BOUGHT WITH THE INCOME FROM THE SAGE ENDOWMENT FUND THE GIFT OF Henrg M. Sage 1891 A^0.oS''t^ tlWI'M". Cornell University Library The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924003039561 THE PHILOSOPHY OF BIOLOGY CAMBRIDGE UNIVERSITY PRESS 5onll*n: FETTER LANE, E.C. C. F. CLAY, Manager ejinlnttjh: loo PRINCES STREET Sttlia: A. ASHER AND CO. Stipeig: F. A. BROCKHAUS Uttofotk: G. P. PUTNAM'S SONS Ssmtusanlieslnittit: MACMILLAN AND CO., Ltd. «i>rontO! J. M. DENT & SONS, Ltd. mk2«: THE MARUZEN-KABUSHIKI-KAISHA AU r if his reservtd THE PHILOSOPHY OF BIOLOGY BY "^JAMES JOHNSTONE, D.Sc. Cambridge : at the University Press I 9 1 4 ^'^ 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 atteinpt 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 per- ceptions, 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 motiojis and transformations, but it understood these motions and transformations as matter and energy. Yet more vi INTRODUCTION 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 conscious- ness, 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 conscious- ness. 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 trans- formations, -understood that there was something that moved and transformed — ^this was matter and energy. Mental Science, stud5dng 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 dis- proved 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 evolu- tion 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 anj^hing 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 INTRODUCTION vii 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 dis- appear 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 con- ception of a d5mamical, Newtonian Universe is a use- ful 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, con- tinuous Universe. That which existed behind the appearances of atoms and molecules and energy was viii INTRODUCTION the ether of space. It must be admitted that the conception appears to the layman to involve oiJy contradictions : heterogeneous, discontinuous, ponder- able 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 Philo- sophy — ^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 Given- ness, 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 investiga- tion 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 INTRODUCTION ix physico-chemical constellations capable of independent existence, and capable of indefinite growth by dis- sociation. 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 descrip- tion 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. Given- ness 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 genera- tion 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 reflect- ing on its origin. If it was borrowed from the Philo- sophy 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 X INTRODUCTION of life took origin. The embryologists and the natura- lists of our own generation have studied the whole organism in its normal functioning and behaviour, and have obtained results which cannot easily be under- stood 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 con- sidered 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 191 3 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 con- venience' 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 ^punc- tuate 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 xl xii CONTENTS 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 becom- ing. This is the Vital Impetus of Bergson, or the Entelechy of Diiesch. CONTENTS xiii CHAPTER V PAGE THE INDIVIDUAL AND THE SPECIES 1 62 Afgument. — 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 indi- vidual organism from which it has proceeded. The ofispring 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 TEANSFORMISM 208 Argument. — A reasoned classification of organisms suggests that- a process of evolution has taken place. It suggests logical relation- ships between organisms, while the results of embryology and palaeontology suggest chronological relationships. Yet this kin- ship 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 experi- mentally, and so science has adopted a mechanistic hypothesis of the nature of the process. Transformism of species depends on theoccurtgnce_ of variations, but these arise spontaneously and ind^aadently of each other, and they must be co-ordinated. This co-ordination of variations cannot be the work of the environ- ment. 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. xiv CONTENTS CHAPTER VII PACE THE MEANING OF EVOLUTION 245 Argument. — If we eissume the existence of an evolutionary process, the results of morphology, embryology, and palaeontology 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 arthro- pods, 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 trans- formation 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-transforma- tions begun in the tissues of the plants and animals. Immobility and unconsciousness characterise the plant, mobility and con- sciousness the animal. Animals indicate two types of actions — intelUgent 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 environ- ment 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 CONTENTS XV 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 obUgation of mechanistic hypotheses of evolution and develop- ment to accept this view has shaped modem theories of heredity. Life is an intensive manifoldness, but in individual or racial evolu- tion this intensive manifoldness becomes an extensive manifold- ness. 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 some- where 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 probabiUty. Matter, force, mass, and inertia. Energy-transformations. Isothermal and adiabetic transforma- tions. The Carnot engine and cycle. Entropy. Inert matter. Indkx 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 intel- lectually 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 cafe a band is playing " rag- time." 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 2 THE PHILOSOPHY OF BIOLOGY 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 termin- ations 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 odori- ferous 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 THE CONCEPTUAL WORLD 3 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 out- side 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 smelhng 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 stimu- lated 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 gangHon, (i) those which we call reflex actions, and (2) those actions which we re- cognise as resulting from deliberation. We must now 4 THE PHILOSOPHY OF BIOLOGY consider what are the processes that are involved in these kinds of neuro-rauscular 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 pheno- mena. In a reflex three things happen, (i) 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 quern 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 Paramcecium for instance, responds to an external stimulus by some kind of bodily activity, and yet it is a homogeneous, or nearly homogeneous, piece of pro- toplasm, 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 in- tegument are modified for the reception of auditory stimuli, becoming more susceptible for these but less susceptible for other kinds of stimuli than the adjacent THE CONCEPTUAL WORLD 5 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 pro- cesses that are included in the typical reflex are pro- cesses 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 6 THE PHILOSOPHY OF BIOLOGY 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 un- consciously 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 perform- ance of some difficult task, or in some keenly apprec- iated 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 THE CONCEPTUAL WORLD 7 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 re- flected 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 bodUy 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 8 THE PHILOSOPHY OF BIOLOGY the stimulation of our organs of seiise 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 per- formed reflex action, because the latter is the result of intra-cerebral activities that have become so habitual that they proceed without friction. There are innumer- able paths in the brain along which impulses from the receptor organs may psiss 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 6f the THE CONCEPTUAL WORLD 9 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 aim- less, 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 alterna- tive 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 hesita- tion, 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 modem 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 10 THE PHILOSOPHY OF BIOLOGY subject all that is in the stream of consciousness to conceptual analysis.^ That is to say, in thinking about the flux of con- sciousness 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 experi- ence 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 ' All this is, of course, the argument of Bergson's earlier books, MatUre et Mimoire and Dannies immldiates de la Conscience. THE CONCEPTUAL WORLD 11 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 Paramoecium, 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 environ- ment, than the means whereby it analyses that environment. This ana- lysis is the work of animal. 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 Fig. I. the consciousness of the 12 THE PHILOSOPHY OF BIOLOGY 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 computa- tions 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 js a greater resemblance between different smells THE CONCEPTUAL WORLD 13 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 rare- faction 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. 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, ii, 22, 33, etc., which are of increasing magnitude. Thus we represent the 14 THE PHILOSOPHY OF BIOLOGY physical cause of the increasing loudness of the sound by space-magnitudes, and then we transfer these magnitudes to the.;Srfeates of consciousness concomitant with the vibrating mol^ctiles^t afe- ^ Suppo.9e^ that we knew nothing at all about the cause of the d!%r^nces of pitch of musical sounds and that we listen fi^he notes of the octave, C, D, E, C, soiiflded by 'an organ ; all that we should experience woul(i'i^e that the sounds were different. If we were to sing. the notes we might attain the intui- tion that the notes G, A, B were " higher " than the notes C, D, E, because a greater effort was re- quired in order to produce these sounds, but ob- viously this is a different thing from sajdng 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 I 256 vibrations, the fork E T 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 Fig. 2. THE CONCEPTUAL WORLD 15 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 conscious- ness 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 16 THE PHILOSOPHY OF BIOLOGY 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, ind 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 AjE + E, A.E being the in- crement of amplitude. Let us call our sensation when the syren first sounds S, and our sensations when the sound has become louder S + aS, AS being the " increment of sensation." Then the relation holds : — — p- = constant. That is to say, the louder is the sound the greater must be the increase of loudness before we notice a difference. Let us assume now that the successive sensations of loudness that we receive as the syren blows louder and louder are, each of them, just the same amount louder than the preceding sound ; that is to say, let us assume that what we experience are " minimal perceptible differences " of sensation— that they are " elements of loudness " — thus we construct a series of sounds each of which difers from that preceding it by an elemental increment of loudness. Now things that THE CONCEPTUAL WORLD IT cannot be further decomposed are necessarily equal to each other ; if, for instance, the atoms represent the ultimate units into which we break up the matter called oxygen, then these atoms are all equal to each other. Therefore the increments of loudness are equal to each other. 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 cer- tain relation exists be- tween the " values " of the sensation and the values of the stim- uli that correspond to them ; a regular in- crease in the loudness of the sensation cor- responds to a regular increase in the log- arithms of the strength of the stimuli. Let S = the sensation, E the stimulus, and C and Q constants ; then S = Clog ^ ; so that we seem to establish a mathematical relation between the intensity of our sensations and the intensity of the stimuli that give rise to those sensations, but this relation depends on the assumption that what we call " minimal perceptible differences " of sensation are numerical differepces that are equal to each other, and this is, of course, an assumption that cannot possibly be proved. S'i irn u /uS Fig. 3. 18 THE PHILOSOPHY OF BIOLOGY Thus we decompose our stream of consciousness into a series of quantitatively different and qualitatively different things, upon each of which we confer in- dependent existence. We attribute to these different aspects of our consciousness extension, but the ex- tension is due only to our analysis ; for the qualities of pitch, loudness, colour, odour, etc., which we dis- entangle 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. THE CONCEPTUAL WORLD 19 and right and left, occurs; and we have to recognise that in it there is something fundamental, as funda- mental 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 com- ponents 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 in- •telligent 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-dimen- sional 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 20 THE PHILOSOPHY OF BIOLOGY 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 i8o° 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 THE CONCEPTUAL WORLD 21 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 stiU 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 neatly i8o°, 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 22 THE PHILOSOPHY OF BIOLOGY 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 1 80°. Some of the results would be considerably less than the ideal, and some of them would be con- siderably 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 " ^ 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 fath along which we move in imagination, and a path which stUl 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 shovdd 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 ' See appendix, p. 350. THE CONCEPTUAL WORLD 23 becomes " infinitesimally " small ; and at the same time we think of ourselves as becoming smaller and smaller, so that we can stiU 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 td their limits^ in the way which we have tried to indicate above — a process of thought which is the foundation of the reasoning of the in- finitesimal 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 : — y -JC See appendix, p. 346. y Fig. 4. 24 THE PHILOSOPHY OF BIOLOGY 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 bodtly motion, but a very little consideration will show that our knowledge of space attained by scientific measure- ments depends just as much on our intuition of our bodUy 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 THE CONCEPTUAL WORLD 25 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 representa- tion. 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 relation- ships. 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 26 THE PHILOSOPHY OF BIOLOGY parabola having the equation y=J 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 ? y y/is yos ih-,i 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 OXo-s. OX^ OXi-s, OXi, and so on, the small numerals indicating the distance of each point {OXo-s, etc.) from the origin 0. 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^-^, OX^, etc., and then we mark off these calculated lengths along the perpendicular lines. The point A, for instance, is ^(0.5)2 from the point X,.„ B is |(i)2 from Zi, 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. THE CONCEPTUAL WORLD 27 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 there- fore draw a curved line freehand through them, and at once, in so doing, we aban- don our intellectual methods, for our curve depends on our intui- tion of continuously p^^ ^ 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 considera- tion. We cannot conceive of the point moving along the locus OD. We can think of it only as at the places 0,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 /, g, i, j, between the points A and B, for instance. Yet, no matter how many these 28 THE PHILOSOPHY OF BIOLOGY intervals may be, we can only think of the point as being at the places 0,A,B, C, D, E, or at /, 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 0, A, B, C, D, E, and so on, nor in that of the occupancy of the inde- finitely 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 con- ceptualise 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. THE CONCEPTUAL WORLD 2» 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 obser- vation. 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 30 THE PHILOSOPHY OF BIOLOGY 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 conceptuaUse 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 : — (The pendulum of , ., , ^, ,■ the dock has cU- and^tf^<^ and now The time ready swung now swung and so on ^^"P^^^ M times . M + n times. M + 2n times . . . .P swings ^"^Mnr^r^ a ■ The water in the kettle is at T° . . 1 it is now at T + t° . 1 and now T + it" 1 and so on the kettle boils IOO° 1 .MPERA-, TURE The volume of 1 it %s now 1 and now It' is mercury in the thermometer is ^ v V+v . V+2V and so on W What we call time here is only a series of simul- taneously 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 THE CONCEPTUAL WORLD 31 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 boU, and the temperature ioo° was attained afier 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 conscious- ness. We felt fatigue, thirst, a lack of satisfaction, wandering attention, and irritation — all that was our duration. But the maid was identifjdng 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 : — ,«« , Jitshiclr h ,k, £.ncl. shack nffff^mvwtfffmvmJOO jeCOflu. Fig. 7. 32 THE PHILOSOPHY OF BIOLOGY 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 re- laxes 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- THE CONCEPTUAL WORLD 33 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 o.i second. This is what the experimenters might have perceived, had human un- aided 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 ex- periment 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 experi- ment : 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 simul- 34 THE PHILOSOPHY OF BIOLOGY taneity 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 mathema- tical physicist. Let us suppose that he is investigating the change that occurs in a material system between the two moments of time ^ and t^, 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 t^ to U 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 t^ to t^ by the differential dt, which means that the two phases of THE CONCEPTUAL WORLD 35 the system, motionless earth and moving moon at the time ti, and motionless earth and moving moon at the time ^2, 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 ^ to ti has elapsed. Thus mathematics, incapable of dealing with real intervals of time, evades this diffi- culty 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 HI 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 36 THE PHILOSOPHY OF BIOLOGY 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.^ But physiological science has the much more formidable task of explain- ing 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 origin- ally produced by the reaction of the tissues to the ' Except that, of course, the reactions that are supposed to occur are very complex ones. THE CONCEPTUAL WORLD 37 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 organis- ation 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 38 THE PHILOSOPHY OF BIOLOGY 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 function- ing of the animal. In our behaviour certain cerebral nerve tracts become laid down and continue to exist throughout Hfe, 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, con- stitutes an unique event in our lives, and we experience a " new sensation." What the blase 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 modem 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 pro- duced. The difference in all these cases between the THE CONCEPTUAL WORLD 39 repetitions of the same stimuli was that the later ones became added to the earlier onea, 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 un- conscious ones (as, for instance, in the case of the ac- quirement 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 trans- mitted 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 ourselyes 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 40 THE PHILOSOPHY OF BIOLOGY 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 there- fore " 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 THE CONCEPTUAL WORLD 41 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 advertise- ments 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 descrip- tions 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 w^ mark out boundaries and division lines in it that do not reallv 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 descrip- tions. 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 42 THE PHILOSOPHY OF BIOLOGY our thought, concepts that faciUtate 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 in- herence. 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 THE CONCEPTUAL WORLD 4» 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 reahty ? 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. 44 THE PHILOSOPHY OF BIOLOGY 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 sub- stances which at other times strongly affect our olfac- tory 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 THE CONCEPTUAL WORLD 45 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 meta- physics 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 sUghtly 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- 46 THE PHILOSOPHY OF BIOLOGY 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 incon- ceivable. The universe therefore consists of a homo- geneous 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 phenomenal- ism. 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 profes- sions of reason. We find on strict self -analysis that we believe that there is an Ego that perceives and THE CONCEPTUAL WORLD 47 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 beUeve that there were other men and women that perceived — other consciousnesses hke 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.^ Even if we do surrender ourselves to phenomenal- ism 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 con- sciousness ; 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 ' The reader may recognise in this argument that of Driesch's Three Windows into the Absolute. 48 THE PHILOSOPHY OF BIOLOGY 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 discus- sions of the last chapter. Let us, for the moment, cease to regard the organism as a structure — a " con- stellation 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 sur- roundings. 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 favour- able 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 function- ing 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 50 THE PHILOSOPHY OF BIOLOGY region intvdtively, 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, adjust- ment of the instinctive or automatically acting organism to the objects on which it operates, know- ledge of all else in the environment becomes of little consequence. It is clear that intelligent acting involves delibe- ration. The almost inevitable motor response to a stimulus, which is characteristic of the reflex or in- stinct, 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, know- ledge 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 THE ORGANISM AS A MECHANISM 51 once the tj^pe 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 en- vironment 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 convinc- ing 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 specula- tion 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 equa- tions or inequalities, i& based on these principles. The first principle of energetics,^ 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 1 See appendix, p. 356. 52 THE PHILOSOPHY OF BIOLOGY 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.^ 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 '■ The principal reason why we do not believe in phantasms is that these appearances are not conserved. THE ORGANISM AS A MECHANISM 53 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 bum 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 54 THE PHILOSOPHY OF BIOLOGY energy. It may pass through numerous transfor- mations — 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 transfor- mations ; 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 mathe- matical function, called entropy,'^ 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. ' See appendix, p. 369. Entropy is a shadowy kind of concept, dif&cult to grasp. But again we may point out that the reader who would extend the notion of mechanism into life simply must grasp it. THE ORGANISM AS A MECHANISM 55 The energy of the solar system is in part the kin- etic energy of those parts of it which are in motion — planets, planetesiraals,^ and satellites. This quantity of energy is enormously great. In the case of our earth it is Imv^, 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 equi- librium, 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,^ and this friction has been transformed into low-temperature heat, and this heat has been radiated off into space. ' Meteorites, cosmic dust, and other small particles moving in the solar system within influence of the sun's gravity. ' Not entirely, of course, but whatever be the trajisformation it ends in heat production. 56 THE PHILOSOPHY OF BIOLOGY 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.^ 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 • Absolute temperature is Centigrade temperature +273. This is, of course not a full definition, but it is sufficient for our present discussion. THE ORGANISM AS A MECHANISM 57 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. 68 THE PHILOSOPHY OF BIOLOGY 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 6i 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 (bvirning) into high temperature heat. We can cause this potential energy of coal to trans- form 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 transfor- mations. 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 trans- THE ORGANISM AS A MECHANISM 59 formation 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 tem- perature 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 60 THE PHILOSOPHY OF BIOLOGY 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 rnuch 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 con- ductivity of electricity in the wires, and by imperfect insulation of the current. Friction, imperfect con- ductivity, 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 trans- forms to light, but along with the light, which was the object of the transformation, heat is produced, and this heat radiates away. j!ir .i r .f;i y S v t , . 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. Con- versely, if N ergs of mechanical energy be employed to rotate the d5mamo, we should obtain electrical energy equal to this amount. Now as a matter of THE ORGANISM AS A MECHANISM 61 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 : — Mechanicalenergy of water power = quantity of water x height at which it is situated above the water-motor. Energy of an electric current = quantity of electricity x electrical potential. Chemical energy = equivalent weight of the substance x chemical potential. 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 62 THE PHILOSOPHY OF BIOLOGY 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 trans- formations while it forms part of its isolated system.^ 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 in- volved 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 ^ : — (i) " If a system can undergo an irreversible change, it will do so." (2) "A perfectly reversible change cannot take place by itsdf." In the phenomena studied by physics we see only ' It is really necessary to lay stress on the distinction between available and unavailable energy, as it is one which many biologists appear to ignore. Thus, a popular book on the making of the earth attempts to argue that essential distinctions between living and inorganic matter are non-existent. One of these distinctions is that organisms absorb energy, and this author points to the absorption of " latent heat " by melting ice as an example of the absorption of energy in a purely physical process. Consider a system consisting of a block of ice and a small steam boiler. We can obtain work from this by the melting of the ice — that is, its " absorption of latent heat." The system, ice at 0° C. + steam at 100° C, possesses available energy, but the system, melted ice + condensed steam, both at the same temperature, contains none. The molecules of water at 0° C. " absorb energy," that is to say, their kinetic energy becomes greater, but their available energy in the system has disappeared. In saying that the organism absorbs energy, we mean, of course, that it accumulates available energy, that is, the power of producing physical transformations. (See further, appendix, p. 366.) ' Bryan, Thermodynamics: Teubner, Leipzig, 1907, p. 40. THE ORGANISM AS A MECHANISM 63 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." ^ 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 conduc- tion 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 * Bryan, Thermodynamics, p. 195. 64 THE PHILOSOPHY OF BIOLOGY ultimate extinction of all becoming ; an universal physical death. In this conclusion there is nothing that is specu- lative. 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 begin- ning. 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 modem 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. Every- where 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 com- pensatory 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 THE ORGANISM AS A MECHANISM 65 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 con- servation, 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- 66 THE PHILOSOPHY OF BIOLOGY engine we have (i) 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 tempera- ture 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-tempera- ture heat (increased kinetic energy of water molecules, to be more precise). This heat is then transformed into mechanical work (the kinetic energy of the mole- cules 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 trans- formation 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 ahmentary canal and THE ORGANISM AS A MECHANISM 67 in the metabolic tissues. The proteids of the food are broken down into animo-substances in the ali- mentary canal, and these animo-substances are synthesised into the specific proteids of the animal's body. Corresponding changes occur with the carbo- hydrates 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 trans- formation 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 <3f 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 chmates 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 68 THE PHILOSOPHY OF BIOLOGY 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 consider- ing 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 there- fore 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 perform- THE ORGANISM AS A MECHANISM 69 ing work. In the heat-engine chemical energy trans- forms to heat, and then to mechanical energy, and of the total quantity transformed a certain large pro- portion suffers dissipation by conversion into low- temperature heat. In the animal organism chemical energy transforms directly to mechanical energy with- out 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 produc- tion, 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 com- pared 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-transform- ations 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.^ This is a system in which we have (i) 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 ' See appendix, p. 363. 70 THE PHILOSOPHY OF BIOLOGY 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 trans- formation. 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 THE ORGANISM AS A MECHANISM 71 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 im- portant thing to notice is, that we have here a process closely analogous to that of a reversed Camot 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 state- ment 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 re- stricted 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 72 THE PHILOSOPHY OF BIOLOGY mechanism which does work. The source of its energy is the potential chemical energy of its food- stuffs, 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 com- bustion. 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, animo-acids, and then other enzymes rearrange these animo-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 mechani- cal 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 residt of chemical changes, oxida- THE ORGANISM AS A MECHANISM 73 tions, 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 carbo- hydrate of the tissues represent the condition of high potential ; and the carbon dioxide, the water, and the urea, into which these substances are trans- formed, represent the condition of low potential. Let us suppose a Camot heat-engine in which the temperature of the reservoir of heat is (say) i20°C., and that of the refrigerator 5o°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 o°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 there- fore combined with several subsidiary ones. 74 THE PHILOSOPHY OF BIOLOGY Chemical Energy at high potential Carbohydrate, fat, ^»-ote4ii\ Metabolism break down into /of the animal Carbon dioxide Water Urea Urea \MetaboUsm of ^J^ / urea bacteria passes into ammonium carbonate- ammonium I metabolism carbonate \ of nitrifying ■^ I bacteria oxidises to nitrite — Nitrite -j Metm. of ^j^ I nitrify- oxidises f ing to nitrate; bacteria ^ chemical energy at low potential The arrows show that energy is descending the incline indicated by a direct Camot cycle. There is no more work to be obtained from the carbon dioxide and water excreted by the mammal, but more work can be ob- tained 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 them- selves, is perhaps a better way of putting it. We will consider these transformations later ; in the meantime THE ORGANISM AS A MECHANISM 75 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 com- pounds 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 carbo- hydrates, are thus built up by the plant and accumulate, 76 THE PHILOSOPHY OF BIOLOGY 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 \ Metabolism — - Water j- of the green Nitrate J plant Chemical energy at high potential. Chemical energy at -vjijot^ * systeC^ 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 be- haviour 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- sjmthetic process, in the general sense, may be present in the metabolism of some animals. Certain lower plants, the zoospores of algae, exhibit movements identical in character with those of lower animals. At the base of both kingdoms are organisms, the THE ORGANISM AS A MECHANISM 71 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 tjrpical 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 ex- ample, 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 : — (i) 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, con- trolled, " 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. 78 THE PHILOSOPHY OF BIOLOGY From the point of view, then, of energetic processes these are the characters of life, using the term in the general sense indicated above. ^ 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 trans- formations 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 tfe^m 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 • This is, of course, the argument of part of Chapter II. of Bergson's Creative Evolution. The reader will not find the essential differences between plants and animals stated so clearly anywhere else in biological literature. THE ORGANISM AS A MECHANISM 79 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 meta- bolism of the cold-blooded animal, though this must 80 THE PHILOSOPHY OF BIOLOGY be a very small proportion of the total energy trans- formed. 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 funda- mental 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 ihX)rganic 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 THE ORGANISM AS A MECHANISM 81 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 infini- tesimal 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 pro- duced 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 modem 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 one^. 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 82 THE PHILOSOPHY OF BIOLOGY 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 degrad- ation 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 accumula- tion 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 Camot'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 thermodjmamics does so apply with all its exclusive- ness. 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 corre- spondence 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 8S 84 THE PHILOSOPHY OF BIOLOGY from those which exist in inorganic nature in their greater complexity. It was also seen that physico- chemical reactions occurred in living substance ana- logous 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 cer- tain 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 differen tkinds 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 THE ACTIVITIES OF THE ORGANISM 85 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 correla- tive 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 86 THE PHILOSOPHY OF BIOLOGY 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 WiUiam 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 organ- ism and those of in- organic matter that we may consider it in some Fig. 8. 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. 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." THE ACTIVITIES OF THE ORGANISM 87 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 in- finitesimal 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 reactioii is one which may take place by itself ; ^ the other is one which requires a compensatory energy-transform- ation in order that it may happen. In the first reaction energy is dissipated ; in the second one it is accumulated. ' ' It is no use saying that apart from the electric spark the combination would not take place, for we do not know that the O and H of the mixture do not combine very slowly, molecule by molecule, so to speak. At all events there is no functionality between the infinitesimal quantity of energy supphed by the spark, and the energy which becomes kinetic in the explosion. 88 THE PHILOSOPHY OF BIOLOGY 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 physio- logical writings we usually find that two categories of metabohc changes are described : (i) 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-transform- ations, 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 carbo- hydrates 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 algae " (that is the chlorophyll - containing cells of some plant THE ACTIVITIES OF THE ORGANISM 89 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 be- come 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 trans- form into chemical energy, as when light impinges on a photographic plate, but as a general rule it is trans- formed 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 com- pensatory 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. 90 THE PHILOSOPHY OF BIOLOGY (2) Katabolic changes in the animal body corre- spond 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 dissoc- iation 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 com- plex 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 THE ACTIVITIES OF THE ORGANISM 91 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 : (i) 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 sub- stances, 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 imper- ceptible ; (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. 92 THE PHILOSOPHY OF BIOLOGY element, or compound which cannot act as a catalyser." ^ Enzymes, then, are agents which are produced by the organism, and which act by influencing (accelerat- ing 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. Asso- ciated with many enzymes are anti-enzymes, substances which undo what their corresponding enzymes have done. Finally some, perhaps most, enzymes are re- versible, 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 ' A statement of interest in view of the enormous number of " ferments " or enzymes discovered by physiologists. It would appear that any tissue in any organism is capable of yielding an enzyme to modern investigation. THE ACTIVITIES OF THE ORGANISM 93 other tissne 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 sub- stances allied to these, but this has not been clearly demonstrated, and it is possible that the phenomena of enzyme activity may belong to some othet 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 GF ^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. 94 THE PHILOSOPHY OF BIOLOGY 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 con- tains lipase (the fat-splitting enzyme)? The explan- ation is, apparently, that either an anti-enzyme is pro- duced, or that the enzyme passes into a zymoid con- dition. 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, absorp- THE ACTIVITIES OF THE ORGANISM 95 tion, 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) dis- solved 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 concen- tration 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. 96 THE PHILOSOPHY OF BIOLOGY 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 IkiasiSy, (Stand Fig 9. 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 con- sider the mode of working of some well-known organ, and the best possible example of such an organ, con- sidered as a mechanism, is that of the sub-maxillary salivary gland of the mammal. 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. THE ACTIVITIES OF THE ORGANISM 97 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 sym- pathetic 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-saUva " 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 98 THE PHILOSOPHY OF BIOLOGY into the cavity of the gland. If this were the case, then the Uquid in the gland would be the same in com- position and concentration as the liquid part of the blood — the plasma. But it is really different in com- position 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 con- centrated 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 hydro- static 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 tjdng 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 proto- plasm 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 proto- plasm of the cells, as the result of stimulation, elaborates THE ACTIVITIES OF THE ORGANISM 99 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 them- selves ; 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 giyen off to the venous blood and lymph. The problem thus is pushed back from the mechani- cal events occurring in the nervous and circulatory pro- cesses, to the physico-chemical ones occurring in the cells oi 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 ? 1 1 We have not referred to " psychical secretion." If we smell some very savoury substance our " mouth waters," that is, secretion of saliva occurs. If we even see some such substance the same secretion occurs. All this is clear and can be " explained " mechanistically ; the stimulation of the olfactory or visual organs begins a kind of reflex process. But if we even ihink about some very savoury morsel saUva may be secreted. We must 100 THE PHILOSOPHY OF BIOLOGY Irritability and contractility are general pro- perties of the organism. These properties are illus- trated by the irritability of an Amoeba or Paramecium 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 re- membered 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 com- municated to the receptor or the nerve itself by a stimulus of minimal strength. How does it so move ? suppose now that our consciousness, something which has nothing to do, it must be noted, with energy — changes in the body, can react on the body. If we show a dog an attractive bone it will secrete saliva; if we show it again, and again, the same thing occurs. But after certain such trials the dog will realise that he is being played with, and the exhibition of the bone no longer evokes a flow of secretion. Why is this ? The whole process has now become more mysterious than ever. THE ACTIVITIES OF THE ORGANISM 101 Several facts of capital importance result from the experimental work, (i) 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 stimula- tion ; (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 meta- bolism in the nerve substance — ^that is if the energy- change is a thermod3mamic 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 102 THE PHILOSOPHY OF BIOLOGY 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 ? Ob- viously not, since the substance of the nerve is not altered appreciably, while that of the explosive sub- stance 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 con- stituent : — (2) (I) ■.a+h a + b a + b a + b a + b: : ^^ H H H H : •.c + d c + d c + d c + d c+d: 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 da.sc and d pass into a and 6. There will be equilibrium. But now let a stimulus alter the physical conditions : prior to the stimulus the phase was a„+b„ = Cp+d, — ^the suffixes m, n, p, r^ denoting the concentrations of a, b, c, and d — but after the stimulus the phase may be a„i + b„i=Cpi + d^i. Now the element of the nerve substance (i) forms a system THE ACTIVITIES OF THE ORGANISM 103 with the element (2). The condition in (2) is a„ + b„ = Cp + d„ and that of (i) a„,+b„,=Cp,+d,u 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 magni- tude of that of chemical changes. If the stimulus remains constant (a constant electric current for in- stance), 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 inter- mittent one (an interrupted electric current, light- vibration, sound- vibrations) , then in the intervals the former condition of equilibrium will become re-estab- lished 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, prob- ably, 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 104 THE PHILOSOPHY OF BIOLOGY 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 trans- formed 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 pro- duced 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 sub- stance 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 stimu- lation 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 ACTIVITIES OF THE ORGANISM 105 the carbon contained in the latter gas corresponds roughly with the carbon contained in the muscle sub- stance 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 trans- formation energy is generated. Suppose that these simpler substances are poisonous and that they must be removed as rapidly as formed. The r61e 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 rdle 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 enz57mes 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 transform- ing 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 106 THE PHILOSOPHY OF BIOLOGY 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 proto- plasm 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 demon- strated 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 AmcehcB 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 THE ACTIVITIES OF THE ORGANISM 107 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, there- fore, abolishes some of the activities of the organism, but not all of them. If, however, we heat the muscle paste dbove 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 ph5^ico-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 108 THE PHILOSOPHY OF BIOLOGY 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 pro- perties), etc. ; and the molecules of which are com- pound ones consisting of combinations of the moleciiles of the substance with the molecules of the solvent, or with each other, that is, they are molecular aggre- gates. 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 " sus- pensoids " 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. THE ACTIVITIES OF THE ORGANISM 109 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 sub- stance." 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 110 THE PHILOSOPHY OF BIOLOGY 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 suc- cession 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 aU 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 in- vestigated at one time, and then the results are pieced THE ACTIVITIES OF THE ORGANISM 111 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 dis- sociated 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 infini- tesimal straight lines. Let us adopt Bergson's illustration, with a non - essential modification. The curve i-8 is a line which we draw freehand with a single in- divisible 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 mathe- matical point — ^the points i-8 in the figure. The tangent then has something in common with the curve, but would a series of infinitesimally small tangents Fig. 10. 112 THE PHILOSOPHY OF BIOLOGY reproduce the curve ? Obviously not, for the equa- tions of the tangents would have the form ax + h, 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 per- formed. Now in this illustration we have doubtless something more than an analogy with our physico- chemical analysis of life. The activities of the organsim 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 mathe- matical 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 physio- logical investigations we proceed a certain length with perfect success ; thus the elements, so to speak, of the function of the secretion of saliva are (i) the blood- pressure, (2) the hydrostatic pressure of the secretion in the lumina of the gland tubules, (3) the diffus- bility 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 THE ACTIVITIES OF THE ORGANISM 113 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 hypo- thesis 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 Wilham Thomson published his paper " On a Universal Tendency of Nature to Dissipation of Energy," and a year or two before that Clausius had applied Camot'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 recog- nised 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 114 THE PHILOSOPHY OF BIOLOGY 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 differ- ences 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, (i) potential energy due to the position of the molecules (0 and H molecules are separated) ; and (2) kinetic energy of the molecules (which are moving about in the masses of gas) . Af ter|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 explo- sion 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^ THE ACTIVITIES OF THE ORGANISM 115 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, depend- ing on the constants of the systems. After this re- distribution 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 un- sound, 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 limi- tations 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 hmited to " differential ele- ments " 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 (i cubic centimetre of a gas 116 THE PHILOSOPHY OF BIOLOGY may contain about 5.4 x 10^^ of them) that even such a minute part of a body, or liquid, or gas as approxi- mates 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 pro- perties 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. We can best illus- trate this by consider- ing Maxwell's famous fiction of the " sorting demons." Let us im- agine a mass of gas contained in a vessel the walls of which do not conduct heat. Let there be a par- tition 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 Fig. II. THE ACTIVITIES OF THE ORGANISM 117 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." ^ 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 equi- valent 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 unexception- able 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 * Impossible, in the sense that while we are unable to " abrogate " a physical law. Maxwell's finite demon could, although his faculties were similar in nature to ours. 118 THE PHILOSOPHY OF BIOLOGY like so to term them. Physics considers only the statistical mean velocities and free paths. The irre- versibility of physical phenomena, the fact that energy tends to dissipate itself, the second law of thermo- dynamics, 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 con- dition 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 — hut 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 con- cepts 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 THE ACTIVITIES OF THE ORGANISM 119 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 Brown- ian 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 dis- tinguish 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 sug- gested by the physicists. In Brownian movement, says Poincare, " 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 proto- trophic 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 Two main conclusions emerge from the discussions of the last three chapters : (i) that physiology encourages no notions as to a " vital principle " or force, or form of energy pecuUar to the organism ; and (2) that although physiological analysis resolves the meta- bolism of the plant and animal body into physico- chemical reactions, yet the direction taken by these is not that taken by corresponding reactions occurring in inorganic materials. From these two main con- clusions we have, therefore, to construct a conception of the organism which shall be other than that of a physico-chemical mechanism. The ordinary person, unacquainted with the results of physiological analysis, and knowing only the general modes of functioning of the human organism, has, probably, no doubt at all that it is " animated " by a principle or agency which has no counterpart in the inorganic world. This is the " natural " conclusion, and the other one, that life is only an affair of physics and chemistry, must appear altogether fanciful to any- one who knows no more than that the heart propels the blood, that the latter is " purified " in the lungs, that the stomach and liver secrete substances which digest the food, and so on. It is difficult for the modem student of biology, saturated with notions of bio- chemical activities, gels and sols and colloids and 120 THE VITAL IMPETUS 121 reversible enzymes and kinases and the like, to realise that the belief in a vital agency is an intuitive one, and that the mechanistic conception of life is only the result of the extension to biology of methods of investigation, and not a legitimate conclusion from their results. To the anatomist, the embryologist, and the natu- ralist, as well as to the physicist unacquainted with the details of physiology, no less than to the ordinary person this is perhaps by far the most general attitude of mind. It would probably be impossible for anyone to study only organic form and habits and come to any other conclusion than that there was something immanent in the organism entirely different from the agencies which, for instance, shape continents, or deltas, or river valleys. And this conclusion would probably come with still greater force to the embryo- logist, even though he still possessed a general know- ledge of physiological science. The mechanistic conception of life has, without doubt, been the result of the success of a method of analysis. One sees clearly that just in proportion as physical and chemical sciences have been most prolific of discovery, so physiology, leaning upon them and borrowing their methods, has been most progressive and mechanistic. Mechanistic hypotheses of the organism may all be traced back to Descartes, who built upon the work of Galileo and Harvey. The anatomy of Vesalius and his successors would have led to no such notions, had not the discoveries of Copernicus, Tycho, and Kepler shown men an universe actuated by mechanical law. To a thinker like Descartes, at once the very type of philosopher and man of science, Haryey's discovery of the circulation of the blood must have suggested 122 THE PHILOSOPHY OF BIOLOGY irresistibly the extension of mechanical law to the functioning of the human organism, and it is significant that he made this extension without including a single chemical idea, and yet produced a logical hypothesis of life as satisfactory and complete in its day as, for instance, the Weismannian h3^othesis of heredity has been in ours. His hypothesis of the organism was purely mech- anical. It has been said that his organism was an automaton, like the mechanical Diana of the palace gardens which hid among the rose-bushes when the foot of a prjdng stranger pressed upon the springs hidden in the ground. Its functions were matters of hydraulics : of heat, and fluids, and valves. His physi- ology was Galenic, apart from Harvey's discovery of the motion of the blood in a circuit, for he did not accept the notion of the heart as a propulsive apparatus. The food of the intestine was absorbed as chyle by the blood and carried to the liver, where it became endued with the " natural spirits," and then passing to the heart it became charged with the " vital spirits " by virtue of the flame, or innate heat, of the heart, and the action of the lungs. This flame of the heart, fed by the natural spirits, expanded and rarefied the blood, and the expansion of the fluid produced a motion, which, directed by the valves of the heart and great vessels, became the circulation. The more rarefied parts of the blood ascended to the brain, and there, in the ventricles, became the " animal spirits." Subtle and rarefied though they were, these animal spirits were a fluid, amenable to all the laws of hydro- dynamics. This was contained in the cerebral ven- tricles, and its flow was regulated just like the water in the pipes and fountains of the garden mechanisms. From the brain it flowed through the nerves, which THE VITAL IMPETUS 123 were delicate tubes in communication with the ventricles, and which were provided with valves ; and this outward flow corresponds to our modern efferent nervous impulse. The afferent impulse was represented by the action of the axial threads contained in the nerve tubuli. When a sensory surface was stimulated, these threads became pulled, and the pull, acting on the wall of the cerebral ventricle, caused a valve to open and allowed animal spirits to flow along the nerve to all the parts of the body suppUed by the latter. In the effector organs, muscles or glands, this influx of animal spirits produced motion or other effects. This, in brief, was the physiology of Descartes. He spoiled it, says Huxley, by his conception of the "rational soul." Fearing the fate of Galileo, he introduced the soul into his philosophy of the organism as a sop to the Cerberus of the Church. It was un- worthy : a sacrifice of the truth which he saw clearly. Is it likely that Descartes deliberately made part of his philosophy antagonistic to the rest with the object of averting the censure of the Church ? He was not a man likely to rush upon disaster, but the conviction that what he wrote had in it something great and lasting must have made it hardly possible that he should traffic with what he held to be the truth. The rational soul was something superadded to the bodily mechanism. It was not a part of the body though it was placed in the pineal gland ; a part of the brain, which by its sequestered situation and rich blood supply suggested itself as the seat of some important and mysterious function. Its existence was bound up with the integrity of the body, and on the death of the latter the soul departed. But the body did not die because the soul quitted it, it had rather become an unfit habitation for the soul. Without 124 THE PHILOSOPHY OF BIOLOGY the latter the functions of the healthy body might still proceed autoniatically, and if the soul influenced action it actuated an existing mechanism, and without that mechanism it could not act, though the mechanism might act without the soul. Thought, understanding, feeling, will, imagination, memory, these were the prerogatives of the soul, and not those of the automatic body. But the movements of the latter, even volun- tary movements, depended on a proper disposition of organs, and without this they were wanting or imperfect. Thus to a thoroughgoing mechanism Descartes joined a spiritualistic and immortal entity ; and this, to the materialism of the middle of the nineteenth century, was the blemish on his philosophy. Now of all men who have ever lived he is probably the one who has most profoundly influenced modern thought and investigation : to us what he wrote seems strangely modem, and this apparently arbitrary association of spiritualistic and materialistic elements in life seems almost the most modern thing in his writings. Being, he said, was indeed thought, but how could he derive thought from his clockwork body, with its valves and conduits and wires ? No more can we derive con- sciousness from the wave of molecular disturbance passing through afferent nerve and cerebral tracts. We must account for all the energy of this disturbance, from its origin in the receptor organ to its transforma- tion into the wave of chemical reaction in the muscle, and we must regard its transmission as a conserva- tive process. But how does the state of consciousness accompanying the passage through the cortex of this molecular disturbance come into existence ? None of the energy of the nerve disturbance has been trans- formed into consciousness : the latter is not energy THE VITAL IMPETUS 125 nor anything physical. It is something concomitant with the physico-chemical events involved in a nervous process, an " epiphenomenon." We have to imagine a " parallelism " between the mechanistic body and the mind. But if we admit that consciousness may be an effective agency in our behaviour, what is the differ- ence between modern theories of physico-psychic parallelism and the Cartesian theory of a rational soul in association with an automatic body ? Descartes denied the existence in animals other than man of the rational soul ; the latter was not necessary. But he, like us, must have been familiar with reflex actions and must have seen that consciousness was not invariably associated, even in himself, with bodily activity. And he must have recognised the great distinction between the intelligent acting of man and the instinctive behaviour of the lower animals. There was something in man that was not in the brute. Thus the first physiology, borrowing its ideas and methods from the first physics, was, like the latter, a mechanical science. After Galileo and Torricelli came Borelli with his purely mechanical conceptions of animal movement, and of the blood circulation, intro- ducing even then mathematics into biology. There was no chemistry in these speculations, though Basil Valentine and Paracelsus and Van Helmont had preceded Descartes and BoreUi. This chemistry was mystical, and though chemical reactions had been studied in the organism, they were supposed to be controlled by spiritual agencies, the " archei " of the first bio-chemists. But that notion was to disappear, and with Sylvius the conception of the animal body as a chemical mechanism arose. All that was valuable in Van Helmont's chemistry was taken up by Sylvius, but in his mind the fermentations of the older chemists 126 THE PHILOSOPHY OF BIOLOGY were sufficient in themselves without the mystical " sensitive soul " and " archei." With Sylvius and Mayow physiology became based upon chemical dis- covery and again became mechanistic, and remained so until the time of Stahl, when chemical discovery attained for the time its greatest development. The seventeenth century ended with the work of Stahl. It is well known to students of science how the views of this great chemist sterilised chemical investigation almost until the time of Lavoisier. The notion of phlogiston as an active constituent of material bodies entering and leaving them in their reactions with each other was a clear and simple one, and it served as a working h5^othesis for the chemists who immediately followed Stahl. It was, of course, a false hypothesis, and retarded discovery to the extent that the greater part of the eighteenth century is a blank for chemistry, when compared with the seventeenth and nineteenth centuries. Deprived therefore of the stimulus afforded by new physico-chemical methods of investigation, physiology ceased to maintain the progress it had made during the previous century, and the only great name of this period is that of von HaUer. Comparative anatomy, and zoological exploration, on the other hand, made enormous advances, and for these branches of biology the eighteenth century was the great period. It was the period of the historic vitalistic views — vital principles, and vital and formative forces. Stahl's teaching dominated physiology just as it did chemistry. Chemical and physical reactions occurred in the living body just as they did in non-living matter, but they were controlled and modified by the soul, or vital principle. It has been said that Stahl's vitalistic teaching retarded the progress of physiology, but it does not seem clear that this was the case. What did THE VITAL IMPETUS 127 retard physiological discovery was the lack of progress made by chemistry and physics, and this may have been the result of the Stahlian phlogistic hypothesis. However this may be, it seems clear that it was the discoveries of the great chemists of the close of the eighteenth century that again introduced mechanistic views into physiology. With the discoveries of Lavoisier and his successors the latter science ac- quired new methods of research and the older working hypotheses were re-introduced. There has been no recession from this position during the nineteenth century. Mechanistic biology culminated in the writings of Huxley and Max Verwom and received a new accession of strength almost in our own day in the modern discoveries of physical chemistry ; and when physiology became truly a comparative science, and embraced the lower invertebrates, it became perhaps most mechanistic — witness the writings of Jacques Loeb. Of far greater philosophical importance than the physico-chemical investigation of the functioning of individual organisms has been the essentially modern experimental study of embryological processes. The former deals essentially with the means of growth, reproduction, and so on. We can no longer doubt that the changes which we can observe taking place in the organism, either the developing embryo or the fully formed animal, are, in the long run, physico- chemical changes ; and in ultimate analysis we cannot expect to find anything else than processes of this nature. But physiological investigation has failed to provide anything more than this analysis. If we watch the development of the egg of an animal into a larval form, and continue to trace the metamorphosis 128 THE PHILOSOPHY OF BIOLOGY of the larva into the perfect animal, we cannot fail to conclude that, beside the individual physico-chemical reactions which proceed, there is also organisation. The elementary processes must be integrated. There must be a due order and succession in them. In studying developmental processes, in considering the developing organism as a whole, we are impressed above all else with the notion that not only do physico- chemical reactions occur, but that these are marshalled into place, so to speak. When we attempt to make a description of this integration of those ultimate pro- cesses which we can describe in terms of physical chemistry, physiology fails us. " At present," says Morgan, " we caimot see how any known principles of chemistry or of physics can explain the development of a definite form by the organism or by a piece of the organism." It is true that we can attempt to imagine a physico-chemical mechanism which is the organisation of the developing embryo ; but this must be a logically constructed mechanism, not only incapable of expe- rimental verification, but which can also be demon- strated, purely by physical arguments, to be false. This conclusion may, without exaggeration, be said to be that of modem experimental embryology. There have always been (in modem times) two views as to the nature of the embryological process : (i) that the egg contained the fully formed organism in a kind of rolled-up condition, and that the process of development consisted merely in the unfolding {evolu- tion) of this embryonic organism, and in the increase in volume of its parts. This was the hypothesis of preformation held in the beginning of embryological science. It involved various consequences: the limi- tation, for instance, of the duration of a species, since each generation of female organisms contained in their THE VITAL IMPETUS 129 ovaries all the future generations ; with other conse- quences which the preformationists did not hesitate to accept. (2) The other view was the later one of epigenesis : the egg was truly homogeneous and the embryo grew from it. Obviously the acceptance of this hypothesis led to vitalism, and we find that it was abandoned just as soon as the embryologists recog- nised that physics provided a corpuscular theory of matter, when a return was made to the preformation views of earlier times ; views which lent themselves to the construction of a ^_, ,, ^ mechanistic hypothesis o^"'". ^'^s^- ^p^ of development " " " ^' "^ ^ We may state very briefly the main facts of ^.^^^^.^.^^^ the development of a ^c^x ^^ typical animal ovum, such as that of the sea- urchin. The fertilised ovum fig. 12. divides into two (2), and then each of these blastomeres divides agiain in a plane perpendicular to the first division plane (3). The third division plane is at right angles to the first two, and it cuts off a tier of smaller blastomeres from the tops of the first four. There are now (4) two tiers of blastomeres, a lower tier of large blastomeres and an upper tier of smaller ones. This is the 8-cell stage. Next, each of these blastomeres divides in two simultaneously so that the embryo now consists of sixteen cells. After this the divisions proceed with less regularity, but after about ten divisions the embryo consists of about 1000 cells (2^°), and these are arranged to form a hollow sphere consisting of a singre layer of cells. The latter are furnished with cilia, and the whole embryo, 130 THE PHILOSOPHY OF BIOLOGY now known as the blastula, can swim about by the movements of these cilia. Further development results in another larval form — the gastrula, and yet another, the pluteus larva. After this the transformation into the fully formed sea-urchin occurs. With various modifications this scheme represents the early development of a very large number of animals belonging to most groups. If we study the process of cell-division we shall find it very complicated. The ovum, immediately after fertilisation, consists of two main parts, the nucleus and the c5rtoplasm. Within the nucleus is a substance distinguishable from the rest ; it is distri- buted in granules and is called the chromatin (i). When the cell is about to divide this chromatin becomes arranged in a long coiled thread (2), and then (3) this chromatic thread breaks into short rods called chromosomes. Two little granules now appear, one at each end of the nucleus, and very delicate threads, the asters, appear to pass from each of these bodies towards the chromosomes (4). Each of the latter then splits lengthways into two, and a half chromosome appears to be drawn by the asters towards the poles of the nucleus. The latter then divides (5) and then the whole cell divides. What thus, in essence, happens in nuclear divisions is that the chromatin of the nucleus is more or less accurately halved. Apparently this substance consists of very minute granules and the whole process is directed towards the splitting of each of these granules into two. A half-granule then goes to each of the daughter nuclei. Fig. 13. THE VITAL IMPETUS 131 Every time the embryo divides this process is repeated. Thus each of the (theoretically) 1028 cells of the blastula contains iw^th of the substance of each chromatic granule in the fertilised ovum. Pfluger and Roux (in 1883 and 1888 respectively) were the pioneers in the experimental study of the development of the ovum, and the results of their work and that of their successors has, more than any- thing else in biology, modified and shaped our notions of the activities of the organism. Roux found, or thought so at least, that the first division of the frog's egg marked out the right and left halves of the body, the one blastomere giving rise to the right half, the other to the left half. The next division, which separates each of these blastomeres, marked out the anterior and posterior parts of the embryo. Thus : — LeFf y PN^ ^'^^.^ Anteriorf--- ^^Anfenor Fosterio\^ yPosferior Fig. 14. — ^The frog's egg in the 4-blastoiueTe stage seen from the top. Now in an experiment which has become classical Roux succeeded in killing one of the blastomeres in the 2-cell stage, while the other remained aUve. The uninjured blastomere then continued to develop, but it gave rise to a half-embryo only. Upon these experiments the Roux-Weismann hypothesis of development— the " Mosaik-Theorie "— was developed. The lay reader will see how obviously the facts of nuclear division and the experimental results indicated above lend themselves to a mechanistic 132 THE PHILOSOPHY OF BIOLOGY hypothesis. Notice that but for the physical concep- tion of matter as made up of molecules and atoms the mosaic-theory would hardly have shaped itself in the minds of biologists. But this notion of matter con- sisting of corpuscles must have suggested that the essential " living material " of the organism consisted also of corpuscles, as soon as a microscope powerful enough to see the chromatic granules was turned on a dividing cell prepared so as to render these bodies visible. Obviously the primordial ovum contained all the elements of the organisms into which it was going to develop. But then in the process of division of the ovum all these chromatic granules are shared out among the cells, and a really very pretty mechanism comes into existence for this purpose of distribution. Weismann built up his hypothesis of the germ-plasm upon the observations we have outlined. The chro- matic matter of the nucleus consists of elements called determinants, the determinants themselves being com- posed of ultimate bodies called biophors. Each de- terminant possesses all the mechanism, or factors, necessary for the development of a part of the body : there are determinants for muscles, nerves, connective tissues, for the retina of the eye, for hairs of each colour, for the nails, and so on. All these determinants are contained in the chromatin of the nucleus of the egg, and in the divisions of the latter they are gradually separated so that ultimately each cell of the larva contains the determinants for one individual part, or organ, or organ-system of the adult body. The right blastomere, for instance, contains all the determinants for the right side of the frog's body, those for the left side being contained in the left half. The process of cell-division involved in the segmentation of the egg consists then in the orderly disintegration of this THE VITAL IMPETUS 133 complex of determinants, and in the marshalling into place of the isolated elements. The cell body — ^the cjrtoplasm — carried out a very subordinate r61e, mainly that of nourishing the essential chromatic substance. Such was the Roux-Weismann Mosaic-theory of development in its pristine form. It is clearly a preformation hypothesis. It is true that the actual organism is not contained in the germ, but all the parts of the latter, even the colours of the eyes or hair, are present in it in the form of the de- terminants. Obviously it involves a mechanism of almost incredible complexity. But if we regard it as a working hypothesis of development this complexity of detail does not matter ; its truth would be indicated by the fact that all analysis of the processes involved would tend to simplify it and to smooth out the com- plexity. But this is exactly what has not happened, for all subsequent investigation has necessitated sub- sidiary hypothesis after hypothesis. As a theory of development it has failed entirely. If, after one of the blastomeres in the frog's egg at the 2-cell stage be killed, the egg is then turned upside down, the results of the experiment become totally different ; the uninjured blastomere develops into a whole embryo, differing from the normal one chiefly in that it is smaller. If the uninjured egg in the 2-cell stage be turned upside down two whole embryos, con- nected together in various ways, develop. In the frog's egg the two first blastomeres cannot be separated from each other without rupturing them, but in the egg of the salamander they can be separated. After this separation two perfect, but small, embryos develop. In the egg of the newt a fine thread can be tied round the furrow formed by the first division. If this ligature be tied loosely it does not affect development, and then 134 THE PHILOSOPHY OF BIOLOGY it can be seen that the median longitudinal plane of the embryo does not correspond, except by chance, with the first division plane. If the ligature be tied tightly, then each of the blastomeres gives rise to an entire embryo. If it is tied in various places monsters of various types are produced. Therefore there is no segregation of the determinants in the first two blasto- meres. These results, moreover, are not exceptional, for similar ones have been obtained with other animal embryos, in fishes, Amphioxus, ascidians, medusae, and hydrozoa, and in some cases even each of the first four blastomeres develops into an entire embryo when it is separated from the rest. In the sea-urchin embryo the blastomeres can be shaken apart ; or by removing the calcium which is contained in sea water the blasto- meres can easily be separated from each other. It was then found by Driesch that each of the blasto- meres in the i6-cell stage could develop into an entire embryo. It is plain, then, that up to this stage at least there has been no segregation of the determinants. Upon the results of these experiments Driesch based his first proof of vitalism. Let us suppose that there is a mechanism in the developing egg. Now the embryo which results from the latter sooner or later acquires a three-dimensional arrangement of parts : head-end differs from tail-end, dorsal surface differs from ventral surface, and the parts differ on either side of the median plane. The mechanism must, therefore, be one which acts in three dimensions, anterior and posterior, laterally, and dorso-ventrally. We may represent it by a diagram of three co-ordinate axes, x,y, z; X and y being in the plane of the paper, and z at right angles to the plane of the paper. Now in the 2-cell stage the same mechanism must be present, for this stage develops normally into one entire embryo. The vital impetus 135 Fig. 15 But since either of the blastomeres may develop into an entire embryo, the mechanism must also be present in each of them, and since in the i6-cell stage each blastomere may develop an entire embryo, it must be present in each of the sixteen blastomeres. A three - dimensional mechanism is there- fore capable of division down to certain limits. Suppose now that we allow the sea-urchin egg to develop normally up to the blastula stage. In this stage it is a hollow sphere, the wall of which is a single layer of cells. It is similar all round, that is, we cannot distinguish between top and bottom, right and left, anterior and posterior regions ; but since it develops into a larva in which all these distinctions become apparent very soon, it must possess the three-dimensional mechanism, since the ^activity of the developmental process is going to produce different structures in each direction. Now the blastula, by very careful manipulation can be divided, cut into parts with a sharp knife. Since it is similar all round the direction of the cut is purely a matter of chance. It can be cut through along the planes i 2, 3 4, 5 6, 7 8, for in- stance ; really there are an infinite number of planes along which the blastula can be cut into two separate parts, and the direction of the plane is not a matter of choice. Fig. 16. 136 THE PHILOSOPHY OF BIOLOGY M r but purely a matter of chance. Nevertheless, each of the parts into which the larva is cut becomes an entire embryo. For a time the partial blastula — approxi- mately a hollow hemisphere in form — goes on develop- ing as if it were going to become a partial embryo, but soon the opening closes up and development becomes normal. It does not matter even if the two parts into which it is divided are not alike in size ; provided that a part is not too small, it will follow the ordinary course of development. Suppose the blastula opened out on the flat, like the Mercator pro- jection of a globe on a flat map. Suppose that a is a small ele- ment of it. Suppose that the rectangles hcde, FGHe, IJcL, MNoe, and as many more as we care to make, represent the pieces of the blastular wall separated by our operation — they all contain the element a, but this is in a different position in each case. There are really an infinite number of such parts of the blastula and a occupies an infinitely variable position in each of them. This demonstration is very important, so let us make it as clear as possible : Driesch's logical proof of vitalism may be stated as follows : — The diflerent parts of the blastula are going to become different parts of an embryo. The part a, occupying a definite position in the entire blastula, is going to become a definite part, having a definite position, in the embryo ; AF a I m c 3 J: / Fig. 17. THE VITAL IMPETUS 137 But each partial blastula becomes an entire embryo and the same part a occupies a different position in each. Therefore any part of the blastula may become any part of the embryo. Now if a mechanism is involved, it must, according to our ideas of mechanism, be one which is different in its parts, for each part of it produces a different result from the others ; But since any part of the mechanism may produce any of the different results contained in the embryo, every one of its parts must be similar to every other one. That is, all the parts of the mechanism are the same, though the hypothesis requires that they should be different. We conclude, then, that a mechanism such as we understand a mechanism to be in the physical sciences cannot be present in the developing ovum. Nevertheless, an organisationi using this term as an ill-defined one for the present, must exist in the ovum, or the system of undifferentiated cells into which the ovum divides, during the first stages of segmentation. In certain animals, Ctenophores (Chun, Driesch, and Morgan), and MoUusca (Crampton), for instance, separation of .the blastomeres in the first stages of segmentation produces different results from those mentioned above. In these cases the isolated blasto- meres develop as partial embryos, that is, the latter are incomplete in certain respects, and this incompleteness corresponds, in a general way, to the incompleteness of the part of the ovum undergoing development. We have thus the apparently contradictory results : (i) each of the first few blastomeres resulting from the first divisions of the ovum is similar to the entire ovum. 138 THE PHILOSOPHY OF BIOLOGY and develops like it ; and (2) each of the first few blastomeres is different from the others, and from the entire ovum, and develops differently from the others, and from the entire ovum. Let us try to construct a notion of what this organi- sation in the developing ovum must be. In the i6-blastomere stage of the sea-urchin egg we have a " system " of parts. In the case of normal develop- ment each of these parts has a certain actual fate — it will form a part of the larva into which the embryo is going to develop : It has, as Driesch says, a pro- spective value. But let the normal process be inter- fered with, and then each of these parts does something else. In the extreme case of interference, when the blastomeres are separated from each other, each blastomere, instead of forming only a part of a larva, forms a whole larva. The prospective potency of the part, that is its possible fate, is greater than its pro- spective value. Normally it has a limited, definite function in development, but if necessary it may greatly exceed this function. What any one blastomere in the system will become depends upon its position with regard to the other blastomeres. When the egg of the frog is floating freely in water it lies in a certain position with the lighter part uppermost, and then development is normal, each of the two first blastomeres giving rise to a particular part of the body of the larva ; that is, each of them is affected by the contact of the other and develops into whatever part of the normal embryo the other does not. But let the egg in the 2-cell stage be turned over and held so that the heavy part is uppermost : the protoplasm then begins to rotate so as to bring the lighter part uppermost; but the two blastomeres do not, as a rule, adjust themselves to the THE VITAL IMPETUS 139 same extent, and at the same rate, and corresponding parts may fail to come into contact with each other. Lacking, then, the normal stimulus of the other part, each blastomere begins to develop by itself, and a double embryo is produced. It is clear, then, both from this case and the last one, that the actual fate of any one part of the system of blastomeres is a function of its position. What it will become depends precisely on where it is situated with respect to the other parts. Driesch, then, calls the system of parts in such cases as the 2-cell frog embryo, or the i6-cell sea-urchin embryo, an equipotential system, since each part is potentially able to do what any other part may do, and what the whole system may do. But in normal development each part has a definite fate arid its activity is co-ordinated with that of all the other parts. It is, therefore, an harmonious equipotential system, each part acting in harmony, and towards a definite result, with all the others ; although if necessary it can take the place of any or all of the others. Such an harmonious equipotential system exists only at the beginning of the development of the egg. It is represented by the 8-cell stage of Echinus but not by the i6-cell stage, since, though the ^-blasto- meres produce gastrulae (the first larval stage), they do not produce plutei (the second stage). It is repre- sented by the 4-cell stage of Amphioxus but not by the 8-cell stage. It is not exhibited even by the 2-cell stage of the Ctenophore egg. What does this mean ? It means that ttie further development pro- ceeds, the less complete does the " organisation " inherent in any one part of the system become. " The ontogeny assumes more and more the character of a mosaic work as it proceeds " (Wilson). 140 THE PHILOSOPHY OF BIOLOGY Or perhaps it means, and this is the better way of putting it, that the " organisation," whatever it may be, depends on size. We see this very clearly in the experiment of cutting in two the blastula of the sea- urchin. If the pieces are of approximately equal size each will form an entire Pluteus larva, but if one of them is below a certain limit of size it will not continue to develop. The " organisation," therefore, has a certain volume, and this volume is much greater than that of any one of the cells of which the fragment exhibiting it is composed. It is enormously greater than the volume of any group of determinants which we can imagine to represent the different kinds of cells composing the body of the Pluteus larva, and still more enormously greater than the volume of a " mole- cule " of protoplasm. Now this association of " organisation " and size is of immense philosophical importance, for it does away, once and for all, with the idea that the " organisation " is solely a series of chemical reactions. If it were, one cell of the blastula would contain it, for on the mechanistic hypothesis one cell, the egg-cell, contains it, and this cell can be divided innumerable times and still contain it. The egg is a complex equipotential system (Driesch), which divides again and again throughout innumerable generations, and still contains the " organisation." It is in vain that we attempt the misleading analogy of the " mass action " of physical chemistry, to show that volume may influence chemical action. In such a mass action what we have is this : — the letters A , B and C standing for chemical substances present, and the letters a and h, etc., representing the THE VITAL IMPETUS 141 active masses of these substances. But variations in this active mass affect only the velocity of the reaction. What we have to account for in our blastula experi- ments is the nature of the reaction, and how can velocity or even nature of reaction affect form ? If we could show that the form of the crystals deposited from a solution in some reaction depended on the volume of the solution, the analogy would be closer, though even then the difficulties in pressing it would be so enormous as to render it futile to attempt ta entertain it. A chemical mechanism cannot, then, be imagined, much less described, and the only other mechanism so far suggested is the Roux-Weismann one, involving the disintegration of the determinants supposed to be present in the egg nucleus. Let us suppose (in spite of the incredible difficulty in so doing) that there is such a mechanism. It must usher the nuclei contain- ing the determinants of the embryonic structure into- their places : those for the formation of the nerve- centre go forward ; those for the mouth, gut, and anus^ go backwards and downwards ; those for the arms go forwards, ventrally, and posteriorly, in a very definite way ; and those for the complicated skeleton are distributed in a variety of directions which defy description. These nuclei are, in short, moved up and down, right and left, backwards and forwards, and become built up into a comphcated archi- tecture. Suppose we prevent this. Suppose we com- press the segmenting egg between glass plates so that the nuclei are compelled to distribute themselves in one plane only : to form a flattened disc in which the only directions are right and left and anterior and posterior. This has been done by Driesch and others. On the Roux-Weismann original hypothesis 142 THE PHILOSOPHY OF BIOLOGY a monstrous larva ought to result, for the first nuclei separated from each other have been forced into positions altogether different from those which they should have occupied had they developed normally. Yet on releasing the pressure readjustment takes place. New divisions occur so as to restore the normal form of larva. The Roux-Weismann subsidiary hypothesis is that the stimulus of the pressure has compelled the nuclei to divide at first in such a way as to compensate for the disturbance. Let us remove some of the blastomeres. On the original hypothesis the determinants for the structures which the nuclei of these blastomeres contained have been lost. These structures should, therefore, be missing in the embryo. But nothing of the sort is the result. Other nuclei divide and replace the lost ones, and the embryo develops as in the normal mode. The reply is that in addition to the determinants which were necessary for their own peculiar function, these nuclei contained a reserve of all others. On disturbance these determinants, " latent " in all other conditions, became active and restituted the lost parts. Let us remove some organ from an adult organism. The most remarkable experiment of this kind is the removal of the crystalline lens from the eye of the salamander. Now the lens of the eye develops from the primitive integument (ectoderm) of the head, but the iris of the eye develops mainly from a part of the primitive brain. After the operation a new lens is formed from the iris and not from the cornea. There- fore the highly specialised iris contains also deter- minants of other kinds. Does it contain those for itself and lens only, or others ? If it contains many kinds, then we conclude that even the definite adult structures contain determinants of many other kinds THE VITAL IMPETUS 143 than their own, that is, reserve determinants are handed down in all cells capable of restitutive pro- cesses, practically all the cells of the body. Or does it contain only its own and those of the lens ? Then this highly artificial operation was anticipated, an absurd hypothesis which need not be considered. This particular mechanistic process (and no other one is nearly so plausible) crumbles away before attempts at verification, and it survives only by the addition of subsidiary hypothesis after hypothesis. In itself this demonstrates that it is an explanation incompetent to describe the facts. What, then, is the " organisation " ? It is some- thing elemental, and we may just as well ask what is gravity, or chemical energy, or electric energy. It cannot be said to be any of these things or any com- bination of them. " At present," says a skilful and distinguished experimenter, T. H. Morgan, " we cannot see how any known principle of chemistry or of physics can explain the development of a definite form by the organism or a piece of the organism." " Probably we shaU never be able," concludes Morgan, who is anything but a vitalist. But does not this mean just that in biology we observe the working of factors which are not physico-chemical ones ? We have seen that the physiologist studies some- thing very different from that which the embryologist or naturalist studies. The former investigates a part of the animal, arbitrarily detached from the whole because the complexity of the functions of the simplest organism is such that all of them cannot be examined at once. He adopts the methods of physical chemistry in his investigation and whatever results he obtains are necessarily of the same order. Inevitably, from the mere nature of his method, he can see, in the organism, 144 THE PHILOSOPHY OF BIOLOGY only physico-chemical phenomena. The embryologist, on the other hand, studies the organism as a whole and seeks to determine how definite forms are produced, and how a change in the external conditions affects the assumption of these forms. We have seen with what little success the attempts to relate embryological processes with physico-chemical ones alone have met. In all studies of organic form mechanism has failed. It is useless to attempt to press the analogies of crystalline form, and the forms assumed in nature by dynamical geological agencies. If the reader examines these analogies critically he will see that they are superficial only. We seem, however, to see in those actions of the organism which are called " tropistic " or " tactic," reactions of a purely physico-chemical nature, and starting with these as a basis a plausible theory of organic movements on a strictly mechanistic basis might be built up.^ A " tropism " is the movement of a fixed organism with respect to a definitely directed external stimulus. This movement may be that pro- duced by growth of its parts, or by the differential contraction or expansion of its parts. A " taxis " we may call the motion of a freely-moving organism in response to the same directed stimuli. The move- ments whereby a green plant turns towards the light are called heliotropic, and those of its roots in the perpendicular direction are called geotropic. The motion of the freely-moving larva of a barnacle, for instance, in swimming towards a source of light are called " phototactic." In all these cases we have to think of the stimulus as a " field of energy " in the sense in which physicists speak of electric, or magnetic, or electromagnetic, or ' Many of Jacques Loeb's remarkable investigations point in this direction. THE VITAL IMPETUS 145 thermal, or gravity fields. In all these cases the factors affecting the movements of the organism are directed ones. An electric field, for instance, (i), is produced by placing the electrodes of a galvanic cell at opposite extremities of a water-trough : we imagine the electrons moving from one side of the trough to the other in parallel lines, and in a certain direction. A light field (2) would be produced by the radiation of light travelling in straight lines through the water. The movements of the organism displaying a -h' (1) (B) Fig. 18. tropism or a taxis are not caused by the stimuli of the field, but are only directed by it. In the absence of these stimuli it would swim at random. In a field, however, it will orientate itself in some direction with reference to the lines of force. A " positively photo- tactic " animal swims towards the focus from which the light radiation emanates, and a " negatively phototactic " one swims in the other direction. On the theory of tropistic and tactic movements this orientation is produced by the differential stimulation of the opposite sides of the organism. Let us take as a concrete example the case of a caterpillar which creeps up the stem of a plant to feed on the tender shoots near the apex. The animal possesses an 146 THE PHILOSOPHY OF BIOLOGY elongated body, with muscles beneath the integument, and sensory nerve-endings in the latter. Its muscles are in a state of "tone," that is, they are normally always slightly tense. The incident rays of light affect the dermal sense-organs, stimulating ganglionic centres and setting up efferent impulses which descend to the muscles. Let us suppose the animal is moving so that the longitudinal axis of its body is at an angle, say of 45°, to the direction of the incident light : one side of the body is therefore stimulated and the other is not. The stimiilation of the lighted side sets up efferent nerve impulses which descend to the muscles of this side and increase their tone (or else the lack of stimulation of the other side produces impulses which inhibit the muscular tone, or impulses which would otherwise preserve the tone cease in the absence of light stimulation). In any case the muscles of the lighted side contract, and the body of the caterpillar moves so that it sets itself parallel to the direction of the radiation. Both sides of the body are then equally stimulated and the animal moves towards the light. The animal feeds and it then creeps back down the plant. Why does it do this ? Because, says Loeb, the act of feeding has reserved the " sign " of the taxis. Before, when it was hungry, it was positively photo- tactic, but the act of feeding (all at once, it would appear, before digestion and assimilation of the food itself) has produced chemical substances in the muscles which cause the latter to relax in response to an impulse which previously produced contraction. The nervous link is not, of course, a necessary one. The stimulation by the energy of the field may affect the muscle substance directly, or it may, as in the case of a protozoan animal, affect the general body proto- plasm in the same way. In the majority of cases. THE VITAL IMPETUS ^ 147 however, the orientation would be affected through the chain of sense-organ, afferent nerve, nerve centre, efferent nerve, and effector organ. This is the chain of events which on this hypothesis causes a moth to fly into a flame, or a sea-bird to dash itself against the lantern of a lighthouse. A taxis is, then, an inevitable response by move- ment in a definite direction, to a directed stimulus. Including also tropisms it may be admitted that the movement is a purposeful, or at least, a useful one in some cases, as for instance the heliotropism and geotropism of the green plant. If we admit that Loeb's description of the feeding of the caterpillar, as a tactic act, is true, we may also call this a useful act. But in the majority of cases tropisms and tactes are acts which appear to be of no use to the organism. The invasion of a part of the body which is irritated by a poison (as in inflammation) by leucocytes, is useful to the body itself, but we must regard the leucocytes as organisms, and their tactic motion leads to their destruction, and so also with other analogous acts. Just because of this we find difficulty in accounting for their origin in terms of natural selection. This does not matter so much, since it can hardly be maintained now that the tropistic or tactic act has any reality except in a very few cases — ^the motions of plants, galvano-taxis, the chemico-taxic movements of bacteria and leucocytes, and some other analogous cases, perhaps, are these exceptions. It can hardly be doubted that the extension of the concept to cover the motions of many invertebrates, and even some vertebrate actions, by Loeb and his school is a straining after generality which has not been justified. The hypothesis, as Loeb has stated it, is evidently almost certainly a logical one and was obviously elaborated 148 THE PHILOSOPHY OF BIOLOGY as a protest against the anthropomorphism which saw- in the flying of a moth into a flame the expression of an emotion ; or in the movements of a caterpillar on a green shrub the expression of hunger and satiety and of the inherited experience of the animal ; or in the avoidance by a Paramcecium of a drop of acid the emotion of dislike of the feeling of pain. Well, let it be granted that this is so, and that the protest was a useful one, for it is obviously impossible that these notions as to the causes of the movements can be verified : does it improve matters to take refuge in an hypothesis which is just as purely physico-chemical dogmatism as the other is anthropomorphism ? But the former hypothesis is at all events one which is susceptible of experimental verification and in this lies its usefulness, inasmuch as it has stimulated investiga- tion. It is evident, however, that this verification has not yet been made. The differential afferent impulses set up by the energy-field ; the increases or inhibition of muscular tone ; the presence of photo- sensitive substances in the tissues of tactically acting lower animals ; the change of velocity of chemical reaction, in these cases, which ought to follow stimula- tion — all these things could be verified if they possess reality. Yet it is only indirect proofs, capable perhaps of other interpretations, and not direct experimental ones, which have so far been adduced in favour of a general theory of tropisms. Moreover, the close analysis of the actions of some of the lower organisms by Jennings has shown that the tactic hypothesis is probably false in the majority of cases. This observer studied the acting of the organisms themselves and not the beginning and end of the series, and he shows that the behaviour of the organisms is far more obviously described by saying THE VITAL IMPETUS 149 that it adopts a method of " trial and error." Let us suppose a number of infusoria {Paramcecium) in a film of water, at one part of which is a drop of acetic acid slowly diffusing out into the surrounding medium. There is a zone of changing concentrations round the drop : if we draw imaginary contours through the points where the concentration is approximately the same (the concentric rings in the diagram), and then draw straight lines normal to these rings (the radial lines) we can construct a " field " analogous to an electric or magnetic field. The animal on approaching the field ought to orientate itself and take the direction of the " lines of force." It does not, how- ever, behave in this Way, but only enters the field at random. Having entered, it remains within a part where the con- centration is within certain limits. If it approaches the fig. 19. margin of this limited field it stops, swims backwards, revolves round its own axis, and then turns to the aboral side ; and it repeats this series of movements whenever it approaches (by random) a region where the concentration is too high, or one where it is too low. In this, and other organisms we see then what Jennings has called a typical " avoiding reaction," the precise nature of which depends on the " motor-system " of the animal. Its general movements are random ones, but having found a region of " optimum conditions " {conditions which are most suitable in its particular physiological state), it remains there. Suppose (what indeed repeatedly happens) that an 150 THE PHILOSOPHY OF BIOLOGY extensive " bed " of young mussels forms on a part of the sea bottom. In a short time the bed becomes populated by a shoal of small plaice feeding greedily on the little shellfish. In their peregrinations the fishes must repeatedly pass out beyond the borders of this feeding-ground. Usually, however, they will return, for failing to find the food they like they swim about in variable directions and so re-enter the shell- fish bed. Suppose (this was really a fine experiment made by Yerkes) a crab is confined in a box from which two paths lead out but only one of which leads to the water. The animal runs about at random, finds the wrong path, retraces it, tries again and again, and then finds the right path and gets back to the water. If the experiment is repeated the animal finds the right path again with rather less trouble, and after many trials it ends by finding it at once on every repetition of the experiment. All this discussion of concrete cases leads up to our consideration of the modes of acting in the higher organisms. On the strictly mechanistic manner of thinking the actions of the organism in general are based on reactions of the tactic kind — ^inevitable re- actions the nature of which is determined, and which follow a stimulus with a certainty often fatal to the organism displajdng them. Accepting these tactic reactions as, in general, truly descriptive of the be- haviour of the organism, we can build up a theory of instincts. In their simplest form instincts are reflexes — ^tactic movements. In their more complex forms they are concatenated reflexes, or tactes. A complicated instinctive action is one consisting of many individual actions, each of which is the stimulus for the next one ; or, of course, it may also be complex THE VITAL IMPETUS 151 in the sense that several simple reactions proceed simultaneously, upon simultaneous stimulation of different receptors. Now the extension of all this to movements of a " higher " grade is obvious. Let us note in the first place, that the stimuli so far considered in all the examples quoted are simple elemental ones. There are, of course, relatively few such stimuli : gravity, conducted heat (the kinetic energy of material bodies), radiated heat (the energy of the ether), electric energy, chemical energy, and mechanical contact or pressure (including atmospheric vibrations). In all these cases we have a definite, measurable, physical quantity, with which we must relate a definite response in the form of a definite measurable, physico-chemical reaction. There should be a functionality between the stimulus and response, a definite, quantitative energy-transformation. To take a concrete example, a certain quantity of light energy falling upon the receptor organs of Loeb's caterpillar ought to transform into another quantity of " nervous energy," and this travelling in an analogous way to a " wave of explosion " ought to transform into an energy quantity of some kind, which initiates another " wave of explosion " in the muscle substance. All these transformations must be quantitative ones, and the energy of the individual light must be traced from the receptor organ to the points in the muscle where it disturbs a condition of false equilibrium in the sub- stance of the latter. Nothing less than this is required to demonstrate the purely physical nature of a reaction, on the part of the organism, to an external stimulus. It may safely be said that physiological investigation has not yielded anything even approximating to such an experimental demonstration. What are the stimuli to the actions of a higher 152 THE PHILOSOPHY OF BIOLOGY organism ? It is true that their elements are energies such as we have indicated, but these energies are integrated to form individualised stimuli (Driesch). The stimulus in an experimentally studied taxis is, perhaps, a field of parallel pencils of light rays of definite wave length ; but in the action of a man, or a dog say, the stimulus is an immensely compUcated disturbance of the ether, producing an image upon the retina of the animal. A sound stimulus employed in an investigation may be the relatively simple atmospheric disturbance produced by the sustained note of a syren or violin-string ; but the stimulus in listening to an orchestra may consist of dozens of notes, with all their harmonies, sounding simultaneously at the rate perhaps of some hundred or two in the minute. All these are integrated by the trained listener, and one or two false ones among the multitude may entirely spoil the effect of the execution. Surely there is here something more than a mere difference in degree. More important still is the strict functionality between stimulus and action that the theory of tactic responses imposes on itself. Putting this very precisely (but no more precisely than the theory demands), we say that %A =f{x, y, z), that is, the series of actions tiA (the dependent variable) is a mathematical function of the independent variables x, y, z. Now is there anything like this functionality between the acting of the higher animal and the stimulus ? Evi- dently there is not. We recognise someone whom we know very well by any one of a hundred different characters, mannerisms of walk, speech, dress, etc. He or she is the same person, whether seen close at hand, or afar off, or sideways, or in any one of almost infinitely different attitudes, and we respond to each THE VITAL IMPETUS 153 of these very different physical stimuli by the same reaction of recognition : pleasure, dislike, avoidance, greeting, or whatever it may be. To a sportsman shooting wild game the stimulus may be some almost imperceptible tint or shading in cover of some kind, differing so little from its environment as hardly at all to be seen, yet, to his experience, upon this almost infinitesimal variation of stimulus depends his action with all its consequences. In Driesch's example two polyglot friends met and one says to the other, " My brother is seriously ill," or " Mon fr^re est severement malade," or " mein Bruder ist ernstlich erkrankt." Here the physical stimulus is fundamentally different in each case, but the reaction — ^the expressions of sympathy and concern, the discussions of mutual arrangements, etc., are absolutely the same. Or let the one friend say to the other, " My mother is seriously ill," and in spite of the very insignificant difference between the consonantal sound hr in this sentence and the corresponding sound m in the other English sentence, the reaction, that is, the subsequent conversation, and the arrangements between the two friends may be entirely different. Putting this argument in abstract form we may say, generally, that two stimuli, which are, in the physical .sense, entirely different from each other, may produce absolutely the same series of reactions ; and conversely two stimuli differing from each other in quite an insignificant degree may produce entirely different reactions. It is also easy to see, by analysis of the antecedents to the actions of the inteUigent animal, that these stimuli are, in the majority of cases, not elemental physical agencies, but individuaUsed and integrated groupings of these agencies ; and that the animal reacts, not to their mathematical sum, as 154 THE PHILOSOPHY OF BIOLOGY it should do on a purely mechanistic hypothesis of action, but to the typical wholes which are expressed in these groupings.^ It is no answer to this argument to say that it is not the actual atmospheric vibrations (in the case of the conversation), nor the optical image (in the case of the recognition of a friend), which are the true stimuli, but rather the mental conditions, or states of consciousness, aroused by these physical agencies. If we are to adopt a strictly mechanistic method of ex- plaining actions, such a method as that indicated by Loeb's hypothesis of the purely tactic behaviour of his caterpillars, then these atmospheric vibrations and optical images are most undoubtedly the true stimuli, and the reactions must be functions of them in the mathematical sense. But since this strict functionality does not exist in any behaviour-reaction closely analysed, we must grant at once that it is, indeed, not the physical series of events that deter- mines the actual response, but truly the conscious state immediately succeeding to these physical sense- impressions. Now let us see to what conclusions this admission leads us. Between the external stimulus (the atmospheric undulations impinging on the auditory membranes, or the light radiations impinging on the retinae) and the behaviour-reaction something intervenes. This is the individual history of the organism, the " associa- tive memory " of Jacques Loeb, the " physiological state " of Jennings, the " historical basis of reacting " (historische Reaktionsbasis) of Driesch, or the " dura- tion " of Bergson. The last concept is the most subtle 1 Thus to the ordinary woman the sight of a cow in the middle of a country road produces a certain definite feeling of apprehension, which is always the same although the optical image of the animal differs remarkably in different adventures. THE VITAL IMPETUS 155 and adequate one and we shall adopt it. The physical stimulus, then, leads to a state of consciousness, a perception, and this is succeeded by the action. What is the perception ? There may be no perception in a reflex action ; there is none in a taxis.^ These kinds of reaction follow inevitably from the nature of the stimulus — depend upon the latter, in fact ; but we cannot fail to observe that the intelligent behaviour of the higher animal involves choice between alternative kinds of action. The perception, then, is this choice, or it is intimately associated with it. But it is some- thing more than the choice of one among many kinds of response. The whole past experience of the animal enters into the perception, or at least all that part of the past experience which illuminates, in any way, the present situation. What the intelligent animal does in response to a stimulus depends not only on the stimulus but on all the stimuh that it has received in its past, and on all the effects of all those stimuli. Into the perception that intervenes between the external stimulus, then, and the action by which the animal responds what we usually call its memory enters. Its duration is really the something which is changed by the stimulus, and which then leads to the behaviour- reaction. Duration, then, is memory, but it is more than memory as we usually think of this quality. The past endures in us in the form of " motor habits," and when we recall it we may act over again those motor events. Careful introspection will readily convince the reader that in recalling a conversation he is really speaking inaudihly, setting in motion the nerves and muscles ^ We do not find this explicitly stated in this way in mechanistic biological writings. None the less it is implied, and is the legitimate conclusion from the arguments used. 156 THE PHILOSOPHY OF BIOLOGY of his vocal mechanisms. Actions that have been learned endure ; in some way cerebral and spinal tracts and connections become established and persist : undoubtedly when a cerebral lesion destroys or impairs memory it is these physical nerve tracts and cells that become affected. But in addition to this we have pure memory (Bergson's " souvenir pur "). What, for instance, is the visual image of some thing seen in the past, which most people can form, but pure recollection ? ^ All the past experience of the organism — all its perceptions, and all the actions it has performed — endures, either as motor habits or mechanisms, or as pure memories. All this need not be present in its consciousness ; the motor habits would not, of course, and only so much of the past would be recalled as would be relevant to the choice which the organism was about to make of the many kinds of responses possible to its motor organisations. Out .of this past it would select all that was connected in any way with the actions which were possible to it in the present. It would recall all actions previously performed which resembled the one provisionally decided upon ; but recalling also the other circumstances associated with those past actions, it would discover something which would lead it to modify that provisional action. Now in describing the whole behaviour of the acting organism in this way are we doing any more than simply ex- pressing in more precise terms the " commonsense " notions of the ordinary person ? The latter would sum up all this discussion by sajdng that what he would do in any set of circumstance depended not only on the circumstances themselves but upon his experience. 1 A visual image may, of course, be something that has never been actually- seen. But then its elements have had actual perceptual existence in the past. THE VITAL IMPETUS 157 Physiology shows us as clearly as possible that in the stimulation of a receptor organ, the propagation of a nervous impulse along an afferent nerve, the trans- mission of this impulse through the cord or brain,' or both — in the propagation again of the impulse through an efferent nerve and the transformation of this impulse into a releasing agency, setting free the energy potential in the muscle substance — ^that in all this there can be nothing more than physico-chemical energy-transformations. All this is clear and certain. But why should the same afferent stimuli, entering the central nervous system at different times by the same avenues, and in the same manner, traverse different tracts, and issue along different efferent nerves, producing different results ? Or why should different stimuli entering the central nervous system take the same intra-cerebral paths and then affect the same efferent nerves and effector organs ? It is because these stimuli lead to perceptions which fuse with, and become part of the duration of, the organism. And the response then becomes a response not to the physical stimulus, but to the duration modified in. this way. Can we, conceive of any physical mechanism in which the duration of the organism accumulates ? Can we think of any way in which memories are stored in the central nervous system ? When we say " stored," it is our ingrained habit of thinking in terms of space and number that makes us regard memories as laid by somewhere, in the way we file papers in a cabinet, or store specimens in a museum. Supposing perceptions are stored in this way, we think of them as stored or recorded in the same way as a conversa- tion is recorded and stored in a phonograph. The phonograph can reproduce the conversation just as 158 THE PHILOSOPHY OF BIOLOGY it was received, but what we make use of when we utilise our experience is obviously the elements of that experience, selected and re-integrated as we require them. There must, then, be something like an analysis of our perceptions, a dissociation of these into simple constituents, and a means of restoring and recording these constituents in such a way that they can be re- combined in any order, and again made to enter into our consciousness. It is quite possible to imagine such a mechanism. Let us suppose that an efferent impulse enters the cerebral cortex via any one axon : there is a perfect labyrinth of paths along which the impulse may travel. Ever5Avhere in the central nervous system we come upon interruptions of nervous paths formed by inter- digitating arborescent formations. The twigs of these arborescences do not, apparently, come into actual contact with each other and the impulse leaps across the gap between them. This gap is, of course, ex- ceedingly narrow, and one can almost speak of it as a membrane, since it must be occupied by some organised substance. It has been called the synaptic membrane. Let us suppose that a stimulus of a certain nature passes through the S5aiapse, modifying it physico- chemically as it passes. Thereafter a stimulus of similar nature wUl tend to pass across this particular synapse, the resistance of the latter having been decreased. It will thus tend to travel by a definite tract through the central nervous system. Now "the latter we may regard in a kind of way as a very com- plicated switchboard, the function of which is to place any one stimulus (or series of stimuli) out of many in connection with any one motor ^ mechanism (or series 1 Or more generally effector mechanism. This enables us to include reactions, such as secretory ones, which are not motor. THE VITAL IMPETUS 159 of mechanisms) out of many. A motor habit, or path, is then estabhshed and will persist. Such a conception is clear and reasonable in principle, and all work on nervous physiology tends to show that it is a good working hypothesis. We cannot read modern books without feeling that immense advances will be made by its aid. But the complexity of the brain of the higher vertebrate is so incredibly great, and the difficulties of imagining the nature of the necessary physico-chemical reactions in the synapses, and elsewhere, are so immense that experimental verification may be impossible. And all that we have said applies to a single elemental stimulus, yet in any common action the stimulus is a S3nithesis of almost innumerable simple ones, while the response is also a synthesis. The optical image of almost any object contains a very great number of tints and colours differing almost imperceptibly : there must at least be as many simple stimuli as there are rod or cone elements in the part of the retina covered by the image. The motor responses consist of a multitude of delicately adjusted and co-ordinated muscular con- tractions and relaxations. If we are to accept a mechanistic hypothesis of action, of this kind, and which includes only such processes as are suggested above, it is not enough that a logical description, con- sistent in itself, and consistent with physico-chemical knowledge, should be formulated. The mere state- ment of such an hypothesis does not carry us far. If it is, in essence, mechanistic, it must be capable of experimental verification in detail. Even if it were verified experimentally it would still leave untouched the problem of consciousness. All that we have considered are series of physico- chemical energy-transformations. How, then, does 160 THE PHILOSOPHY OF BIOLOGY consciousness arise ? We cannot even imagine its association in a functional sense with the train of events forming an afferent impulse. In some form or other mechanism must assume a dualism — a parallelism of physical and psychical processes. Physical events in the central nervous system are associated with psychical ones — ^when the former occur so do the latter — yet the former are not "causes " in any physical sense of the latter. Consciousness follows cerebral energy- transformations as a parallel " epiphenomenon." At once we leave the province of mechanism, and how can we remain content with such a limitation of our descrip- tions ? And if we conclude, as we seem obliged to do, that consciousness is an affective agency in modifying our responses to external stimuli, does not this in itself show that our concept of behaviour as a purely physico- chemical process is insufficient in its exclusiveness ? We return to a consideration of the main results of experimental embryology in a later chapter, but let us notice here what is the direction in which these results, and those of the analysis of instinctive and intelligent action, carry us. It is towards the con- clusion that physico-chemical processes in the organism are only the means whereby the latter develops, and grows, and functions, and acts. In the analysis of these processes we see nothing but the reactions studied in physical chemistry ; but whenever we consider the organism as a whole we seem to see a co-ordination, or a control or a direction of these physico-chemical processes. Nageli has said that in the development of the embryo every cell acts as it if knew what every other cell were doing. There is a kind of autonomy in the developing embryo, or regenerating organism, such that the normal, typical form and structure comes into existence even when unforeseen interference with THE VITAL IMPETUS 161 the usual course of development has been attempted : in this case the physico-chemical reactions which proceed in the normal train of events proceed in some other way, and the new direction is imposed on the developing embryo by the organisation which we have to regard as inherent in it. This same direction and autonomy must be recognised in the behaviour of the adult organism as a whole. What is it ? We attempt to think of it as an impetus which is conferred upon the physico-chemical reactions which are the manifesta- tions of the life of the organism. It is the dan vital of Bergson, or the entelechy of Driesch. What is included in these concepts we consider in the last chapter of this book ; and before so doing it will be necessary to consider the organism from another point of view, that of its mutability when it is regarded as one member of a series of generations. CHAPTER V THE INDIVIDUAL AND THE SPECIES What is an individual organism ? A Protozoan, such as an Ameeba or a Paramcecium, is a single cell : it is an aggregate of physical and chemical parts, nucleus, cytoplasm, etc., and no one of these parts can be removed if the organism is to continue to live. The cell can be mutilated to some extent, but, in general, its life depends on the integrity of its essential structures, and it caimot be divided without ceasing to be what it was. It contains the minimum number of parts which are necessary for continued organic existence. Such an organism as a Hydra consists of an aggre- gate of cells which are not all of the same kind. The outer layer, or ectoderm, is sensory and protective, and contains organs of aggression ; while the inner layer consists of cells which subserve the functions of digestion and assimilation. All these parts are, in general, necessary for the life of the Hydra. They can be mutilated ; the animal can be cut into two parts, and each of these parts may regenerate, by growth, the part that was removed. Yet the existence of ectoderm and endoderm, in a certain minimum of mass, is necessary for this regeneration. The higher animal, or Metazoon, is therefore an aggregate of cells, each of which is equivalent to the individual Protozoon ; but these cells are not all alike — that is, THE INDIVIDUAL AND THE SPECIES 163 there is differentiation of tissues in the multicellular organism. Again, the Coelenterates provide examples of animals which are aggregates of parts, each of which is the morphological equivalent of a single Hydra. Such an animal as a Siphonophore, for instance, consists of zooids, and each of these units has the essential structure of a Hydra. But the zooids are not all alike : some of them subserve the function of locomotion, others of aggression, others of digestion and assimilation, and so on. Here, again, the whole organism may be mutilated ; parts may be removed and regeneration may occur ; but, as a Siphonophore, all of the different zooids must be present if the char- acteristic functioning of the animal is to continue. The Protozoon is, therefore, an individual of the first order, the Hydra an individual of the second order, and the Siphonophore an individual of the third order. Some such conception of degrees of individuality will probably be regarded as satisfactory by most zoologists, yet consideration will show that it is very inadequate. Many unicellular plants and animals may consist of a number of cells, which are all alike. The Diatoms and Peridinians reproduce by the division of their cell bodies and nuclei, and the parts thus formed may remain in connection with each other. A Diatom may consist of one cell, or it may consist of a variable number of such connected together by filaments, or in other ways ; and the dissociation of such a series may occur without interfering in any way with the functioning of the parts separated. A Tapeworm consists of a " head " or scolex, containing a central nervous mass and organs of fixation ; and organically continuous with this is a series of segments or proglottides. These proglottides are formed con- 164 THE PHILOSOPHY OF BIOLOGY tinuously from the posterior part of the scolex, and they may remain in connection with each other, and with the central nervous system and some other organs which are concentrated in the scolex. Never- theless, each proglottis contains a complete set of reproductive organs ; it has locomotory organs so that it can move about, and can fix itself to any surface into which it comes in contact. It can lead, for a considerable time, at least, an independent existence apart from that of the scolex and the other proglottides with which it was originally in continuity. In the majority of Polyzoa, the common Sea-Mat, for instance, the organism consists of a very large number of polypes or zooids, each of which secretes an investment of some kind round itself, but all of which may be con- nected together by a common flesh. In many Zoo- phytes there is essentially the same structure. In Corals there are very numerous zooids, each of which lives in a calcareous calyx secreted by itself. Polyzoa, Zoophytes, and Corals are individuals of the third order, and we might regard the tapeworm strobila — the scolex with its chain of proglottides — as belonging also to the same category. Nevertheless, a part of a Polyzoan or Hydrozoan colony, or a proglottis from a tapeworm, may become detached, when it will continue to live and reproduce and exhibit all the character- istic functioning of the species to which it belonged. Such an animal as a Hydra, or a Planarian or Chae- topod worm, or a starfish, may be cut into several pieces, and provided that each of these pieces exceeds a certain minimum of mass, it will regenerate the whole structure of the organism of which it formed a part. In the developing embryo of the Sea-urchin the eight- cell stage may be treated so that the blastomeres may come apart from each other : each of them will then THE INDIVIDUAL AND THE SPECIES 165 begin to segment again and will reproduce the typical larval Sea-urchin. The parasitic flat-worm, known as the liver-fluke, produces larvae which develop to form other larvae called rediae. Each redia normally develops into another larval form, called a cercariai which finally develops into the adult worm. But in certain circumstances each redia may divide and reproduce a number of daughter-rediae, and there may even be several generations of these larvae. In many lower animals buds may be formed from almost any part of the body, and each of these buds may reproduce the entire organism. In plants the entire organism may be grown from a very restricted part or cutting. Thus the individual, whether of the first, second, or third order, may be divided without necessarily ceasing to be what it was. Regeneration of fragments detached from the fully developed adult body so as to form complete organisms does not, in general, occur among the higher animals, nor, as a general rule, does reproduction by bud-formation occur. When such animals reproduce, an ovuttx develops to form a large mass of cells, which later on become differentiated to form the tissues and organs of the adult body. But a relatively small number of the undifferentiated cells persists in the ovaries of the females, or in the testes of the males, and each of these cells may again develop and reproduce the organism. There is apparently no limit to this process : any animal ovum may become divided successively so that an infinite geometrical series is produced, and in every term of this series all the potentialities of the first one are contained. The physical concept of individuality — that which cannot be divided, or which may not be divided with- out ceasing to be what it was — such individuaUty as IM THE PHILOSOPHY OF BIOLOGY the chemical molecuk possesses cannot be appUed to the organism. Any definition that involves the idea of materiaUty fails. Obviously the notion of the mdiyidual most commonly met with in zoological wntmgs— that it is the product of the development of a single ovum— fails, for, logicaUy apphed, it would regard the entire progeny of the ovum, that is, all the organisms belonging to the species, as the individual. It is clear that the difficulties of the concept arise from our attempt to identify the hfe of the organism with the material constellation in which this life is manifested. In the coiirse of generation after genera- tion the ovum becomes divided and grows and is again divided, and so on without apparent limit. But if we assume that the " organisation " or " en- telechy " is material and is capable of this infinite divisibility without impairment of its attributes, do we not extend to matter a property which belongs only to the concepts dealt with by mathematics ? The discussion of individuality with regard to the organism, considered as a morphological entity, is, indeed, rather a formal one, and it is valuable only in so far as it has for its object the establishment of the most convenient terminology. Nevertheless, the notion of organic individuality is clear to us though it is a notion felt intuitively and incapable of analysis. We see in nature animals like ourselves, and we do not doubt that each of them is an entity isolated from the rest of the universe, and to which the rest of the universe is relative. We ourselves are primarily centres of action. Motion, or change of position with respect to some object apart from ourselves in nature, is only relative, and there is no standard or point in the universe which is motionless and to which we can refer the motion of a body apart from our THE INDIVIDUAL AND THE SPECIES 167 own. But the motion of our own body is something felt or experienced intuitively, something absolute. As we move, the universe, our universe rather — that is, all that we act ■upon, actually or in our contemplation — contracts in one direction and expands in another. We feel ourselves to be apart from it although we may, to some extent, control it. We have no doubt that the higher animals have this feeling of isolation from, and relation to, an universe which is something apart irom themselves ; though, of course, the attempt to demonstrate this leads to all the kinds of difficulties suggested in our attempt to discuss individuality. It is a conviction so strongly felt that we have no doubt about it. The organic individual we may then describe as an isolated, autonomic constellation of physico-chemical parts capable of indefinite growth or reproduction .1 What is reproduction ? It is organic growth by dissociation accompanied in the higher organisms by differentiation and reintegration. To make this state- ment clear, we must now consider the phenomena of reproduction in the lower and higher organisms. We know purely physical growth. If a small crystal of some suitable substance be suspended in an indefinitely large quantity of a solution of the same chemical substance it will begin to grow, and there is no apparent limit to the mass which it may attain. Such giant crystals may be grown in the laboratory or they may be found in rock masses. Growth here is a process of accretion in which a particular form is maintained. Form in inorganic nature may be essential or accidental. Accidental forms are such 1 The description is, of course, only a convenient one. The notion of individuality, as it is expressed in the earlier part of this paragraph, is an intuitively felt, or subjective, one. It is best called personality. 168 THE PHILOSOPHY OF BIOLOGY as are partially the regult of a very great number of small and unco-ordinated causes : the form of an island or a mountain suffering erosion, or the shape of a river valley or delta, or the arrangement of the stones forming a moraine at the side of a glacier. Essential forms are such as are assumed as the result of the operation of one or a few co-ordinated causes, and such are the forms of crystals. They are invari- able, or they vary within very small limits about an invariable mean form. The form of a crystal depends on the structure of the molecules of the chemical substance from which it is produced. We cannot, of course, speak of the shape of a molecule, but we know that the atoms of which it is composed have certain positions in space relative to each other — positions which are con- ceptualised in the structural formulae of the chemists. In the solution, or mother-liquor, these molecules move freely among each other, but in the crystal they become locked together and their motions are re- stricted. The shape of the crystal depends on the way in which the molecules are locked together, or on the way in which they are arranged. A cube may be built up by the arrangement of a number of very small cubes : obviously we could not make a cube from a number of very small hexagonal prisms if the latter were to be packed together in such a way as to occupy the minimum of space. An infinitely great number of cubes might also be formed by adding single layers of very small cubes to the faces of an already existing one — that is, by the accretion of elements of essentially similar form. In every cube (or crystal) of this infinite number the geometrical form would be the same, and if we were to measure any one side of any cube of this series we should find that the total surface THE INDIVIDUAL AND THE SPECIES 169 would always be a definite function of the length of this side. The mass of a cube would also be a function of such a measurement : it would be aP, a being a constant depending on the unit of mass and on the specific weight of the substance of which the crystal was composed. If we take a series of crystals of increasing size, this relation holds for every one of them : M=al^, M being the mass, a the constant referred to above, and I, the independent variable, being any one length of a side of the crystal. If the organism grows by accretion in the same way as does a crystal, this relation ought also to hold in all the exclusiveness with which we expect it to hold in the growth of a crystal. But it does not so grow. Its growth is something essentially different, and none of the superficial analogies so prevalent nowadays ought to obscure this difference. The organism may grow by accretion, thus layers of calcareous matter may be added to the outside of a membrane bone from the investing periosteum, or it may grow by the deposition of matter within the actual cell bodies, (the process of growth by intussusception of the plant physiologists). But the extent of growth by accretion is strictly limited in all organisms : for each there is a maximal mass determined by the nature of the animal or plant, and this mass is that of the uni- cellular organism itself, or that of the cells of which the multi-cellular organism is composed. There may also be growth by accretion in the case of the formation of skeletal structures, which are laid down by the agency of the cells of the organism ; but if we confine our attention to the growth of the actual living sub- stance we shall see that accretion ceases when the mass characteristic of the cells has been attained, when growth by dissociation begins. The cell then 170 THE PHILOSOPHY OF BIOLOGY divides, and each of the parts into which it has divided grows to the limiting size, and division again occurs. This is what happens in the case of the growth of the Sea-urchin egg to form the larva, or blastula. The ovum segments into two blastomeres, each of which then grows to a certain extent, and again segments into two blastomeres. After the completion of ten divisions there are about looo cells which are arranged so as to form a hollow ball — ^the blastula. Differentiation is now set up. In the blastula stage all the cells are alike, actually and potentially. But soon one part of the - . J hollow ball of cells be- comes pushed mwards, It is assumed that the universe is a finite one. If it were infinite the whole discussion becomes meaningless, and we must give up this and other problems. THE ORGANIC AND THE INORGANIC 311 concomitant segregation of energy. We see as clearly as possible that the tendency of all inorganic happening is the transformation of potential into kinetic energy, and the equal distribution of this kinetic energy through- out all the parts of the system in which the happening occurred. On the other hand, the tendency of organic happening is the transformation of kinetic energy into potential energy, (i) in the stores of chemical com- pounds which result from the metabolism of the green plants, and which are capable of jdelding energy again ; and (2) in the results of the instinctive or intelligent activities of the animal's organism. The first result of organic evolution is clearly to be traced and needs no further explanation, the second is apparent on reflection, but is perhaps not clearly apprehended in all its signifi- cance by the student of biology and physics. Organic evolution is the process which has had, or is having, for its tendency the development of the putrefactive and fermentation bacteria, the chlorophyl- lian organisms, the Arthropods, and man and other mammals. All that we have said has been futile if this teleological description of the evolutionary pro- cess has not been clearly suggested. The indefinitely numerous forms of life that have appeared on the earth in the past, and are now appearing, seem to be experiments most of which have been unsuccessful. Only in the organisms mentioned, organisms which are complementary in their metabolic activities, has life been successful in manifesting itself in activities which are compensatory to those of inorganic nature. The energy which is dissipated in the radiation of the cooling sun is again made potential in the form of the carbohydrates, synthesised from water and carbon dioxide by the agency of the chlorophyllian organisms, and this energy accumulates. It is emjployed by the 312 THE PHILOSOPHY OF BIOLOGY instinctive and intelligent animaiFin that it is used as food and converted into bodily energy, which can then be utilised for any purpose that is contemplated. These plant substances taken in by the animal as sources of energy are broken down into excretory substances, which are further broken down by the metabolic activity of the fermentation and putrefaction bacteria, and be- come the substances used as foods by the chlorophyllian organisms. If the activities of man were only those of un- directed or misapplied muscular movements (as indeed most of his activities have so far been), then cosmic energy would truly be dissipated after it had become the energy of organisms. But does not all the history of man point to his ever-increasing activity in the conquest over nature, that is, the effort to hoard and employ natural sources of energy, and to arrest its tendency towards dissipation ? It must be admitted that the past history of human civilisation has been almost entirely that of the irre- sponsible exploitation of natural resources — for it has been founded on the thoughtless and wasteful utilisa- tion of energy which was made potential by the plant and animal organisms of the past. Man, the hunter, maintained himself and multiplied by the destruction of other animals or plants, or by the mere collection and utilisation of naturally occurring fruits and other plant-substances. During historic times the bison and other animals have almost become extinct owing to his ruthless activity, just as in our own days the whale, sole, and turbot are disappearing before the activity of the machine-aided fisherman. Industrial man has been successful with his factories and railroads and steamships, and his electrical power and transport, only because he has been able to utilise the stores of THE ORGANIC AND THE INORGANIC 313 energy contained in the coal and oil accumulated in the rocks of the earth. The progress of civilisation has been a progress rendered possible by discovery and invention, and by the application of the knowledge so obtained to the practical things of human life, but in this specu- lation and its application two different things are indicated. For the scientific man and the philosopher the reduction of the apparent chaos of nature to law and regularity is the beginning and end of his mental activity ; but the object of the " entrepreneur " or " organiser " or the " captain of industry " has been to employ these results of thought to the irresponsible exploitation and the selfish depletion of natural sources of energy. Just as the bison and other animals have disappeared or are disappearing before the hunter and fisherman, so the stores of coal and oil are disappearing before the activities of commerce. It has been said that the triumphs of industrialism are only the triumphs of the scientific childhood of our race. Human effort has so far only contributed to the general dissipation of natural energy. Yet just as man, the hunter, has been succeeded by man, the agriculturalist, so this irresponsible depletion of natural wealth must be succeeded by the endeavour to retard, and not to accelerate, the degradation of energy. Plants and animals which were simply killed by primitive man are now sown and harvested, or cultivated and bred ; so that the energy of solar radia- tion, which formerly ran to waste, so to speak, is now being fixed by the metabolic activity of the green plants of our crops and harvests. Rainfall and winds, tides and rivers, all represent energy primarily derived from solar radiation and from the orbital and rotatory motions of the earth and moon. This energy even now is almost entirely dissipated as waste, irrecoverable, 314 THE PHILOSOPHY OF BIOLOGY low-temperature heat ; but more and more as our stores of coal and oil are being depleted, the attention of men is being directed to these sources of kinetic energy. Waterwheels and windmills, and the more effective mechanisms that must be evolved from these primitive motors, will capture this waste energy and convert it into the kinetic energy of machines serviceable to man, or into the potential energy of chemical compounds capable of storage and future utilisation. The study of radio-activity has made us acquainted with the enormous stores of potential energy locked up in the atoms, and if it ever should become possible to utilise this by the disintegration of these particles, the down- ward trend of natural energetic processes will further be retarded. Life, when we regard it from the point df yiew,of energetics, appears therefore as a tendency which is opposed to that which we see to be characteristic of inorganic processes. The direction of the latter is towards the conversion of potential into kinetic energy, and the equal distribution of the latter throughout all the parts of the universe. The direction of the tendency .which we call life is towards the conversion of kinetic into potential energy, or towards the establishment and maintenance of differences of kinetic energy, where- by the latter remains available for the performance of work. In general terms, the effect of the movement which we call inorganic is towards the abolition of diversities, while that which we call life is towards the maintenance of diversities. They are movements which are opposite in their direction. What is cosmic ^volution ? In all the hypotheses which astronomical physics has imagined we see the transformation of a system — a part of the universe arbitrarily detached from all the rest — ^through a series THE ORGANIC AND THE INORGANIC 315 of stages, each phase of the series being marked by a progressive decrease of diversity, that is, by some degradation of energy. Two main series of hypotheses accounting for the present condition of the universe seem to have been the result of physical investigation : (i) the origin of discrete solar and planetary bodies by a' process of condensation of a gaseous nebular sub- stance ; and (2) the origin of the same systems by aggregations of meteoric dust. Plausible as is the nebular hypothesis on first consideration, it fails when it is subjected to minute analysis. What is a gaseous nebula ? It is a mass of heated vapour 'contracting by the mutual gravity of its parts as its molecules lose their heat by radiation — so the hypothesis states. But it has been pointed out that we cannot be certain that the gaseous nebulae known to astronomy are hot, or even that they gravitate. The great nebula in Orion, it ife stated, is at an enormous distance from us, and making a minimal estimate of this distance the volume of the nebula must still be incredibly great. There are good reasons for believing that the mass of the visible universe cannot be greater than that of a thousand million of suns such as our own. Assuming that all this matter is contained in the great nebula in Orion (and obviously only a small portion of it can be so contained) , we find on calculation that the " gas " so formed would be much less dense than even the trace of gas contained in a high vacuum artificially produced.^ How, then, can we speak of such a body as this nebula as an extended mass of hot gas, cooling and gravitating as it loses heat ? Even on the other hypotheses, those of the forma- tion of discrete suns and planets by the aggregation of meteoric dust, and the compensatory dispersal of such • Its density would be -= jth that of our atmosphere. 316 THE PHILOSOPHY OF BIOLOGY dust by radiation pressure, apparently insurmount- able difficulties arise. All such hypotheses as we have indicated assume material substance and modes of energy-transformation similar to those that we study in laboratory processes, and all such hypotheses involve the notion of the degradation of energy. So long as we suppose that all cosmic processes are transforma- tions of extended systems of material substances we must assume that energy is dissipated at every stage of the transformation, and whenever we assume this we admit that the processes are irreversible ones, and that the material universe as a whole tends towards a condition of inertia. Yet this, we see, cannot be true, for the universe teems with diversity. Is the progress towards the ultimate state of inertia an asymptotic one, as Ward suggests ? This does not help us, since all that the suggestion does is to misapply a mathematical device of service only in the treatment of the problems for which it was developed. Somewhere or other, it has been said, the second law of thermodynamics must be evaded in our universe. How can it be evaded ? That movement or pro- gress which we call inorganic is a movement of energy- transformations in one direction — ^towards their cessa- tion. It is .a movement which we can easily reverse in imagination. A cigarette consumed by a smoker represents the downfall of energy : the cellulose and oils of the tobacco bum with the liberation of heat, and the formation of water, carbon dioxide, and some soot ; and this is what happens when potential energy contained in an organised substance becomes converted into kinetic energy. Now, the opposite process can clearly be conceived — it can even be pictured. If we make a kinematographic record of the smoking of the cigarette and then reverse the direction of motion of the THE ORGANIC AND THE INORGANIC 317 film, we shall see the particles of soot recombining to form the substance of the cigarette, and we can imagine the concomitant combination of the water, carbon dioxide, and other substances formed during the combus- tion with the absorption of kinetic energy. This is not a mere analogy, for the same reversal of ordinary chemi- cal happening occurs whenever a green plant builds up starch from the water and carbon dioxide of the atmos- phere ; and it also occurs whenever a chemical syn- thesis of an " organic " compound, like that of urea by Wohler, or that of the sugars by Fischer, is brought about in the laboratory. In all such syntheses the experimenter reverses the direction of inorganic chemical happening. He may cause endothermic chemical re- actions, reactions accompanied by the absorption of available energy, to take place, and in these kinetic energy becomes transformed into potential energy. All the syntheses of organic compounds so complacently instanced by mechanistic biologists and chemists as indicative of the lack of distinction between the organic and the inorganic point to no such conclusion. Sugar is built up in the cells of the green plant from the in- organic compounds, water, and carbon dioxide, and is therefore a compound prepared by life — ^that of the plant organism. But sugar may also be built up in the laboratory from inorganic compounds, which may further have been synthesised by the chemist from their elements. Does this destroy the distinction between compounds formed by the agency of the organism and those formed by inorganic agencies ?. Obviously it does not, for in the green plant the sugar was formed as the result of the vital agency of the living chloro- phyllian cell, while in the laboratory it was built up because of the intelligence of the experimenter. Apart from this intelligence or vital agency, the series of 318 THE PHILOSOPHY OF BIOLOGY chemical transformations beginning with the elements carbon, oxygen, and hydrogen, and ending with the substance sugar, would not have occurred. We have no right to say, therefore, that such syntheses destroy th^ distinction between the organic and the inorganic. What they do indicate is the distinction between the tendency expressed by the second law of thermo- dynamics (inorganic processes), and those that occur as the result of direction conferred upon processes taken as a whole, either by the vital agency of the living cell, or by the intelligence of man (vital processes). The direction, therefore, that may be conferred on a series of physico-chemical processes is what we must understand by the " vital impetus " of Bergson, or the " entelechy " of Driesch. It must be admitted that it is difficult to describe more precisely than we have done above what is meant by these terms. It is with very much the same em- barrassment that is experienced by the physicist when he has to apply the concepts of mass and inertia, in their eighteenth-century meaning, to his description of an universe in terms of electro-magnetic theory, that we seek to describe the modem concept of entelechy. Yet the physicist has had to make this step forward, and the same adventure awaits the biologist if the speculative side of his science is to make further pro- gress, and if he is disinclined to make his science an appendage of physics and chemistry. Entelechy does not correspond to the eighteenth-century notion of a " vital force," or to the " soul " of Descartes, as the writer of a book on evolutionary biology seems to suggest. It is a concept which is forced upon us mainly because of the failure of mechanistic? hypotheses of the organism. If our physical analysis of the behaviour of the developing embryo, or the evolving THE ORGANIC AND THE INORGANIC 319 race or stock, or the activities of the organism in the midst of an ever-changing environment, or even the reactions of the functioning gland, fail, then we seem to be forced to postulate an elemental agency in nature manifesting itself in the phenomena of the organism, but not in those of inorganic nature. This argument per ignorantium possesses little force to many minds : it makes little appeal to the thinker, or the critic, or the general reader, but it is almost impossible to over- estimate the appeal which it makes to the investigator, as his experience of the phenomena of the organism increases, and as he feels more and more the difficulty of describing in terms of the concepts of physics the activities of the living animal. We may, however, attempt to illustrate mainly by analogy what is meant by Driesch's entelechia, a more precise concept than is Bergson's Han vital. We return to the consideration of the behaviour of the embryo at the close of the process of segmentation. The organ- ism at this stage consists of a number of cells organically in continuity with each other, either by actual proto- plasmic filaments or by the apposition of parts of their surfaces, thus constituting " semi-permeable " mem- branes. These cells are all similar to each other, both structurally and functionally. It does not matter that modem speculations on heredity describe them as unlike in that each contains a different part of the original germ-plasm which had been disintegrated in the process of the division of the ovum and the first few blastomeres ; and it does not matter that these hypotheses are compelled to assume that a part of the original germ-plasm remains intact, being destined to form the goiiads of the adult animal. These are hypo- theses invented to account for the differentiation of the embryo in terms of eighteenth-century physics and 320 THE PHILOSOPHY OF BIOLOGY chemistry, and they have yet to be supported by experiment before we can accept them as a description of what is to be observed in the processes of nuclear division and segmentation. Further, it is certainly the case that any one cell of the early embryo can give rise to any part of the larva. The segmented embryo is therefore a system of parts, all of which are potentially similar to each other. But actually each of these parts has a different fate in the process of the development of the larva, and this fate depends on what is the fate of the adjacent cells. There is also a plan or design in the development of the embryo — ^that is, a very definite structure results from this process — and each of the cells shares in the evolution of this design. The system of cells is therefore an harmonious equipotential system. The cells themselves are not the ultimate parts of this system, for each of them is an aggregate of a very great number of substances which are physico- chemically characterised — at least our methods of analysis seem to show that each cell is a mixture of a number of chemical compounds, but we must never forget that it is the dead cell which we thus subject to analysis, and not a living organism. Let us call these supposed chemical constituents of the living cells the elements of the system ; then at the beginning of the process of development the latter is composed of elements which are not definitely arranged but which are distributed in an " homogeneous " manner very like the distribution which is effected on shuffling a pack of cards. But as differentiation proceeds, the elements of this system become unequally distributed, and the diversity becomes greater and greater, attain- ing its maximum when the definitive tissues and organs of the adult become established, just as at the close of a game of bridge the cards acquire a particular arrange- THE ORGANIC AND THE INORGANIC 321 ment indicative of a very definite plan which was present in the minds of the players shortly after the game began. Mechanistic biology would seek to explain this transformation of a homogeneous system of elements into a heterogeneous and specific arrangement by the interaction of the elements with each other, and by the reaction of the environment. But, given a homo- geneous arrangement of elements capable of interacting with each other, then only one final phase can be supposed to be produced. A mixture of sulphur, carbon dust, copper and iron filings raised suddenly to a high temperature will only interact in one way, and the final phase of the system will depend on the com- position of the mixture, on the temperature, and on the conduction of heat into the mixture in the initial stage of heating. A mixture of chloroform and water shaken up in a bottle is at first a " homogeneous " mixture of the particles of the two substances, but under the influence of gravity the liquids separate from each other and form two distinct layers, each of which will contain in solution some of the other liquid. A homogeneous mixture of different substances there- fore becomes a heterogeneous arrangement in the in- organic system, as in the organic one, but while we can predict the former one we cannot predict the latter. We can express the result of the combination of the elements of the inorganic mixture as something that depends on chemical and physical potentials, but this is quite impossible in the case of the development of the embryonic system. It is not only that our know- ledge of the developmental process is imperfect : the distinction between the two processes of differentiation is a fundamental one. A change in the conditions under which the inorganic system differentiates leads 322 THE PHILOSOPHY OF BIOLOGY of necessity to a different final phase, but a change in the conditions under which the embryo develops need have no such effect. If some unforeseen occurrence takes place — some artificial interference with the process of segmentation, which could never have been experienced in the racial history of the organism — a regulation by the parts of the embryo occurs, and the final phase of development may be the same as if no interference had been experienced. That which is operating in the development of the embryo is some- thing that is permitting, or suspending, or arranging physico-chemical reactions. Let us think of the developing embryo merely as an aggregation of substances contained in an inorganic medium : the segmented frog's egg floating on the water at the surface of a pond is an example. As an inorganic system its fate is determined. Autolysis of the substances in the cells will occur and the proteids will break down with the formation of amido-bodies, while other chemical changes, strictly predictable if our knowledge of organic chemistry were more complete than it is, would also occur. Putrefactive and fermen- tative bacteria will attack the proteids, fats, and carbo- hydrates, and in the end our aggregation of chemical substances will become an aggregation of much simpler compounds — ^water, carbon dioxide, marsh gas, sulphur- etted hydrogen, phosphoretted hydrogen, ammonia, nitrates, etc., all of which will dissolve in the water of the pond, or will diffuse into the adjacent atmosphere. But in the living embryo this is not what occurs : an entirely different, and much more complex, arrange- ment of the chemical substances originally present in the segmented egg, or at least a physical and chemical re-arrangement, is brought about. The entelechy of the developing embryo prevents some reactions from THE ORGANIC AND THE INORGANIC 328 occurring and directs the energy which is potential in the system towards the performance of other reactions. Two analogies, suggested by Driesch, will perhaps make the r61e of entelechy more clear. A workman, a heap of bricks, some mortar, some food, and some oxygen constitute a system in the physico-chemical sense. From his heap of bricks and mortar the work- man may build one of several different kinds of small house, or he may perhaps construct several walls with- out any definite arrangement, or he may merely con- vert one " disorderly " heap of bricks and mortar into another " disorderly " heap. In the same way a man, a case of movable types, some food, and some oxygen constitute another system. The initial phase of this system consists of the compositor, his food, and some fifty-odd boxes of types, each of which contains a large number of similar elements. A final phase of the system may be the arrangement of the types to form an epic poem, or a series of dramatic criticisms, or a meaningless jumble of correctly spelt words. In all these cases the same amount of energy was expended : the bricklayer used up the same quantity of food and oxygen and excreted the same quantities of water, carbon dioxide, and urea, whether he made a house, or a small chimney, or a heap of bricks without archi- tectural arrangement. The system of bricks and mortar acquired during the process of differentiation a gradually increasing complexity ; while in the case of the type-setting the diversity of arrangement acquired in the final phases may be of a very high order. Yet the intelligent mind of the worker remained in either case unchanged. Let us consider further a man walking along the ties, or sleepers, of a railway track. The ties are at variable distances apart, so that the steps of the walker 324 THE PHILOSOPHY OF BIOLOGY must vary in length, being sometimes closer together, sometimes further apart. The mean step has a definite length and requires the expenditure of a certain amount of energy, and the condition that the man takes some- times a long step and sometimes a short one does not require that the energy expended on the steps should be more than if every one of them were of the mean length, for the additional energy that is required for the long steps is saved from the short ones. That which operates here is the power of regulation exercised by the walker regarded as a mechanism. There is no purely inorganic process precisely similar to this. It might be thought that the governor of a steam engine did very much the same thing, admitting more steam into the cylinder when the load on the engine increases, and vice versa. But the governor is a mechanism designed to compensate for variations that are given in advance. In the case of the man walking on the rail- way track, entelechy operates by suspending energetic happening (the muscular contractions of the short steps) when necessary, and allowing it to proceed when necessary. Entelechy itself, whatever it may be, need not be affected by these regvdations. The organism is therefore an aggregation of chemi- cal substances arranged in a tjrpical manner. These substances possess energy in the potential form, capable of undergoing transformation so that they may give rise to other chemical substances — secretions, for instance — or to energy in the kinetic form, that is, the movements of muscles. In the resting organism these transformations do not take place : the energy remains potential, so that chemical happening is suspended. In the unfertilised ovum, for instance, nothing happens although all the potentialities of segmentation are contained in the cell. If reactions did occur in con- THE ORGANIC AND THE INORGANIC 325 sequence of the chemical potentials contained in the substances of the cells, the progress of these would be such as to lead to the formation of substances in which potential energy was minimal, and in which the original energy of the cell would be represented by the un- co-ordinated kinetic energy of the molecules resulting from the breakdown of the substances undergoing the chemical changes. This is not what happens in the differentiation of the ovum : the developing cell forms new substances from those of its inorganic medium similar to the substances of which it is already com- posed, and then these substances become arranged to produce the specific form of the organism into which the ovum is about to develop. All hypotheses which attempt to describe the functioning of the differentiating ovum, or the function- ing organism, in terms of the physical concepts of matter and energy alone, fail on being subjected to close analysis. The manifestations of the life of the organism are, it is said, particular " energy-forms," of the same order as light, heat, chemical and electrical energy, etc. All these energy-forms are "concaten- ated," that is, each can be converted into any of the others. A particular frequency of the vibration of the ether can be converted into a movement of the molecules of a material body, and so become heat, while chemical energy may become converted into electrical energy, or vice versa, and so on. It is said that life may be merely a transformation of some "energy-form" known to us : the potential energy of food may be converted into " biotic energy," and this may then manifest itself in the characteristic behaviour of the organism. This is the method of physical science. Energy continually disappears from our knowledge : the mechanical energy which was employed to carry a 326 THE PHILOSOPHY OF BIOLOGY weight to the top of a hill, or that which raises a pendulum to the highest point of its swing, apparently disappears. If we pass a current of electricity through water, energy disappears, for it requires more current to pass through water than through a piece of metal of the same section. In these and similar cases physics invents potential energies in order to preserve the validity of the law of conservation. The kinetic energy of the weight, or that of the swinging pendulum, be- comes the potential energy of the weight resting at the top of the hill, or that of the bob of the pendulum at its highest point, while the electrical energy that has apparently been lost becomes the potential energy of the changed positions of the molecules of oxygen and hydrogen. This assumption that the visible kinetic energy of motion becomes converted into the invisible potential energy of position is justified by our experience, for (neglecting dissipation) we can recover this lost energy, in its original quantity, from the con- dition of the bodies which became changed physically when the kinetic energy disappeared. Apply the same method to the phenomena of the organism and suppose that the chemical potential energy of the food con- sumed becomes converted into the kinetic energy of motion of the parts of the body : we are justified in this assumption by the results of physiology. But then some of this chemical energy undergoes a transforma- tion of quite another kind and becomes the " biotic energy," which is apparently that which is in us which enables us to perform regulations, or establishes that condition which we call consciousness. We cannot say exactly what this " biotic energy " is, or what are the steps by which the energy of food becomes converted into it ; but no more can we say what is electrical energy, nor what are the steps by which chemical energy THE ORGANIC AND THE INORGANIC 327 becomes converted into it. Thus our ignorance of the precise nature of the energy-transformations of in- organic things — an ignorance which is all the while disappearingr-becomes the excuse for a comparison of these with vital transformations, and for the assump- tion that there is a fundamental similarity in the two kinds of happening. Less is assumed in the assumption of an entelechian agency than in assuming that the manifestations of life are the consequences of a vital " energy-form," different from inorganic forms, though belonging to the same order, inasmuch as it may be concatenated with these inorganic energy-forms. We need not sup- pose that a particular kind of transformation occurs only in the sphere of the organic : all that we need assume is that, by some agency inherent in the activities of the organism, chemical reactions that would occur if the constellation of parts were an inorganic one are suspended. Nothing unfamiliar to physical science is involved in this assumption. Hydrogen and chlorine, gases that combine together when mixed with the production of heat and light, may be mixed under conditions such that the combination may be delayed for an indefinite time. Iron which dissolves in nitric acid may nevertheless be brought into the " passive " form when it remains in contact with the re-agent but is not dissolved by it. Enzymes which are in contact with the walls of the alimentary canal do not dissolve these membranes so long as the tissues are alive, and they do not dissolve the food stuff until they have been " activated." Oxygen which is contained in the tissues does not oxidise the tissue substances until an enzjnne or a catalase has exerted its influence. More and more, as physiology has become more searching in its study of the functions of the animal, has it sought 328 THE PHILOSOPHY OF BIOLOGY to explain the metabolic processes by assuming the intervention of enzymes, until the number of these substances has become legion, and much of the original simplicity of the notion of ferment-activity has been lost. But why do not these enzymes, if they are always present in the tissues, always act ? They must be activated, says modem physiology ; that is, the enzyme really exists in the tissues as a " zymogen " or a sub- stance which is not, but which may become, an enzyme ; or they exist as " zymoids," that is, substances which appear to be chemically enzymes, but which must be activated by "kinases" before they can become functional. Undoubtedly it is along these lines that physiology is making advances, has increased our knowledge of the activities of the animal, and is conferring on the physician greater power of combating disease ; but the h5rpotheses of the activity of the enzymes is obviously one which has been based on the results of the physico-chemical investigation of inorganic reactions, and it has taken the precise form it has because of the attempted analogy of many metabolic processes with catalytic processes. Why do the inert zymoids becojne activated by the kinases just when they are required by the general economy of the whole organism ? We do know that kinases are produced by the entrance of digested food into certain parts of the alimentary canal, and that these kinases are carried in the blood stream to other parts where they activate the z5?moids already there. But of the nature of the machinery by means of which all this is effected physiology gives us no hint, and it is an assumption that the mechanism involved is a purely physico-chemical one. Suppose we say that the entelechy of the organism possesses the power of suspending the activation of the enzyme, THE ORGANIC AND THE INORGANIC 329 that is to say, of arresting the drop of chemical potential involved in the process of the hydrolysis of (say) a proteid. When this process of hydrolysis is necessary in the interest of the organism entelechy can then institute the reaction which it has itself suspended^ all this is in accord with the law of conservation. Entelechy does not cause chemical reactions to occur which are " impossible " : it could not, for instance, cause sulphuric acid and an alkaline phosphate ^t'o react with the formation of hydrochloric acid. Bul^ chemical reactions which are possible may be sus- pended, and suspended reactions may then become actual when this is necessary in the interest of the organism. Entelechy is therefote not energy, nor any parti- cular form of energy-transformation, and in its opera- tions energy is neither used nor dissipated. In all that it does the law of conservation holds with all the rigidity with which we imagine it to hold in purely in- organic happening — at least we need not assume that ■it does not hold — and this is the essential difference between the entelechian manifestations and the mani- festations of the " vital " or " biotic " forces or energies of the historic systems of vitalism. It is essentially arrangement, or orders of happening, and it is therefore a non-ehergetic agency. The workman who may build half-a-dozen zigzag walls, or an archway, or a small house, from the same materials and with the ex- penditure of the same -quantity of energy, is indeed an energetical agent, but he is more than that. He is a physico-chemical system in which any one phase is not determined by the preceding phase. Different results may arise from the same initial arrangement of materials and energies, and this is because the system contains more than the material and energetical 230 THE PHILOSOPHY OF BIOLOGY stable race or " variety." Nevertheless some effect is produced, and this may be accounted for by suppos- ing that the observed variations are really of two kinds — fluctuating variations, which are not inherited, and mutations, which are inherited. The small ob- served effect is due to the selection of the mutations alone : it is a real effect of selection, an undoubted transmutation of the specific form, but experimental and statistical investigations seem to show that sel^ tion from the variations that we usually observe is too slow a process to account for the existing forms of life. Natural selection acts, therefore, on mutations. Now it seems that we are forced to recognise the exist- ence of two categories of mutations, (i) those stable modifications of an " unit-character " which we term " Mendelian characters," and (2) those groups of stable modifications to which de Vries applied the term mutations. It seems at first difficult to see how per- manent modifications of the specific form can be brought about by the transmission of Mendelian char- acters, for these characters are always transmitted in pairs. Let us take a concrete case — ^that of a man who has six fingers on his right hand, and let us suppose that this was a real, spontaneously appearing character or mutation which had not previously occurred in the ancestry of the man. Two contrasting characters would then be transmitted, (i) the normal five-fingered hand, and (2) the six-fingered hand. Both of these characters are supposed to be present at the same time in the organisation of the men and women of the family originating in this individual, but one of them is always latent or recessive. There would, however, be individuals in which only one of the char- acters would be present — either the normal or abnormal TRANSFORMISM 281 number of digits, but intermarriage with individuals belonging to the other pure strain would immediately lead again to the transmission of the contrasting characters, or allelomorphs, although marriage with an individual belonging to the same pure strain would carry on the normal or abnormal unmixed character into another generation. But if the possession of six fingers conveyed an undoubted advantage, and if ^ natural selection did really act in civilised man as regards the transmission of morphological characters, then a stable variety {Homo sapiens hexadactylus, let us say) might be produced by its agency. The muta- tions which we consider in the investigation of the inheritance of alternating characters are therefore just as much the material for natural selections as the mutations which occur among the ordinary va,riations displayed by organisms in general : but since only one or two characters appear to be subject to this mode of transmission, the process would be so slow as to be inadmissible as an exclusive cause of evolution. If we assume that de Vries' mutations are the material on which selection works, this difficulty is immediately removed, for we now have to deal with groups of stable deviations: not one or two, but all the characters of the organism appear to share in the mutability. But another difficulty now arises. A species of plant or animal may have got along very well with its ordinary structural endowment, and then a number of individuals begin to mutate. Some of the deviations from the specific type may be of real advan- tage, but others may not : we can, indeed, imagine an in-co-ordination between the mutating parts or organs which would be fatal to the animal ; on the other hand, there might be complete co-ordination, with the result that great advantage might be conferred upon the 332 THE PHILOSOPHY OF BIOLOGY organism that we are considering, and this is a pure conception, for our typical organism does not occur in nature. The organisms that are accessible to our observation are constellations of physico-chemical parts, but these constellations tend continually to deviate from the conceptual arrangement. Progressive varia- tion from the type is something that distinguishes the organic constellation from the inorganic one. The organism is an entity in which energy-trans- formations of a particular nature are effected. These transformations raise energy from a state of low, to a state of high potential. This is the general tendency of terrestrial life, and it is expressed most fully in the metabolism of the green plant. The energy-transformations that are effected here are those in which the kinetic energy of radiation is employed to buUd up chemical compounds of high potential, from inorganic substances incapable in them- selves of undergoing further transformations. The general tendency of all inorganic transformations is towards inertia. In them energy is not destroyed, but it is dissipated : it becomes uniformly distributed throughout material bodies as the un-co-ordinated motions of the molecules of which those bodies are composed, and it ceases to be available for further transformations. The green plant reverses this trans- formation, and accumulates energy in the form of chemical compounds of high potential. Inorganic processes are those in which available energy becomes uniavailable, and this unavailable energy can only become available again if a compensatory energy- transformation is effected. Life is that which effects these compensatory energy-transformations. The organism is a constellation capable of indefinite growth by dissociation. THE ORGANIC AND THE INORGANIC 33a That is to say, it is a constellation which reproduces itself in all its specificity. Growth consists in the separation from the organism of a part, or reproductive cell, which divides (or dissociates) repeatedly, each dissociated part growing again in mass by the addition of substances similar to its own, but which are taken from a medium dissimilar in composition to itself. The aggregate of parts so formed then differentiates so that the constellation is reproduced in all its specificity. There is nothing precisely similar to this in inorganic happening. The growth of a crystal consists simply of the accretion of elements similar in nature to those of the growing body, and there is no differentiation. The organism exhibits autonomy. It is a constellation which persists in the midst of an ever-changing environment, and the typical organic form remains the same, although the material of which it is composed undergoes continual change. There are inorganic entities which resemble the organism in this respect : the form of a cyclone or atmospheric dis- turbance, for instance, remains the same even though the air of which it is composed is continually changed. But the form of the organism does not vary strictly with the changes in the environment in which it is placed, for it may respond to an environmental change by a regulation, or compensatory change in form or functioning, the effect of which is to maintain the con- stellation in all its specificity. The regulation is not a complete or perfect one, for environmental changes do, to some extent, produce changes in the organic constellation, but there is no functionality between the environmental change and the organic response. In inorganic happening a change in one part of a trans- forming system necessarily determines the nature and 334 THE PHILOSOPHY OF BIOLOGY extent of the changes that occur in the other parts of the system. The organism is a centre of continuous action. It is first of all a part of nature in which energy- transformations continually take place — a description which applies equally well to plants and animals. It is only when we attempt to seek an inorganic system to which this definition would apply that we find how well it differentiates the organic from the inorganic. An inorganic system which transforms energy is either one which tends continually towards stability, or it is a machine made by man for a definite purpose, and it is therefore a system involving a teleological idea. An organic centre of action is one in which energy-trans- formations proceed without cessation. In the plant organism the energy-transformations re- present, with the exception of the reproductive processes, the whole activity of the organism. In the animal organ- ism they are accessory to regulated and purposeful motile activity, that is, muscular action. The object of this mus- cular activity varies with the stage of evolution attained by the animal. Its sole object in the lower animal is that of individual or racial preservation. Living in an organic and inorganic environment which is always hostile and tends continually towards its destruction, the whole activity of the organism is directed to the attempt to master this environment : it struggles for its individual existence, and that of its offspring. The activities of man are also these, but they are more than these, for, knowing that physical processes tend con- tinually towards inertia, he seeks to control these processes, and to preserve the instability of nature on which the possibility of further becoming depends. The activity of the organism, whether it be the energy-transformations of the plant or the motile THE ORGANIC AND THE INORGANIC 335 activities of the animal, are directed and regulated activities. The activity of the organism is not a functional activity in the sense that the activity of a djmamo is a function of the nature of the machine, and of the nature and quantity of the energy supplied to it. The nature of the activity of the organism is regulated autonomously by purposes which it " wills " to carry out. The organism is a phase in an evolutionary ^ux. Categories of organisms — varieties, species, genera, etc. — are fictions. They are arbitrary definitions de- signed to facilitate our description of nature. They are types or ideas. In constructing them we follow the method of the intellect, and we represent by im- mobility that which is essentially mobile and flows. Between the fertilised egg and the senile organism there is absolute continuity. Our description of the individual organism is a description of it at a typical moment of its life-history, and this description includes all that has led up to, as well as all that will fall away from, the morphology at this particular typical moment. Even then the arbitrarily defined organism is only a phase. In defining it we arrest, not only the individual, but also the racial, evolutionary flux. The specific morphology is that of a tjrpical moment in a racial flux. Leading up to it at this moment are all the variations that have joined it with its ancestry, and leading away from it wUl be all the variations that will convert it into its descendants. The individual and racial developments are true evolutions. They are the unfolding of an organisation which was not expressed in a system of material particles or elements interacting with each other, and with the elements of the environment, but which we must seek in an intensive, non-spatial manifoldness. 336 THE PHILOSOPHY OF BIOLOGY In the evolutionary flux the changes are non- functional ones, that is to say, any phase, whether it be one in an individual or a racial development, is not merely a rearrangement of the elements of the preceding phases, as in the case of a transforming system of material particles and energies. There is inherent, spontaneous variability. The organism endures. That is, all its activities persist and become part of its organisation. It does not matter whether or not we decide that characters which are acquired are transmitted, nor does it matter whether or not we conclude that the environment is the cause of these acquirements. Some time or other in the individual or racial history new characters arise by the activity of the organism itself, and these characters either persist in an individual or in a race. They endure. All its activities, even its thoughts, persist and form the experience of the animal — an experience which continually modifies its conduct. In man those true acquirements, the results of education and of investiga- tion, persist as written language, or as tradition, even if they are not inherited. Duration is not time. The mathematician does not employ, in his investigations, intervals of duration. When he relates something which is happening now to something which happened some time ago he employs the differential co-efficient dyjdx, so that the interval between the two occurrences becomes an " infini- tesimal " one. When the astronomer predicts events that will happen some years hence, or describes those that happened some years ago, he is really describing things that are all there at once, so to speak, things which are given. If we unfold a fan, stick by stick, we see the separate members in succession, but they THE ORGANIC AND THE INORGANIC 337 are all there, and we can, if we like, see them all at once. The more we reflect on it the more we see that mathematical time is only a way in which we see things apart from each other. Things become extended in time as they become extended in space. Whether occurrences capable of analysis by the methods of physics are what we call past or future occurrences, they are all given, in that each of them is only a phase of the others. Duration belongs to the organism. The past is known because all that has occurred to the organism still persists in its organisation. The future is unknown because it has still to be made. Duration is therefore a vector — something having direction, and the organism progresses out of the past into the future. It grows older but not younger. Such appears to be the nature of life. Can we discuss the problem of its origin ? Did life originate on our earth ? We must first consider what we mean when we speak of an origin. The organic world of the present moment, with all its environment — ^that is to say, the totality of organisms on the earth, with all the materials which they can utilise in any way, the energy of radiation from which they ultimately derive their energy, and all the parts of the cosmos which interact with them — constitute a system in the physical sense. The present condition of the organic world, that is, the kinds and numbers of organisms, and their distribution, and the distribution of the materials which they can utilise, and the quantity and nature of the energy which is available to them, are the present phase of this system. All the conditions of life in the past, that is to say, the kinds, and numbers, 338 THE PHILOSOPHY OF BIOLOGY and distribution of organisms, and the quantity and nature of their environment at any time, together formed phases of this system. If there was a time when life, as we know it, did not exist, then the materials and the energies, which were antecedent to life when it did appear, were also a phase of the system. On a strictly mechanistic hypothesis there could be no origin : there could only be a transformation of a system which was already in existence. All that exists to-day was given then. When, therefore, we speak of the origin of life from non-living materials we mean simply a transformation of those materials and energies. There was a time, it is said, when life could not exist on the earth. For the organism is essentially that aggregate of chemical compounds which we call protoplasm, and this cannot exist at temperatures higher than ioo° C, and it cannot function at tempera- tures lower than o° C. It requires carbon dioxide, and ammonia or nitrate, as the materials for its constructive metabolism, and there was a time when these com- pounds could not exist, for they must have been dis- sociated by the heat of the gaseous nebula from which our earth originated. The organism requires energy in the form of solar radiation of a particular frequency of vibration, and there was a time when the sun's radiation was different from what it is now. Therefore life did not exist then. Even if we believe that life came to the earth as germs, which existed previously in outer cosmic space, this belief does not solve the problem, which simply becomes transferred from our earth to some other cosmic body. But life, as we know it, makes use of the materials and the energies which are available to it in the con- ditions in which it exists. The plant organism obtains THE ORGANIC AND THE INORGANIC 339 its energy from solar radiation because this is the most abundant source of terrestrial energy. The human eye is most susceptible to light of a particular frequency of wave-length, but this is the radiation that is most abundant in the light of the sun. Does this not mean that the organism has merely adapted itself to the material and energetic conditions in which it exists ? Does it necessarily mean that because the conditions were very different life could not exist ? Protoplasm could not exist at a temperature of several thousand degrees Centigrade, but does that mean that life, which on any hypothesis of mechanism must be described in terms of energy, could not exist in these conditions ? It must have had an origin, says Weismann, because it has an end. Organic things are destroyed, inasmuch as they disintegrate into inorganic things. Organisms die. Thus the organic process comes to an end, and because it comes to an end it must have a beginning. Spontaneous generation of life is thus, for Weismann, a " logical necessity." Need this logical necessity exist ? The argument clearly implies that life is a reversible process. Organic things become inorganic, and therefore inorganic things must become organic things. The first statement is a fact of our experience, but the second one would only be logically true if we were to postulate that the process of life, whatever it may be, is a reversible process. But we must not postulate this if we are to hold to a physico-chemical mechanism, for it is a fundamental result of physical inveistigation that all inorganic pro- cesses are irreversible : reversible inorganic processes are only the limits to irreversible ones. Physical pro- cesses go only in one way, and that organic substance is destroyed to the extent that it becomes inorganic is a 340 THE PHILOSOPHY OF BIOLOGY particular case of this irreversible physical tendency. Now the mechanism of Weismann must base itself on the concepts of physics and chemistry, and it must postulate the origin of life from non-living substances. Why ? Because life is a reversible process, that is, it exhibits a tendency which does not exist in inorganic processes. Clearly the logic is faulty ! And must we conclude that life has an end ? Weismann himself suggests that nothing in the results of biology indicates that physical death is a necessity : it is rather an adaptation. The soma, or body, is the envelope of the germ-plasm, and exposed as it is to the vicissitudes of an environment which is always hostile, it becomes at length an unfit envelope. But with the reproductive act the germ-plasm acquires a new soma, and it is no longer necessary that the former one should continue to exist as an unfit envelope. Physical death therefore occurs as an adaptation serving for the best inter- ests of the race. The organism need not die, for the germ-plasm may be a physical continuum throughout innumerable generations. Somatic death is only a destructive metabolism : it is a catastrophic meta- bolism, if we like. We may legitimately discuss such problems as the origin of the protoplasm of the prototrophic organism, or that of the chlorophyll-containing cell, or that of the nerve-cell. On the mechanistic view each of these conditions is a phase of a transforming physico-chemical system, and it is within the scope of the methods of physical science to investigate the nature of these transformations. But if the argument of this book is sound, then the problem of the origin of life, as it is usually stated, is only a pseudo-problem ; we may as usefully discuss the origin of the second law of thermo- dynamics ! If Ufe is not only energy but also the THE ORGANIC AND THE INORGANIC 341 direction and co-ordination of energies ; if it is a tendency of the same order, but of a different direc- tion, from the tendency of inorganic processes, all that biology can usefully do is to inquire into the manner in which this tendency is manifested in material things and energy-transformations. But the tendency itself is something elemental. APPENDIX MATHEMATICAL AND PHYSICAL NOTIONS * INFINITY What is really meant when the mathematician uses the concept of infinity in his operations ? Suppose that we take a line of finite length and divide it into halves, and then divide each half into halves, and so on ai infinitum. We make cuts in the line, and these cuts have no magnitude, so that the sum of the lengths into which we divide the line is equal to the length of the undivided line. We can divide the line into as many parts as we choose, that is, into an "infinite" number of parts. Suppose that we are making a thing which is to match another thing, and suppose that we can make the thing as great as we choose. If, then, no matter how great we make the thing, it is still too small, the thing that we are tr5dng to match is infinitely great. Substitute " small " for " great," and this is also a definition of the infinitely small. Clearly the idea of infinity does not reside in the results of an operation, but in its tendency. It inheres in our intuition of striving towards something, but not in the results of our striving. ' It must be understood that some of the things dealt with in these appen- dices are very hard to understand by the reader acquainted only with the results of biological science. We urge, however, that they are all relevant if biological results are to be employed speculatively. 342 APPENDIX 343 FUNCTIONALITY If we pour some mercury into a U-tube closed at one end, the air in this end will be contained in a closed vessel under pressure. We can increase the pressure by pouring more mercury into the open end of the tube. We can measure the volume of the air by measuring the length of the tube which it occupies. We can measure the pressure on this air by measuring the difference of length of the mercury in the two limbs of the tube. By taking all necessary precau- tions we shall find that for each value which the pressure attains there is a correspond- ing value of the volume of the air. We thus find the pressure values, pi, p^, ps, p4, pi, etc., and the corresponding volumes, Vu Vj, Vi, Vi, Vs, etc., and we may then plot these values so as to make a graph. In this figure the values represented along the horizontal axis are pressure-values, and those repre- sented along the vertical axis are volume-values. We have so made the experiment that we can make the pressure-values whatever we choose — ^let us call them the values of the independent variable or argument. For each value of the pressure, or argument, there is a corresponding value of the volume, which depends on the pressure — ^let us call these values of the volume values of the dependent variable or functiojt. Fig. 27. 344 THE PHILOSOPHY OF BIOLOGY We can make arbitrary values of the pressure, but whenever we do this the corresponding values of the volume are fixed. We say, then, that the volume is a function of the pressure. In general, when we choose one value of an independent variable, or argument, there can be only one, or a small number, of values of the dependent variable, or function. If there are two or more values of the function for one value of the argument each of these is necessarily determined by the value which we choose to assign to the argument. There is a strict functionality between the two series of variables. In the experiment we have chosen this functionality is expressed by the equation pv=k{i+at), where p is the pressure, v the volume, k and a constants, and t is the temperature at which the experiment is carried out. In a number of experiments like that which we have mentioned, k, a, and t are the same throughout, and this is why we call them constants. We give p any value we like, and then v can be calculated from the equation. RATE OF VARIATION If we know the equation ^u = A (/ + fli) , we can find how much the volume changes when the pressure changes, that is, the rate of variation of v with respect to p. But even if we don't know that this equation applies, we can still find the rate of variation from our experi- ments. We see from the graph that, when the pressure increases from pi to p^, the volume decreases from v^ to Vj, but that if the pressure is again increased to ps, that is, by a similar amount to the increase of pressure from pi to pi, the volume decreases from Vt to v^. Now we find, by measurements made on the graph, that the decrease Vi to v, is greater than the decrease v, to »,, APPENDIX 345 and the latter decrease is greater again than the decrease from Vg to Vt. Evidently the rate of variation of volume is not like the rate of variation of pressure, that is, the same throughout, and when we look at the graph we see that the rate of variation is greatest where the slope of the curve is steepest. The latter is steepest near the point a, less steep near the point b, and still less steep near the point c. Now any small part of the curve is indistinguishable from a straight line. Let us draw astraightline eCi, which appears to coincide with a small part of the curve near a, and similarstraight lines^i,andggi, which also appear to coin- cide with small parts of the curve near b and c. Then the steepness of the curve will be proportional to the angles which these straight lines make with the axis op, and these angles are measured by the ratio — which ■^ oe e^e makes with op, the ratio ^, and the ratio ^\ 0/ og The point a on the curve corresponds with a pressure Ui and a volume an. The point b corre- sponds with a pressure 61 and a volume b^, and c with a pressure 5. 6, 7, 8, 9, lo, ii, 12, 13. No. 0/ times this hand was held — 0, o, o, i, 9, 29, 53. 52, 35. 14. 6, I, o, o. He should note also the number of times that trumps were spades, clubs, diamonds, and hearts : he will get some such results as the following : spades, 46 ; clubs, 53 ; diamonds, 51 ; hearts, 50. The numbers in the lower line of the first series form a " frequency distribution," for they tell us the frequency of occurrence of the hands indicated in the numbers above them. "No. of trumps " is the in- dependent variable, and " no. of times these nos. of trumps were held " is the dependent variable. A frequency distribution represents the way in which the results of a series of experiments differ from the mean result. A particular result is expected from the operation of one, or a few, main causes. But a number of other relatively unimportant causes lead to the deviation of a number of results from this mean or characteristic one. Yet since one, or a few, main causes are predominant, the majority of the results of the experiment will approximate closely to the mean ; and a relatively small proportion will deviate to vari- able distances on either side of the mean. If a pack of cards were shuffled so that all the suits were thoroughly mixed among each other, then we should expect the trumps to be as equally divided as possible between the four players. But a number of causes lead to irregularities in this desired uniform distribution, and so the results of a large number of deals deviate from the mean result. It is possible, by an application of the theory of probability, to calculate ideal, or theoreti- cal frequency distributions, basing our reasoning on the considerations suggested above. We then find that the 352 THE PHILOSOPHY OF BIOLOGY observed and calculated frequency distributions may- be very much alike. In biological investigation, far more than in physi- cal investigation, we deal with mean results. It is, however, just as important that the mean should be considered as the individual divergences from the mean. We want to know the mean results, and the way and the extent in which the individual results diverge from the mean. There is a mean or " ideal " result, but we must think of a great number of small independent causes which cause the actually obtained results to diverge from this mean. If these small un-co-ordinated causes are just as likely to cause the results to be less than the mean, as greater than the mean, we shall obtain a fre- quency distribution resembling the one given above, in that the variations from the mean are equal on both sides of the mean. But if the general tendency of the small un-co-ordinated causes is to cause the results, on the whole, to tend to be greater than the mean, then the frequency distribution will be " one-sided," that is, if we represent it by a curve the latter will be an asym- metrical one. Curves which are asymmetrical are those most frequently obtained in biological, statistical investigations. MATTER Our generalised notion of matter is that it is the physical substance underlying phenomena. Immedi- ately, or intuitively, we attain the notion of matter because of our perceptions of touch, and our perception of muscular exertion. The distance sense-receptors, visual, auditory, and olfactory, would not give us this intuition of matter. APPENDIX 353 Material things are extended, that is, they have form, and they exclude each other, so that they cannot occupy the same place. They appear to us to be aggregates of different nature : they may be solid and homogeneous, like a piece of metal ; or solid and porous, like a piece of pumice-stone ; or loose and granular, like sand ; or viscous or liquid, like pitch or water. They may have colour. They are opaque, or transparent in various degrees. They may have odour. Material things, as they are perceived by the distance sense- receptors, appear to have qualities. Material things are aggregates of molecules. The aggregates may possess essential form, like that of a crystal, or an organism. The form of the aggregate may be essential and homogeneous, so that it consists of molecules, all of which are of the same kind, like a crystal. It may be heterogeneous and essential, like the body of the organism, when it consists of molecules which are not all of the same kind. The aggregates may have accidental form, like that of a river valle5^ or a delta, or a mountain, and the form in these, and similar cases, is not a part of the essential nature of the aggregate. The molecules are selections (in the mathematical sense) of some of about eighty different kinds of atoms. A molecule is a small number of atoms arranged to- gether in a definite way, and its nature depends, not only on the kinds of atoms of which it is composed, but also on the arrangement of these atoms. Two or more different arrangements of the same atoms are, in general, different molecules. MASS When matter is perceived by the tactile and muscular sense organs, we have the intuition of mass. 354 THE PHILOSOPHY OF BIOLOGY It is heavy, and the degree of heaviness is proportional to the quantity of matter in the body which we feel, that is, to its mass. Heaviness is synon37mous with weight, but weight does not depend alone on the quantity of matter in the body. If the latter were removed to an infinite distance from the earth or other cosmic bodies, its weight would disappear, but its mass would remain. We could still touch and move it, and we should still find that different degrees of muscular exertion would be necessary when bodies of different masses had to be moved. INERTIA If the body were in motion, we should find that muscular exertion is necessary in order that it might be brought to rest ; and if it were at rest, we should find that muscular exertion was necessary in order that it might be moved. The body, matter in general, possesses inertia, and this is its most fundamental attribute. Mass we can only conceive in terms of inertia. If two bodies were at rest, and if the same degree of muscular exertion conferred on each the same initial velocity of motion, their masses would be equal. If the same degree of muscular exertion conferred diffe- rent velocities on different bodies, their masses would be different, and would vary directly with the initial velocities conferred. FORCE The feeling which we experience when we move a body from a state of rest, or stop a body which is moving, is what we call force. If on climbing a stair in the dark we think there is one step more than there is, and so have the queer, familiar, feeling of treading on APPENDIX 355 nothing, we have the intuition of energy ; but when we tread on the steps, and so raise our body, we have the intuition of force. Force is that which accelerates the velocity of a rnass. If the latter is at rest, we consider it to have zero velocity. If it is moving, and we stop it, there is still acceleration, but this is negative. Matter, that is, the substantia physica, is clearly to be conceived only in terms of energy. It is, to our direct intuitions, resistance, or inertia, that which re- quires energy in order that it may be made to undergo change. Our static idea of physical solidity, or massiveness, disappears on ultimate analysis. Mole- cules are made up of atoms, and the atoms are assumed to have all the characters of matter : we could not see them, of course, even if we possessed all the magnifying power that we wished, for they would be too small to reflect light. Modern physical theory is compelled to regard atoms as complex, and imagines them as being composed of moving electrons. The electron is im- material — ^it is the unit-charge of electricity. It is said to possess mass, but mass is now understood to mean inertia. So long as the electron is moving, it sets up a field of energy round it, and this field — ^the electro- magnetic one — extends in all directions. Periodic dis- turbances in it constitute radiation, and this radiation travels with the velocity of light. It is because of the existence of this field that we are obliged to postulate the existence of an ether of space. Unfamiliar to us until the discovery of Hertzian waves and " wireless " telegraphy, this electro-magnetic radiation in space is now accessible to our direct intuitions. We can initiate it by setting electrons in motion, that is, by expending energy (producing the sparking in the transmitters of the wireless telegraphy apparatus) ; and we can stop it, if it is in existence, by absorbing the energy (in the 356 THE PHILOSOPHY OF BIOLOGY receivers of the wireless telegraphy apparatus). This is essentially what we understand by the inertia of gross naatter. We set a body in motion by expending energy on it (the explosion of the powder in a cartridge, which converts potential chemical energy into the kinetic energy of the moving projectile) ; and we can stop a body which is in motion by absorbing this energy of motion (by causing the projectile to strike against a target, when the kinetic energy of its motion becomes the kinetic energy of the heat of the arrested body). Inertia is therefore the same thing whether it be the inertia of visible, material bodies, or the inertia of invisible, material molecules, or the inertia of the immaterial, non-tangible ether. It is the condition that energy-changes must occur if an5rthing accessible to our observation is to change its state of rest or motion. ENERGY Energy is therefore indefinable. It is an elemental aspect of our experience. Nature to us is an aggregate of particles in motion. We have; to speak of massive particles, whether we call these visible material bodies, or molecules, or atoms, or electrons, in order that we may describe nature. We must employ the fiction of a substantia physica. We only know the substance or matter in terms of energy ; it is really the latter that is known to us. It is the poverty of our language, or rather it is the legacy of a materialistic age, that compels us to speak of par- ticles that move, rather than of motions as entities in themselves. Considering, then, the idea of particles in motion as a fiction necessary for clear description, we can study APPENDIX 35r energy. There is only one kind, or form, of energy which presents itself to our aided or unaided intuitions, that is kinetic energy. Bodies that move possess this energy represented by their motion : they can be made to do work, that is, their energy can be transformed into other forms of energy. All things are in motion. A gas consists of molecules incessantly moving with high velocity, and colliding and rebounding from each other. The energy of a gas is the sum of one-half of the masses of all the molecules, multiplied by the squares of the velocities of all the molecules, that is, tlmv^. This is also the kinetic energy of a projectile, or of a planet revolving round the sun. Kinetic energy is that of the uniform, unchanging motion of some entity possessing mass, but we must extend our notion of mass so as to include immaterial, imponderable entities such as electrons. This energy cannot be destroyed or created — ^the law of conservation of energy. This is a principle or mode of our thought. We are unable scientifically or philosophically to think of an entity ceasing to be. Dreams and phantoms show us entities which are real while they last, but which cease to exist. If we do attempt to think of entities that appear from, or dis- appear into, nothing, we surrender the notion of reality. The more we think of it the more clearly we shall see that the things which we call real are the things which are conserved. Yet energy, to our immediate intuitions, seems to disappear. A flying bullet strikes against a target and becomes flattened out into a motionless piece of lead. A red-hot piece of iron cools down to the temperature of its surroundings. A golf-ball driven up the side of a hill comes to rest in the grass. A current of electricity passing through water is used up, that is, electricity 358 THE PHILOSOPHY OF BIOLOGY of a higher potential is required to force the current through water than to force it through thick copper^wire. In all these cases we might think that energy is lost, but we cannot believe this. The kinetic energy of the flying bullet becomes transformed into the increase of the kinetic energy of the molecules of the metal of which the bullet was composed ; for the latter becomes greatly heated when its fUght is arrested ; and this increased heat ought to be equal to the kinetic energy of the bullet in flight. The red-hot piece of iron cools, and the kinetic energy of its molecules becomes less and less, but this does not cease to exist, for the energy is simply transferred by radiation and conduction to the sur- rounding bodies, the temperature of which it raises. The golf-ball driven up the hill comes to rest and loses its kinetic energy. Some of this has been transferred to the air through which it passes, the latter being heated very slightly ; some of it is expended by friction with the grass over which the ball rolls before coming to rest, and this energy is traceable in heat-effects, or in mechanical effects, but the rest of it apparently ceases to exist. But this would be contradictory to the principle of conservation, and so we say that the lost kinetic energy has become potential. The current of electricity may heat the water through which it passes, and some of the energy which seems to disappear is so to be traced, but the greater fraction is apparently lost. A quantity of free hydrogen and oxygen is, however, generated, and we say that the kinetic energy of the moving electrons has become transformed into the potential chemical energy of the gaseous mixture. POTENTIAL ENERGY Therefore, if energy disappears or appears, we do not say that it is destroyed or is created : we invent APPENDIX 859 potential energies, into which we suppose that the energies- in question have become transformed, in order that we may still think of them as being subject to an a priori principle of conservation. Although a particle of radium continually generates heat, we do not there- fore think of the first principle of energetics as being invalidated, for we suppose that the energy which thus appears was really potential in the atoms of radium. But it was contrary to all our former experience of atoms that they should contain any other energy than that of their own motion, and so the further assumption was made that the atom, at least the atom of the radio- active substance, is really complex, and not simple, as chemical theory demands. It is made up of smaller particles, and possesses a definite structure. In certain circumstances the atom may disintegrate, and the energy which held together its particles, whether these were simpler corpuscles or electrons, is given off as the heat which the radio-active substance apparently generates. The potential energy of the chemical atom is therefore a hjrpothesis which has been devised in order to preserve the validity of the law of conservation, and the reality of this hypothesis is being tested by investigation. If we accept it as true, are the deduc- tions made from it justified in our experience ? That is the test which must be satisfied in all the hypotheses where potential energies are invented, and the potentials are only real if the test is satisfactory. The golf ball at rest at the top of the hill is a different entity from the golf ball at rest at the bottom of the hill : it is capable of developing energy, for a touch may cause it to roll down the hill, when most of the energy which was expended in order to drive it to the top of the hill will reappear in the form of the kinetic energy of motion of the ball. The atoms of hydrogen and oxygen which 360 THE PHILOSOPHY OF BIOLOGY were dissociated by the energy of the electric current are different things from the atoms of hydrogen and oxygen which are combined together to form the mole- cules of water. Their state when the gases are in the elementary condition, or are " free," is that of mole- cules moving rapidly and incessantly, rebounding from each other after colliding with each other : they possess energy of position — ^potential energy — ^because they are separate from each other. If they " combine," as when a minute electric spark explodes the mixture of gases, they tractate together, and remain in proximity to each other, becoming molecules of water. The energy which became potential in the gaseous mixture, when the electric energy of the current seemed to disappear, now appears as the heat generated by the combustion, that is, as the greatly increased kinetic energy of the mole- cules of the gas (steam) which takes the place of the mixture of hydrogen and oxygen. Previous to the explosion this gas was a mixture of molecules of hydrogen and oxygen (2H2+2O) at the ordinary temperature, but after the explosion it consists of a smaller number of molecules at a very much higher temperature. What is " energy of position " ? The golf ball at the bottom of the hill was at a distance of R feet from the centre of the earth, but at the top of the hill it is at a distance of R+100 feet from the centre of the earth. In the first case it was free to fall R feet, but in the second case it is free to fall R+100 feet. The atoms of the constituent molecules of water occupy the position H - O - H, the bonds ( - ) indicating that the atoms are very close together; but when the water is decomposed by an electric current, the atoms occupy the positions O- 0-l-H - H+H- H, the (+) indicating that the atoms are relatively APPENDIX 361 far apart from each other. Now the golf ball and the earth, or the atoms of hydrogen and oxygen, are physically the same material entities, whether they are close together or far apart, yet when the earth and the ball, or the atoms of oxygen and hydrogen, are separated from each other, their " pro- perties " are different from what they are when they are close together. What is it that makes the difference ? It is that which is between them. Is it, in the last case, " the potential energy of chemical affinity " ? This dreadful phrase is actually used in a recent book on biology : "In the elements carbon and oxygen, so long as they remain separate, a certain amount of energy remains latent. When the carbon and oxygen atoms are allowed to come together and unite, this potential energy of chemical affinity is liberated as kinetic energy." What is changed by the tractation and pellation (the terms suggested by Soddy in place of the anthropomorphic ones, "attraction" and " re- pulsion ") ? It is the ether which has become changed in some way. Potential energy resides therefore in the ether of space. ISOTHERMAL AND ADIABATIC CHANGES Let us consider the changes which occur in a gas under the influence of changes in temperature and pressure, premising that the remarks which we have to make can be applied to bodies in the liquid and solid conditions, with some necessary modifications. A gas, then, consists of a very great number of particles, or molecules, in motion. These molecules move in straight lines at very high velocities, and if the envelope in which the gas is contained is a restricted one, the molecules collide with each other, and with the walls 362 THE PHILOSOPHY OF BIOLOGY of the envelope ; and, being assumed perfectly elastic, they rebound from each other, and from the walls of the vessel, with the same velocity which they had when they collided. The pressure of the gas (say that of steam at a temperature of iio° C, and a pressure of 120 lbs. to the square inch in a steam boiler) is the sum of the impacts of the molecules on the waUs of the containing vessel. When the temperature is high the molecules are moving at a higher mean velocity than when the temperature is lower, and their mean free path tends to become greater. The volume of a certain mass of gas, that is, the volume occupied by a certain very great number of molecules, is greater the higher is the temperature, provided the envelope is one capable of jdeldingl^ If we reduce the capacity of the envelope in which the gas is contained, the pressure will rise, for the intrinsic energy of the gas is still the same ; but we have done work on it, and by the law of conservation this work, or at least the energy represented by it, must still exist. It is represented by the decreased length of free path of the molecules, and this means that the impacts on the walls of the vessel will be greater than they were. There is, therefore, a certain relation between the volume of a gas and its pressure, and this relation can be represented by an equation involving the temperature, the pressure, and the volume. The diagram represents the pressure and the volume of a gas when these things change. There are two Fig. 29. APPENDIX 36a conditions, (i) when the heat developed by the com- pression is allowed to escape through the walls of the vessel to the outside, or when the heat lost in the ex- pansion of the gas is compensated by the conduction of heat through the walls of the vessel from outside ; and (2) when the heat developed is retained in the gas, as when the latter is contained in a vessel the walls of which do not conduct heat. The pressure of the gas is measured along the horizontal axis, and the volume is measured along the vertical axis, and a curve is drawn so that for any value of the pressure there is a cor- responding value of the volume. Thus the values of the pressures p and pi in the diagram correspond to the value of the volume v. The curve relating the change of pressure with a corresponding change of volume is, in general, that called a rectangular h5rperbola. But there are two kinds of such curves : (i) that which we obtain by plotting the corresponding values of pressure andi^olume, when the temperature of the gas remains constant throughout the series of changes, that is, when Hhe rise of temperature which would occur when the gas is compressed is compensated by the conduction of this heat to the outside of the vessel containing the gas. Such a series of changes of pres- sure and volume is called an isothermal one. (2) When the heat developed by the compression of the gas is retained in the gas, as when the walls of the vessel in which these changes are effected are such as do not conduct heat : such a series of changes is called an adiabatic one. Adiabatic curves are steeper than are isothermal ones. THE CARNOT ENGINE This is an imaginary mechanism which performs a certain cycle of operations. It does not really exist,. 364 THE PHILOSOPHY OF BIOLOGY but the conception of its operation is of the greatest value in the consideration of energy-trans- formations, and it is for this reason that we discuss it here. Consider a gas, or some other substance capable of expanding or contracting. It contains intrinsic energy, and it is capable of doing work. Thus, since a gas can expand indefinitely it can be made to do mechanical work. A mass of gas at a pressure pi, and having a volume v^, and at a temperature T°, can do work by expanding till its pressure is reduced to po y.0 p, and its volume y \ increased to v. If \ Y it expands adia- \f^ b^tically its tem- ^\^^^ perature will fall i _ ""^^^^^^Si^o^^ o P°se that t° is the r ^f; ——f temperature of 1 1 P the surrounding Fig. 3o. ' medium : the gas cannot therefore cool further, and we can obtain no more work from it. If the gas is the substance which we wish to employ as the working substance in the Carnot engine, we must therefore bring it back to the condition repre- sented by A . That is, we must raise its temperature to T°, we must reduce its volume to Vi, and we must increase its pressure to pi. Thus the steam of an engine is (say) at a temperature of 110° C, and a pressure of 120 lbs. to the square inch. When it has passed through the cylinder and condenser it is water at a temperature of, say, 15° C, and it is at atmospheric pressure. We must, therefore, bring it back to its former condition by heating this water in APPENDIX 865 the boiler till it is steam under the former conditions of temperature and pressure. Therefore we must, in order to obtain a self-acting engine, cause the working substance, and the mechanism of the engine, to perform a series of cyclical operations. The Camot engine is a cylinder containing a gas called the working substance S, and this gas can be brought into thermal contact with a source of heat, or a refrigerator, that is, the gas can be heated or cooled by a mechanism outside itself. The walls of the cylinder are made of some substance which is a perfect non-conductor of heat, but the bottom of the cylinder is made of a substance which con- ducts heat perfectly. There is a piston in the cylinder which fits it closely, but which moves up and down without friction. At the bottom of the latter is a valve which can be turned so as to place the bottom of the cylinder, and therefore the gas, in thermal contact with a reservoir of heat (4-), or a refrigerator (-). But when the valve is turned so that the non-con- ducting part fills the bottom, the gas is perfectly insulated, and heat can neither enter nor leave it. Such an engine is, of course, an imaginary one, since there can be no mechanism in which there is not a certain amount of friction between moving parts, and there are no substances which conduct or insulate heat perfectly. The engine is, in fact, the limit to a series of engines each of which is supposed to be more perfect than the last one. It is a fiction which is of considerable use in theoretical work. Fig. 31. 366 THE PHILOSOPHY OF BIOLOGY THE CARNOT POSITIVE CYCLE We have therefore a substance which can be heated by contact with a hot body, and which can then expand, doing mechanical work by raising a piston, and perhaps turning a flywheel, and on which work is then done so that it returns to its original condition. This is a cycle of operations. If we consider only the changes which occur in the working substance we can represent these changes by a diagram. Qg uni'h oF I h&cLt enter Q, units /■ of heat lecLfe IncreoLSinff uolume. Fig. 32. First operation, (i->2). We suppose that the valve is turned so that the non-conducting plug closes the cylinder. The piston is in the position II (Fig. 31). Heat cannot then enter or leave the gas. But the latter already contains heat : it is at a temperature of r,°, so that it can expand doing work. Let it expand, forcing up the piston. During this operation the pressure of the gas will fall from a point on the vertical axis opposite i to a point opposite 2, and its volume will increase from a point on the horizontal axis beneath i to a point beneath 2. It will cool because it has expanded, and no heat is allowed to APPENDIX 367 enter it during this act of expansion. The expansion is therefore adiabatic ; the temperature falls from Ta° to Ti° ; and work is done by the gas. Second operation, (2-^3). The piston is now at the position I, that is, at the upper end of its stroke, and we must bring it back again to the lower end of the cylinder. The valve is turned so that the bottom of the cylinder is placed in thermal communication with the refrigerator ( - ) , and the piston is pushed in to the position II. The gas is therefore compressed until its volume decreases from a point beneath 2 to a point beneath 3. As it is being compressed, heat is generated and its temperature would rise, but as this heat is generated it flows into the refrigerator, so that the temperature of the gas remains the same during the operation. The contraction is therefore an isothermal one ; the temperature remains at Ti° ; and work is done on the gas from outside. Third operation, (3^4). But the piston is not at the lower end of its stroke yet. We turn the valve so that the bottom of the cylinder is closed by the non-conducting plug 0, and then push in the piston until it reaches the position III. The gas is still further compressed, and this compression generates heat. But the heat cannot escape, so that the tempera- ture of the gas rises until it reaches T^". The con- traction is therefore an adiabatic one. Work is done on the gas. Fourth operation, (4-;?-i). The piston is now at the lower end of its stroke. We turn the valve so that the bottom of the cylinder is placed in communication with the source of heat {+). The gas expands from the point beneath 4 to the point beneath i, raising the piston to the position II. This expansion of the gas would lower its temperature, but it is in com- 368 THE PHILOSOPHY OF BIOLOGY munication with the source of heat, and so it does not cool, but draws heat from the source and remains at a constant temperature, T^^- The expansion is there- fore an isothermal one. Work is done by the gas. This completes the cycle. But the gas is heated, and when the piston is at position II, the valve is turned so as to close the cylinder by the non-conduct- ing plug 0. The heat already contained in the gas continues to expand, the latter doing more work, but this expansion causes the temperature to fall from T° to T°. This is the operation with which the cycle commenced. Summarising the positive Carnot cycle, we see that the engine takes heat from a source (-I-) and gives up part of this to a refrigerator ( - ), (in an actual steam- engine heat is taken from the boiler and given up to the condenser water). If we measure the quantity of heat taken from the boiler in the steam which enters the cylinders we shall find that this quantity of heat is greater than the quantity which is given up to the condenser water. What becomes of the balance ? It is converted into the mechanical work of the engine. The Carnot engine therefore takes a quantity of heat, Q^, from the source and gives up another quantity of heat, Qu to the refrigerator. We find that Q^ is greater than Qu and the balance, Q^ - Qi is represented by the work done by the engine. Heat-energy falls from a state of high, to a state of low potential, and is partly transformed into mechanical work. THE CARNOT NEGATIVE CYCLE This is simply the positive cycle reversed. The reader should puzzle it out for himself if he is not already familiar with it. It consists of an adiabatic APPENDIX 369 contraction 2->i, an isothermal contraction i->4, an adiabatic expansion 4->3, and an isothermal expansion 3-^2. A quantity of heat, Qi, is taken from the refrig- erator at a temperature Ti°, and another quantity, Q2, is given up to the source at a temperature T^". But Qi is greater than Qi, and the engine therefore gives up more heat than it receives, while, further, heat flows from a body at a low temperature to another body at a higher temperature. Where does the engine get this energy from ? It gets it because work is done iipon it by means of an outside agency, and all of this work is converted into heat. REVERSIBILITY The Camot engine and cycle are therefore perfectly reversible. Not only can the engine turn heat into work, but it can turn work into heat. This perfect, quantitative reversibility is, however, a property of the imaginary mechanism only, and it does not exist in any actual engine. ENTROPY Let us consider the cycle more closely. In the operation 4->i, which is an isothermal expansion, there is a flow of heat-energy from the source and a trans- formation of energy into work. The gas in the con- dition represented by the point 4 had a certain pressure and a certain volume . In the condition represented by the point i, its pressure has decreased, its volume has increased, and its temperature is the same. Its physical condition has been changed, and to bring it back into its former condition something must be done to it. Let, then, the gas continue to expand without receiving any more heat, or parting with any : that is, let it 2a 370 THE PHILOSOPHY OF BIOLOGY undergo the adiabatic expansion 1^2 until its tem- perature falls to that of the refrigerator, T°. We now compress the gas while keeping it at this temperature, that is, we cause it to undergo the isothermal con- traction 2^3, during which operation it is giving up heat to the refrigerator, so that there is again a flow of heat-energy. We then compress it still further without allowing heat to escape from it, that is, we cause it to undergo the adiabatic contraction 3^4. During this operation the gas rises in temperature to Ti°. It is now in the condition that it was when the cycle commenced. In this cycle of operations heat first entered, and then left the gas, and with this entrance or rejection of heat, the condition of the gas with respect to its power of doing work changed. We investigate this flow of heat, and the concomitant change of properties of the substance, with regard to which the flow took place, by forming the concept called entropy. We make the convention that when heat enters a substance the entropy of the latter increases, and when heat leaves it its entropy decreases. We call the quantity of heat entering or leaving a substance Q, and the temperature of the substance T. Then ^ is pro- portional to the change of entropy of the substance when the quantity of heat, Q, enters or leaves it. Now it is a fact of our experience that heat can only flow, of itself, from a hotter to a colder body. Consider two such bodies forming an isolated system, the temperature of the hotter one being T^ , and that of the colder one Ti°. Let Q units of heat flow from the body at J/ to that at TC no work being done. Then the loss of entropy of the hotter body is ^, and J- 2 APPENDIX 371 the gain of entropy of the colder body is ^,. The -1 1 nett change of entropy of the system is ^--9^. Since 7^° is greater than T-,°, ^, is less than $-, . There- fore the expression ^<, - ^„ is positive, that is, the entropy of the system, as a whole, has increased. When heat flows from a hotter to a colder body the nett entropy of the two bodies, therefore, in- creases. But we can also cause heat to flow from a colder to a hotter body hy effecting a compensatory energy-trans- formation. Such a compensation would not occur hy itself in any system capable of effecting an energy- transformation, if it is to be effected some external agency must act on the transforming system. We can suppose it to happen in a perfectly reversible imaginary mechanism. Suppose a Camot engine works in the positive direction, taking heat from a reservoir at temperature T^ , and giving up part of this heat to a refrigerator at Ti , and doing a certain amount of work W. Suppose that this work is stored lip, so to speak, say by raising a heavy weight, which can then fall and actuate the same Camot engine in the opposite (negative) direction. The engine then exactly reverses its former series of operations. The work it did is reconverted into heat, and as much of this heat flows from the refrigerator into the source, that is, from a colder to a hotter body, in the negative operations, as flowed from the soui^ce to the refrigerator in the positive operations. In this primary energy-transfor- mation, combined with a compensatory energy-trans- formation, there is no change of entropy. The 372 THE PHILOSOPHY OF BIOLOGY mechanism is an ideal one— the limit to an irreversible mechanism. But — and now we appeal to experience and cease to work with ideal mechanisms — the actual engine which we can design and work is one in which there will be friction, in which some parts will conduct heat im- perfectly, and other parts will insulate heat imperfectly. Let the friction generate q units of heat, and let the quantity of heat which is " wasted " by imperfect conduction and insulation be q^. This heat will flow into the refrigerator, or will be radiated or conducted to the surrounding medium, which we suppose to be at the same temperature as the refrigerator. If, then, we divide this total quantity of heat by the temperature T°, we get 2;if-'=5i as the quantity of entropy which is generated as the result of the imperfections of the engine, in addition to the quantity of entropy, 5, which would be generated if the engine were a perfect one. Both S and Si are positive. Also in the working of the engine in the negative direction a certain quantity of entropy, Sj, is generated for reasons similar to those mentioned above. The entropy generated when the engine works in the positive direction is therefore S+Si, and when it works negatively the quantity generated is also Si. The entropy destroyed when the engine works negatively is S. The total change of entropy is therefore 2S1+S - S, that is, 2S1. In an actual energy-transformation combined with a compensatory energy-transformation there is therefore an increase of entropy. We can generalise these statements so that they will apply not only to a heat-engine but to all mechan- isms which effect energy-transformations. In all such APPENDIX 373 transformations entropy is generated. Therefore the Entropy of the Universe tends to a maximum. AVAILABLE AND UNAVAILABLE ENERGY Consider the Carnot engine as a perfect mechanism. It takes heat-energy from a source at a temperature Ta°, and it gives up heat to a refrigerator at a tempera- ture T°, T^° being greater than T°. In the adiabatic expansion 1-^2 the gas continues to expand until its temperature becomes equal to that of the refrigerator. It cannot, then, expand and do work any longer, and thus the proportion of the heat, Q^, received from the source, which can be converted into work, depends on the difference of temperature Ti° - T°. The greater is this difference the greater will be the proportion of the heat-energy received which can be converted into work. If the engine were a J)erfect one, and if the gas were also a perfect one (that is a gas which would continue to expand according to the equation for the adiabatic expansion of gases), and if the refrigerator were absolutely cold, then all the heat energy received from the source could be converted into work. We cannot produce a refrigerator of absolute tem- perature 0°, and therefore only a certain proportion of the heat which is received by the engine can be transformed into mechanical work. But this work can be used to reverse the action of the engine, and thus the same fraction of the total heat-energy which was given to the refrigerator can be taken from it and given back to the source. The perfect engine is there- fore reversible without loss of available energy. Now consider still the engine as a mechanism which takes heat from a source and gives it to a refrigerator, but let it be an actual engine. Instead of giving up 874 THE PHILOSOPHY OF BIOLOGY a certain fraction of the heat received to the refriger- at or — a fraction equal to Qi ^, it gives up rather more, because it is not a perfect mechanism, that is, it generates friction, etc. Some of the heat received thus ceases to be available for the performance of work; and passes into the refrigerator. The fraction of the heat-energy which passes into the refrigerator in the perfectly reversible engine was unavailable energy in the conditions in which the mechanism worked, or was imagined to work, but in the actual engine this fraction is increased. If we divide the increase of unavailable energy by the temperature of the refrigerator, the product is the increase of entropy generated in the actual engine over that generated in the ideal engine. Because of this reduction of available energy the actual engine is an irreversible mechanism. This is the connection between unavailable energy and entropy. In all transformations some fraction of the transforming energy becomes heat, and this heat flows by conduction and radiation into the sur- rounding bodies. In general this heat simply raises the temperature of the medium into which it flows, and becomes unavailable for further transformations. With every transformation that occurs some part of the energy involved becomes unavailable. Therefore although the sum of the available and unavailable energy of the Universe remains constant, the fraction of unavailable energy tends continually to a maximum. INERT MATTER We can see now what is indicated by Bergson's inert matter." It is not matter deprived of energy APPENDIX 375 — such an expression has no meaning — it is energy which is unavailable for further transformations. The matter in which we choose to say that this energy is inherent has become inert. Let us substitute for the Carnot engine the actual steam-engine of a ship, the condenser of which is cooled by the sea water which is taken in, and which is then heated and flows out again into the sea. The heat derived from the source, that is, from the furnace of the boiler where coal is burned to raise steam, thus passes out into the sea. Now the heat capacity of the sea is so great that the temperature of the water is not appreciably raised by this heat, which drains into it from the engine : even if it were appreciably raised, the heat would be conducted into the earth, or would be radiated out into space, and would then raise the temperature of the material bodies of the universe. But let all this heat remain in the sea. It then simply raises the temperature of the water by an exceedingly small amount, and the motions of the molecules become in- finitesimally increased. But the heat becomes equally distributed by conduction and convection throughout the mass of the water in the sea, and as there are no differences in adjacent parts there are no means where- by the energy which thus passes into the sea can be again transformed. A new order of things is the result of the processes we have indicated. The segregated, available heat- energy of material bodies has become transferred to the un-co-ordinated, diffuse, unavailable energies of the molecules which compose these bodies. The transformations which we can effect depend on the condition that the energy which we utilise is that of aggregates of molecules which are in a different physical condition, as regards this energy, from adjacent aggre- 876 THE PHILOSOPHY OF BIOLOGY gates. But when this energy becomes equally dis- tributed among the molecules of all the aggregates, the matter in which it inheres becomes inert. If we could, by a sorting process like that of Maxwell's hypothetical demons, a process which does not expend the energy with which it deals, separate the molecules which were moving slowly from those which were moving more quickly, we could make this energy again available. But it must clearly be understood that our physics is the physics not of individual mole- cules, but of aggregates of molecules. INDEX Absolute, Driesch's theory of, 47. Acceleration (in physics), 355. Acquired characters induced by the environment, 216 ; a means of transformism, 230 evidence of transmission scanty, 225 ; transmission not inconceivable, 226. Actions, categories of, and consciousness, 282 ; deliberative, 283 ; mechanistic hypothesis of, 157 ; stereotyped, 283 ; at a distance, 304, Activation of the ovum, 176. Adaptability, indicative of dominance, 258. Adaptation, 217 ; and acquired characters, 219 ; and changes of morphology and function, 219 ; not inherited, 220; causes of, 239. Adaptive response, 219. Adiabatic changes, 361. Aggregates, molecular, 353. Algae, distribution of, 260. Allelomorphs, Mendelian, 231. Alternation of generations, 175. Amido-substances, 88 Anabolism, 88. Anatomical parts, homologies of, 251. Animal action, considered objectively, 278. Animal and plant contrasted, 269 Animality, 269. Annectant forms of life, 253. Annelids, morphology of, 248. Anthropomorphism in theories of action, 148. Anti -enzymes, 94. Antitoxins, 36. Ants, a dominant group, 260. Appendix vermiformis, 250. Approximation, standards of, 347. Armoured animals, 263. Arthropods, morphology of, 249 ; a dominant group, 259 ; distribution, 260 ; musculature of, 275 ; adapta- tions for mobility, 275 ; limits to size of, 275. Assimilation, 67. Atoms, constitution of, 355 ; arrangements of, 353. 377 378 THE PHILOSOPHY OF BIOLOGY Automatism of animals deduced from mechanistic theories, 280. Autonomy in development, 322. Available energy, 62 ; and entropy, 374. Bacteria, a dominant group, 259 ; distribution, 259 ; geological history, 259, 261 ; morphology, 268 ; metabolism, 266 ; specialisation, 263 ; parasitism, 259 ; nitrogen, 73 ; prototrophic, 119, 266; paratrophic, 266 ; putrefactive, 266; fermenta- tion, 266 ; and Brownian movements, 119 ; compensatory to plants, 267. Bergson, 28 ; creative evolution, 244 ; duration, 154 ; animals and plants, 78 ; eye of Pecten, 234 ; inert matter, 375 ; infinitesimal analysis of the organism, III; kinematographic analysis, no; theory of intellectuahsm, 51; memory, 156 ; morphological themes, 250 ; theory of pain, 281 ; theory of perception, 7, 10 ; the vital impetus, 318. Biology, systematic, 201, 203. Biophors, 132 ; size of, 183 ; growth of, 185. Biotic energy, 325. Borelli and animal mechanism, 125. Brownian movement, ii8 ; significance of, 119. Bryan and thermodynamics, 62. Bud-formation, 165. Calculus, infinitesimal, 25, 115, 350. Calorimetric experiments, 65, 68. Capacity-energy factors, 61. Carnot's cycle, 69, 78, 113 ; negative, 368 ; description of, 363, 366 ; compared with plant meta- bolism, 75 ; compared with the organism, 73. Catalysis, 90 ; universality of, 91. Catalysts, characters of, 91. Categories of organisms, 209. Central nervous system, specialisation of, 273 ; a switchboard, 273 ; evolution of, parallel with evolution of muscular system, 281. Chance in evolution, 237. Chemical affinity, 361. Chemical energy, degradation of, 75. Chemical reactions, direction of, 78 ; exothermic, 86 ; explosive, 86 ; similar in organic and inorganic systems, 78. Chemical synthesis, involve vital activity, 318. Chemistry, medieval, 125. INDEX 379 Chlorophyll, 69. Chlorophyllian organisms, 88 ; metabolism of, 265 ; a dominant group, 259 ; essential morphology ot, 268 ; distribution of, 260. Chromatin of the nucleus, 130; the material basis of inheritance, 182. Chromosomes, 130, 182, 183. Classification of organisms, 209. Classificatory systems, are artificial arrangements, 289 ; suggest evolutionary process, 210. Clausius, 54 ; and Camot's Law, 113. Ccelenterates, morphology of, 248. Ccelomate animals, 256. Colloidal platinum, 91. Colloids, 107. Colonial organisms, 164. Comparative anatomy, task of, 251. Compensatory energy-transformations eftected by life, 309. Conjugation, 173 ; and heredity, 176 ; a stimulus to growth, 175. Consciousness involves analysis of the environment, 11 ; analysis of, is an arbitrary process, 12; a feeling of normality, 6 ; a part of crude sensation, 40 ; simplified by reasoning, 41 ; an intensive multiplicity, 303 ; degree of, is parallel to development of sensori-motor system, 280 ; not existent outside ourselves, 278 ; not a function of chemico- physical mechanism, 160 ; intense in difficultly performed operations, 281 ; and activity of cerebral cortex, 281 ; absent in parasites, 291. Conservation a test of reality, 357. Conservation of energy, 52 ; in organisms, 83. Conservation of structure, 253, 256. Constants, mathematicaJ^ 344. Continuity of cells in embryo, 171. Contractility, 100 ; muscular, 103. Co-ordinates, systems of, 23. Corals, 164. Cosmic evolution, 314 ; is a tendency towards degradation of energy, 316. Creation, special, 214. Curvature, 27. Curves, isothermal and adiabatic, 362. Cuttle-fishes, 250. Cytoplasm, 130. 380 THE PHILOSOPHY OF BIOLOGY Darwin, and natural selection, 221 ; acquired characters are inherited, 220 ; hypothesis of pangenesis, 181. Death, is catastrophic katabolism, 340. Degradation of energy, 81. Deliberation and consciousness, 281. Demons, Maxwell's, 116. Descartes and mechanism, 121 ; the rational soul, 123, 318 ; his physiology, 122 ; his spiritualism, 124 ; and animal automatism, 125. Descent, collateral, 257. Determinants in embryology, 132, 183 ; arrangement of, 184 ; latent in regenerative processes, 142. Development, organisation in, 128 ; parthenogenetic, 176 ; reverses inorganic tendencies, 324 ; impossibility of chemical hypotheses, 141 ; is the assumption of a mosaic structure, 301 ; blastula stage in, 129 ; gastrula stage in, 130; pluteus stage in, 140 ; individual, 300. Developmental systems prospective value of, 138 ; prospective potency of, 138. Diatoms, 163 ; distribution of, 260. Differential elements, 1 1 j. Differentiation in development, 170. Diffusion in the animal body, 95. Digestion, 67 ; chemistry of, 72. Dinosaurs, an unsuccessful line of evolution, 275. Dissipation of energy, 114; in physical mechanisms, 59 ; by the organism, 68, 79. Distribution of organisms, 262 ; limits to, 259 ; indicative of dominance, 258. Diversity, physical, 54. effective and ineffective, 115. Dominance in geological time, 258 ; implies long geological history, 261 ; Mendelian, 196. Dominant organisms, 258, 259, 264. Driesch natural selection, 229 ; analytical definition of the organism, 331 ; entelechy, 318; experimental embryology, 134; historical basis of re- acting, 154 ; logical proof of vitalism, 136 ; proof of vitalism firom behaviour, 153 ; theory of the absolute, 47. Duration, 28 ; duration and time illustrated, 30 ; illustrated by immunity, 35 ; more than memory, 155 ; a factor in responding, 155. Ecdysis, 276. INDEX 381 Echinoderms, morphology of, 248. Ectoderm, 177. Effector organs, 158, 271. I^lan vital, 161. Electromagnetism, 355. Electrons, 304, 355. Elimination, natural, 229. Embryological stages compared with physical phases, 308. Embryology, 127 ; hypotheses of, 128; physical hypotheses fail, 128 j experimental, 128; suggests phylogenetjc history, 213. Emulsoids, io8. Endoskeleton, 177, 276. Energetics, first law of, 51; second law of, 113. Energy, 356 ; available and unavailable, 55 ; biotic, 325 ; chemical, 61 ; and causation, 54 ; degradation of, 63 ; dissipation of, S3 ; electrical, 61 ; forms 0^ 325 ; kinetic, 52, 357 ; mechanical, 60, 61 ; potential, 53, 358 ; of posi- tion, 360. Energy-transformations, 54, 371 ; anabolic, 89 ; in the animal, 70 ; compensatory, 88 ; compensatory organic, 268; irreversible, 59 ; in physical mechanisms, 58 ; in the plant, 71. Engelmann, and the artificial muscle, 105. Entelechy, 161, 318 ; not energy, 329 ; is power of direction, 329 ; not spatial but acts into space, 330 ; an intensive manifoldness, 330 ; is arrangement, 323 ; involves regulations, 323 ; arrests inorganic happening, 327 ; initiates chemical happening, 327 ; compared with enzyme action, 327 ; illustrated by analogy, 322. Entropy, 54 ; augmentation of, 75 ; and Carnot engine, 369. Environment, does not select variations, 235 ; made by the organism, 236. Enzymes, 90 ; nature of, 92 ; pancreatic, 93 ; reversible, 93 ; activation of, 92. Enzyme activity, 93. Epigenesis in development, 129. Equilibrium, chemical, 102. false, 86j 151. Ether of space, 46, 304. 361 ; potential energy resides in, 361. Evolution tendencies of, 252, 264, 276, 295 ; separation of tendencies, 296 ; a trans- formation of intensive into extensive manifoldness, 309 ; a dissociation of tendencies originally coalescent, 305 ; increases diversity, 310 ; segregates energy, 311 ; compared with permutations and combinations. 382 THE PHILOSOPHY OF BIOLOGY 301 ; a series of phases in a transforming system, 298 ; a logical hypo- thesis, 214 ; parallel processes in, 234 ; geological time inadequate for 237 ; side paths in, 262 ; mechanistic hypotheses inadequate, 237 ; cosmic, 214, 297, 314 ; of the crust of the earth, 264. Excretory products, 269. Exoskeleton, 276. Exothermic reactions, 86. Experience and duration, 156. Experimental biology proves evolution, 246. Explosive reactions, loi. Extension in space, 18. Extinct groups, 263. Fats, digestion of, 93. Fecundity of animals, 179, 239. Ferments, 92. Fertilisation (in reproduction), 176. Finalism, 216. Fishes, distribution of, 261. Fluctuating variations, 200. Food-stuffs, absorption of, 89. Force, 354. Form, accidental and essential, 167, 353 ; geological, 168 ; crystalline, 168. Frequency distributions, 22, 187, 350. Frog, development of egg of, 131. Functionality, 343 ; in physical systems, 307. Galvanotropism, 145. Gases, compression of, 362 ; kinetic theory of, 117, 361. Gastrea-theory, 177 ; illustrated, 255 ; limitations of, 256. Genera, stability of, 186. Geometry, Cartesian, 25 ; Euclidean, 19, 25 ; perceptual and conceptual limits, 21. Geotropism, 144. Germ-cells, 175 ; and soma, 179. Germinal selection, 241. Germ-layers, 177 ; theory of, 256. Germ-plasm, a mixture, 240 ; stability of, 240. Givenness, 47. Gonads, 179 INDEX 383 Growth law of, in the organism, 172; by accretion, 169; by ecdysis, 276; geometrical, 169 ; physical, 167 ; of crystals, 167 ; and difierentiation, 170; variability of, 172. Haeckel, the Gastrea-Theorie, 177, 254. Harmonic analysis, 11. Harvey, and the circulation of the blood, Heat, flow of, 117 ; production of, in physical changes, 1 14. Heliotropism, 144.. Heredity, 181. Hertzian waves, 355. Homoiothermic animals, 67. Hormones, 225. Human activity, tends to arrest dissipation of energy, 312. Huxley, 84 ; and mechanistic biology, 127 ; and the physical basis of life, 113 ; and mechanism, 106; and universal mathematics, 215. Hybrids, Mendelian, 196 ; infertility of, 195 ; between Linnean species, 194. Hydra, regeneration of, 162. Idants, 183. Idealism founded on pure reasoning, 45 ; of Berkeley, 45. Ids, 183. Immunity, 35. Individual, 162 ; definition of, 167. Individuality, orders of, 163 ; physical concept of, 165 ; morphologically an artificial concept, 166 ; in societies, 171. Inertia, 354- Infinity, a definition of, 342. Inorganic happening abolishes diversity, 310. Instinct, a problem for naturalists, 283 ; an inheritable adaptation of behaviour, 287. Instinct and intelligence, 283 ; distinction not absolute, 294 ; may coexist, 306. Instinct and functioning, 286. Instinctive actions not necessarily unconscious, 283 ; not learned, 286 ; not necessarily perfect, 284 ; effective from the first, 285 ; capable of improvement, 285. Intelligent actions, non-inheritable adaptations of behaviour, 287 ; involve deliberation, 50, 287 ; involve conscious relations with the environment, 288 ; involve use of tools, 284. 384 THE PHILOSOPHY OF BIOLOGY Intensity-factors, 6l. Intensive multiplicity, 303. Irreversibility, 62. Irritability, 100. Isothermal changes, 361. James, William (and academic philosophies), 80. Jennings, and physiological states, 154 ; behaviour of Protozoa, 293 ; animal movements, 149 ; the avoiding reaction, 149. Katabolism, 90. Kinases, 92. Kinematographic analysis, 316. Lamarck, hypotheses of evolution, 220. Lamarckian inheritance, an inadequate cause of transformism, 227. Lankester, acquired characters not inherited, 221. Laplace, and universal mathematics, 215. Laplacian mind, 299. Larval stages, 170. Latency (of characters), 195. Lavoisier, and. chemistry of the organism, 127. Life and adaptation to physical conditions, 338 ; and reversibility, 339 ; a direction of energies, 341 ; defined energetically, 337 ; cosmic origin of, 338 ; physical conditions for, 338 ; limited in power, 306 ; sparsity of, on the earth, 306 ; tends to arrest dissipation of energy, 314 ; its origin a pseudo-problem, 337. Life-substance, the primitive, 301. Locomotion, 258. Loeb and the associative memory, 155; and artificial parthenogenesis, 176 ; mechanism and life, 127 ; stereo- tropism, 19 ; theory of tropisms, 144 ; tropistic movements, 146 ; theories of heredity, 181. Limit, the mathematical, 346. Limits to perceptual activity, 23. Links, missing, 252. Linnean species, 201. Manifoldness, intensive, 302. Mass, 353. Mass action, 140. Materialism, 85. Mathematics, evades consideration of time, 35. Matter, 353 ; inert, 375 ; notion of is an intuitive one, 352. Maxwell, and sorting demons, 116, 377. INDEX 385 Mayow, and chemical physiology, 126. Mechanical work, done by the animal, 67 ; not done by the plant, 71. Mechanism, organic and inorganic, 78 ; the thermodynamic, 66 ; radical, 215 ; in life, 121. Membranes, semi-permeable, 95. Memory, 39 ; a possible cerebral mechanism of, 158 ; mechanistic hypotheses impossible, 157. Mendelism, 196 ; a logical hypothesis, 199 ; terminology is a symbolism, 198 ; analogy of unit characters with chemical radicles, 197 ; transmission of characters of, 230. Mesoderm, 177 ; origin of, 255. Metabolism, 37, 88, 209 ; analytic, 269 ; of animals, 65, 67 ; constructive, 269 ; destructive, 269 ; direction of, 69 ; in green plant, 70, 75 ; intra-cdlular, 99 ; integration of its activities, 11 1 ; r61e of oxygen in, 105; specialisation of during evolution, 305 ; synthetic, 269. Metaphysics of science, 45. Metazoan animals, 162. Mitosis, 182. Mobility, organic, 269 ; structural adapta:tions tending to, 275. Modifications of structure adaptive and non-adaptive, 251. Molecules, 353; size of, 116 ; in a gas, 115 ; aggregations of, 108. Molluscs, morphology of, 249. Morgan, and physico-chemical mechanisms, 128, 143. Morphogenesis, 257. Morphological evolution, tendencies of, 295. Morphological structures degeneration of, 251 ; suppression of, 250 ; coalescence of, 250 ; replace- ment of, 250 ; specialisation of, 250 ; change of function of, 251. Morphology, 209 ; a basis of classification, 210; relates groups of organisms, 211 ; dis- tinctions of, not absolute, 285, 290 ; generalised, 250 ; suggests blood relationships, 213 ; schemata of, 249, 291 ; cannot be considered apart from physiology, 285. Mosaic-theory of development, 131. Motion not an intellectual concept, 27 ; not considered in Euclidean or Cartesian geometry, 26 ; bodily motion is absolute, 24 ; outside ourselves is relative, 24. Motor-habits, 38, 155. Multicellular organisms, evolution of, 223. 2b 386 THE PHILOSOPHY OF BIOLOGY Muscular contraction, 104 ; metabolism in, 104 ; heat production in, 104. Muscular and nervous organs, 275. Musculature and weight of body, 275. Mutations, 189 ; essential nature of, 193; causes of, 200 j must be co-ordinated, 231; physical model of, 192 ; the material for selection, 230. Nageli, and autonomy in development, 160. Natural selection, 228 ; generality of, 229 ; a slow process, 230. Nebula, 315. Nebular hypothesis, 296. Nerve impulses, 100 ; velocity of, loi ; integration of, 273. Nervous system, 272 ; in co-ordination of activities, 171 ; paths in, 157. Nervous activity, 107 ; metabolism in, 107 ; electric changes in, 107 ; influence of metabolism on, 97. Nothing, a pseudo-idea, 18. Nucleus, evolution of, 222. division of, 130, 182. Ontogenetic stages, 255. Orders of individuality, 171. Organism, definition of, 331 ; analysis of its activities, 109 ; animal and plant, 76 ; considered energet- ically, 77; the dominant, 258; a function of the environment, 216; a mechanism, 5 1 ; the primitive, 222 ; a physico-chemical system, 65 ; a thermodynamic mechanism, 104. Organic chemical syntheses, 317. Organisation in development, 137. Organ-rudiments, 257. Osmosis, 95, 99. Ostracoderms, 291. Ostwald on catalysis, 91. Ovum, development of, 129; maturation of, 198, 239 ; an intensive manifoldness, 302 Oxidases, 105. Oxygen in metabolism, 69. Pain, Bergson on, 281. Palaeontology, 210 ; relates groups of organisms, 211. INDEX 387 Pangenesis, i8i. Paramoecium, division of, 173, 175 ; responses of, 4. Parasitism, 259 ; tends to immobility, 290. Parthenogenesis, 176 ; artificial, 176. Particles, 356. Pecten, eye of, 233. Perception not merely physical stimulation, 7 ; involves effector activity, 7 ; involves deliberative action, 9 ; arises from acting, 50 ; and choice of response, 155; is unfamiliar cerebral activity, 8 ; skeletonises conscious- ness, 40. Peridinians, 77, 163 ; distribution of, 260. Personal equation, 45. Personality, 167 ; an intuition, 1^7 ; division of, 173 ; is absolute, 48. Pfliiger, and experimental embryology, 131. Phases in physical systems and organic systems, 321 ; in transforming systems, 308. Phenomenalism, 46. Photosynthesis, 70, 76, 86. Phototaxis, 144. Phyla animal, 247 ; morphology of, 247 ; relations between, 252 ; ancestries of, 252. Phylogenies, 253 ; are summaries of morphological results, 254 ; indicative of directions of evolution, 254 ; criteria of, 253. Phylogeny, 246. Phylum, 210. Physical basis of life, 84. Physico-chemical reactions, 80 ; are directed, 118; the means of development and behaviour in the organism, 160. Physico-psychical parallelism, 160. Physics, a statistical sciencej 116, 377. Physiology Galenic, 122 ; an analysis of organic activity, 120, 328. Plants, geological history of, 261 ; characterised by immobility, 277 ; contrasted with animals, 277. Platonic ideas, 204. Platyhelminths, morphology of, 248. Poikilothermic animals, 68. Poincar6, and Brownian movement, 1 19. 388 THE PHILOSOPHY OF BIOLOGY Polar bodies, 198. Polyzoa, 164. Porifera, 248. Potential, 61. Potential energy, 58, 114. Preformation an embryological hypothesis, 128. Probability, 350. Proteids, digestion of, 90. Proto-forms, 254. Protoplasm, nature of, 106 ; artificial, 10&; disintegration of, 107; activities of, 107; similar in plant and animal, 294. Protozoa, 247 ; behaviour of, 293. Pterodactyls, 274. Races (in specific groups), 194. Radiation, 355 ; of sun, 51 ; transformation of energy of, 57. Radio-activity, 56, 359. Reality, objective, 43. Reception, 3 ; organs of, 271 ; by specialised sense-organs, 11. Recessiveness, Mendelian, ig6. Reflex action, 4, 272 ; concatenated, 150; a complex series of actions, 6; not necessarily accompanied by perception, 155; the basis of instincts, 150; a schematic description, 5 ; in decapitated frog, 6 ; frictionless cerebral activity, 8 ; involves a limited part of the environment, 50. Reflex arcs, 272. Regeneration, 142 ; in Hydra, 164 ; in sea-urchin embryo, 164 ; in Planaria, 164. Regression, 189. Reinke, and structure of protoplasm, 106. Reintegration in development, 171. Rejuvenescence, 175. Releasing agencies, 157. Reproduction, 167; asexual, 175 ; by brood-formation, 173 ; by conjugation, 173 ; sexual, 174; by division, 172; compared with minting machine, 242; of the tissues, 180. Responses of organisms, 217 ; directed, 269 ; of magnet, 279 ; of green plant, 279. Reversibility, physical, 369. Rodewald, chemical nature of protoplasm, 106. Roux, experimental embryology, 131 ; development the production of a visible manifoldness, 307. INDEX 389 Saliva, secretion of, 96. Salivary glands, metabolism of, 96. Salivary secretion, not a purely mechanistic process, 112. Sea, not really rich in life, 306. Sea-urchin gastrula, 170. Secretion described mechanistically, 98. Secretion, psychical, 99. Segmentation of the ovum, 129. Selection, natural, 228 ; from fluctuating variations, 189 ; from mutations, igo. Semon, mnemic hypothesis of heredity, 181. Senescence, 175. Sensation, 2 ; analysis of, 13. Sense-receptors and the idea of matter, 352. Sensori-motor system, 270 ; dominant in animals, 271, 273 ; specialisation of, 271, 273 ; essentially the same in all animals, 294 ; absent in plants, 269 ; vestigial in some parasites, Sexuality, 174. Siphonophores, regeneration in, 163. Size of animals, 274. Skeleton of vertebrates, 276 ; of arthropods, 276 ; and mobility, 276. Soddy, and chemical energy, 361. Soma, 179 ; evolution of, 223. Space, form of, 18 ; 3 -dimensional, i8; 3-dimensional space an intuition, 19; 2-dimensional, 19; the form of, depends on modes of activity, 21, 25. Species, are categories of structure, 201 ; comparison with Platonic ideas, 204 ; criteria of, 202 ; elementary, 193 ; are intellectual constructions, 203 ; individuality of, 203 ; Linnean, 201, 289 ; are phases in an evolutionary flux, 206 ; are families in the human sense, 208 ; systematic, 201. Specific organisation, stability of, 186. Stahl, and the phlogistic hypothesis, 126 ; and vitalism, 126. Stimuli, elemental, 151; physico-chemical, 151 ; formative, 176 ; complex auditory, 152 ; integra- tion of, 152; individualised, 152, 270; contractile, 103. Stimulus and response, functionality of, 152. Substantia physica, 46, 355. Surface tension, 105, io6. Suspensoids, 108. Sylvius, the organism a chemical mechanism, 125. 390 THE PHILOSOPHY OF BIOLOGY Symbiosis, "JT. Symbiotic organisms, 88. Synapses, in central nervous system, 158, 272. Synthetic chemistry, 236, 317. System, isolated, 63. Systems in development ,, equipotential, 139; harmonious equipotential, 139; complex equi- ^ potential, 140. ^ Taxis, 144 ; no perception in, 155 Telegraphy, wireless, 355. Temperature of sun, 56 ; of space, 57. Thermodynamics, 51 ; 1st law of, 51 ; 2nd law of, 54, 63, 309, 316; and Maxwell's demons, 118 ; laws of subject to limitations, 115. Thermodynamical mechanism, the organism not a, 6g. Thomson, W., dissipation of energy, 113. Time a series of standard events, 28 ; astronomical, 34 ; time differentials, 34. Tissues, evolution of, 223. Tools, nature of, 285 ; use of must be learned, 2 s ; bodily, 285. Toxins, 36. Transformism, 213. Trematodes, larval stages of, 165. Trial and error, 293 ; in reasoning, 293 ; a hypothesis of animal movements, 1 50. Trigger reactions, 87. Trilobites, an ancient group, 261. Tropisms, 144 ; in plants, 269, 279 ; in moths, 280 ; and natural selection, 147 ; and movements of caterpillars, 146 ; an inadequate basis for a theory of animal movements, 147. Tunicates, suppressed notochord of, 250. Unavailable energy and entropy, 375 ; tendency to increase of, 375. Unicellular organisms, energy-transformations in, 177. Unit-characters, 230. Van't Hoff's law, 218. Variability, 172, 186 ; continuous, 188 ; discontinuous, 188 ; examples of, 187 ; and the en- vironment, 189 ; independent of the environment, 239 ; and growth, 188 ; tendencies of, 235. INDEX 391 Variation, rate of (mathematical), 344 ; in biology, 1 86 ; atavistic, 195 ; direction of, 233; fluctuating, 189; must be co-ordinated, 231 ; mathematical probability of co-ordination of, 233 ; the material for selection, 229 ; origin of, 230 ; selected by the organism, 237 ; cause of, a pseudo-problem, 242 ; arise de novo, 244. Variables (mathematical), 343. Varieties, specific, 194. Vegetable life, 265. Vertebrates, 249 ; adaptations securing mobility, 275 ; ancestry of, 253 ; morphology of, 249 ; a dominant group, 259 ; distribution of, 260. Verworn, and mechanism in life, 127. Vesalius, anatomical school of, 121. Vital activities, integration of, 128; co-ordination of, 171 de Vries and mutations, 191 ; fluctuating variations inherited, 220. Vital force, 318. Van der Waal's equation, 308. Weber's law, 16 ; a quasi-mathematical relation, 17. Weismann, hypothesis of heredity, 182 ; hypothesis of germinal selection, 241 ; hypothesis of development, 132 ; mosaic-theory, 131 ; preformation hypothesis, 133 ; hypothesis of the germ -plasm, continuity of the germ-plasm, 181 ; germinal changes in- conceivable, 224 ; size of biophors, 183 ; origin of life, 339 ; spontaneous generation a logical necessity, 339. Weismannism, a series of logical hypotheses, 320 ; physico-chemical analogies, and subsidiary hypotheses, 223. Whales, an unsuccessful line of evolution, 274. Whitehead, and mathematical reasoning, 347. Wilson, mosaic-theory of development, 139. Yerkes, and behaviour of Crustacea, 293. Zymogens, 92. Zymoids, 94 PKIKTED BY TUIlNBrLL AND SPEAKS, BDINBOBGH