton or wheat) are acted upon by the enzymes of the alimentary canal and are decomposed into their immediate constituents, amino-acids, and then other enzymes rearrange these amino-acids so as to form proteid again, but proteids of the same kinds as those characteristic of the tissues. This decomposition and re-synthesis is carried out also with respect to the fats and carbohydrates ingested. The result is that the food taken into the alimentary canal, or at least a part of it, is built up into the living substance of the animal’s body. The energy expended upon these processes of digestion and assimilation is probably inconsiderable. During these processes the animal absorbs available chemical energy.

The energy thus taken into the animal is then transformed. The major part of it appears as mechanical energy—that of bodily movement, the movements of heart, lungs, blood, etc.—and heat. Some part of it becomes nervous energy, by which rather vague term we mean the energy involved in the propagation of nervous impulses. Some of it is used in glandular reactions, in the formation of the digestive juices, for instance. The most of it, however, transforms to mechanical energy and heat. Just how these energy transformations are effected we do not know. The heat is, of course, the result of chemical changes, oxidations, decompositions, or changes of the same kind as that of the dilution of sulphuric acid by water, but the mechanical energy appears to result directly from chemical change without the intermediation of heat. We shall return to this point in a later chapter, and content ourselves with saying here that the chemical compounds contained in the metabolic tissues of the animal body undergo transformation from a state of high to a state of low chemical potential, and that this difference of potential is represented by the work done and the heat generated. The proteid, fat, and carbohydrate of the tissues represent the condition of high potential; and the carbon dioxide, the water, and the urea, into which these substances are transformed, represent the condition of low potential.

Let us suppose a Carnot heat-engine in which the temperature of the reservoir of heat is (say) 120°C., and that of the refrigerator 50°C. The heat of the refrigerator can still be made a further source of energy by constituting it the heat reservoir of another Carnot engine which has a refrigerator at a temperature of 0°C. Our animal organism may be compared with a Carnot cycle; its energy reservoir is the proteid, fat, and carbohydrate ingested, and its refrigerator (or energy sink) is the carbon dioxide and urea excreted. Now the urea of the higher mammal becomes infected with certain bacteria, which convert it into ammonium carbonate. Another species of bacteria converts the ammonia into nitrite, and yet another turns the nitrite into nitrate. The main process of the animal is therefore combined with several subsidiary ones.

	Carbohydrate, fat, proteid break down into		Metabolism of the animal
	↓
	Carbon dioxide Water Urea—————Urea		Metabolism of urea bacteria
Chemical Energy at high potential	↓
	passes into ammonium carbonate————ammonium         carbonate				metabolism of nitrifying bacteria
			↓
			oxidises to nitrite—————Nitrite				Metm. of nitrifying bacteria
					↓
			oxidises to nitrate
	chemical energy at low potential

The arrows show that energy is descending the incline indicated by a direct Carnot cycle. There is no more work to be obtained from the carbon dioxide and water excreted by the mammal, but more work can be obtained from the urea when it is used by bacteria, and “ferments” to ammonia. Work can again be obtained from the ammonia by bacteria, which convert it into nitrite, and yet again from the nitrite by other bacteria, which convert it into nitrate. The nitrate represents the energy-zero so far as the organisms considered are concerned.

Other nitrogenous residues are contained in the urine of animals, and several other excretory products may be formed. But in all these cases we can easily find subsidiary energy-transformations effected by bacteria, as in the above scheme. This, then, is the positive, or direct half, of that reversible Carnot cycle with which we are comparing life. In it energy falls in potential (or intensity, or level), and in this fall of potential transformations are produced—exhibit themselves, is perhaps a better way of putting it. We will consider these transformations later; in the meantime it should be noted that in this fall of potential is a degradation of chemical energy. Compounds, carbon dioxide, water, and nitrate are produced which are chemically inert. It is no use to say that carbon dioxide may react with (say) glowing magnesium, water with metallic sodium, and nitrate with (say) glowing carbon. A condition of chemical equilibrium would result from purely inorganic becoming on our earth in which there was no metallic sodium or magnesium or incandescent carbon; in which the metals would become inert oxides, and the carbon would become dioxide. The formation of these compounds represents a limit to energy-transformations. Note also that all these energy-transformations are conservative; the total quantity remains unchanged throughout, and is the same at the end as at the beginning. But entropy has been augmented: unavailable energy has increased at the expense of available energy.

Consider now the indirect, or reversed, Carnot cycle. We begin with the inert matter, resulting from the metabolism of the animal, carbon dioxide, water, nitrate, and a few more mineral substances. We have the energy of solar radiation. By virtue of the living chlorophyll plastid in the cells of the green plant, this solar radiation uses the carbon dioxide and water as raw materials in the elaboration of starch. At the same time it absorbs nitrate, with some other inert mineral substances from the soil, and takes these into its tissues. The starch formed in the chlorophyll is converted into soluble sugar, which circulates through the vessels of the plant and is associated with the nitrogenous salt in the elaboration of proteid. Proteid, oils, fats and resins, and to a greater extent carbohydrates, are thus built up by the plant and accumulate, for mechanical work is not done by it, nor is heat dissipated—or at least these processes occur to an insignificant extent.

				are synthesised to—
					proteid fat carbohydrate
Carbon dioxide Water Nitrate		Metabolism of the green plant
				Chemical energy at high potential.
Chemical energy at low potential

The “working substance” of our organic cycle has therefore returned to its original state.

We have considered the process of metabolism in two categories of organisms, the typical animal and the green plant, and we have combined these so as to obtain a picture of a reversible cycle of physico-chemical processes. When we speak of the “organism” in the most general sense, we mean that it exhibits these two modes of metabolism. This is, of course, not the case in any actual organism which we can investigate, or at least the typical modes of behaviour which characterise animal and plant life are not seen in any one individual. But we find that there is no absolute distinction between the two kingdoms. The plant may exhibit a mode of nutrition closely resembling that of the animal (as in the insectivorous plants), and it is possible that photo-synthetic process, in the general sense, may be present in the metabolism of some animals. Certain lower plants, the zoospores of algæ, exhibit movements identical in character with those of lower animals. At the base of both kingdoms are organisms, the Peridinians, for instance, which have much of the structure of the animal (though cellulose is present in their skeleton), which possess motile organs, but which also possess a photo-synthetic apparatus, and exhibit the typical plant mode of nutrition. Further, there are symbiotic partnerships, that is, associations of plant and animal in one “individual” form (as, for instance, among the lower worms, Echinoderms, polyzoa, molluscs, and other groups of animals). In these cases green algal cells, capable of forming starch from carbon dioxide and water under the influence of light, become intercalated among the tissues of the animal. We find, also, that with regard to some fundamental characters, plant and animal display close similarities: the structure of the cell, for example, and the highly special mode of conjugation of the germ-nuclei in sexual reproduction. We must regard all the distinctive characters of the plant as represented in the animal and vice versa. Why they have become specialised in different directions is a question that we discuss later.

The organism, then, in so far as we regard it as a physico-chemical mechanism, as the theatre of energetic happenings, exhibits the following general characters:—

(1) It slowly accumulates available energy in the form of chemical compounds of high potential, work being done upon it.

(2) It liberates this energy in relatively rapid, controlled, “explosive reactions,” transforming into movements carried out by a sensori-motor system of parts, work being done by it.

(3) In all these transformations the amount of energy which is dissipated is relatively small, and tends to vanish.

From the point of view, then, of energetic processes these are the characters of life, using the term in the general sense indicated above.[16]

Is there an absolute distinction between the organic mechanism and the inorganic one? Let us note, for the first time, that the actual physico-chemical transformations themselves, which we study in inorganic matter, are identical with those which we study in the organism. Molecules of carbon dioxide, water, nitrate, sodium chloride, potassium chloride, phosphate, and so on, are just the same in inert matter as in the organism. Chemical transformations, such as the hydrolysis of starch, the inversion of cane sugar, or the splitting of a neutral fat, are certainly just the same processes, whether we carry them out in the glass vessels of the laboratory, or observe them to proceed in the living tissues of the animal body. The same molecular rearrangements, and the same transfers of energy, occur in both series of events. This, however, is not the material of a distinction: what we have to find is, whether the direction of a group of physico-chemical reactions is the same in the organism and in a series of inorganic processes.

Let us return to the Carnot cycle. This is a series of operations which occur in an imaginary mechanism in such a manner that the whole series can be easily reversed. Heat is supplied to the imaginary engine, which then performs work and yields up its heat to a refrigerator. Work is then performed on the engine, which thereupon takes heat from the refrigerator and returns it to the source. The work done by the engine in the direct cycle is equal to the work done on it in the indirect cycle. The heat taken from the source and given to the refrigerator in the direct cycle is equal to the heat taken from the refrigerator and given to the source in the indirect cycle. But it is a purely imaginary mechanism, and all experience shows not only that it has not been realised in practice, but that it cannot so be realised. If it could be realised, we should show that the second law of thermo-dynamics is not physically true.

Do the energy processes of life realise such a perfectly reversible cycle of operations? In order to answer this question we must consider the fate of the energy which is absorbed in the plant metabolic cycle, and that which is given out in the animal one. Does all the energy of solar radiation which is absorbed by the plant pass into the form of the potential chemical energy of the carbohydrates and other substances manufactured? Does any of the energy of the animal which results from the metabolism of its body pass into the unavailable form—that is, into a form in which it cannot be utilised by other organisms? That is to say, is energy dissipated by the organism?

Undoubtedly it is to some extent, but to a far less extent than in the inorganic train of processes. Some of the energy of solar radiation absorbed by the plant must become transformed, by the friction of whatever movements occur, into low-temperature heat, and some quantity of heat, however small, is generated by the metabolism of the plant. Again, some of the heat of the warm-blooded animal must be radiated into space, or conducted away from its body; and this energy becomes dissipated—let us assume, at least, that it is so dissipated in the physical sense. Probably also some quantity of heat is generated by the metabolism of the cold-blooded animal, though this must be a very small proportion of the total energy transformed. We see, then, that the distinction is one of degree, though the difference between inorganic and organic energetic processes is very great in this respect; so great that we must regard it as constituting a fundamental difference, and as indicative of the limitation of the second law when extended to the functioning of the organism.

But we have also to consider the effect of the work done by the organism. We consider the nature and meaning of the evolutionary process in a later chapter, but in the meantime we may state this thesis: that the process of evolution leads up to man and his activity. It leads, if we regard the process as a directed one; but even if we regard it as a fortuitous process we still find that man, far more than any other organism, is the result of it. All the facts of biology and history show that man dominates the organic world, plant or animal; that the whole trend of his activity is to eliminate whatever organisms are inimical, and to foster those that are useful. Already, during the brief period of his rational activity, the wolf has disappeared from civilised lands while the dog has been produced. Species after species of hostile or harmful organisms have been, or are being, destroyed or changed, while numerous other species have been preserved and altered for his benefit. In the future we see an organic world subservient to him either entirely or to an enormous extent.

So also in the inorganic world. Rivers which formerly rushed down through rapids, dissipating their energy of movement in waste irrecoverable heat, now pour through turbines and water wheels, generating electricity and accumulating available energy. Winds which “naturally” dissipated their mechanical energy in waste heat now propel ships and windmills. Tides, with their incredibly great mechanical energy, now simply warm up the crust of the earth by an infinitesimal fraction of a degree daily, and produce heat which at once radiates into space. Who doubts that by and by this energy too will become accumulated for human use? Multitudes of chemical reactions were potential, so to speak, in the molecules of petroleum, while the energy which might have produced them ran to waste. But under human activity this energy became directed and made to produce chemical reactions formerly existing only in their possibility, and all the substances of modern organic chemistry came into existence.

The energy, then, of human activity has been directed towards averting or retarding the progress towards dissipation, or irrecoverable waste, of cosmic energy—that of the sun’s radiation, and of the motions of earth and moon. Human activity has accumulated available energy. The difference of water-level between Niagara and the rapids below represents available mechanical energy. A few years ago an enormous quantity of this energy became irredeemably lost in waste heat every twenty-four hours: now it remains available for work; and this quantity of work retained is enormously greater than is the human energy which was expended on erecting the water-power installation there.

The processes studied by physics and chemistry are therefore irreversible ones. We can conceive a perfectly reversible process, as in the Carnot heat-engine, but this is a purely intellectual conception, formed as the limit to a series of operations which approximate closer and closer to an ideal reversibility. It is a conception that has no physical reality—a guide to reasoning only. On the other hand we see that all naturally occurring physical processes are irreversible and in their sum tend to complete degradation of energy. Mechanistic biology isolates physico-chemical processes in the functioning of the organism, and sees that they conform to the law of dissipation, as well as to that of the conservation of energy.

Yet the organism as a whole, that is, life as a whole, on the earth, does not conform to the law of dissipation. That which is true of the isolated processes into which physiology decomposes life is not true of life. In all inorganic happenings energy becomes unavailable for the performance of work. Solar radiation falling on sea and land fritters itself away in waste irrecoverable heat, but falling on the green plant accumulates in the form of available chemical energy. The total result of life on the earth in the past has been the accumulation of enormous stores of energy in the shape of coal and other substances. By its agency degradation has been retarded. Whenever, says Bergson, energy descends the incline indicated by Carnot’s law, and where a cause of inverse direction can retard the descent, there we have life.

CHAPTER III THE ACTIVITIES OF THE ORGANISM

The rather lengthy discussion of the last chapter was necessary in order to show just how far the principles of energetics established by the physicists applied to the organism. We have seen that the first law of thermodynamics does so apply with all its exclusiveness. The more carefully a physiological experiment is made; the more closely do its results correspond with those which theory demands. It is true that relatively few experimental investigations can be controlled in this way, but in those that can be checked by calculation (as, for instance, in the well-known calorimetric experiments) everything tends to show that precisely the same quantities of matter and energy enter the body of an organism in the form of food-stuff, that leave it as radiated and conducted heat, as work done, and as the potential chemical energy of the excretions. Even when we are unable (as in most investigations) to apply the test of correspondence with theory, we have the conviction that the law of conservation holds with all its strictness.

Then, whenever it was possible to apply the methods of chemistry and physics to the study of the organism, it was seen that the processes at work were chemical and physical. The substance of the living body was seen to consist of a large (though limited) number of chemical compounds, differing mainly from those which exist in inorganic nature in their greater complexity. It was also seen that physico-chemical reactions occurred in living substance analogous with, or quite similar to, those which could be studied in non-living substance. The conclusion, then, was irresistible that the life of the organism was merely a phase in the evolution of matter and energy, and differed in no essential respect from the physico-chemical activities that could be observed in the non-living world.

These conclusions were stated so well by Huxley in his famous lecture on “The physical basis of life,” over forty years ago, that all subsequent utterances have been merely reiterations of this thesis in a less perfect form. The existence of the matter of life, Huxley said, depended on the pre-existence of certain chemical compounds—carbonic acid, water, and ammonia. Withdraw any one of them from the world and vital phenomena come to an end. They are the antecedents of vegetable protoplasm, just as the latter is the antecedent of animal protoplasm. They are all lifeless substances, but when brought together under certain conditions they give rise to the complex body called protoplasm; and this protoplasm exhibits the phenomena of life. There is no apparent break in the series of increasingly complex compounds between water, carbon dioxide, and ammonia, on the one hand, and protoplasm on the other. We decide to call different kinds of matter carbon, oxygen, hydrogen, and nitrogen and to speak of their activities as their physico-chemical properties. Why, then, should we speak otherwise of the activities of the substance protoplasm?

“When hydrogen and oxygen are mixed in certain proportions and an electric spark is passed through them they disappear, and a quantity of water, equal in weight to the sum of their weights, appears in their place. There is not the slightest parity between the passive and active powers of the water and those of the oxygen and hydrogen that have given rise to it. . . . We call these and many other phenomena, the properties of water, and we do not hesitate to believe that in some way they result from the properties of the component elements of the water. We do not assume that a something called “aquosity” entered into and took possession of the oxide of hydrogen as soon as it was formed and guided the aqueous particles to their places in the facets of the crystal, or among the leaflets of the hoar frost.”

“Is the case in any way changed when carbonic acid, water, and ammonia disappear, and in their place, under the influence of pre-existing protoplasm, an equivalent weight of the matter of life makes its appearance?”

“It is true that there is no sort of parity between the properties of the components and the properties of the resultant. But neither was there in the case of water. It is also true that the influence of pre-existing protoplasm is something quite unintelligible. But does anyone quite understand the modus operandi of an electric spark which traverses a mixture of oxygen and hydrogen? What justification is there, then, for the assumption of the existence in the living matter of a something which has no representative or correlative in the non-living matter which gave rise to it?”

All the investigations of over forty years leave nothing to be added to this statement of what, in Huxley’s days, was called materialistic biology. It was a very unpopular statement to make then, but it has become rather fashionable now. Let the reader compare it with all that has been spoken and written since 1869, even with the utterances of the British Association of the year 1912, and he will find that it expresses the point of view of mechanistic biology far better than all the subsequent restatements. The only difference he will find is that the latter have become (as William James has said about academic philosophies), rather shop-soiled. They have been reached down and shown so often to the enquiring public, that each display has taken away something of their freshness.

Now Huxley’s example leads up so well to the consideration of the differences between the chemical activities of the organism and those of inorganic matter that we may consider it in some detail. What, then, is the difference between the explosion of a mixture of oxygen and hydrogen, and the photo-synthesis of starch by the green plant?

In the case of the synthesis of water we have an example of an exothermic chemical reaction. We are to think of the mixture of oxygen and hydrogen as existing in a condition of “false equilibrium.” It may be compared with a weight resting on an inclined plane.

Fig. 8.

Suppose that the plane is a sheet of smoothly polished glass, and that the weight is a smooth block of glass. By canting the plane more and more an angle will be found at which the slightest push starts the weight sliding down. Now in the case of the explosive mixture of oxygen and hydrogen we have a chemical analogue. Either the gases do not combine at all at the ordinary temperature or they combine “infinitely slowly.” But the slightest impulse, an electric spark requiring an almost infinitesimally small quantity of energy, starts the combination of the gases, and this continues until all is changed into water vapour. In this reaction a large quantity of energy is liberated in the form of heat. This heat becomes transformed into the kinetic energy of the water particles which condense from the steam formed in the explosion, and these particles assume the temperature of their surroundings. The energy which was potential in the explosive mixture, and which was capable of doing work, still exists as the kinetic energy of the water formed, but it has become unavailable for any natural process of work.

We have seen what is the general character of the reaction series in the course of which carbon dioxide and water become starch; and then this, becoming first soluble, and becoming associated with the ammonia or nitrate taken into the plant, becomes protoplasm. It is a reaction which differs from that just described, in that available energy becomes absorbed and accumulated, and retains the power of doing work. It is not a reaction which can be initiated by an infinitesimal stimulus, but one in which just as much energy is required in order that it may happen as is represented in the energy which becomes potential in the living substance generated. The first reaction is one which may take place by itself;[17] the other is one which requires a compensatory energy-transformation in order that it may happen. In the first reaction energy is dissipated; in the second one it is accumulated.

We are thus led to the consideration of the second principle of energetics and its limitations, but before entering upon this discussion we must consider the nature of the activities of the organism.

By the term “metabolism” we understand the totality of the physico-chemical changes which occur in the living substance of the organism. In physiological writings we usually find that two categories of metabolic changes are described: (1) anabolic processes, in the course of which simple chemical compounds possessing relatively little energy are built up into much more complex substances, containing a relatively large quantity of available energy, and therefore capable of doing work. The transformations constituting an anabolic change must be accompanied by corresponding compensatory energy-transformations, to account for the energy which becomes potential in the substances formed. The formation of starch from carbon dioxide and water, by the green plant, is such an anabolic change, and the compensatory energy-transformation is the absorption of radiation from the ether by the cells of the plant. A further anabolic change in the plant organism is the formation of amido-substances from the ammonia or nitrate absorbed from the soil, and from the soluble carbohydrates formed from the starch manufactured in the green cells.

The typical activities of the chlorophyll-containing organism are of this nature; they are anabolic. The organism may be a green land-plant; a marine green, red, or brown alga; a yellow-green diatom, a yellow, green, red, or brown peridinian or other holophytic protozoan; an ascidian, mollusc, echinoderm, polyzoan, worm, or coral containing “symbiotic algæ” (that is the chlorophyll-containing cells of some plant organism which have become associated with the animal and incorporated in its tissues). In all these cases the presence of this chlorophyllian substance confers on the organism the power of effecting the compensatory energy-transformation, by the aid of which carbon dioxide and water are built up into starch. What this transformation is, and what are the steps by which the carbon dioxide and water become carbohydrate we do not exactly know. Solar radiation impinging upon an inorganic substance is partly reflected and partly absorbed. The absorbed fraction may become transformed in such a way as to render the substance phosphorescent, or it may transform into chemical energy, as when light impinges on a photographic plate, but as a general rule it is transformed into heat. In the green plant, however, the transformation of radiation into heat does not occur—at least the heating is very small—and it passes directly or indirectly into the potential chemical energy of the starch which is synthesised. We must regard this power of absorbing radiation and utilising it in compensatory transformations as a general character of protoplasm. It is true that it is now specialised in the cells containing the chlorophyll bodies, but there are indications that it may be present in the tissues of the animal devoid of chlorophyll.

Other anabolic transformations occur in the animal. The food-stuffs which are absorbed from the intestine are substances which have undergone dissociations, the nature of which is such as to render them capable of absorption and of reconstruction. These anabolic changes in the higher animal are exceptional, and their usefulness lies in the fact that by their means substances become capable of being transported by the tissue fluids of the body.

(2) Katabolic changes in the animal body correspond in their frequency of occurrence to the anabolic changes of the plant organism. In them complex chemical substances undergo transformation into relatively simple substances, and the contained energy at the same time undergoes a parallel transformation, passing into the form of heat and mechanical energy, while a fraction becomes dissipated. Food-stuffs taken into the alimentary canal break down in this way, but to a very limited extent. Proteids undergo dissociation or decomposition into amido-substances, while fats are dissociated into fatty acids and glycerine. Doubtless energy is dissipated in these processes, serving no other purpose but to heat the contents of the alimentary canal, but this energy-transformation has not been worked out very completely and it is a question whether, given a healthy animal and perfect food-stuffs, any energy would necessarily be lost during the digestive processes. The reactions involved in the latter do not belong to the category of chemical changes proceeding from the complex to the simple, with a liberation of energy; but appear to involve rather a rearrangement of the constituents of a complex molecule, a process in which the contained energy need not undergo change in quantity. These processes involve the action of enzymes.

Enzymes play a great part in modern physiological theory and we must consider them in detail. Let us attach a concrete meaning to the general notion of enzyme-activity by considering the phenomena known as catalysis. The metal platinum can be brought into a very fine stage of division when it is known as platinum black. In this condition it brings about reactions in chemical mixtures or substances which would not otherwise occur: a mixture of oxygen and hydrogen explodes when brought in contact with platinum black, and a mixture of coal gas and air inflames, a reaction which is made use of in the little gas-lighting apparatus which most people have seen. If, again, a powerful electric current be passed between platinum wires which are a little distance apart, and are immersed in water, the metal becomes torn away from the points of the wire in the form of an impalpable powder, colloidal platinum. The liquid containing this colloid then has the power of setting up chemical changes in other substances, changes which would not otherwise occur, or, at least, would occur very slowly.

In general such catalysts, platinum black or colloidal platinum for instance, have the following characters: (1) a small quantity is sufficient to cause change in a large (theoretically an infinite) quantity of the substance acted upon; (2) the nature and quantity of the catalyst remain at the end the same, as at the beginning of the reaction; (3) a catalyst does not start a reaction in any other substance or substances, it can only influence the rate at which this reaction may occur: apparently it does, in some cases, start a reaction, but in such cases we suppose that the latter proceeds so slowly as to be imperceptible; (4) the final state of the reaction is not affected by the catalyst; it depends only on the nature of the interacting substance or substances; (5) the final state is not affected either by the nature or quantity of the catalyst: it is the same if we employ different catalysts, or a large or small quantity of the same catalyst. Finally, it appears that the phenomena of catalysis are universal: “There is probably no kind of chemical reaction,” says Ostwald, “which cannot be influenced catalytically, and there is no substance, element, or compound which cannot act as a catalyser.”[18]

Enzymes, then, are agents which are produced by the organism, and which act by influencing (accelerating or retarding) chemical reactions. An enzyme, as such, need not exist in a tissue; it is there as a zymogen, a substance which may become an enzyme when required. An enzyme need not be active: it may be necessary that it should be “activated” by a kinase, another substance produced at the same time. Associated with many enzymes are anti-enzymes, substances which undo what their corresponding enzymes have done. Finally some, perhaps most, enzymes are reversible, that is, if they produce a change in a certain substance they can also produce the opposite kind of change: the meaning of this will become clearer a little later on. We have spoken of enzymes as “agents” or “substances,” but it is not at all certain that they are definite chemical compounds. In the preparation of an enzyme what the bio-chemist obtains is a liquid, a glycerine or other extract which possesses catalytic properties. An actual catalytic substance, like platinum black, cannot be obtained from this liquid. A white powder may be obtained, but this usually proves to be proteid in composition; it is not the actual enzyme itself but is the impurity associated with the latter. Now the very great number of enzymes “isolated” by the physiologists has rather destroyed the original simplicity of the idea of enzyme activity and suggests a parallel statement to that made by Ostwald about catalysts: any tissue substance may influence the reactions that may possibly occur in other tissue substances. But while pure chemistry has to deal with definitely known chemical compounds in the phenomena of catalysis, this cannot be said to be the case with physiology in dealing with enzymes. Reasoning by analogy, we may say that it is probable that enzymes are definite proteids, or chemical substances allied to these, but this has not been clearly demonstrated, and it is possible that the phenomena of enzyme activity may belong to some other category of energy-transformations.

However this may be, the conception is a useful one in describing the reactions of the organism, and it may be illustrated by considering the digestion and absorption of fat in the mammalian intestine, a process which appears to be better known than that of proteid digestion. A neutral fat consists of an acid radicle, oleic, palmitic or stearic acids, for instance, united with glycerine. The action of the pancreatic or intestinal enzymes is to dissociate this fatty salt. Let us write the formula of the latter as G F, G being the glycerine base, and F the fatty acid; then

G F

G + F

which means that the enzyme can cause the neutral fat to dissociate into glycerine and fatty acid. This action will go on until a state of equilibrium is attained, in which there is a certain quantity of each of the radicles, and a certain quantity of unchanged neutral fat, the ratio of all these to each other depending on various things. When this state of equilibrium is attained the enzyme does indeed go on splitting up more neutral fat, but it is a reversible enzyme, and it also causes the glycerine and fatty acid already split up to recombine, forming neutral fat. A condition is, therefore, reached in which the composition of the mixture remains constant.

Now there is dissociated fat in the intestine after a meal, but there is only neutral fat in the wall of the intestine. The fat itself cannot pass through the cells forming the intestinal wall, but the glycerine and fatty acid into which it is dissociated can so pass, since they are soluble in the liquids of the intestine. We suppose that the cells of the wall of the intestine also contain the fat-splitting ferment; this ferment in the cells acts on the glycerine and fatty acid immediately they enter and recombines these radicles again into neutral fat, the above equation now reading from right to left. But after a time this reaction in the cells will also begin to reverse, for the enzyme will begin to split up the synthesised neutral fat when the state of chemical equilibrium in the new conditions is attained. Fatty acid and glycerine will then diffuse out from the cells into the adjacent lymph stream or blood stream—perhaps neutral fat will also pass from the cells into these liquids, we are not sure. At all events the lymph and blood after a meal containing much fat are crowded with minute fat globules. But why are there no fatty acids or glycerine in the blood, for the latter also contains lipase (the fat-splitting enzyme)? The explanation is, apparently, that either an anti-enzyme is produced, or that the enzyme passes into a zymoid condition. Why also does fat accumulate in the tissues? Here, again, the activity of the enzyme, which from other considerations we may regard as being universally present almost everywhere in the body, must be supposed to be arrested by some means.

The conception of a catalytic agent, such as we can study in pure chemistry, thus carries us a long way in our description of the processes of digestion, absorption, and assimilation. We have applied it to the case of fat-digestion, but very much the same general scheme might also apply to many other processes in the body. Obviously it enables us to describe these processes in terms of physico-chemical reactions, but we cannot fail to see that ultimately we are compelled to assume the existence of reactions which were not included in the original conception—the activation of the enzyme at the proper moment by the kinase, the operation of the anti-enzyme, and the passage of the enzyme into the zymoid. Just why these things happen as they do we do not know, yet the whole problem becomes shifted on to these reactions.

In the same way we apply the purely physical processes of the osmosis and diffusion of liquids to the circulation of substances in the animal body. The nature of these processes will probably be familiar to the reader, nevertheless it may be useful to remind him that by diffusion we understand the passage of a liquid, containing some substance in solution, through a membrane; and by osmosis the passage of a solvent (but not of the substance dissolved in it) through a “semi-permeable membrane.” The molecules of the solvent (water, for instance) pass through the membrane (the wall of a capillary, or lymphatic vessel), but the molecules of the substance (salt, for instance) dissolved in the solvent do not pass. Let us suppose that a strong solution of common salt in water is injected into the blood stream: what happens is that osmosis takes place, the water in the surrounding lymph spaces passing into the blood stream because the concentration of salt there is greater than it is in the lymph. While this is happening, the capillary walls are acting as semi-permeable membranes, allowing the molecules of water to pass through but not the molecules of salt. Very soon, however, the process of osmosis becomes succeeded by one of diffusion, and the salt molecules pass through the capillary wall into the lymph and are excreted.

Undoubtedly the purely physical processes of diffusion and osmosis occur all over the animal body and are the means whereby food-materials, secretory, and excretory substances are transported from blood to lymph, or vice versa, from lymph to cell substance or to glandular cavities, and so on. But it is also the case that in very many processes the activity of the cells themselves plays an important part. It may even be the case that a particular process, after all physical agencies are taken into account, reduces down to this action of the cells. To understand this we must consider the mode of working of some well-known organ, and the best possible example of such an organ, considered as a mechanism, is that of the sub-maxillary salivary gland of the mammal.

Fig. 9.

What, then, is this mechanism and how does it act? The gland is a compound tubular one, its internal cavity being prolonged into the duct which opens into the mouth. The saliva prepared in the gland issues from this duct. Blood is carried to the gland by twigs of the facial artery, and, after circulating through it, is carried away by factors of the jugular vein. Two nerves supply the gland: one is the chorda tympani, a branch of a cranial nerve, and the other is a sympathetic nerve. Lymph also leaves the gland by a little vessel.

Now suppose we have laid bare all this mechanism in a living animal and make experiments upon it. If we stimulate the chorda tympani there is a copious flow of thin watery saliva, but if we stimulate the sympathetic there is a less copious flow of thick viscid saliva. Why is this? We find on closer analysis that the chorda contains fibres which dilate the small arteries so that there is an increased flow of blood through the gland; but that, on the other hand, the sympathetic contains fibres which constrict the arteries, thus leading to a reduced flow of blood. This accounts for the fact that “chorda-saliva” is abundant and thin, while “sympathetic-saliva” is scarce and thick. It was thought at one time that the chorda contained fibres which stimulated the gland to produce watery saliva, while the sympathetic contained fibres which stimulated it to produce mucid saliva. This, however, is not the case. Both nerves contain the same kind of secretory fibres: their other fibres differ mainly in that they act differently on the arteries.

It might be the case—indeed it was at one time thought that it was the case—that secretion of saliva was simply a matter of blood-flow: an abundant arterial circulation gave rise to abundant saliva, a sparse flow to a sparse saliva. Undoubtedly the secretion depends on blood supply, but not solely. If it did, then the whole process might be conceived to be a very simple mechanical one—filtration or diffusion of the saliva from the blood stream through the thin walls of the blood vessels, and the walls of the tubules into the cavity of the gland. If this were the case, then the liquid in the gland would be the same in composition and concentration as the liquid part of the blood—the plasma. But it is really different in composition and it is not so concentrated. Now osmotic pressure—on the action of which so much is based—cannot help us, for the liquid in the gland is less concentrated than that in the blood vessels, so that water ought to pass from gland to blood instead of from blood into gland. Again, if we tie the duct, so that the saliva cannot escape, secretion still goes on, though the hydrostatic pressure of saliva in the cavity of the gland may be considerably greater than that of the liquid in the blood vessels. Yet again, if we stop the blood flow by tying the artery, secretion of saliva may still go on for a time.

Therefore the only physical agencies we can think of do not explain the secretion. The latter is actually the work of the individual cells, stimulated by the nerves. If the volume of the gland be measured just while it is being stimulated to secrete, it will be found that the organ becomes smaller, yet while it is being stimulated the blood-vessels are being dilated so that the volume of the whole structure ought to become greater. Obviously part of the substance of the gland is being emptied out through its duct as the secretion.

If we examine the cells of the gland in various states we see clearly that granules of some material, different in nature from the substance of the protoplasm itself, are being formed within them. Evidently these granules swell up during secretion and discharge their contents into the ducts. Further changes in the characters of the cell-substance, and in the nucleus, can be observed, and all these indicate that the protoplasm of the cells, as the result of stimulation, elaborates certain substances; that these substances are then washed out, so to speak, into the duct by the withdrawal of water from the cell; and that thereafter the cell absorbs fresh nutritive material from the lymph which exudes from the blood vessels, along with water. The distinctive part of the whole train of processes is, then, this elaboration of material by the cells themselves; while the concomitant changes in the calibre of the blood vessels and in the flow of blood and lymph are subsidiary ones. In the process of secretion of saliva energy is absorbed from the chemical substances of the blood to bring about the passage of water from a region of high to a region of low osmotic pressure; oxygen and nitrogen, with other elements of course, are withdrawn from the arterial blood stream for the purpose of the secretion, and carbon dioxide and other substances are given off to the venous blood and lymph.

The problem thus is pushed back from the mechanical events occurring in the nervous and circulatory processes, to the physico-chemical ones occurring in the cells of the gland tubules; and it thus becomes much more obscure. It is true that we can formulate a hypothesis which describes, in a kind of way, these intra-cellular metabolic changes, in terms of physico-chemical reactions, and, without doubt, reactions of this kind must occur within the cell. But if we could test any such hypothesis as easily as the mechanical ones suggested, should we find it any more self-sufficient?[19]

Irritability and contractility are general properties of the organism. These properties are illustrated by the irritability of an Amœba or Paramœcium to stimuli of many kinds; by the movements of the pseudopodia of the former animal, or of the cilia of the latter; by the nervous irritability of the higher animal, and the contraction of its muscles when they are stimulated. They are among the fundamental properties or functions of living protoplasm, and their study is of paramount interest, and carries us to the very centre of the problem of the activities of the organism. Naturally physiologists have never ceased to attempt to describe irritability and contractility in terms of physics, but though we may be quite certain that the things that do occur in these phenomena are controlled physico-chemical reactions, it must be remembered that what we positively know about their precise nature is exceedingly little.

What is the nature of a nervous impulse? When a receptor organ is stimulated, as, for instance, when light impinges on the cone cells of the retina, or when the nerve-endings in a “heat-spot” in the skin are warmed, or when the wires conveying an electric current are laid on a naked nerve, an impulse is set up in the nerve proceeding from the place stimulated, and we must suppose that approximately the same amount of energy moves along the nerve as was communicated to the receptor or the nerve itself by a stimulus of minimal strength. How does it so move? Several facts of capital importance result from the experimental work. (1) The impulse travels with a velocity variable within certain limits, say from 8 to 30 metres per second; (2) it travels faster if the temperature is raised (up to a certain limit); (3) it is difficult to demonstrate that the passage of this impulse is accompanied by definite chemical changes in the nerve substance: it is stated that carbon dioxide is produced, but this is not certainly proved; (4) an electric current is produced in the nerve as the result of stimulation; (5) no heat is produced, or at least the rise of temperature, if it occurs, is less than 0.0002° C.

Thus it is quite certain that physical changes accompany the propagation of the nerve-impulse, for the latter has a certain velocity, which depends on the temperature, and an electric change also occurs in the substance of the nerve. Is this electric change the actual nerve impulse? It is hardly likely, since the velocity of the impulse is very much less than that of the propagation of an electric change through a conductor; besides, the passage of the impulse is not accompanied by a measurable heat evolution, although the flow of electricity along a poor conductor must generate heat and dissipate energy. Is it a chemical change? Then we should be able to observe metabolism in the nerve substance—that is if the energy-change is a thermodynamic one—while it is not at all certain that metabolic changes do occur. Nevertheless it seems probable that a physico-chemical change is actually propagated when we consider the chemical specialisation of the substance of the axis-cylinder of the nerve. Now the velocity of propagation of the nervous impulse is of the same order of magnitude as that of an explosive change in chemical substances (using the term “explosion” to connote chemical disintegrations rather than combustions). If we imagine a long rod of dynamite, or picric acid, or a long strand of loosely-packed gun-cotton to be exploded by percussion at one end, then a transmission of the chemical disintegration of any of these substances will pass along the rod, etc., with a velocity which will certainly vary with the physical condition of the material. It would be a high velocity in a rod of dynamite, or fused picric acid, but a lower velocity in a loosely aggregated strand of gun-cotton, or a trail of picric acid powder. Is this what happens in the nerve when an impulse travels along it? Obviously not, since the substance of the nerve is not altered appreciably, while that of the explosive substance passes into other chemical phases. We might imagine, then, such a change in the nerve fibrils as that of a reversible transformation of some chemical constituent:—

Let us imagine the substance of the fibril to be composed of, or at least to contain, the substances a + b which dissociate reversibly into the substances c + d. At any moment, and in any particular physical state, as much of a and b pass into c and d as c and d pass into a and b. There will be equilibrium. But now let a stimulus alter the physical conditions: prior to the stimulus the phase was a_m + b_n = c_p + d_r—the suffixes m, n, p, r, denoting the concentrations of a, b, c, and d—but after the stimulus the phase may be a_m¹ + b_n¹ = c_p¹ + d_r¹. Now the element of the nerve substance (1) forms a system with the element (2). The condition in (2) is a_m + b_n = c_p + d_r, and that of (1) a_m¹ + b_n¹ = c_p¹ + d_r¹, but these two together now fall into a new state of equilibrium and this is transmitted along the whole nerve-fibril with a velocity which belongs to the order of magnitude of that of chemical changes. If the stimulus remains constant (a constant electric current for instance), the new condition of equilibrium will be established throughout the whole length of the fibril and the nervous impulse will be a momentary one (as it is in this case). But if the stimulus is an intermittent one (an interrupted electric current, light-vibration, sound-vibrations), then in the intervals the former condition of equilibrium will become re-established and the nervous impulse will be intermittent (as it is). There would be no work done on the whole in the changes, except that done by the transmission of the changed state of equilibrium to the substance of the effector organ in which the nerve-fibril terminates—the substance of a muscle fibre, or the cell of a secretory gland, for instances. There would, probably, be a certain dissipation of energy as in the case of the propagation of an electric impulse through a poor conductor, but all our knowledge of the chemistry of the nerve fibre points to this amount of dissipation as tending to vanish.

Something analogous to this may be expected to take place in a muscle fibre when it contracts; except that, of course, energy is transformed in this case. What precisely does happen we do not know and at the present time no physico-chemical hypothesis of the nature of muscular contraction exactly describes all that can be observed to take place. Certain positive results have, of course, been obtained by chemical and physical investigation of the contracting muscle: carbon dioxide is given off to the lymph and blood stream, and the amount of this is increased when an increased amount of work is done by the muscle; heat is produced and this too increases with the work performed; glycogen is used up, and lactic acid is produced; finally oxygen is required, and more oxygen is required by an actively contracting muscle than by a quiescent one. Now the obvious hypothesis correlating all these facts is that the muscle substance is oxidised, and that the heat so produced is transformed into mechanical energy. “We must assume,” says a recent book on physiology, “that there is some mechanism in the muscle by means of which the energy liberated during the mechanical change is utilised in causing movement, somewhat in the same way as the heat energy developed in a gas-engine is converted by a mechanism into mechanical movement.”

Now, must we assume anything of the kind? To begin with, life goes on, and mechanical energy is produced in many organisms living in a medium which contains no oxygen. Anaerobic organisms are fairly well known, and we cannot suppose that in them energy is generated by the combustion of tissue substance in the inspired oxygen. A muscle removed from a cold-blooded animal will continue to contract in an atmosphere containing no oxygen, and it will continue to produce carbon dioxide. It is true that the contractions soon cease, even after continued stimulation under conditions excluding the fatigue of the muscle, but do the contractions cease because the oxygen supply is cut off, or because the muscle dies in these conditions? We know that some complex chemical substance is disintegrated during contraction and that mechanical energy and heat are produced and that carbon dioxide is also produced. We know that the carbon contained in the latter gas corresponds roughly with the carbon contained in the muscle substance which undergoes disintegration, but does all this justify us in saying that this substance is oxidised in order that its potential chemical energy may be transformed into mechanical energy? Obviously not, since we might equally well suppose that the complex metabolic substance of the muscle splits down into simpler substances and that in this transformation energy is generated. Suppose that these simpler substances are poisonous and that they must be removed as rapidly as formed. The rôle of the oxygen may be to oxidise them, thus transforming them into carbon dioxide, an innocuous substance which can be carried away quickly in the blood stream. This line of thought, according to which the rôle of oxygen is an anti-poisonous one, is held at the present day by some physiologists, and many considerations appear to support it; the existence of “oxidases,” for instance, enzymes which produce oxidations which would not otherwise occur in their absence. Such enzymes exist in very many tissues, and they may, apparently, be present in an inactive form, requiring the agency of a “kinase” before they are able to act.

The usual view among physiologists is that the muscle fibre is a thermodynamic apparatus transforming the heat generated during metabolism into mechanical energy. How is this transformation effected? It cannot be said that we have any one hypothesis more convincing than another. It has been suggested that alterations of surface tension play a part, or that the heat produced by oxidation causes the fibre to imbibe water and shorten. Engelmann has devised an artificial muscle consisting of a catgut string and an electrical current passing through a coil of wire, and by means of this he has reproduced the phenomena of simple contraction and tetanus. But it remains for future investigation to verify any one of these hypotheses.

When Huxley published his Physical Basis of Life, probably few physiologists had any doubt that protoplasm was a definite chemical substance, differing from other organic substances only by its much greater complexity. But in 1880 Reinke and Rodewald published the results of an analysis of the substance of a plant protoplasm and these appear to have demonstrated that the substance was really a mixture of a number of true chemical compounds and was not a single definite one. Now all of these substances might exist apart from protoplasm, and in the lifeless form, and a simple mixture of them could hardly bring forth vital reactions. These results were followed by the morphological study of the cell—the discovery of the architecture of the nucleus, and so on, and so opinion began to turn to the hypothesis that the vital manifestations of protoplasm were the result of its structure. Microscopical examination of the cell appeared to disclose a definite arrangement, the “foam” or “froth” of Butschli, for instance. But, again, it was easily shown that the foam, or alveolar structure of protoplasm was merely the expression of physical differences in the substances composing the cell-stuff—they reduced to phenomena of surface tension and the like. Artificial protoplasm and artificial Amœbæ were made—at least mixtures of olive oil and various other substances were made which simulated many of the phenomena of protoplasm in much the same way as crystalline products may be made which simulate the growth of a plant stem with its branches. For instance, one has only to shake up a little soapy water in a flask to see what resembles surprisingly the arrangement of certain kinds of connective tissues in the organism. Obviously these artificial phenomena have nothing to do with living substance.

Yet if we grind up a living muscle with some sand in a mortar we do destroy something. The muscle could be made to contract, but after disintegration this power is lost. We have certainly destroyed a structure, or mechanism, of some kind. But, again, the paste of muscle substance and sand still possesses some kind of vital activity, for with certain precautions it can be made to exhibit many of the phenomena of enzyme activity displayed by the intact muscle fibres, or even the entire organism. Mechanical disintegration, therefore, abolishes some of the activities of the organism, but not all of them. If, however, we heat the muscle paste above a certain temperature, the residue of vital phenomena exhibited by it are irreversibly removed, so that heating destroys the mechanism. This we can hardly imagine to be the case (within ordinary limits of temperature at least) with a physical mechanism, but again a mechanism which is partly chemical might be so destroyed. We see, then, that protoplasm possesses a mechanical structure, but that all of its vital activities do not necessarily depend on this structure. The full manifestation of these activities depends on the protoplasmic substance possessing a certain volume or mass, and also on a certain chemical structure.

If living protoplasm has a structure, and is not simply a mixture of chemical compounds, what is it then? Two or three physico-chemical concepts are at the present time very much in evidence in this connection. When the substances known as colloids were fully investigated by the chemists, much attention was paid to them by the physiologists, so that life was called “the chemistry of the colloids,” just as after the investigation of the enzymes it was called the “chemistry of the enzymes,” and when the discovery of the relative abundance of phosphorus in cell-nuclei and in the brain was discovered, it was called the “chemistry of phosphorus.” Colloids (e.g. glue) are substances that do not readily diffuse through certain membranes, in opposition to crystalloids (e.g. solution of common salt) which do readily so diffuse. They form solutions which easily gelatinise reversibly, that is, can become liquid again (glue); or coagulate irreversibly, that is, cannot become liquid again (albumen); which have no definite saturation point; which have a low osmotic pressure (and derived properties), etc.; and the molecules of which are compound ones consisting of combinations of the molecules of the substance with the molecules of the solvent, or with each other, that is, they are molecular aggregates.

Colloids pass insensibly into crystalloids on the one hand and into coarse suspensions (water shaken up with fine mud, for instance) on the other. We may replace the concept of a colloid by those of “suspensoids” and “emulsoids.” A suspensoid is a liquid containing particles in a fine state of division—if the division is that into the separate molecules we have a solution, if into large aggregates of molecules we have a suspension. If the substance in the liquid is itself liquid, the whole is called an emulsoid. On the one hand this approaches to a mixture of oil in soap and water—an emulsion—and on the other hand to such a mixture as chloroform shaken up with water, when the drops of chloroform readily join together so that two layers of liquid (chloroform and water) form. What we see, then, in protoplasm is a viscid substance possessing a structure of some kind, and containing specialised protoplasmic bodies in its mass (nuclei, nucleoli, granules of various kinds, chlorophyll, and other plastids, etc.). It may contain or exhibit suspensoid or emulsoid parts or substances, or it may contain truly crystalloid solutions. These phases of its constituents are not fixed, but pass into each other during its activity. Nothing that we know about it justifies us in speaking about a “living chemical substance.” On analysis we find that it is a mixture of true chemical substances rather than a substance. It is no use saying that in order to analyse it we must kill it, for what we can observe in it without destroying its structure or activities indicates that it is chemically heterogeneous.

This is not a textbook of general physiology, and the examples of physico-chemical reactions in the organism which we have selected have been quoted in order to show to what extent the chemical and physical methods applied by the physiologists have succeeded in resolving the activities of the organism. The question for our consideration is this: do these results of physico-chemical analysis fully describe organic functioning? Dogmatic mechanism says “yes” without equivocation.

Now it is clear, from even the few typical examples that we have quoted, that physiological analysis shows, indeed, a resolution of the activities of the organism into chemical and physical reactions. How could it do otherwise? How could chemical and physical methods of investigation yield anything else than chemical and physical results? The fact that these methods can be applied to the study of the organism with consistent results shows that their application is valid; that we are justified in seeing physico-chemical activities in life. But are these results all that we have reason to expect?

We turn now to Bergson’s fertile comparison of the physiological analysis of the organism with the action of a cinematograph. If we take a series of photographic snapshots of, e.g., a trotting horse and then superpose these pictures upon each other, we produce all the semblance of the co-ordinated motions of the limbs of the animal. Yet all that is contained in the simulated motion is immobility. From a succession of static conditions we appear to produce a flux. Yet if we could contract our duration of, e.g., a week, into that corresponding to five minutes—if we could speed up our perceptual activity—should we not see the cinematographic pictures as they really are—a series of immovable postures and nothing more: truly an illusion? If, again, we reverse the direction of motion of the film, we integrate our snapshots into something which is absolutely different from the reality which they at first represented; and by such devices the illusions and paradoxical effects of the picture-house farces are made possible. Well, then, in the physiological analysis of the activity of the organism do we not do something very analogous to this? The complexity of even the simplest function of the animal is such that we can only attend to one or two aspects of it at once, arbitrarily neglecting all the rest. We find that the hydrostatic pressure of blood, and lymph, and secretion, the osmotic pressure, the diffusibility, vaso-motor actions, and other things must be investigated when considering the question of how the submaxillary gland secretes saliva. One, or as many as possible, of these reactions are investigated at one time, and then the results are pieced together—integrated—in order to reproduce the full activity of the whole indivisible process. But in doing this do we not introduce something new—a direction or order of happening—into the elements of the dissociated activity of the organism? Each elemental process must occur at just the right time.

What right have we to say that the activity of the organism is made up of physico-chemical elements? Just as much as we have in saying that a curve is made up of infinitesimal straight lines. Let us adopt Bergson’s illustration, with a non-essential modification.

Fig. 10.

The curve 1–8 is a line which we draw freehand with a single indivisible motion of the hand and arm and eye. It is something unique and individualised, in that no other curve ever drawn, in a similar manner, exactly resembles it. Let us investigate it mathematically. We can select very small portions of it—elements we may call them—and each of these elements, if it is small enough does not differ sensibly from a straight line. Let us produce each of these straight lines in both directions, it is then a tangent to the curve, and it does actually coincide with the curve at one mathematical point—the points 1–8 in the figure. The tangent then has something in common with the curve, but would a series of infinitesimally small tangents reproduce the curve? Obviously not, for the equations of the tangents would have the form ax + b, while that of the curve itself would be quite different, containing x as powers of x, or as transcendental functions of x. In this investigation what we succeed in obtaining are the derivatives of the curve, and to reproduce the latter from its elements we have to integrate the derivatives; that is, another operation differing in kind from our analytical one must be performed. Now in this illustration we have doubtless something more than an analogy with our physico-chemical analysis of life. The activities of the organism do reduce to bio-chemical ones (the elemental straight lines on the curve), and each of these reactions has something in common with life (it is tangent to life, touching it at one point). But if we attempt to reconstitute life from its physico-chemical derivatives we must integrate the latter, and in doing so we over-pass the bounds of physics, just as integrating a mathematical function we necessarily introduce the concept of the “infinitely small.”

The physico-chemical reactions into which we dissociate any vital function of the organism have, then, each of them, something in common with the vital function. But their mere sum is not the function. To reproduce the latter we have to effect a co-ordination and give directions to these reactions. In all physiological investigations we proceed a certain length with perfect success; thus the elements, so to speak, of the function of the secretion of saliva are (1) the blood-pressure, (2) the hydrostatic pressure of the secretion in the lumina of the gland tubules, (3) the diffusibility of the substances dissolved in the blood and lymph through the walls of these vessels, (4) the osmotic pressure of the same substances, and (5) the stimulation of the gland cells by “secretory nerve fires.” Now the investigations carried out—and no part of the physiology of the mammal has been so patiently studied as the salivary gland—fail, so far, completely to describe the function in terms of these elements. In the end we have to refer the secretion to intra-cellular processes, and then we begin to invoke again processes of osmotic pressure, diffusibility, and so on with reference to the formation of the drops of secretion which we can see formed in the gland cells. We are forced to the formulation of a logical hypothesis as to the nature of these intra-cellular processes, and since much that goes on in the cell substance is, so far, beyond physico-chemical investigation, our hypothesis will be as difficult to disprove as to verify.

Let us return now to Huxley’s comparison of the activity of the green plant with the chemical reaction which occurs when an electric spark is passed through a mixture of oxygen and hydrogen. The lecture on the “Physical Basis of Life” was published in 1869; in 1852 William Thomson published his paper “On a Universal Tendency of Nature to Dissipation of Energy,” and a year or two before that Clausius had applied Carnot’s law to the kinetic theory of heat: the second principle of energetics had therefore even then been exactly formulated, but its significance for biological speculation had not been recognised by Huxley, any more than it has generally been recognised by most biologists since 1869. What, then, does the comparison of Huxley show? Clearly that the physical changes which occur in the explosion of a mixture of oxygen and hydrogen trend in a different direction from those which occur in the photo-synthesis of starch by a green plant. Generally speaking, chemical activity, that is, the possibility of occurrence of chemical reactions, is a case of the second law of energetics. Energy passes from a state of high to a state of low potential. A chemical reaction will occur if this change of potential is possible.

In all such changes energy is dissipated. What exactly does this mean? It means that, generally speaking, the potential energy of chemical compounds tends to transform into kinetic energy; while differences in the intensity factor of the kinetic energy of the bodies forming a system tend to become minimal. In a mixture of oxygen and hydrogen there is energy of two kinds, (1) potential energy due to the position of the molecules (O and H molecules are separated); and (2) kinetic energy of the molecules (which are moving about in the masses of gas). After the explosion the potential energy acquired in the separation of the molecules of O and H has disappeared (the molecules having combined to form water), but the kinetic energy has greatly increased, since the explosion results in the formation of steam at high temperature. But now this steam radiates off heat to adjacent bodies, or becomes cooled by direct contact with the envelope which contains it. The energy of the explosion is therefore distributed to the adjoining bodies, and the temperature of the latter becomes raised. But these again radiate and conduct heat to other bodies, and in this way the heat generated becomes indefinitely diffused.

The general effect of all physico-chemical changes is therefore the generation of heat, and then this heat tends to distribute itself throughout the whole system of bodies in which the physico-chemical changes occur. The energy passes into the state of kinetic energy, that is, the motion of the molecules of the bodies to which the heat is communicated. This molecular motion is least in solids, greater in liquids, and greatest in gases. If solids, liquids, and gases are in contact, forming complex systems, the kinetic energy of their molecules becomes distributed in definite ways, depending on the constants of the systems. After this redistribution the kinetic energy of these molecules is unavailable for further energy transformations, so that phenomena or change in the system ceases. There is no longer effective physical diversity among the parts of the system.

We find that this conception of dissipation of energy cannot be applied to the organism, at least not with the generality in which it applies to physical systems. Why? Not because the conception is unsound, or because the physico-chemical reactions that occur in material of the organism are of a different order from those that occur in inorganic systems—they are of the same order. The second law of energetics is subject to limitations, and it is because it is applied to organic happenings without regard to these limitations that it does not describe the activities of the organism as well as it describes those of inorganic nature.

What, then, are these limitations? We note in the first place that the laws of thermodynamics apply to bodies of a certain range of size; or at least the possibility of mathematical investigation (on which, of course, all depends) is limited to “differential elements” of mass, energy, and time. We cannot apply mathematical analysis to bodies, or time-intervals of “finite size,” since the methods of the differential and integral calculus would not strictly be applicable. But molecules are so small (1 cubic centimetre of a gas may contain about 5.4 × 10¹⁹ of them) that even such a minute part of a body, or liquid, or gas as approximates to the infinitesimally small dimensions required by the calculus, contains an enormous number of molecules.

Obviously we cannot investigate the individual molecules. Even if experimental methods could be so applied, such concepts as density, pressure, volume, or temperature would have no meaning. Physics, then, is based on collections of molecules, and the properties of a body are not those of a molecule of the same body. Such concepts as temperature and pressure are statistical ones, and are applied to the mean properties of a large number of molecules.

Fig. 11.

We can best illustrate this by considering Maxwell’s famous fiction of the “sorting demons.” Let us imagine a mass of gas contained in a vessel the walls of which do not conduct heat. Let there be a partition in this vessel also of non-conducting material, and let there be an aperture in this partition greater in area than a molecule, but smaller than the mean free path of a molecule. Now this mass of gas has a certain temperature which is proportional to the mean velocity of movement of the molecules. The second law says that heat cannot pass from a cold region in a system to a hot region without work being done on the system from outside, nor can an inequality of temperature be produced in a mass of gas or liquid except under a similar condition. But “conceive a being,” says Maxwell, “whose faculties are so sharpened that he can follow every molecule in its course; such a being, whose attributes are still as essentially finite as our own, would be able to do what is at present impossible to us.”[20] For the temperature of the gas depends on the velocities of the molecules, and in any part of the gas these velocities are very different. Suppose that the demon saw a molecule approach which was moving at a much greater velocity than the mean: he would then open the door in the aperture and let it pass through from − to +. On the other hand, should a molecule moving at a velocity much less than the mean approach he would let it pass from + to −. In this way he would sort out molecules of high from those of low velocity. But the collisions between the molecules in either division of the vessel would continually produce diversity of individual velocity, and in this way the difference of temperature between + and − would continually be increased. Heat would thus flow from a region of low to a region of high temperature without an equivalent amount of work being expended.

Now we must not introduce demonology into science, so, lest this fiction of Maxwell’s should savour of mysticism, or something equally repugnant, we shall state the idea involved in it in quite unexceptionable terms. The conclusions of physics are founded on the assumption that we cannot control the motions of individual molecules. In a mass of gas, or liquid, or in a solid, the molecules are free to move and do move. Their individual velocities and free paths vary considerably from each other. These motions and paths are un-co-ordinated—“helter-skelter”—if we like so to term them. Physics considers only the statistical mean velocities and free paths. The irreversibility of physical phenomena, the fact that energy tends to dissipate itself, the second law of thermodynamics, depend on the assumption that Maxwell’s demons exist only in imagination. We must appeal to experience now. There is no a priori reason why the phenomena of physics should be directed one way and not the other, for it is possible to conceive a condition of our Universe in which, for instance, solid iron would fuse when exposed to the atmosphere. In such conditions organisms would grow backwards from old age to birth, with conscious knowledge of the future but no recollections of the past. Experience shows, however, that phenomena do tend in one way—but this experience is that of experimental physics, so that for the latter science Maxwell’s demons do not exist. Now physiology has borrowed from physics, not only the experimental methods, but also the fundamental concepts of thermodynamics. The organism, therefore (so physiology must conclude), cannot control the motions of individual molecules, and so vital processes are irreversible. But we have seen that the processes of terrestrial life as a whole are reversible, or tend to reversibility. We must therefore seek for evidence that the organism can control the, otherwise, un-co-ordinated motions of the individual molecules.

The Brownian movement of very small particles of matter is so familiar to the biologist that we need not describe it. It is doubtless due to the impact of the molecules of the liquid in which the particles are suspended. Groups of molecules travelling at velocities above the mean hit the particle now on one side, and again on the other, and so produce the peculiar trembling which Brown thought was life. Now the particle must be below a certain size in order to be so affected. Are there organisms of this size? Undoubtedly there are, for many bacilli show Brownian movements, while we have reasons for believing that ultra-microscopic organisms exist. Also, on the mechanistic hypothesis there are “biophors,” the size of which is of the same order as that of the molecules of the more complex organic compounds. All these must be affected by the molecular impacts of the liquid in which they are suspended. Can they distinguish between the impacts of high-velocity molecules and those of mean-velocity ones, and can they utilise the surplus energy of the former? This has been suggested by the physicists. In Brownian movement, says Poincaré, “we can almost see Maxwell’s demons at work.”

The suggestion is not merely a speculative one, for it is well within the region of experiment. To prove it experimentally we should only have to show that the temperature of a heat-insulated culture of prototrophic bacteria falls while the organisms multiply.

Is it not strange that the biologists, to whom the Brownian movement is so familiar, should have failed to see its possibly enormous significance? Is it not strange that the biologists, to whom the distinction between the statistical and individual methods of investigation is so familiar, should have failed to appreciate this distinction when it was made by the physicists? Is it not strange that while we see that most of our human effort is that of directing natural agencies and energies into paths which they would not otherwise take, we should yet have failed to think of primitive organisms, or even of the tissue elements in the bodies of the higher organisms, as possessing also this power of directing physico-chemical processes?

CHAPTER IV THE VITAL IMPETUS