,transcriber's notes3 ,the text of this e-book has mostly been preserved in its original form1 but a number of typographic errors have been corrected silently - they are listed at the end of the book4 ,missing or inconsistent punctuation has been corrected silently in a few places1 but inconsistent hyphenation has not been altered4 ,an index item that lacked a page reference has been remedied1 and an archaic symbol representing the mathematical #8factorial' function has been replaced by the standard exclamation mark 7674 ,footnotes have been numbered and positioned below the relevant paragraphs4 ,the marker for footnote #ca was missing from the original text and has been arbitrarily placed at the end of the relevant paragraph4 ,in this plain text version1 italic text is denoted by underscores4 ,superscripted characters are surrounded by curly brackets preceded by a caret symbol1 e4g4 #baj1 and subscripted characters are surrounded by curly brackets preceded by a downward arrow1 e4g4 ,h4 ,,the ,,philosophy ,,of ,,biology ,,cambridge ,,university ,,press ,london3 ,,fetter ,,lane1 ,e4,c4 ,c4 ,f4 ,,clay1 ,manager ,illustration ,edinburgh3 #ajj ,,princes ,,street ,berlin3 ,a4 ,,asher ,,and ,,co4 ,leipzig3 ,f4 ,a4 ,,brockhaus ,new ,york3 ,g4 ,p4 ,,putnam',s ,,sons ,bombay and ,calcutta3 ,,macmillan ,,and ,,co41 ,,ltd4 ,toronto3 ,j4 ,m4 ,,dent ,,sons1 ,,ltd4 ,tokyo3 ,,the ,,maruzen-,,kabushiki-,,kaisha ,all rights reserved ,,the ,,philosophy ,,of ,,biology ,,by ,,james ,,johnstone1 ,d4,sc4 ,cambridge3 at the ,university ,press #aiad ,,introduction ,it has been suggested that some reference1 of an apologetic nature1 to the title of this book may be desirable1 so ,i wish to point out that it can really be justified4 ,science1 says ,driesch1 is the attempt to describe ,givenness1 and ,philosophy is the attempt to understand it4 ,it is our task1 as investigators of nature1 to describe what seems to us to happen there1 and the knowledge that we so attain--that is1 our perceptions1 thinned out1 so to speak1 modified by our mental organisation1 related to each other1 classified and remembered--constitutes our ,givenness4 ,this is only a description of what seems to us to be nature4 ,but few of us remain content with it1 and the impulse to go beyond our mere descriptions is at times an irresistible one4 ,fettered by our habits of thought1 and by the limitations of sensation1 we seem to look out into the dark and to see only the shadows of things4 ,then we attempt to turn round in order that we might discover what it is that casts the shadows1 and what it is in ourselves that gives shape to them4 ,we seek for the ,reality that we feel is behind the shadows4 ,that is ,philosophy4 ,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 motion4 ,what it described were only motions and transformations1 but it understood these motions and transformations as matter and energy4 ,yet more subtle minds than the great physicists of the beginning of the nineteenth century had already seen that sensation might mislead us4 ,there was something in us that continually changed--that was our consciousness1 and it was all that we knew4 ,if external things did exist they existed only because we thought them4 ,but we ourselves exist1 for we are not only a stream of consciousness that continually changes1 but there is in us a personality1 or identity1 which has remained the same throughout all the vicissitudes of our consciousness4 ,if the things that exist for us exist only because we think them1 and if we also exist1 then we must exist in the thought of an ,absolute ,mind that thinks us4 ,physical ,science1 studying only motions and transformations1 understood that there was something that moved and transformed--this was matter and energy4 ,mental ,science1 studying only thought1 understood that nature was only the thought of an ,universal ,mind4 ,either conclusion was equally valid ,philosophy 7or metaphysics71 and neither could be proved or disproved by the methods of ,science4 ,the speculative game is drawn1 said ,huxley1 let us get to practical work6 ,both ,physics and ,biology did get to work1 with the results that we know4 ,but ,physics advanced far beyond the acquirement of the results that stimulated ,biology to formulate our present hypotheses of evolution and heredity4 ,as its knowledge accumulated1 it began to doubt whether matter and energy1 atoms and molecules1 mass and inertia--all those things which it thought at first were so real--were anything else after all than ways in which our mental organisation dealt with crude sensations4 ,they might1 as ,bergson said later on1 be the moulds into which we pour our perceptions4 ,physics set up a test of ,reality1 the law of the conservation of matter and energy4 ,there are existences which may or may not persist4 ,visions and phantasms and dreams are existences while they last4 ,they are true for the mind in which they occur4 ,but they seem to arise out of nothing1 and to disappear into nothing1 and physical ,science cannot investigate them4 ,they are existences which are not conserved4 ,on the other hand those images which we call moving matter and transforming energy can be investigated by the methods of physics4 ,molecules change1 but something in them1 the atoms1 remain constant4 ,energy becomes transformed1 and it may even seem to cease to exist1 but if it disappears1 then something is changed so that the lost energy can be traced in the nature of the change4 ,matter and energy are conserved and therefore they are the only ,realities4 ,but the test is obviously one that has an a priori basis1 and we may doubt whether it is a test of ,reality4 ,thus ,physics constructed a dynamical ,universe1 that is1 one which consisted of atoms which attracted or repelled each other with forces which were functions of the distances between them4 ,even now this conception of a dynamical1 ,newtonian ,universe is a useful one1 though we recognise that it is only symbolism4 ,but it was not a conception with which ,physics could long remain content4 ,how could atoms separated from each other by empty space act on each other1 that is1 how could a thing act where it was not8 ,there must be something between the atoms4 ,the ,universe could not be a discontinuous one1 and so ,physics invented an ,universe that was full4 ,it was an immaterial1 homogeneous1 imponderable1 continuous ,universe4 ,that which existed behind the appearances of atoms and molecules and energy was the ether of space4 ,it must be admitted that the conception appears to the layman to involve only contradictions3 heterogeneous1 discontinuous1 ponderable atoms are only singularities in a homogeneous1 continuous1 imponderable medium1 or ether4 ,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 energy1 and in spite of ourselves we attempt to think of the new ,reality in terms of the old one4 ,in its attempt to understand all its later results ,physics had therefore to invent a new ,philosophy--that of the ether of space4 ,it is only in our own times that ,biology has become sceptical and has begun to doubt whether its earlier ,philosophy is a sound one4 ,that which it describes--the object-matter of its ,science--is not that which ,physics describes4 ,there are two domains of ,givenness1 the organic and the inorganic4 ,biology1 leaning on ,physics1 studied motions and transformations1 just as ,physics did1 though the motions which it studied were more complex and the transformations more mysterious4 ,but borrowing the methods of investigation of ,physics it borrowed also its ,philosophy1 and so it placed behind its ,givenness the ,reality that ,physics at first postulated and then abandoned4 ,the organism was therefore a material system actuated by energy4 ,the notion1 it should be noted1 is not a deduction from the results of ,biology1 but only from its methods4 ,did ,physiology1 that is1 the ,physiology of the ,schools1 ever really investigate the organism8 ,a muscle-nerve preparation1 an excised kidney through which blood is perfused1 an exposed salivary gland which is stimulated1 even a frog deprived of its cerebral hemispheres--these things are not organisms4 ,they are not permanent centres of action1 autonomous physico-chemical constellations capable of independent existence1 and capable of indefinite growth by dissociation4 ,they are parts of the organism1 which1 having received the impulse of life1 an impulse which soon becomes exhausted1 exhibit for a time some of the phenomena of the organism4 ,what ,physiology did attain in such investigations was an analytical description of some of the activities of the organism4 ,it did not describe life1 but rather the physico-chemical reactions in which life is manifested4 ,the description1 it should be noted1 is all-important for the human race in its effort to acquire mastery over its environment2 and there is no other way in which it may be carried further but by the methods of physical ,science4 ,givenness is one1 though we arbitrarily divide it into the domains of the organic and the inorganic1 and there can be only one way of describing it4 ,that is the mechanistic method4 ,nevertheless all this is only a description1 and our ,philosophy must be the attempt to understand our description4 ,the mechanistic biologist1 in the attempt to identify his ,philosophy with that of a former generation of physicists1 says that he is describing a physico-chemical aggregate--an assemblage of molecules of a high degree of complexity--actuated by energy1 and undergoing transformations4 ,but our scepticism as to the validity of this conclusion is aroused by reflecting on its origin4 ,if it was borrowed from the ,philosophy of a past ,physics1 and if the more penetrating analysis of the ,physics of our own time has made a new ,philosophy desirable1 should not ,biology also revise its understanding of its descriptions8 ,for ,biology has not stood still any more than ,physics1 and the ,physiology of our own day has become different from that of the times when the mechanistic ,philosophy of life took origin4 ,the embryologists and the naturalists of our own generation have studied the whole organism in its normal functioning and behaviour1 and have obtained results which cannot easily be understood as physico-chemical mechanism4 ,life is not the activities of the organism1 but the integration of the activities of the organism1 just as ,reality for ,physics is not the atoms and molecules of gross matter1 but the integration of these in the ether of space4 ,this1 then1 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 investigations4 ,philosophy1 in the academic sense1 we have not considered in relation to the subject-matter of our science1 though there is much in the classic systems that is of absorbing interest1 even to the working investigator of the nineteenth century4 ,the biological education is not1 however1 such as to predispose one towards these studies4 ,the reader will recognise that the point of view1 and the methods of treatment1 adopted in this book are those suggested by ,driesch and ,bergson1 even if no references are given4 ,he may1 perhaps1 appreciate this limitation2 for1 influenced by the modern scientific training1 he may be inclined to regard ,philosophy as ,mark ,twain regarded his ,egyptian mummy3 if he is to have a corpse it might as well be a real fresh one4 ,j4 ,j4 ,,liverpool ,november #aiac ,,contents ,,chapter ,i ,,page ,,the ,,conceptual ,,world #a ,argument4--,the conscious organism is one that acts4 ,its consciousness of an external world is not simply the result of the stimuli made by that world on its organs of sense1 for it becomes fully aware only of those stimuli which result in deliberated bodily activity4 ,this awareness of an outer world on which it acts is the perception of the organism4 ,its consciousness is an intensive multiplicity4 ,this multiplicity is arbitrarily dissociated1 for convenience' sake1 by the mental organisation1 which confers extension and magnitude and succession on those aspects of consciousness which it arbitrarily dissociates from each other4 ,our notion of space is an intuitive one and depends on our modes of bodily exertion4 ,our notions of motion and continuity are also intuitive ones1 and they cannot be represented intellectually1 but we can approximate to them by the methods of the infinitesimal calculus4 ,mathematical time is only a series of standard events which punctuate our duration4 ,duration is the accumulated existence and experience of the organism4 ,we cannot prove intellectually that there is a world external to our consciousness1 but that this world exists is a conviction intuitively held4 ,,chapter ,,ii ,,the ,,organism ,,as ,a ,,mechanism #di ,argument4--,if the organism is a physico-chemical mechanism its activities must conform to the two principles of energetics3 the law of conservation of energy and matter1 and the law of entropy-increase4 ,they conform strictly to the law of conservation4 ,the law of the degradation of energy is true of our experience of inorganic nature1 but we can show that it cannot be universally true4 ,inorganic processes are irreversible ones1 and they proceed in one direction only1 and in them energy is degraded4 ,organic processes1 that is1 the processes carried on in the generalised organism1 are irreversible2 or1 at least1 there is a tendency for them to be carried on without necessary dissipation of energy4 ,,chapter ,,iii ,,the ,,activities ,,of ,,the ,,organism #hc ,argument4--,if the organism is investigated by the methods of physical and chemical science1 nothing but physico-chemical activities can be discovered4 ,this is necessarily the case1 since methods which yield physico-chemical results only are employed4 ,the physiologist makes an analysis of the activities of the organism1 and he reduces these activities to certain categories2 although all attempts completely to describe the functioning of the organism solely in terms of physical and chemical reactions fail4 ,in addition to the reactions which make up the functioning of an organ or organ-system1 there is direction and co-ordination of these reactions4 ,the individual physico-chemical reactions which occur in the functioning of the organism are integrated1 and life is not merely these reactions1 but also their integration4 ,,chapter ,,iv ,,the ,,vital ,,impetus #abj ,argument4--,the notion of the organism as a physico-chemical mechanism is a deduction from the methods of physiology1 and not from its results4 ,the notion of vitalism is a natural or intuitive one4 ,the historic systems of vitalism assumed the existence of a spiritual agency in the organism1 or of a form of energy which was peculiar to the activities of the organism4 ,modern investigation lends no support to either belief4 ,but the study of the organism as a whole1 that is1 the study of developmental processes1 or that of the organism acting as a whole1 afford a logical disproof of pure mechanism4 ,it shows that there cannot be a functionality1 in the mathematical sense1 between the inorganic agencies that affect the whole organism and the behaviour or functioning of the whole organism4 ,mechanism is only suggested in the study of isolated parts of the organism4 ,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 becoming4 ,this is the ,vital ,impetus of ,bergson1 or the ,entelechy of ,driesch4 ,,chapter ,v ,,the ,,individual ,,and ,,the ,,species #afb ,argument4--,the concept of the organic individual is one which is arbitrary1 and is convenient only for purposes of description4 ,life on the earth is integrally one4 ,personality is the intuition of the conscious organism that it is a centre of action1 and that all the rest of the universe is relative to it4 ,the individual organism1 regarded objectively1 is an isolated1 autonomous constellation1 capable of indefinite growth by dissociation1 differentiation1 and re-integration4 ,this growth is reproduction4 ,the dissociated part reproduces the form and manner of functioning of the individual organism from which it has proceeded4 ,the offspring varies from the parent organism1 but it resembles it much more than it varies from it4 ,there are therefore categories of organisms in nature the individuals of which resemble each other more than they resemble the individuals belonging to other categories3 these are the elementary species4 ,hypotheses of heredity are corpuscular ones1 and are based on the physical analogy of molecules and atoms4 ,the concept of the species is a logical one4 ,the organism is a phase in an evolutionary or a developmental flux1 and the idea of the species is attained by arresting this flux4 ,,chapter ,,vi ,,transformism #bjh ,argument4--,a reasoned classification of organisms suggests that a process of evolution has taken place4 ,it suggests logical relation- ships between organisms1 while the results of embryology and palontology suggest chronological relationships4 ,yet this kinship of organisms might only be a logical1 and not a material one4 ,evolution may have occurred somewhere1 but it might be argued that the ideas of species have generated each other in a ,creative ,thought4 ,but transformism may be produced experimentally1 and so science has adopted a mechanistic hypothesis of the nature of the process4 ,transformism of species depends on the occurrence of variations1 but these arise spontaneously and independently of each other1 and they must be co-ordinated4 ,this co-ordination of variations cannot be the work of the environ ment4 ,variations are cumulative1 and they exhibit direction1 and this direction is either an accidental one1 or it is the expression of an impetus or directing agency in the varying organism itself4 ,the problem of the cause of variation is only a pseudo-problem4 ,,chapter ,,vii ,,the ,,meaning ,,of ,,evolution #bde ,argument4--,if we assume the existence of an evolutionary process1 the results of morphology1 embryology1 and palontology ought to enable us to trace the directions followed during this process4 ,but these results are still so uncertain that they indicate only a few main lines of transformism4 ,phylogenetic trees are largely conjectural in matters of detail4 ,evolution has resulted in the establishment of several dominant groups of organisms--the metatrophic bacteria1 the chlorophyllian organisms1 the arthropods1 and the vertebrates4 ,each of these groups displays certain characters of morphology1 energy-transformation1 and behaviour2 and a certain combination of characters is concentrated in each of the groups4 ,but there is a community of character in all organisms which have arisen during the evolutionary process4 ,the transformation of kinetic into potential energy is characteristic of the chlorophyllian organisms4 ,the utilisation of potential energy1 and its conversion into the kinetic energy of regulated bodily activity1 by means of a sensori-motor system1 is characteristic of the animal4 ,the bacteria carry to the limit the energy-transformations begun in the tissues of the plants and animals4 ,immobility and unconsciousness characterise the plant1 mobility and consciousness the animal4 ,animals indicate two types of actions--intelligent actions and instinctive actions4 ,instinctive activity involves the habitual exercise of modes of action that have been inherited4 ,intelligent activities involve the exercise of modes of action that are not inherited1 but which are acquired by the animal during its own lifetime1 and are the results of perceptions which show the animal that its activity is relative to an outer environment4 ,,chapter ,,viii ,,the ,,organic ,,and ,,the ,,inorganic #bhi ,argument4--,a strictly mechanistic hypothesis of evolution compels us to regard the organic world1 and the inorganic environment with which it interacts1 as a physico-chemical system4 ,all the stages of an evolutionary process must therefore be equally complex3 they are simply phases1 or rearrangements1 of the elements of a transforming system4 ,the physics on which these mechanistic hypotheses were based was that of a discontinuous1 granular1 ,newtonian universe1 that is1 one consisting of discrete particles1 or mass-points1 attracting or repelling each other with forces which are functions of the distances between them4 ,it was a spatially extended system of parts4 ,therefore at all stages in an evolutionary process1 or one of individual development1 the elements of the system constitute an extensive manifoldness1 and the obligation of mechanistic hypotheses of evolution and development to accept this view has shaped modern theories of heredity4 ,life is an intensive manifoldness1 but in individual or racial evolu- tion this intensive manifoldness becomes an extensive manifoldness4 ,life is a bundle of tendencies which can co-exist1 but which cannot all be fully manifested1 in the same material constellation1 therefore these tendencies become dissociated in the evolutionary process4 ,in this dissociation there is direction and co-ordination1 which are the ,vital ,impetus of ,bergson1 or the ,entelechy of ,driesch4 ,entelechy is an elemental agency in nature which we are compelled to postulate because of the failure of mechanism4 ,it is not spirit1 nor a form of energy1 but the direction and co-ordination of energies4 ,there is a sign1 or direction of inorganic happening which absolutely characterises the processes which are capable of analysis by physico-chemical methods of investigation1 and the result of this direction of inorganic happening is material inertia4 ,yet this direction cannot be universal3 it must be evaded somewhere in the universe4 ,it is evaded by the organism4 ,the problem of the nature of life is only a pseudo-problem4 ,,appendix ,,mathematical ,,and ,,physical ,,notions #cdb ,infinity and the notion of the limit4 ,functionality4 ,frequency distributions and probability4 ,matter1 force1 mass1 and inertia4 ,energy-transformations4 ,isothermal and adiabetic transformations4 ,the ,carnot engine and cycle4 ,entropy4 ,inert matter4 ,,index #cgg ,,the ,,philosophy ,,of ,,biology ,,chapter ,i ,,the ,,conceptual ,,world ,let us suppose that we are walking along a street in a busy town2 that we are familiar with it1 and all the things that are usually to be seen in it1 so that our attention is not likely to be arrested by anything unusual2 and let us further suppose that we are thinking about something interesting but not intellectually difficult4 ,in these circumstances all the sights of the town1 and all the turmoil of the traffic fail to impress us1 though we are1 in a vague sort of way1 conscious of it all4 ,electric trams approach and recede with a grinding noise2 a taxicab passes and we hear the throb of the engine and the hooting of the horn1 and smell the burnt oil2 a hansom comes down the street and we hear the rhythmic tread of the horse's feet and the jingle of the bells2 we pass a florist's shop and become aware of the colour of the flowers and of their odour2 in a caf a band is playing 8ragtime40 ,there are policemen1 hawkers1 idlers1 ladies with gaily coloured dresses and hats1 newsboys1 a crowd of people of many characteristics4 ,it is all a flux of experience of which we are generally conscious without analysis or attention1 and it is a flux which is never for a moment quite the same1 for everything in it melts and flows into everything else4 ,the noise of the tram-cars is incessant1 but now and then it becomes louder2 the music of the orchestra steals imperceptibly on our ears and as imperceptibly fades away2 the smell of the flowers lingers after we pass the shop1 and we do not notice just when we cease to be conscious of it2 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 consciousness1 and this changes from moment to moment without gap or discontinuity4 ,it is not a condition of 8pure sensation10 but it is as nearly such as we can experience in our adult intellectual life4 ,it is easy to discover that many things must have occurred in the street which did not affect our full consciousness4 ,we may learn afterwards that we have passed several friends without recognising them2 we may read in the newspapers about things that happened that we might have seen1 but which we did not see2 we may think we know the street fairly well1 but we find that we have difficulty in recalling the names of three contiguous shops in it2 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 see4 ,why is it1 then1 that so much that might have been perceived by us was not really perceived8 ,we cannot doubt that everything that came into the visual fields of our eyes must have affected the terminations of the optic nerves in the retinas2 the complex disturbances of the air in the street must have set our tympanic membranes in motion2 and all the odoriferous particles inhaled into our nostrils must have stimulated the olfactory mucous membranes4 ,in all these cases the stimulation of the receptor organs must have initiated nervous impulses1 and these must have been propagated along the sensory nerves1 and must have reached the brain1 affecting masses of nerve cells there4 ,nothing in physiology seems to indicate that we can inhibit or repress the activity of the distance sense-receptors1 visual1 auditory1 and olfactory1 with their central connections in the brain2 they must have functioned1 and must have been physically affected by the events that took place outside ourselves1 and yet we were unconscious1 in the fullest sense of this term1 of all this activity4 ,why is it1 then1 that our perception was so much less than the actual physical reception of external stimuli that we must postulate as having occurred8 ,sherlock ,holmes would have said that we really saw and heard all these things although we did not observe them1 but the full explanation involves a much more careful consideration of the phenomena of perception than this saying indicates4 ,there is1 of course1 no doubt that we did see and hear and smell all the things that occurred in the street during our aimless peregrination1 that is1 all the things which so happened that they were capable of affecting our organs of sense4 ,this is true if we mean by seeing and hearing and smelling merely the stimulation of the nerve-endings of the visual1 auditory1 and olfactory organs1 and the conduction into the brain of the nervous impulses so set up4 ,but merely to be stimulated is only a part of the full activity of the brain2 the stimulus transmitted from the receptor organs must result in some kind of bodily activity if it is to affect our stream of consciousness4 ,two main kinds of activity are induced by the stimulation of a receptor organ and a central ganglion1 7#a7 those which we call reflex actions1 and 7#b7 those actions which we recognise as resulting from deliberation4 ,we must now consider what are the processes that are involved in these kinds of neuro-muscular activity4 ,the term 8reflex action0 is one that denotes rather a scheme of sensori-motor activity than anything that actually happens in the animal body2 it is a concept that is useful as a means of analysis of complex phenomena4 ,in a reflex three things happen1 7#a7 the stimulation of a receptor organ and of the nerve connecting this with the brain1 7#b7 the reflection1 or shunting1 of the nervous impulse so initiated from the terminus ad quem of the afferent or sensory nerve1 to the terminus a quo of the efferent or motor nerve1 and 7#c7 the stimulation of some effector organ1 say a motor organ or muscle1 by the nervous impulse so set up4 ,the simplest case1 perhaps1 of a reflex is the rapid closure of the eyelids when something1 say a few drops of water1 is flicked into the face4 ,stated in the way we have stated it the simple reflex does not exist4 ,in the first place1 it is a concept based on the structural analysis of the complex animal where the body is differentiated to form tissues--receptor organs1 nerves1 muscles1 glands1 and so on4 ,but a protozoan animal1 a ,paramcium for instance1 responds to an external stimulus by some kind of bodily activity1 and yet it is a homogeneous1 or nearly homogeneous1 piece of protoplasm1 and this simple protoplasm acts at the same time as receptor organ1 conducting tissue or nerve1 and effector organ4 ,in the higher animal certain parts of the integument are differentiated so as to form visual organs1 and the threshold of these for light stimuli is raised while it is lowered for other kinds of physical stimuli4 ,similarly other parts of the integument are modified for the reception of auditory stimuli1 becoming more susceptible for these but less susceptible for other kinds of stimuli than the adjacent parts of the body4 ,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 protoplasm2 these are the nerves4 ,other parts are modified so that they can contract or secrete the more easily2 these are the muscles and glands4 ,the conception of a reflex action1 as it is usually stated in books on physiology1 therefore includes this idea of the differentiation of the tissues1 but all the processes that are included in the typical reflex are processes which can be carried on by undifferentiated protoplasm4 ,it is also a schematic description that assumes a simplicity that does not really exist4 ,as a rule a reflex is initiated by the stimulation of more than one receptor organ1 and the impulses initiated may thus reach the central nervous system by more than one path4 ,there is no simple shunting of the afferent impulse from the cell in which it terminates into another nerve1 when it becomes an efferent impulse2 but1 instead of this1 the impulse may 8zigzag0 through a maze of paths in the brain or spinal cord connecting together afferent and efferent nerves and ganglia4 ,further1 the final part of the reflex1 the muscular contraction1 is far from being a simple thing1 for usually a series of muscles are stimulated to contract1 each of them at the right time and with the right amount of force1 and every contraction of a muscle is accompanied by the relaxation of the antagonistic muscle4 ,there are muscles which open the eyelids and others which close them1 and the cerebral impulse which causes the levators to contract at the same time causes the depressors to relax4 ,it is quite necessary to remember that the simple reflex is really a process of much complexity and may involve many other parts and structures than those to which we immediately direct our attention4 ,but leaving aside these qualifications we may usefully consider the general characters of the reflex1 regarding it as a common1 automatically performed1 restricted bodily action1 involving receptor organ1 central nervous organ1 and effector organ4 ,there are certain kinds of external stimuli that continually affect our organs of sense1 and there are certain kinds of muscular and glandular activity that occur 8as a matter of course10 when these stimuli fall on our organs of sense4 ,the emanation from onions or the vapour of ammonia causes our eyes to water2 the smell of savoury food causes a flow of saliva2 and anything that approaches the face very rapidly causes us to close the eyes4 ,reflexes are1 in a way1 commonly occurring1 purposeful and useful actions1 and their object is the maintenance of a normal condition of bodily functioning4 ,we dare hardly say that the simple reflex is an unconsciously performed action1 although we are not conscious1 in the fullest sense of the term1 of the reflexes that habitually take place in ourselves4 ,but even in the decapitated frog1 which moves its limbs when a drop of acid is placed on its back1 something1 it has been said1 akin to consciousness may flash out and light up the automatic activity of the spinal cord4 ,we must not think of consciousness as that state of acute mentality which we experience in the performance of some difficult task1 or in some keenly appreciated pleasure1 or in some condition of mental or bodily distress2 it is also that dimly felt condition of normality that accompanies the satisfactory functioning of the parts of the bodily organism4 ,but this dim and obscure feeling of the awareness of our actions is easily inhibited whenever what we call intellectual activity proceeds4 ,much of the stimulation of our receptor organs is of this generally occurring nature1 and we are not aware of it although the stimuli received are such as to induce useful and purposeful bodily activity4 ,in walking along the street we automatically avoid the people1 and the other obstacles that we encounter1 by means of regulated movements of the body and limbs1 but this is activity that has become so habitual and easy that we are hardly aware of it1 and not at all1 perhaps1 of the physical stimuli which induce it4 ,but not only do we receive stimuli which are reflected into bodily actions without our being keenly aware of this reception1 but we also receive stimuli which do not become reflected into bodily activity4 ,it is1 ,bergson suggests1 as if we were to look out into the street through a sheet of glass held perpendicularly to our line of sight2 held in this way we see perfectly all that happens in front of us1 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 receives4 ,this is1 of course1 a physical analogy1 and no comparison of material things with psychical processes can go very far1 but in a way it is more than an analogy4 ,in our indolent absorbed state of mind we do not as a rule see the objects which we are not compelled to avoid1 and which do not1 in any way1 influence our immediate condition of bodily activity4 ,the optical images of all these things are thrown upon our retinas and are1 in some way1 thrown or projected upon the central ganglia1 but there the series of events comes to an end1 for the images are not reflected out towards the periphery of the body as muscular actions4 ,we cannot doubt that this is why we do not perceive all the stimulation of our organs of sense that we are sure that take place4 ,these stimuli pass through us1 as it were1 unless they are reflected out again as actions4 ,in this reflection1 or translation of neutral into muscular activity1 perceptions arise4 ,but even then perception need not arise4 ,it does not1 as a rule1 accompany the automatically performed reflex action1 because the latter is the result of intra-cerebral activities that have become so habitual that they proceed without friction4 ,there are innumerable paths in the brain along which impulses from the receptor organs may pass into the motor ganglia1 but in the habitually performed reflex actions these paths have been worn smooth1 so to speak4 ,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 muscular1 or some other kind of activity4 ,the things that matter in the life of an animal which lives 8according to nature0 are cyclically recurrent events in which1 after a time1 there is nothing new4 ,most of them proceed just as well in the animal deprived of its cerebral hemispheres by operation as in the intact cerebrate animal4 ,in the performance of actions of this kind the organism becomes very much of an automaton4 ,let something unusual happen in the street while we are walking through it--a runaway horse1 or the fall of an overhead 8live0 wire1 for instance1 something that has seldom or never formed part of our experience1 and something that may have an immediate effect on us as living organisms4 ,then perception arises at once because the stimulation of our organs of sense presents us with something which is unfamiliar1 and yet not so unfamiliar that it does not recall from memory1 or from derived experience1 reminiscences of the images of somewhat similar things1 and of the effects of these4 ,the train of events that now proceeds in our central nervous system becomes radically different from that which proceeded in our former1 rather aimless1 series of actions4 ,the stimuli no longer pass easily through the 8lower0 ganglia of the brain1 but flash upwards into the cortical regions1 where they become confronted with the possibility of innumerable alternative paths and connections with all the parts of the body4 ,they waver1 so to speak1 before adopting one or other1 or a combination of these paths2 there is hesitation1 deliberation1 and finally choice of a path1 with the result that a series of muscular organs become inervated and motor actions1 of a type more or less competent to the situation in which we find ourselves1 are set up4 ,in this hesitation and deliberation perception arises4 ,it is when the animal may act in a certain way as the result of a stimulus which is not a continually recurrent one1 but at the same time may refrain from acting1 or may act in one of several different ways1 that perception of external things and their relations arises4 ,that is to say1 we perceive and think because we act4 ,we do not look out on the environment in which we are placed in a speculative kind of way1 merely receiving the images of things1 and classifying and remembering them1 while all the time we are passive in so far as our bodily activities are concerned4 ,if the results of modern physiology teach us anything in an unequivocal way they teach us this--that the organs of activity1 muscles1 glands1 and so on1 and the organs of sense and communication1 are integrally one series of parts1 and that apart from motor activity nervous activity is an aimless kind of thing4 ,it is because we act that we think and disentangle the images of things presented to us by our organs of sense1 and subject all that is in the stream of consciousness to conceptual analysis4#a #a ,all this is1 of course1 the argument of ,bergson's earlier books1 ,matire et ,mmoire and ,donnes immdiates de la ,conscience4 ,that is to say1 in thinking about the flux of consciousness we decompose it into what we regard as its constituent parts1 and we confer upon these parts separate existence in space and time4 ,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 others4 ,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 bells1 the music of the orchestra1 and the throb of the motor car in the impressions transmitted by our auditory organs4 ,it is difficult to see that all these things1 with the multitude of other things which we perceive1 constitute a 8multiplicity in unity10 that is an assemblage of things which are separate things1 but which do not lie alongside each other in space and mutually exclude each other1 but which are all jammed into each other1 so to speak4 ,it is easy to see that we are conscious of a heterogeneity1 and whenever we think of this multitude of things it seems natural that we should separate them from each other4 ,the stream of our consciousness is so complex that we cannot attend to it all at once1 not even to the few things that we have picked out in our example4 ,if we concentrate our attention on any part1 or rather aspect of it1 all the rest ceases to exist1 or rather we agree to ignore it1 and this very concentration of thought upon one part of our experience isolates it from all the rest4 ,to a certain extent the analysis of the complex of sensation is the result of the work of different receptor organs2 certain fields of energy1 which we call light1 radiation1 etc41 affect the nerve-endings in the retina2 chemically active particles in the atmosphere affect the nerve-endings in the olfactory membranes2 and rapidly repeated changes of pressure in the atmosphere 7sound vibrations7 affect the auditory organs in the internal ear1 and so on4 ,but this reception of different stimuli by different receptor organs exists only in the higher animal2 there are no specialised sense organs in a ,paramcium1 for instance1 and the whole periphery of the animal must receive all these different kinds of external stimuli at once4 ,the specialisation of its receptor organs in the higher animal is rather the means whereby the organism becomes more receptive of its environment1 than the means whereby it analyses that environment4 ,this analysis is the work of the consciousness of the animal4 ,illustration3 ,,fig4 #a4 ,suppose that we draw a curve ,,ab freehand with a single undivided sweep of the pencil4 ,by making a certain assumption--that the curve which we drew was one that might be regarded as cyclical1 that is1 might be repeated over and over again--we can subject it to harmonic analysis4 ,we can decompose it into a number of other curves 7,,cd1 ,,ef1 etc471 each of which is a separate 8wave0 rising above and falling below the axis ,,ox in a symmetrical manner4 ,if we draw any vertical line ,,mn cutting these curves1 we shall find that the distance between the axis ,,ox and the main curve ,,ab is always equal to the algebraic sum of the distances between the axis and the other curves4 ,these latter we call the harmonic constituents of the curve ,,ab1 supposing them to 8add up0 so as to form it4 ,but ,,ab was something quite simple and elemental and its constituents cannot be said to have existed in it when we drew it freehand2 it was only by an artifice of practical utility in mathematical computations that we constructed them4 ,it may be1 of course1 that the harmonic constituents of a curve had actual existence apart from the curve itself1 but1 in the case that we take1 they certainly had not4 ,now we must think of our stream of consciousness in much the same way4 ,it is something immediately experienced and elementary2 it is the concomitant1 if we choose so to regard it1 of the external processes that go on outside our bodies4 ,we can investigate it by thinking about it1 and attending to one aspect of it after another1 thus arbitrarily detaching one 8part0 of it from all the rest1 but immediately we do this we rise above the flux of experience into the region of intellectual concepts4 ,we have converted a multiplicity of states of consciousness1 all of which co-exist along with each other1 and in each other1 and which have no spatial existence1 into a multiplicity of states1 visual1 auditory1 olfactory1 etc41 which have become separated from each other and have therefore acquired extension4 ,this dissociation of the flux of experience is the process of conceptual analysis carried out by thought4 ,if we dissociate the stream of consciousness in this way1 breaking it up into states which we choose to regard as separate from each other1 we shall see that of the elements which we thus isolate many are like each other and can be associated4 ,obviously there is a greater resemblance between different smells than between smells and sounds4 ,different musical sounds are more like each other than are sounds1 and feelings of heat and cold4 ,there is a greater likeness between the states of consciousness which arise from the stimulation of the same receptor organ1 than between those that arise from the stimulation of different receptors4 ,those differences of sensation accompanying the stimulation of different sense organs we regard as different in kind2 there is absolutely no resemblance between a colour and a sound1 we say1 however much the modern annotator of concert programmes may suggest the analogy4 ,but we say that there may be different degrees of stimulation of the same sense organ1 and that the sensations that we thus receive are of the same kind though they differ in intensity4 ,the whistle of a railway engine becomes louder as the train approaches1 that is to say1 more intense1 and if we study the physical conditions that are concomitant with the stimulation of our tympanic membranes we shall see that waves of alternate rarefaction and compression are set up in the atmosphere outside our ears4 ,all the time that the train approaches the frequency of these waves remains the same1 that is1 just as many occur in a second when the train is distant as when it is near4 ,but the amplitude of the waves has been increasing1 and the velocity with which the molecules of air strike against the tympanic membranes becomes greater the nearer is the source of sound4 ,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 same4 ,the amplitude is represented by the straight vertical lines1 #aa1 #bb1 #cc1 etc41 which are of increasing magnitude4 ,thus we represent the physical cause of the increasing loudness of the sound by space-magnitudes1 and then we transfer these magnitudes to the states of consciousness concomitant with the vibrating molecules of air4 ,suppose that we knew nothing at all about the cause of the differences of pitch of musical sounds and that we listen to the notes of the octave1 ,c1 ,d1 ,e1----,c1 sounded by an organ2 all that we should experience would be that the sounds were different4 ,if we were to sing the notes we might attain the intuition that the notes ,g1 ,a1 ,b were 8higher0 than the notes ,c1 ,d1 ,e1 because a greater effort was required in order to produce these sounds1 but obviously this is a different thing from saying that the notes themselves were 8higher0 or 8lower40 ,but let us match the notes by striking tuning-forks1 and then having selected forks which give the notes of the octave let us fix them so that they will make a tracing1 while still vibrating1 on a revolving strip of paper4 ,we shall then find that the fork emitting the note ,c makes 7say7 #bef vibrations per second1 the fork ,d #i_/h #bef vibrations1 the fork ,e #e_/d #bef vibrations1 and so on4 ,thus we associate the notes of the octave together and we say that their quality was the same but that their pitch differed1 and since the pitch depends on the frequency of vibration of the fork1 or of the air in its vicinity1 we say that pitch differences are quantitative ones1 and that the states of consciousness which accompany these physical events are also quantitatively different4 ,illustration3 ,,fig4 #b4 ,so also with colour4 ,if we had no such apparatus as prisms or diffraction gratings1 which enable us to find what is the wave length of light1 should we have any idea of the spectral hues1 red1 yellow1 orange1 green1 etc41 as differing from each other quantitatively8 ,it is certain that we should not4 ,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 space1 and that the frequency of vibration of light which we call red is less than that which we call orange1 while the frequency of vibration of orange light is less again than that of blue light1 and so on4 ,to our consciousness red1 orange1 yellow1 and blue light are absolutely different1 but we disregard this intuition and we say that our perceptions of light are similar in kind but differ1 in some of them are more intense than are some others4 ,again1 have we any intuitive knowledge of increasing temperature8 ,if we dip our hands into ice-cold water the sensation is one of pain1 if the water has a temperature of #e ,c4 it feels cold1 if it is at #ae ,c4 we have no particular appreciation of temperature1 if at #be ,c4 it feels very warm1 if it is at #fj it is very hot1 and if it is at #ij we are probably scalded and the feeling is again one of pain4 ,if we place a thermometer in the water we notice that each sensation in turn is associated with a progressive lengthening of the mercury thread1 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 stage4 ,we say1 then1 that our different perceptions were those of heat of different degrees of intensity1 so transferring to the perceptions themselves the notions of space-magnitudes acquired by a study of the expansion of the mercury in the thermometer1 or by the adoption of the physical theory of the kinetic structure of the water4 ,yet it is quite certain that what we experienced were quite different things or conditions1 cold1 warmth1 heat1 and pain1 and indeed1 in this series of perceptions different receptor organs are involved4 ,suppose we listen to the note emitted by a syren which is sounding with slowly increasing loudness but with a pitch which remains constant4 ,we do not notice at first that the sound is becoming louder1 but after a little time we do notice a difference4 ,let us call the amplitude of vibration of the air when the syren first sounds ,e1 and then1 when we notice a difference1 let us call the amplitude ,e ,e1 ,e being the increment of amplitude4 ,let us call our sensation when the syren first sounds ,s1 and our sensations when the sound has become louder ,s ,s1 ,s being the 8increment of sensation40 ,then the relation holds3-- ,e_/,e constant4 ,that is to say1 the louder is the sound the greater must be the increase of loudness before we notice a difference4 ,let us assume now that the successive sensations of loudness that we receive as the syren blows louder and louder are1 each of them1 just the same amount louder than the preceding sound2 that is to say1 let us assume that what we experience are 8minimal perceptible differences0 of sensation--that they are 8elements of loudness0--thus we construct a series of sounds each of which differs from that preceding it by an elemental increment of loudness4 ,now things that cannot be further decomposed are necessarily equal to each other2 if1 for instance1 the atoms represent the ultimate units into which we break up the matter called oxygen1 then these atoms are all equal to each other4 ,therefore the increments of loudness are equal to each other4 ,illustration3 ,,fig4 #c4 ,if we plot these equal increments of loudness as the dependent variable ,s in a graph1 and the amplitude of the vibrations of the atmosphere as the independent variable ,e1 we can obtain the following curve4 ,if we investigate this we shall find that a certain relation exists between the 8values0 of the sensation and the values of the stimuli that correspond to them2 a regular increase in the loudness of the sensation corresponds to a regular increase in the logarithms of the strength of the stimuli4 ,let ,s the sensation1 ,e the stimulus1 and ,c and ,q constants2 then ,s ,c log7,e_/,q72 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 sensations1 but this relation depends on the assumption that what we call 8minimal perceptible differences0 of sensation are numerical differences that are equal to each other1 and this is1 of course1 an assumption that cannot possibly be proved4 ,thus we decompose our stream of consciousness into a series of quantitatively different and qualitatively different things1 upon each of which we confer independent existence4 ,we attribute to these different aspects of our consciousness extension1 but the extension is due only to our analysis2 for the qualities of pitch1 loudness1 colour1 odour1 etc41 which we disentangle from each other1 did not exist apart from each other1 any more than do the sine and cosine curves into which we decompose an arbitrarily drawn curved line4 ,the multiplicity of our consciousness is intensive1 like the multiplicity that we see to exist in the abstract number ten4 ,this number stands for a group of things1 but its multiplicity is intensive and only exists because we are able to subdivide anything in thought to an indefinite extent4 ,now1 so far we have only separated what we agree to regard as the elemental parts of our general perception of the environment1 but it is to be noted that we have not given to these elements anything like spatial extension4 ,we may1 if we like1 regard our intuition of space as that of an indefinitely large1 homogeneous1 empty medium which surrounds us and in which we may1 in imagination1 place things4 ,so regarded it is difficult to see in what way our notion of space differs from our idea of 8nothing10 a pseudo-idea incapable of analysis1 except into the idea of something which might be somewhere else4 ,the more we think about it the more we shall become convinced that space1 that is the 8form0 of space1 represents our actual or potential modes of motion1 that is1 our powers of exertional activity4 ,space1 we say1 has three dimensions2 in all our analysis of the universe1 and of the activities that we can perceive in it1 this idea of movement in three dimensions1 forward and backward1 up and down1 and right and left1 occurs2 and we have to recognise that in it there is something fundamental1 as fundamental as the intuitive knowledge that we possess of the direction of right and left4 ,it is because we can move in such a way that any of our motions1 no matter how complex1 can be resolved into the components of backward and forward1 right and left1 and up and down1 these directions all being at right angles to each other1 that we speak of our movements as three-dimensional ones4 ,our geometry is founded1 therefore1 on concepts derived from our modes of activity2 and there is nothing in the universe1 apart from our own activity1 that makes this the only geometry possible to us4 ,euclidean geometry does not depend on the constitution of the external universe1 but on the nature of the organism itself4 ,there is a little ,infusorian which lives1 in its adult phase1 on the surface of the spherical ova of fishes4 ,these ova float freely in sea water1 and the ,infusorian crawls on their surfaces1 moving about by means of ciliary appendages4 ,it does not swim about in the water1 but adheres closely to the surface of the ovum on which it lives4 ,let us suppose that it is an intelligent animal and that it is able to construct a geometry of its own2 if so1 this geometry would be very different from our own4 ,it would be a two-dimensional geometry1 for the animal can move backward and forward1 and right and left1 but not up and down2 it is a stereotropic organism1 as ,jacques ,loeb would say1 that is1 it is compelled by its organisation to apply its body closely to the surface on which it lives4 ,but its two-dimensional geometry would1 on this account1 be different from ours4 ,our straight lines are really the directions in which we move from one point to another point in such a way as to involve the least exertion2 they are the shortest distances between two points1 and if we deviate from them we exert a greater degree of activity than if we had moved along them4 ,for us there is only one straight line that can be drawn between two points1 but this is not necessarily true for our ,infusorian1 and its straight line need not be the shortest distance between two points4 ,it might be either the longest or the shortest distance between the points1 for the latter can always be placed on a great circle passing through the two points and the poles of the egg1 and in moving from a point on which it is placed the animal could reach the other point by moving in two directions1 just as we could go round the earth along the equator by moving to the east or to the west4 ,therefore the straight line of the ,infusorian would be not only a scalar quantity but a vector quantity1 that is1 it would represent1 not only a quantity of energy1 but a quantity of energy that has direction4 ,for us only one straight line can be drawn between two given points1 but this limitation would not exist in the two-dimensional geometry of a curved surface4 ,suppose that the two points are situated on a great circle and that they are exactly #ahj apart2 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 direction1 but all of which were of the same length2 that is to say1 in this geometry an infinite number of straight lines can be drawn between the same two points4 ,again1 its triangles might be different from ours2 our triangles are figures formed by drawing straight lines between three points1 and on a plane surface the sum of the angles of the triangle are together equal to two right angles1 though on a curved surface they may be greater or less than two right angles4 ,but our ,infusorian could not imagine a triangle in which the sum of the angles was not greater than two right angles1 for all its figures would be drawn on a convex surface4 ,our three-dimensional geometry depends1 therefore1 on our modes of activity and the concepts with which it operates2 points1 straight lines1 etc4 are conceptual limits to those modes of activity4 ,we can imagine a straight line only as a direction along which we can move without deviating to the right or the left1 or up or down4 ,but even if we draw such a line on paper with a fine pencil the trace would still have some width1 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 paper4 ,we might make a very small mark on the paper1 but no matter how small this mark is it would still have some magnitude2 otherwise we should be unable to see it4 ,if the straight line had no width and the point no magnitude they would have no perceptual existence4 ,our perceptual triangles are not figures1 the angles of which are necessarily equal to two right angles4 ,if we drive three walking sticks into a field and then measure the angles between them by means of a sextant we shall find that the sum is nearly #ahj1 but in general not that amount4 ,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 angles1 but we should not1 except by 8accident10 obtain exactly this value4 ,we do not1 therefore1 get the 8theoretical0 result1 and we say this is because of the errors of our methods of observation2 but why do we suppose that there is such a theoretical result from which our observations deviate1 if our observations themselves do not in general give this ideal result8 ,we might accumulate a great series of measurements of the angles of our triangle1 and we should then find that these results would tend to group themselves symmetrically round a certain value which would be #ahj4 ,some of the results would be considerably less than the ideal1 and some of them would be considerably more2 but these relatively great deviations would be small in number and most of the results would be a very little less than #ahj or a very little more1 and there would be as many which would be a little less as those that were a little more4 ,we should have formed a 8frequency distribution0#b with its 8mode0 at #ahj4 #b ,see appendix1 p4 #cej4 ,but by 8reasoning0 about the 8properties0 of these lines and triangles in plane two-dimensional space1 we should arrive at the conclusion that the angles of a triangle were equal to #ahj1 and neither more nor less4 ,we should then think of a straight line as still a path along which we move in imagination1 and a path which still has some width4 ,but we imagine the width of the path to become less and less1 so that1 even if we imagine ourselves to become thinner and thinner1 we should be unable to deviate either to the right or left in moving along the path1 because the thinner we make ourselves the thinner becomes also the path4 ,we imagine our intuition of a deviation to the right or left becoming keener and keener1 so that1 no matter how small the deviation we should still be able to appreciate it by the extra exertion which it would involve4 ,we think of a point as a little spot1 and we think of ourselves as being very small indeed1 so that we can move about on this spot4 ,but we can reduce the area of the spot more and more1 until it becomes 8infinitesimally0 small2 and at the same time we think of ourselves as becoming smaller and smaller1 so that we can still move about on the spot4 ,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 it4 ,this means that we substitute conceptual lines and points and triangles for the perceptual ones of our experience1 and then we operate in imagination with these concepts4 ,that is to say1 we carry our modes of exertional activity to their limits1#c in the way which we have tried to indicate above--a process of thought which is the foundation of the reasoning of the infinitesimal calculus4 #c ,see appendix1 p4 #cdf4 ,what we call space1 therefore1 depends on our intuition of bodily exertion4 ,this intuition includes the knowledge that a certain change has occurred as the consequence of the expenditure of a certain amount of bodily energy1 and that1 as the result of this change1 the relation of the rest of the universe to our body has become different4 ,we think of our body as the origin1 or centre1 of a system of co-ordinates3-- ,illustration3 ,,fig4 #d4 ,we imagine three lines at right angles to each other to extend indefinitely out into space1 and we think of ourselves as being situated at the point of intersection of these three straight lines4 ,if anything moves in the universe outside ourselves we can resolve this motion into three components1 each of which is to be measured along one of the axes of our system of co-ordinates4 ,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 changed2 that is1 by supposing that we have changed our position relative to the rest of the universe4 ,therefore motion outside ourselves is not to be distinguished from a contrary motion of our own body--a statement of the 8principle of relativity0--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 thing1 by the absence of the intuition that we have expended a certain quantity of energy in producing the change4 ,conscious motion of our own body is something absolute2 all other motion is relative4 ,so far we have been speaking of our crude bodily motion1 but a very little consideration will show that our knowledge of space attained by scientific measurements depends just as much on our intuition of our bodily activity1 and its direction2 the measurement of a stellar parallax1 or that of the meridian altitude of the sun1 for instance1 by astronomical instruments1 involves bodily exertion1 though of a refined kind4 ,three-dimensional space1 that is our space1 therefore represents the manner of our activity1 just as convex two-dimensional space represents the manner of the activity of the ,infusorian1 and one-dimensional space would represent the manner of activity of an animal which was compelled to live in a tube1 the sides of which it fitted closely1 so that it could move only in one direction--up and down4 ,a parasite1 living attached to some fixed object1 and the movements of which were represented only by the growth of its tissues1 could not form any idea of space2 and the 8higher0 forms of geometry1 that is1 space of four or more dimensions1 present no clear notion to our minds1 even although we regard the operations included in mathematics of this kind as pure symbolism1 because we cannot relate this imaginary space to any form of bodily exertion4 ,geometry1 then1 represents the manner in which our bodily exertion cuts up the homogeneous medium in which we live4 ,motion1 whether it be that of our own body in controlled muscular activity1 or that imaginary motion of the environment which we call giddiness1 or a sensibly perceived motion of some part of the environment1 that is1 a motion which we can compensate by some actual or imaginary change in the position of our own body produced by our own exertion1 is an intuitively felt change1 and is incapable of intellectual representation4 ,it is not clearly conceived either in ancient or in modern geometry4 ,euclidean geometry is1 as we have seen1 based directly on our intuition of bodily exertion1 but it is essentially static in treatment4 ,let it be admitted that we can draw a straight line of any length and in any direction1 and so on2 then we regard these straight lines1 etc41 as motionless1 abstract things1 and we proceed to discuss their relationships4 ,cartesian geometry1 and the methods of the infinitesimal calculus1 do not treat of real motion1 and the concept1 if it is introduced at all1 is introduced illegitimately and surreptitiously4 ,consider what we do when we 8plot a curve40 ,let the latter be a parabola having the equation y #a_/b x4 ,now a parabola is defined as 8the locus of a point which moves1 so that its distance from a fixed point is in a constant relation to its distance from a fixed straight line40 ,how do we construct such a curve8 ,illustration3 ,,fig4 #e4 ,we proceed to fix the positions of a series of points in this way3 there are two straight lines1 ,,ox and ,,oy1 at right angles to each other1 and we measure off certain steps along the line ,,ox2 these steps are ,,ox#je1 ,,ox#a1 ,,ox#ae1 ,,ox#b1 and so on1 the small numerals indicating the distance of each point 7,,ox#je1 etc47 from the origin ,o4 ,we then draw lines perpendicular to the ,x-axis through these points4 ,we have now to calculate one-half of the square of each of these lengths ,,ox#je1 ,,ox#a1 etc41 and then we mark off these calculated lengths along the perpendicular lines4 ,the point ,a1 for instance1 is #a_/b7je7b from the point ,x#je1 ,b is #a_/b7a7b from ,x#a1 and so on4 ,in this way we obtain a series of points1 ,a1 ,b1 ,c1 ,d1 ,e1 etc41 and these are points on the locus of the 8moving0 point4 ,illustration3 ,,fig4 #f4 ,there is nothing at all about motion here4 ,all that we have done is to measure lengths4 ,we have made a kind of counterpoint1 ,x-points against ,y-points1 but we have not even made a curve4 ,we connect the points ,a1 ,b1 ,c1 ,d1 ,e1 etc41 by means of short1 straight lines1 and then we may connect together these short lines1 and1 if we plot a number of intermediate points between those that we have already obtained and join these1 the points may be so close together that they may seem to be indistinguishable from a curve4 ,yet1 no matter how numerous they may be1 they can never be connected together so as to form a curve2 we therefore draw a curved line freehand through them1 and at once1 in so doing1 we abandon our intellectual methods1 for our curve depends on our intuition of continuously changing direction4 ,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 point1 and then by measuring the slope of the tangent4 ,the curve itself we obviously leave out of consideration4 ,we cannot conceive of the point moving along the locus ,,od4 ,we can think of it only as at the places ,o1 ,a1 ,b1 ,c1 ,d1 ,e1 etc41 but we must neglect the intervals ,,oa1 ,,ab1 ,,bc1 ,,cd1 ,,de1 and so on1 or we can divide them into smaller intervals by supposing the point to have occupied the positions f1 g1 i1 j1 between the points ,a and ,b1 for instance4 ,yet1 no matter how many these intervals may be1 we can only think of the point as being at the places ,o1 ,a1 ,b1 ,c1 ,d1 ,e1 or at f1 g1 i1 j1 and so on4 ,we never think of the intervals themselves1 and1 if all we think about is the position of the point1 we do not really think of it as in motion at all4 ,we can see it in motion1 but we cannot form an intellectual concept of its motion4 ,it is not really necessary that we should in the affairs of everyday life1 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 circumvented4 ,but the moving point occupies successively a number of different positions in space4 ,if it is a material point that we observe to move from one place to another1 we perceive that a certain interval of our duration corresponds with the change of position of the point4 ,duration was not used up in the occupancy of the different positions ,o1 ,a1 ,b1 ,c1 ,d1 ,e1 and so on1 nor in that of the occupancy of the indefinitely numerous other positions in which we may place the moving point1 but in the intervals themselves4 ,we have said 8duration0 and not 8time10 using ,bergson's term4 ,by duration and time we understand different things4 ,time is1 for us1 only a series of standard events which punctuate1 so to speak1 our experienced duration4 ,the unit of time is the sidereal day1 that is1 the interval of time between two successive transits of a fixed star across the arbitrary meridian4 ,but if we try to conceptualise this interval we find that we can do so only by breaking it up into smaller intervals1 and this we do by using a pendulum of a certain length which makes a certain number of swings 7#hf1djj7 during the interval between the two transits of the star4 ,thus we obtain a smaller interval of duration and we call this a second of time4 ,but for many purposes this interval is too long1 and we can again sub-divide it by making use of a tuning-fork which makes1 say1 #ajjj complete vibrations in a second2 in this way we obtain still smaller intervals of duration--the sigmata of the physiologists4 ,a sigma1 therefore1 represents the interval between the beginning and end of one complete vibration of a certain kind of tuning-fork2 a second1 that between the beginning and end of one complete swing of a pendulum of a certain length1 placed at certain parts of the earth's surface2 and a day1 that between two successive transits of a fixed star across a selected meridian1 after all the necessary corrections have been made to the observation4 ,these actual occurrences1 the positions of the prongs of the tuning-fork1 or those of the bob of the pendulum1 or those of the fixed star do not involve duration4 ,we consider the meridian of ,greenwich as an imaginary line drawn across the celestial sphere1 and the star as a point of light1 so that the actual transit is1 in the limit1 an occurrence which occupies only an 8infinitesimal0 interval of duration4 ,so also with the pendulum and the tuning-fork2 the positions of these things do not 8use up0 time1 and even if the intervals into which we divide astronomical time are indefinitely numerous no real quantity of duration is taken up by their occurrence4 ,we know that the interval between two successive transits of a fixed star are not really constant1 that is1 the astronomical day is lengthening by an incredibly small part of a second each year1 but how do we know this8 ,it is not that we can feel the increments of duration1 but just that we assume that ,newton's laws of motion are true2 and hence that the tidal friction due to the motions of the earth1 sun1 and moon must retard the period of rotation of the earth so that the intervals between two successive transits of a star must become greater4 ,thus we do not conceptualise the actual intervals of duration of which we are able to mark the end-points2 they are lived by us1 and they are real absolute things independent of our wills4 ,suppose we come in from a long walk1 tired and thirsty1 and ask the maid to get tea ready at once4 ,she puts the kettle on the gas stove and then sits down to read4 ,the water takes1 say1 five minutes to boil4 ,what do we mean by this8 ,this is what we mean3-- ,the pendulum and it has ,the time of the clock now swung and now and so elapses ,time has already on swung ,m times ,m n times ,m #bn times ,p swings ,the water in it is now and now the kettle the kettle at and so boils is at on ,t ,t t ,t #bt #ajj ,tempera- ture ,the volume it is now and now ,it is of mercury in and so the thermo- on meter is ,v ,v v ,v #bv ,w ,what we call time here is only a series of simultaneously occurring events4 ,the standard events are the positions of the hands of the clock on the clock face1 that is1 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 kettle4 ,when this began1 the hands of the clock were at1 say1 #d4cj1 and the temperature of the water was then1 say1 #ag ,c42 and1 when it ended1 the hands of the clock were at #d4ce and the temperature of the water was #ajj ,c4 ,it is only the simultaneities of these events that we have recorded and not the interval of duration that they mark4 ,it does not matter how many times we might have looked at the hands of the clock and the thermometer1 we should still have observed only simultaneities4 ,but we had to wait for the kettle to boil1 and the temperature #ajj was attained after the temperature #ij1 and so on4 ,what does this mean8 ,while we were waiting1 the water seemed to take an intolerably long time to boil4 ,but the maid was reading one of ,mr ,charles ,garvice's novels1 and 8before she knew where she was0 the kettle boiled over4 ,there was a certain interval of duration experienced by her1 and another1 but different1 interval of duration experienced by us4 ,in each case there was a stream of consciousness4 ,we felt fatigue1 thirst1 a lack of satisfaction1 wandering attention1 and irritation--all that was our duration4 ,but the maid was identifying herself with ,lady ,mary1 who had sprained an ankle and was being helped along by the new1 young gamekeeper1 and that was her duration4 ,there need not be any succession of events in the conceptual representation of a physical process4 ,there is1 for instance1 no succession in such a conception as is represented by the following diagram--a conception well worth analysis3-- ,illustration3 ,,fig4 #g4 ,the figure represents a tracing made by a muscle-nerve preparation4 ,a living muscle taken from an animal has been attached to a light lever1 the end of which makes a scratch on a piece of smoked paper4 ,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 paper4 ,but if the muscle is stimulated so that it contracts and then relaxes again the lever is pulled up and is then lowered1 and so its point makes a curve on the paper4 ,the nerve going to the muscle can be stimulated electrically and the moment of the stimulation can be recorded by another lever1 which makes a mark on the paper below the trace made by the lever which is attached to the muscle4 ,two such shocks have been applied to the nerve and they have elicited two contractions of the muscle and these two contractions have fused together4 ,in the actual experiment the operators could see that the muscle moved1 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 shocks4 ,but the extent of motion of the muscle was too small1 and the depressions of the key succeeded each other too rapidly to be easily observed1 and therefore all these events were made to record themselves on the myogram4 ,the series of little notches at the base of the figure represent the movements of the time-lever1 that is1 they are scratches made on the paper by a little lever which moves up and down at a rate fixed beforehand4 ,now when this time lever had made ten notches on the paper the first shock was applied to the nerve1 and at the eleventh the muscle began to contract4 ,at the seventeenth notch the second shock was applied and the muscle continued to contract4 ,at the twenty-fifth notch the muscle ceased to contract and began to relax1 and at the forty-second notch the muscle had ceased to contract4 ,everything now becomes clear and easy to represent mentally2 the time-lever makes #ajj notches on the paper in a second1 so that there was an interval of #j4jg seconds between the two stimuli1 and these two stimuli produced a compound contraction of the muscle lasting for #j4a second4 ,this is what the experimenters might have perceived1 had human unaided senses been sufficiently acute4 ,but they are not1 and so the crude perception of the results of the experiment is replaced by a conception of the train of events involved in the operation4 ,duration and succession disappear and the myogram represents only a series of simultaneous events of this nature2 the first stimulus occurs simultaneously with the tenth movement of the time-lever2 the second stimulus with the seventeenth1 and so on4 ,in seeing the experiment the operators had to wait for one phase to be completed before they could observe another one1 but in reasoning about it all the phases are spread out and are present in the conception at once4 ,the duration was in the operators but not in the experiment3 it was experienced1 but it disappears when the results of the experiment are conceptualised4 ,a succession of events is in ourselves and not in the events observed4 ,if a point is said to move along the locus ,,od through the positions ,a1 ,b1 ,c1 it is we that have the feeling of succession1 and the whole trajectory1 or locus1 or path of the point corresponds with a portion of our duration4 ,the operation of boiling the kettle corresponds with a portion of our duration1 which in its turn corresponds with that part of our duration which was marked by the positions of the hands of the clock4 ,thus we perceive a simultaneity in these two trains of events1 and this enables us to assign a certain period of astronomical time to the operation of raising the temperature of the water1 in the conditions of the experiment1 from #ag ,c4 to #ajj ,c4 ,but there is nothing absolute in this interval of astronomical time3 what is absolute is that certain successions of events always correspond with other successions of events4 ,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 temperature1 and1 no matter how often we repeat this experience1 the same simultaneity is always to be observed4 ,thus what the physicist considers is not intervals of his own duration but series of correspondences--that is1 correspondences of certain standard events with the events which he is studying4 ,in reality time1 in the sense of the astronomer's time1 does not enter into the methods of the mathematical physicist4 ,let us suppose that he is investigating the change that occurs in a material system between the two moments of time t#a and t#b1 these moments being separated from each other by a period of duration that we can feel4 ,let the system be1 say1 the earth and moon2 the first body being supposed to be motionless1 and the second being supposed to have a certain tangential velocity of movement4 ,if the interval t#a to t#b is really an interval of astronomical time1 the problem1 what is the difference of position of the moon owing to the gravitation of the earth1 is incapable of solution1 and even if we reduce the interval of time indefinitely while still supposing that it is a finite interval1 the mathematical difficulty remains4 ,we then replace the finite interval t#a to t#b by the differential dt1 which means that the two phases of the system1 motionless earth and moving moon at the time t#a1 and motionless earth and moving moon at the time t#b1 are separated by an interval of time dt1 which is smaller than any finite interval that we can conceive4 ,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 t#a to t#b has elapsed4 ,thus mathematics1 incapable of dealing with real intervals of time1 evades this difficulty by considering tendencies1 not real occurrences4 ,things that happen in a part of inorganic nature arbitrarily detached from the rest1 and investigated by the methods of mathematical physics1 do not endure4 ,let us suppose that we take some silver and add nitric acid to it3 the metal dissolves4 ,we can then add hydrochloric acid to the solution and precipitate the metal in the form of chloride2 and we can then fuse this chloride with carbonate of soda1 or some other substance1 and so obtain the metal again4 ,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 mass4 ,all the chemical reactions into which it has entered have not affected it in any way2 that is to say1 these reactions have not endured4 ,if we inject a serum1 containing a toxin1 into the blood stream of a susceptible animal1 certain things happen4 ,the animal will become ill1 but1 provided that the amount of serum which has been injected was not too great1 it will recover4 ,if the toxin be again injected a reaction occurs1 but the animal does not become so ill as on the first occasion1 and after a number of injections the dose administered may be so great as to kill a susceptible animal but may yet produce no effect on the animal which is the subject of the process of immunisation3 immunity has been conferred on it4 ,now can we compare the two operations1 that of the solution and precipitation of the metal and that of the immunisation of the animal8 ,we can to some extent1 but the analogy soon fails1 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 involved1 that is to say1 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 organism4 ,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 silver4 ,this antitoxin then neutralises the dose of toxin which may be administered after the process of immunisation has been effected1 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 combine4 ,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 it4#d ,but physiological science has the much more formidable task of explaining the persistence of the immunity4 ,the animal rendered immune to the toxins produced by certain species of bacteria may remain so for many years1 that is1 for a very long time after the antitoxins originally produced by the reaction of the tissues to the toxins first administered have disappeared4 ,we must imagine1 therefore1 that the anti-substances produced originally by the reaction of the toxin are produced again and again by the tissues of the susceptible animal1 for the latter may resist repeated infections1 that is1 repeated doses of toxin1 without illness4 ,but then the tissues of the animal body are transitory substances and they do not persist unchanged4 ,muscles1 glands1 connective tissues1 even nerve-fibres and nerve-cells undergo metabolism1 and the chemical substances of which they are composed break down into the excretory products1 pass out into the blood stream1 and are eliminated from the body2 while at the same time these tissues are continually being renewed from the nutritive substances in the blood and lymph4 ,it is the organisation of the tissues--their form and modes of reaction--that endure1 but the material substances of which they are composed are in a state of continual flux4 ,yet the organisation of these tissues does not persist unchanged1 for it is continually responding to new conditions experienced by it4 ,the reactions that occur when a toxin is administered to a susceptible animal affect the organisation of its tissues in such a way that the latter acquire the capability of producing antitoxins which may--if we like to say so--neutralise the toxins that enter into them when they become infected4 ,the reaction endures4 ,but this is a different thing from saying that the process is a physico-chemical one alone4 #d ,except that1 of course1 the reactions that are supposed to occur are very complex ones4 ,this is what we must understand by the duration of the organism4 ,everything that it experiences for the first time persists in its organisation4 ,it acquires the ability of responding to some stimulus by a definite1 purposeful reaction1 the effect of which is to aid it in its struggle for existence2 and this reaction1 once carried out1 becomes a 8motor habit0 or the basis of a reflex1 or in some other way1 as in the process of immunisation1 remains a part of the modes of functioning of the animal4 ,in our behaviour certain cerebral nerve tracts become laid down and continue to exist throughout life1 modifying all our future experience4 ,our past experience accumulates4 ,there must be direct continuity in our flux of consciousness1 for no perception seems ever to fade absolutely from memory4 ,this continual addition of perceptions to those that already exist makes our consciousness ever become more complex1 so that a perception experienced for the first time is never quite the same when it is again experienced4 ,the first time that we go up and down in an elevator1 or sit on a 8joy-wheel10 or ascend in a balloon or an aeroplane1 or become intoxicated1 constitutes an unique event in our lives1 and we experience a 8new sensation40 ,what the blas man of the world complains of is this accumulation1 or rather persistence1 of his experiences4 ,a repetition of the same stimulus never again begets the same perception4 ,the first hearing of a modern drawing-room song may be enjoyable1 but the next time we hear it we are not interested1 and by-and-bye it becomes very tiresome4 ,the first hearing of a great symphony usually perplexes us1 and we are perhaps repelled by unusual harmonies1 or progressions1 or strange modulations1 but subsequent hearings afford increasing pleasure4 ,we say that there was 8so much in it0 that we did not understand it1 yet precisely the same series of external stimuli affected our auditory membranes on each occasion1 and the same molecular disturbances were transmitted along our afferent nerves to the central nervous system1 where the same physical effects must have been produced4 ,the difference in all these cases between the repetitions of the same stimuli was that the later ones became added to the earlier ones1 so that the state of consciousness produced by1 or which was concomitant with1 these external stimuli was a different state in each case4 ,this is the duration of the intelligently acting animal3 it is not merely memory1 but memory and the accumulation of all its past modes of responding to changes in its environment1 whether these modes of response were conscious ones 7as in the case of an intelligently performed or 8learned0 action71 or unconscious ones 7as1 for instance1 in the case of the acquirement of immunity by an animal which had become able to resist disease74 ,it is not merely the experience of the individual organism1 but also all the experience of those things which were done or experienced by the ancestry of the organism1 and which were transmitted by heredity to the progeny4 ,motor habits are formed1 so that much the same series of muscular actions are carried out when a stimulus formerly experienced is again experienced4 ,pure memory remains1 so that the images of past things and actions somehow persist in our consciousness4 ,physical analogy suggests that these images are inscribed on the substance of the brain or are stored away in some manner2 but1 apart from the incredible difficulty of imagining a mechanism competent for this purpose1 it is obvious that we thus apply to the investigation of our consciousness 7which is an intensive multiplicity71 the concept of extension which can only apply in all its strictness to the things outside ourselves on which we are able to act4 ,all these motor habits1 functional reactions1 and memory images are our duration or accumulated experience4 ,the motor habits and those functional habitual reactions of other parts of the body than the sensori-motor system are the basis of our actions1 but the memory images are1 so to speak1 pressed back into that part of our organisation which does not emerge into consciousness4 ,only so much of them as bear on the situation in which we1 for the moment1 find ourselves and which may therefore influence our actions1 flash out into consciousness4 ,as 8dreamers0 we indulge ourselves in the luxury of becoming conscious of these memory images1 but as 8men of action0 we sternly repress them1 or so much of them as do not assist us in the actions that we are performing4 ,yet it is in the experience of each of us that1 in spite of this continual inhibition1 parts of our memories slip through the barriers of utility and surreptitiously remind us of all that we have been and thought4 99 99 99 99 99 ,thus we simplify the stream of our consciousness4 ,that of which we are conscious at any time is never more than a part of our crude sensation3 we never perceive more than a small part of all that our organs of sense transmit to our central nervous system4 ,but even these chosen perceptions of the external world are so rich1 so chaotic and confused1 that we are unable to attend to them all at once and we therefore 8skeletonise0 the contents of our consciousness4 ,we think about it a bit at a time4 ,it is an unitary thing1 unable to be broken up1 but we look at it from a great number of different points of view1 so to speak2 and then1 fixing our attention on some aspect of it1 we agree to ignore all the rest4 ,we thus detach parts of it from the rest and1 having thus arbitrarily decomposed it1 we call these separate aspects the elements of our perceptions1 and confer upon them separate existence in space and time4 ,we remember and classify things and group together all those that seem to resemble each other4 ,we form genera1 agreeing to ignore all but the most general characteristics of the things which we try to conceptualise4 ,we do not think separately about all the dogs or horses or fishes that we have ever seen1 but we group all these animals into species1 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 consciousness4 ,when we think about a tramcar we do not think about all the separate vehicles that we have seen1 nor about their colours1 nor the advertisements on the boards outside1 nor the people hanging on to the straps inside4 ,just so much of the experience of what is relevant to the purpose of our thought enters into our idea of the tramcar3 it is a conceptual vehicle that we think about4 ,such is the nature of the concepts that form the basis of our reasoning3 they are generalised aspects of our experience of nature1 usually poorer in content than were the actually perceived things1 except when it is necessary that some individual thing seen or otherwise experienced should be investigated or reasoned about4 ,all our descriptions of nature are conceptual schemes4 ,the world of perception1 says ,william ,james1 is too rich to be attended to all at once1 but in conceptualising it we spread it out and make it thinner1 and we mark out boundaries and division lines in it that do not really exist4 ,it is this generalised nature that is the subject matter of our reasoning of pure science2 and it is these concepts that form the matter of all our descriptions4 ,we do not describe nature 8as we see it10 it is our conceptions that we write about4 ,genera and species and varieties do not really exist in the animate world3 all these are logical categories generated by our thought1 concepts that facilitate our descriptions4 ,when an anatomist gives an account of the structure of an animal he does not say what it looks like1 nor as a rule does he content himself by making a photograph of his dissections4 ,for him the animal is a complex of muscles1 skeleton1 nerves1 glands1 and so on1 and in his drawings all these things are given an individuality that they do not really possess4 ,in the living creature there were no such sharply-distinguished organs as a good drawing represents3 all are bound together and are continuous4 ,but for practical convenience in description--that is1 in the long run1 that we may act upon these things1 we isolate from each other aspects that are in reality one unitary whole4 99 99 99 99 99 ,the universe1 that is1 all that is given to us1 presents itself as immediately perceived phenomena which are then conceptually transformed4 ,it is an aggregate of things--gross matter1 particles1 molecules1 atoms1 and electrons4 ,these things have separate existence and shape1 so that each of them lies outside all other things--we apply to them the category of extension4 ,they possess properties--that is1 they are hard1 or heavy1 or hot1 or cold1 or they are coloured1 or they smell1 and so on--we thus apply to them the category of inherence4 ,they are not things that are immutable1 for they change in place1 or are transformed in other ways1 that is1 they are acted upon by energies4 ,but beneath the properties of the things1 or the transformations that they undergo1 we imagine something that has properties and which transforms3 it is not convenient that we speak solely of attributes or transformations as entities in themselves1 for we think of things as having properties and being subject to transformations4 ,thus we apply the category of substance4 ,has this universe that we construct from the data of sensation objective reality8 ,we are led quite naturally by our study of physiology to the notion of idealism4 ,we see that our perception of things1 that is1 our knowledge of the universe1 depends on the integrity of functioning of certain bodily structures1 and upon the condition that in men in general this integrity of functioning is normal1 that is1 common to the great majority of mankind4 ,to say that a thing exists is to say that it is perceived in some way2 that immediately or remotely it affects our state of consciousness4 ,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 nerve1 and that other molecular disturbances are set up in the tissues of the central nervous system4 ,even if we do not see those dark stars that we know to exist1 there are still evidences of their being that in some way affect the instruments of the astronomer and lead to their being perceived4 ,even if we do not actually see the emanations from a radio-active substance1 we can cause these emanations to produce changes in something that we can see4 ,we speak of the star as a minute spot of coloured light4 ,but if we are short-sighted the spot becomes a little flare1 and if we are colour-blind the hue of the star is different from what it is to normal persons4 ,if we put a drop of atropine into one eye and then close the other1 objects appear to lose their distinctness1 but if we close this eye and then open the other1 the original sharpness of vision returns4 ,when we are bilious1 wisps and spots may appear on a sheet of white paper that at other times was blank4 ,if we take an overdose of quinine1 rustlings and singing noises become apparent even in conditions that ought to preclude all sensation of sound4 ,if we have a bad cold1 we do not smell substances which at other times strongly affect our olfactory membranes4 ,when we become intoxicated1 a host of aberrations of sense displace our normal perceptions of things4 ,our perception of the universe1 therefore1 depends on the normal functioning of our organs of sense1 that is1 such modes of functioning as we can describe and communicate to others1 and which are thus common to the majority of other men and women4 ,these perceptions resulting from the normal functioning of the organs of sense constitute givenness1 and we enlarge1 or conceptualise this givenness and call it the subject matter of science4 ,but what is this reality that we say is external to us8 ,it is1 we see1 our inner consciousness4 ,if we walk along a road in the dark we can feel what is the nature of the path on which we tread1 whether stones or gravel1 or sand or grass4 ,but this feeling is obviously not in the soles of our boots1 and neither is it in the skin of the feet1 for we should feel nothing if the afferent nerves in the legs were severed4 ,is it then in the brain8 ,it would appear to be there1 but it disappears if certain tracts in the brain are injured4 ,all that we can say is that the appearance of reality of things outside ourselves is only the ever-changing condition of our consciousness4 ,this is all that we immediately know1 and if we say that there is an universe external to ourselves we thus project outside our own minds what is in them2 and we construct an environment which may or may not exist1 but which we have no right to say does exist4 ,a philosophy based on the science of the organism would appear to be restricted to this idealistic view of the universe4 ,when we come across it for the first time when we are young it appeals to us with all the force of exact reasoning1 and yet it has all the charm of paradox4 ,there is no part of our intuitive knowledge which appears to us to be more certain than this distinction between ourselves and an outer environment3 we know that our conscious ,ego is something different from our body--and we know that outside our body there is something else4 ,yet the idealistic view so appeals to the intellect that we cannot think speculatively about it without1 at times1 almost convincing ourselves of the unreality and shadowiness of all that at other times seems most real and tangible2 and we indulge in these speculations all the more readily because we know that whenever we begin to act1 the intuitively felt body and outer world will return to us with all their original conviction of reality4 ,some such system of idealism must generally characterise a system of philosophy founded on pure reasoning4 ,we cannot but feel that the universe that we construct is one that depends on our perceptions3 it is our perceptions4 ,the essence of a thing is that it is perceived4 ,if there were no mind to perceive it1 would it exist8 ,the universe is our thought1 and we1 that is our thought1 exist only in the ,thought of an absolute ,mind which we call ,god4 ,such is the metaphysics to which the study of sensation led ,berkeley4 ,the metaphysics of science has taken another turn4 ,it is true that men and women see something outside themselves which differs slightly in different individuals--these differences are due to what we call the 8personal equation40 ,the image of the universe seen by some individuals may differ profoundly from the image seen by some others1 or most others2 but a well-marked gap separates these slight individual deviations in the images seen by normal individuals from the large deviations seen by those whose perceptions are what we call pathological ones4 ,the normal universe common to the majority of men and women is an aggregate of molecules in motion4 ,but this is a conclusion with which modern physics has been unable to remain content1 for molecules must be able to act on each other across empty space1 and this is inconceivable4 ,the universe therefore consists of a homogeneous immaterial medium1 the ether of space1 and this is the true substantia physica4 ,molecules and radiation are conditions of the ether1 and for the physicist it is the only reality4 ,the 8materialism0 of our own time is therefore the belief in the existence1 unconditioned by time or anything else1 of the ether1 or physical continuum2 a homogeneous medium1 of which matter and energy1 and the consciousness of the organism1 are only states or conditions4 ,the materialism of the twentieth century1 like the idealism of ,berkeley1 thus finds that there is something outside our own consciousness that possesses absolute existence4 ,to the materialist it is the ether of space1 and to ,berkeley it is the existence of absolute ,mind4 ,but if our desire to avoid metaphysics is a genuine one1 we must reject the notion of the universal ether no less than we must reject the notion of an absolute ,mind1 and we must rest content with pure phenomenalism4 ,for each of us there can be no existence except that which is perceived or conceptualised4 ,there is nothing but our own consciousness2 there cannot even be an ,ego which perceives2 there is only perception4 ,we never do really believe this in spite of our professions of reason4 ,we find on strict self-analysis that we believe that there is an ,ego that perceives and that there are other ,egos that perceive1 and that the universe which our ,ego perceives is also the same universe that other ,egos perceive4 ,if we did not believe that there were other men and women that perceived--other consciousnesses like our own1 all that part of our own behaviour that we call morality would be meaningless4 ,in a philosophy of pure idealism other men and women are only phenomena2 only bodies moving in nature4 ,why1 then1 should these elements of our consciousness influence the rest of our consciousness as if they were men and women like ourselves4 ,all this amounts to saying that while our speculative thought suggests to us that all that exists is our stream of consciousness1 our actions must convince us that there are other thinking individuals like ourselves4#e #e ,the reader may recognise in this argument that of ,driesch's ,three ,windows into the ,absolute4 ,even if we do surrender ourselves to phenomenalism and try to believe that all that exists is our own consciousness1 the fact of our duration would suggest to us that this present consciousness is not all4 ,our reality is not only that which is present in our minds now1 but all that was ever present in our mind4 ,all that we have ever thought and done persists and forms our conscious and unconscious experience4 ,this past of ours is something that is ever being added to1 or becoming incorporated with1 our present state of consciousness2 and if it is something other than that which we now perceive and conceptualise1 it is something that has an existence of its own4 ,we must believe that there is something that we perceive1 and not that we merely perceive4 ,for the phases of our immediate givenness1 that is1 those things which were present in our minds from moment to moment of the past were connected together and had direction1 and this direction was something that could not be influenced by our will1 and may even have been contrary to our will4 ,something that is very hot always cools1 a wheel that is revolving of itself always comes to a stop1 a pendulum ceases to swing1 a stone that is rolling down a hill continues to roll4 ,let us look back at a fire that was going out3 it is now nearly dead2 let us start a pendulum to swing and then go away3 when we come back the pendulum is still swinging but the amplitude of its vibrations is now less than it was2 let us look away from the stone that was falling3 when we look again it is still falling but it is not where it was4 ,in all our givenness1 in all the phenomena that we perceive1 there is something that is determined and unequivocal1 something that goes its own way apart from our consciousness of it4 ,above all1 we have the conviction of absoluteness in our sense of personal identity4 ,we1 that is our ,ego1 are something that endures1 and we can trace no beginning to our identity1 and we have no intuition that it will cease to exist4 ,our ,ego is now the same ,ego that it was in the past1 and round it something has accumulated--the memories of our former perceptions1 and the habits that these have engendered4 ,did our ,ego create this from itself8 ,was it not rather a centre of action which1 residing in an existence other than itself--the absolute which we call the universe--modified that existence and continually acquired new relationships to it8 ,,chapter ,,ii ,,the ,,organism ,,as ,a ,,mechanism ,we propose now to consider the organism purely as a physico-chemical mechanism1 but before doing so it may be useful to summarise the results of the discussions of the last chapter4 ,let us1 for the moment1 cease to regard the organism as a structure--a 8constellation of parts0--and think of it as the physiologist does3 it is a machine2 it is essentially 8something happening40 ,what1 then1 is the object of its activity8 ,whatever else the study of natural history shows us1 it shows us this1 that the immediate object of the activity of the organism is to adapt itself to its surroundings4 ,it must master its environment1 and subdue1 or at least avoid whatever in the latter is inimical4 ,it must avoid accident1 disease1 and death1 it must find food and shelter2 it must seek for those conditions of the environment which are most favourable to its prolonged existence4 ,ultimate aims--the preservation of its race1 ethical ideals--do not concern us in the meantime4 ,the main object of the functioning of the individual organism is that it may dominate its environment1 and obtain mastery over inert matter4 ,consciously or unconsciously it acts towards this end4 ,all those actions which we call reflex1 or automatic1 or instinctive1 have this in common1 that the organism in performing them comes into relation with only a very limited region of its environment4 ,but knowing that region intuitively1 its actions have a completeness that an intelligent action does not exhibit until it has become so habitual as to approach to automatic acting4 ,the relations between the organism and that part of its world on which it acts1 intuitively or instinctively1 is something like that between a key and the lock to which it is fitted3 it opens this lock1 perhaps one or two others which resemble it1 but no more4 ,now just because of this perfect1 but restricted1 adjustment of the instinctive or automatically acting organism to the objects on which it operates1 knowledge of all else in the environment becomes of little consequence4 ,it is clear that intelligent acting involves deliberation4 ,the almost inevitable motor response to a stimulus1 which is characteristic of the reflex or instinct1 does not occur in the intelligent action3 instead of this we find that we choose between two or more responses to the same stimulus4 ,we reply to the latter by doing this now1 and that another time2 and we see at once what results flow from acting differently upon the same part of our environment1 or acting in the same way upon different parts4 ,perception1 that is1 knowledge of the world1 arises from acting2 and as our actions1 when carried out intelligently1 become almost infinitely varied1 the environment appears to us in very many aspects4 ,in every action we modify that part of our surroundings on which we operate4 ,we can produce many modifications that are of no use to us3 these we do not attend to4 ,we produce others that are useful1 and then we note the sequences of events involved in our actions4 ,thus we discover or invent natural law--an environment which is an orderly one4 ,we can calculate and predict what will happen3 we produce1 for instance1 a ,nautical ,almanac1 at once the type of useful knowledge and of knowledge of sequences of events rigidly determined--knowledge in short that is mechanistic2 and which has been engendered by the necessity for acting on our environment in our own interests4 ,all this1 the reader may note1 is ,bergson's theory of intellectual knowledge1 a theory which1 new and paradoxical at first1 becomes more and more convincing the longer we think about it1 until at last it seems so obvious that we wonder that it ever seemed new4 ,our modes of thinking become constrained into certain grooves1 just because these modes of thinking have been those that were generated by our modes of acting4 ,so long as our thinking relates only to our acting1 its exercise is legitimate4 ,but if its object is pure speculation its results may be illusory1 for a method has been applied to objects other than those for which it was evolved4 ,let us now extend our intellectual methods to the investigation of the organism4 ,necessarily we must reason about the latter as a mechanism if we reason about it at all4 ,if it is a mechanism it must conform to the laws of energetics1 for science1 so far as it is quantitative1 whether its results are expressed in the form of equations or inequalities1 is based on these principles4 ,the first principle of energetics1#f or the first law of thermodynamics1 is that of the conservation of energy4 ,let us think of an isolated system of parts such as the sun with its assemblage of planets1 satellites1 and other bodies3 in reality these do not form an isolated system1 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 universe4 ,in this system1 then1 the sum of a certain entity remains constant1 and no conceivable process can diminish or increase its quantity4 ,we call this entity energy1 and we usually extend the principle of its absolute conservation to matter1 though this extension is unnecessary1 for we must think of matter in terms of energy4 ,stated more generally the principle is that whatever exists must continue to exist1 if we are to regard this existence as a real one4#g #f ,see appendix1 p4 #cef4 #g ,the principal reason why we do not believe in phantasms is that these appearances are not conserved4 ,it is not at all self-evident to the mind that energy must be conserved1 for we see that1 to all appearance1 it may disappear4 ,a golf-ball driven up the side of a hill possesses energy while in flight1 kinetic energy or the energy of motion2 but this apparently is lost when the ball alights on the hill-top and comes to rest4 ,we say1 however1 that it now possesses potential energy in virtue of its position2 for if the hill is a steep one a little push will start the ball rolling down with increasing velocity1 and when it reaches the spot from which it was originally impelled it possesses kinetic energy4 ,this is described as one-half of the mass of the ball multiplied by the square of its velocity4 ,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 roll4 ,yet it can easily be shown that this is not the case1 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 flight1 and against the side of the hill on its roll back4 ,we cannot verify this quantitatively1 but we are quite certain that it is the case4 ,if we take a clock-spring and wind it up1 the energy expended becomes potential in the spring1 and when the latter is released most of it is recovered4 ,but we may dissolve the spring in weak acid without allowing it to uncoil4 ,what then becomes of the energy imparted to it8 ,we are compelled to say that it has changed the physical condition of the solution into which it passes1 either becoming potential in this solution1 or becoming dissipated in some way4 ,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 traceable4 ,suppose1 again1 we burn some hundredweights of coal in a steam-boiler furnace4 ,heat is evolved which raises steam in the boiler1 and the steam actuates an engine1 and the latter exhibits measurable kinetic energy4 ,where did this come from8 ,it was potential in the coal1 we say1 though no method known to physics enables us to prove this by mere inspection of the coal4 ,we must cause the latter to undergo some transformation4 ,but by rigid methods we can estimate very exactly the potential energy of the coal1 and we can calculate the kinetic energy equivalent to this4 ,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 coal4 ,what becomes of the balance8 ,we can be quite certain that it has been dissipated in friction1 radiation1 loss of heat by conduction1 loss of heat in the condenser1 and so on1 although we cannot prove this rigidly by experimental methods4 ,think of the universe as an isolated system4 ,it contains an invariable quantity of energy4 ,this energy may be that of bodies in motion--suns1 planets1 cosmic dust1 molecules1 etc4--when it is kinetic energy2 or it may be the energy of electric charges at rest or in motion2 or any one of the many kinds of potential energy4 ,it may pass through numerous transformations--the chemical potential energy of coal may be transformed into the kinetic energy of water molecules 7steam at high temperature71 and this into the kinetic energy of the revolving armature of a dynamo1 and this again into the energy of moving electrons 7the current of electricity in the circuit of the dynamo71 and then again into the energy of ethereal vibration 7light1 heat1 ,x-rays1 or other electro-magnetic waves71 and these again into mechanical or kinetic energy1 and so on4 ,when we say that we can control energy we say that we can produce these transformations2 we can cause things to happen1 we bring becoming into being4 ,in this sense energy is causality4 ,but while the sum-total of energy in the universe remains constant1 the sum of causality continually diminishes4 ,energy is the power1 or condition1 of producing diversity1 but while energy can suffer no diminution of quantity1 diversity tends continually to decrease4 ,in the last two sentences we state1 in one way1 the second law of thermodynamics--in some respects the most fundamental result of our experience in the physical investigation of the universe4 ,in its most technical form1 as enunciated by ,clausius1 this law states that the value of a certain mathematical function1 called entropy1#h tends continually towards a maximum1 when it is applied to the universe as a whole4 ,when we say the 8universe10 we mean all that comes within our power of physical investigation4 ,let us now see what this statement means4 #h ,see appendix1 p4 #cfi4 ,entropy is a shadowy kind of concept1 difficult to grasp4 ,but again we may point out that the reader who would extend the notion of mechanism into life simply must grasp it4 ,the energy of the solar system is in part the kinetic energy of those parts of it which are in motion--planets1 planetesimals1#i and satellites4 ,this quantity of energy is enormously great4 ,in the case of our earth it is #a_/b7mv#b71 m being the mass of the earth1 and v its velocity4 ,translated into numerical symbols we find this quantity almost inconceivable4 ,the greater part of this energy is unavailable1 that is1 it can undergo no transformations4 ,but because the earth is in rotation at the same time as it revolves round the sun1 and because the moon revolves round the earth1 there are tides in the watery and atmospheric envelopes of the earth4 ,the energy of the tides is the kinetic energy of water or air in motion1 and we can employ this energy in the production of transformations1 and it is therefore available4 ,but well-known investigations have shown that the tides produce friction1 and that the period of rotation of the earth is slowly becoming greater4 ,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 length4 ,when that occurs1 the sun1 earth1 and moon will be in equilibrium1 and tidal phenomena due to the sun will cease4 ,the kinetic energy of the earth1 rotating once in #bd hours is obviously greater than its kinetic energy when rotating in the period which will then be its year4 ,what has become of the balance8 ,it has been transformed into the mechanical friction of the tides against the surface of the earth1#aj and this friction has been transformed into low-temperature heat1 and this heat has been radiated off into space4 #i ,meteorites1 cosmic dust1 and other small particles moving in the solar system within influence of the sun's gravity4 #aj ,not entirely1 of course1 but whatever be the transformation it ends in heat production4 ,the solar system also contains energy in the form of the heated sun and planets1 and in the form of chemical potential energy of the substances of which those bodies are composed4 ,let us think of the system1 sun and earth4 ,the sun contains enormous heat energy1 its temperature being some #fjjj ,c4 absolute4#aa ,it contains enormous chemical energy in the shape of compounds existing beneath its outer envelopes1 and it contains energy in the form of its own gravity--its contraction together produces heat4 ,but this heat is being continually radiated away3 chemical reactions must occur in which the potential chemical energy of its substances must become transformed into heat1 and this heat is also radiated away2 contraction of its mass must occur up to a point when the materials are as closely packed together as possible2 heat is developed during the contraction1 and this also passes away by radiation4 ,suppose that modern speculations are well founded and that radio-active substances are present in the sun3 in the atomic disintegration of these substances heat is produced and again radiated4 ,therefore in whatever form energy exists in the sun1 it transforms into heat and this radiates4 ,the ultimate fate of the sun is to cool down and solidify4 ,it will then move through space as a body having a cool1 solid crust1 and an intensely heated interior4 ,slowly1 very slowly1 this heated interior will cool down by the conduction of its heat from the core to the outer shell1 and by the radiation of this heat from the shell into space4 ,for incredibly long periods radio-active substances in the interior must generate heat1 but even this process must reach an end4 #aa ,absolute temperature is ,centigrade temperature #bgc4 ,this is1 of course not a full definition1 but it is sufficient for our present discussion4 ,the energy received by the earth is that of solar and stellar radiation4 ,stellar radiation is minute1 the absolute temperature of cosmic space 7or ether7 being about -#bfc ,c4 ,the absolute temperature of the earth is about #ag ,c41 so that it radiates off more heat into space 7other than that represented by the sun7 than it receives4 ,all energy-transformations on the earth 7except tidal effects1 and energy-conduction from the heated core1 and possibly radio-active effects7 are transformations of this solar energy received by radiation4 ,we see these in oceanic and atmospheric circulations 7currents1 winds1 rainfall1 etc474 ,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 radiation4 ,let us follow the transformations of this energy4 ,oceanic currents transport heat from the equatorial sea-areas to the colder temperate and polar areas1 and compensatory polar currents flow towards the equator1 absorbing heat from the waters of temperate and equatorial areas4 ,winds act in an analogous way4 ,water is evaporated where the solar radiation is intense1 and heat is absorbed in the transformation of water into aqueous vapour4 ,then this water vapour is transported in the winds into regions where it becomes condensed and precipitated as rain or snow1 heat being emitted in this condensation4 ,in all these movements there is friction1 and this friction transforms to heat4 ,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 receive4 ,other mechanical effects are also produced by oceanic and atmospheric circulations--the denudation of the coasts by tides and storms1 the erosion of the land by rivers1 rains1 snow1 and ice1 the transport of dust in winds1 etc4 ,in all these friction is produced1 and this friction passes into heat4 ,the potential chemical energy which results from absorption of solar radiation by plants is principally accumulated as coal4 ,apart from the interference of man1 this coal would slowly accumulate1 perhaps it would more slowly disappear by bacterial action1 or by physical transformations4 ,in these transformations the energy of the coal would become heat energy and the potential energy of the gas produced by bacterial activity4 ,by man's agency the coal suffers other transformations1 and in the present phase of civilisation it is his chief source of energy4 ,it is available for doing work of many kinds1 and in all these forms of work it becomes transformed by chemical action 7burning7 into high temperature heat4 ,we can cause this potential energy of coal to transform into mechanical energy of machines1 vehicles1 and ships in motion by causing it to pass into heat4 ,in the steam-engine1 or gas-engine1 a highly heated gas 7steam1 or the mixture resulting from the explosion of coal gas and air in the cylinder of the engine7 expands and propels a piston or rotates a turbine4 7,obviously in the petrol engine the same essential process takes place47 ,we employ this kinetic energy directly in transport1 or we cause it to undergo other transformations4 ,in the dynamo1 kinetic energy of machinery in motion transforms to electrical energy2 and this may transform to radiant energy 7light1 heat in electric radiators1 wireless telegraphy radiations71 or it may transform to chemical energy 7the manufacture of carborundum in the electric furnace1 for instance71 or it may transform again to the kinetic energy of bodies in motion 7electric traction74 ,in innumerable ways the human power of direction causes transformation of this accumulated potential energy1 and the reader will notice the analogy of all this with the essential1 unconsciously expressed activity of the animal organism in its own metabolism--a point to which we return later4 ,notice now that all the energy-transformations we have noticed are irreversible4 ,this is a matter of deep philosophical importance1 and we must devote some time to it4 ,consider first of all the working of the steam-engine2 what occurs is this--coal is burned in the boiler-furnace1 that is to say1 potential chemical energy passes into heat and this vaporises water in the boiler1 producing a gas at high temperature 7steam74 ,this gas expands in the high-pressure cylinder of the engine1 driving forward a piston2 it expands further in the intermediate cylinder1 propelling its piston also1 and again in the low-pressure cylinder4 ,it is then cooled by passing through the condenser1 and in the contraction further mechanical energy is obtained4 ,the train of events thus begins with a gas at a high temperature and ends with the same gas at the temperature of the water in the condenser4 ,the heat lost is transformed into the mechanical energy of the engine4 ,but not all of it4 ,a certain quantity is lost by radiation from the boiler walls1 the walls of the steam-pipes1 the cylinders1 and other parts of the engine2 also some of the energy is transformed to friction1 and this again to heat4 ,in this way a very considerable part of the energy contained in the coal is frittered away in unavoidable heat-conduction and radiation1 and a last residue of it goes down the drain1 so to speak1 with the condenser water4 ,this loss is inherent in the nature of the mechanism of the engine4 ,suppose that the energy of the engine is employed to drive a dynamo4 ,the armature of the latter rotates against the constraint of powerful electro-magnets1 and in so doing a current of electricity is generated4 ,by the law of conservation this current should contain as much energy as was put into the rotation of the armature2 as a matter of fact it does not1 and the deficiency is represented by the friction of the parts of the machine against each other1 by imperfect conductivity of electricity in the wires1 and by imperfect insulation of the current4 ,friction1 imperfect conductivity1 and imperfect insulation all transform to heat1 and this radiates away4 ,suppose now that the current is used for lighting purposes3 to do this it must heat the metallic filaments in the lamps1 or the points of the carbons in an arc4 ,this heat then transforms to light1 but along with the light1 which was the object of the transformation1 heat is produced1 and this heat radiates away4 ,the actual process in which the particular form of energy required is generated may or may not be reversible in theory4 ,that employed in the steam-engine is not1 for if we start with a cold boiler and then work the engine backwards we could not raise steam4 ,the process in the dynamo is theoretically reversible3 if we send a current of electricity into a dynamo the machine will begin to rotate1 and become a motor1 so that we can obtain mechanical work from it4 ,now in theory all forms of energy are mutually convertible1 and all can be expressed in terms of a common unit4 ,the unit of mechanical energy is called the erg3 let a current1 the energy of which is equal to ,n ergs1 be sent into the dynamo1 then we ought to obtain from the latter mechanical energy equal to ,n ergs4 ,conversely1 if ,n ergs of mechanical energy be employed to rotate the dynamo1 we should obtain electrical energy equal to this amount4 ,now as a matter of fact we do not obtain these theoretical conversions1 for some of the electrical energy is dissipated when we employ the machine as a motor1 and some of the mechanical energy is likewise dissipated when we employ it as a dynamo4 ,the entity that we call energy is the product of two factors1 a capacity-factor and an intensity-factor4 ,thus3-- ,mechanical energy quantity of water height at which it is of water power situated above the water-motor4 ,energy of an quantity of electricity electrical potential4 electric current ,chemical energy equivalent weight of the substance chemical potential4 ,what is it that determines whether or not an energy-transformation will occur8 ,it is the condition that a difference of the intensity-factors of the energy in different parts of a system exists4 ,water will flow from a higher to a lower level1 doing work as it flows1 if it is directed through a motor4 ,electricity will flow if there is a difference of electrical potential4 ,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 interaction4 ,coal and oxygen possess greater chemical potential than do carbon dioxide and water1 therefore they will combine1 forming carbon dioxide and water4 ,energy-transformations will therefore occur wherever it is possible that differences of intensity or potential can become abolished4 ,the energy that may thus flow from a condition of high to a condition of low potential1 undergoing a transformation as it flows1 is the available energy of the system of bodies in which it is contained4 ,a closed vessel surrounded by an envelope impervious to heat1 and containing a mixture of oxygen and hydrogen1 is an isolated system containing available energy4 ,let the mixture be fired by an electric spark1 and heat is evolved4 ,the total energy of the system is unaltered in amount1 but the available energy has disappeared1 since the heated water vapour is incapable of undergoing further transformations while it forms part of its isolated system4#ab #ab ,it is really necessary to lay stress on the distinction between available and unavailable energy1 as it is one which many biologists appear to ignore4 ,thus1 a popular book on the making of the earth attempts to argue that essential distinctions between living and inorganic matter are non-existent4 ,one of these distinctions is that organisms absorb energy1 and this author points to the absorption of 8latent heat0 by melting ice as an example of the absorption of energy in a purely physical process4 ,consider a system consisting of a block of ice and a small steam boiler4 ,we can obtain work from this by the melting of the ice--that is1 its 8absorption of latent heat40 ,the system1 ice at #j ,c4 steam at #ajj ,c41 possesses available energy1 but the system1 melted ice condensed steam1 both at the same temperature1 contains none4 ,the molecules of water at #j ,c4 8absorb energy10 that is to say1 their kinetic energy becomes greater1 but their available energy in the system has disappeared4 ,in saying that the organism absorbs energy1 we mean1 of course1 that it accumulates available energy1 that is1 the power of producing physical transformations4 7,see further1 appendix1 p4 #cff47 ,all physical processes are therefore irreversible1 that is to say1 proceed in one direction only4 ,either a process is irreversible in the sense that it cannot proceed both in the positive and negative directions 7a steam-engine1 for instance71 or it is irreversible in the sense that while it proceeds the energy involved in it becomes less capable of being transformed into other conditions4 7,in the theoretically reversible dynamo1 energy becomes dissipated in the form of heat47 ,the following statements may be regarded as axioms#ac3-- #ac ,bryan1 ,thermodynamics3 ,teubner1 ,leipzig1 #aijg1 p4 #dj4 7#a7 8,if a system can undergo an irreversible change1 it will do so40 7#b7 8,a perfectly reversible change cannot take place by itself40 ,in the phenomena studied by physics we see only irreversible changes4 ,in all these processes energy descends the incline1 and some 7considerable7 fraction of the amount involved passes into conditions in which it is incapable of further transformation2 in all1 energy becomes less and less available4 ,expressed in its most technical form1 the second law of thermodynamics states that entropy tends continually to increase4 ,every such process as we can study in physics 8leaves an indelible imprint somewhere or other on the progress of events in the universe considered as a whole40#ad #ad ,bryan1 ,thermodynamics1 p4 #aie4 ,we cannot observe a truly isolated system4 ,the earth itself is part of the solar system1 and the latter receives energy from1 and radiates it to the rest of1 the universe4 ,our only isolated system is the whole universe4 ,we must think of it1 in so far as we regard it as physical1 as a finite system3 if it is infinite1 our speculations become meaningless4 ,the universe therefore is a system in which energy tends continually towards degradation4 ,in every process that occurs in it--that is to say every purely physical process--heat is evolved1 and this heat is distributed by conduction and radiation1 and tends to become universally diffused throughout all its parts4 ,when this ultimate1 uniform distribution of energy will have been attained1 all physical phenomena will have ceased4 ,it is useless to argue that universal phenomena are cyclical4 ,we vainly invoke the speculations 7founded on rather prematurely developed cosmical physics7 of stellar collisions1 light-radiation pressure1 the distribution of cosmic dust1 etc4 to support our notions of alternate phases of dissipation and concentration of energy2 close analysis will show that all these processes must be irreversible4 ,the picture physics exhibits to us is that of the universe as a clock running down2 of an ultimate extinction of all becoming2 an universal physical death4 ,in this conclusion there is nothing that is speculative4 ,it is the least metaphysical of the great generalisations of science4 ,it represents simply our experience of the direction in which physical changes are proceeding4 ,based upon the most exact methods of science known to us1 nothing seems more certain and more capable of rigorous mathematical investigation4 ,and yet we are certain that it is not universally true4 ,for there must always have been an universe--at least our intellect is incapable of conceiving beginning4 ,if we suppose a beginning1 an unconditioned creation1 at once we leap from science into the rankest of metaphysics4 ,holding1 then1 that the duration of our physical universe is an infinite one1 we see that the ultimate attainment of energy--dissipation--must have occurred if our physics is true4 ,it does not matter what new sources of energy modern investigation has shown to us2 nor do the incredibly great lapses of duration necessary for the depletion of these sources matter4 ,we have eternity to draw upon4 ,everywhere in the universe we see diversity and becoming4 ,is then the whole problem a transcendental one1 or is the second law untrue8 ,we refuse to regard the problem as insoluble1 and we must think of the second law as true of our physical experience only4 ,but our conception of the universe shows that it cannot be true1 and so we have to seek for an influence compensatory to it4 ,if the organism is a mechanism of the physico-chemical kind1 it should therefore conform to the two great principles of energetics established by the physicists4 ,now there can be no doubt that the law of energy-conservation does apply to all the processes observed in animals and plants4 ,let us consider the 8calorimetric experiments40 ,an animal1 together with the food and oxygen supplied to it1 and the various substances excreted by it1 constitutes a physical system4 ,this system can be approximately isolated so that no heat enters it from outside1 while the heat that leaves it can be determined quantitatively4 ,the animal is made to perform mechanical work1 and this is measured4 ,the energy-value of the food ingested by it1 and that of the excreta1 can be estimated4 ,all the physical conditions can thus be controlled1 and the results of such experiments show that energy is conserved4 ,the energy contained in the food is greatly in excess of the energy contained in the excreta1 but the deficit is quantitatively represented by the work done by the animal1 and by the heat lost in conduction and radiation from its body4 ,the difference between the observed results and the theoretical ones are within the limits of error of the experiment4 ,the metabolism of the animal as a whole1 then1 conforms to the law of conservation1 and the general results of physiology all go to show that this is also true of chemico-physical changes considered in detail4 ,it cannot be shown that the second law1 that of the dissipation of energy1 applies to the organism with all the strictness in which it applies to purely physical systems4 ,if we consider only the warm-blooded animal we do indeed find that its general metabolism does proceed in one direction1 and that irreversible changes occur4 ,in the mammal and bird we have organisms which present a superficial resemblance to the heat-engine1 with respect to their chemico-physical processes1 a resemblance1 however1 which is rather an analogy than an identity of processes4 ,in the heat-engine we have 7#a7 a mechanism of parts which do not change in material and relationships to each other 7boiler1 cylinder1 pistons1 cranks1 slide-valves1 etc472 and 7#b7 a working substance 7the steam74 ,energy in the form of the chemical potential of coal and oxygen is supplied to the mechanism4 ,the coal is oxidised1 producing heat4 ,the heat then expands the working substance 7the water in the boiler71 and this working substance--now a gas at high temperature and pressure--propels the piston and confers kinetic energy on the engine4 ,note the essential steps in this process3 substances of high chemical potential 7coal and oxygen7 suffer transformation into substances of low chemical potential 7carbon dioxide and water71 and the difference of energy appears as high-temperature heat 7increased kinetic energy of water molecules1 to be more precise74 ,this heat is then transformed into mechanical work 7the kinetic energy of the molecules of steam is imparted to the piston of the engine74 ,but in this transformation only a relatively small proportion 7#aj to #bj7 of the energy available is transformed into mechanical work3 the rest is dissipated as irrecoverable low-temperature heat1 by radiation from boiler1 steam-pipes1 engine1 and as the heat which passes into the condenser water4 ,in the organism in general there is no distinction between the fixed parts of the mechanism and the working substance4 ,the organism itself 7its muscles1 nerves1 glands1 etc47 is the working substance4 ,further1 it is not quite certain that there is a necessary transformation of chemical energy into heat4 ,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 body4 ,these chemical substances undergo transformations in the alimentary canal and in the metabolic tissues4 ,the proteids of the food are broken down into amino-substances in the alimentary canal1 and these amino-substances are synthesised into the specific proteids of the animal's body4 ,corresponding changes occur with the carbohydrates and fats ingested4 ,these rearrangements of the molecular structure of the foodstuffs are the object of the processes of digestion and assimilation2 and when they are concluded1 a certain proportion of the food taken into the body has become incorporated with1 or has actually become a part of1 the living tissues 7muscles1 nerves1 etc47 of the animal body4 ,this living substance1 compounds of high chemical potential 7proteids1 carbohydrates1 and fats7 undergoes transformation into compounds of low chemical potential 7water1 carbon dioxide1 and urea74 ,there is a difference of energy1 and this appears as mechanical energy1 as the chemical energy required for glandular activity1 and as heat4 ,we must not1 however1 conclude that this heat of the warm-blooded animal is comparable with the waste heat of the steam-engine4 ,the homoiothermic animal maintains its body at a constant temperature1 which is usually higher than that of the medium in which it lives1 and this constancy of temperature obviously confers many advantages4 ,chemical reactions proceed with a velocity which varies with the temperature1 so that in the warm-blooded animal the processes of life go on almost unaffected by changes in the medium4 ,the animal exhibits complete activity throughout all the seasons of the year4 ,it does not1 or need not1 hibernate1 and it can live in climates which are widely different4 ,we therefore find that the most widely-distributed groups of land-animals are the warm-blooded mammals and birds1 while the largest and most cosmopolitan marine animals are the warm-blooded whales4 ,heat-production in the mammals and birds is therefore a direct object of the metabolism of the animal2 it is a means whereby the latter acquires a more complete mastery over its environment4 ,that it is not necessarily a step in the transformation of chemical into mechanical energy we see by considering the metabolism of the cold-blooded animals4 ,in these poikilothermic organisms the body preserves the temperature of the medium4 ,the temperature in such animals may be a degree1 or a fraction of a degree1 higher than that of the environment1 but1 in the absence of exact calorimetric experiments1 we cannot say what proportion of the energy of the food of these animals passes into unavailable food energy4 ,probably it is a very small fraction of the whole1 and we are thus justified in saying that in the cold-blooded animal chemical energy does not1 to a significant extent1 become transformed into heat4 ,the result is1 of course1 that the vital processes in these organisms keep pace1 so to speak1 with the temperature of the environment1 since the chemical reactions of their metabolism are affected by the external temperature4 ,we find therefore that hibernation1 the formation of resting stages1 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 animal4 ,the former has not that mastery over the environment attained by the mammal or bird4 ,the metabolism of the animal therefore resembles the energy process of the heat-engine only in the general way1 that in both series of transformations chemical energy descends from a condition of high potential to a condition of low potential1 transforming into mechanical energy in so doing1 and thus performing work4 ,in the heat-engine chemical energy transforms to heat1 and then to mechanical energy1 and of the total quantity transformed a certain large proportion suffers dissipation by conversion into low-temperature heat4 ,in the animal organism chemical energy transforms directly to mechanical energy without passing through the phase of heat4 ,if heat is produced it is because it is1 in a way1 available energy1 inasmuch as it permits of the continuance of chemical reactions at a normal rate4 ,the analogy of the animal with the heat-engine is therefore a false one4 ,it suggests oxidation of the food-stuffs and heat production1 whereas it is not at all certain that any significant proportion of the energy of the organism is the result of oxidation3 many animal organisms indeed function in the entire absence of free oxygen4 ,further1 the proportion of energy dissipated is always small compared with the heat-engine1 and tends to vanish4 ,the second law of thermodynamics does not1 then1 restrict the energy-transformations of the animal organism to the same extent that it restricts the energy-transformations of the physico-chemical mechanism4 ,the processes involved in the plant organism differ still more in their direction from those of a 8purely physical0 train4 ,to see this clearly we must consider the imaginary mechanism known as a ,carnot heat-engine4#ae ,this is a system in which we have 7#a7 a heat-reservoir at a constant high temperature1 7#b7 a refrigerator at a constant low temperature1 and 7#c7 a working substance which is a gas4 ,energy is drawn from the reservoir in the form of heat1 and this heat expands the gas1 doing work4 ,the gas contracts1 and its heat is then given up to the refrigerator4 ,the work done is equal to the difference between the amount of heat taken from the reservoir and the amount given to the refrigerator4 #ae ,see appendix1 p4 #cfc4 ,this series of operations is called a direct ,carnot cycle4 ,but the mechanism can be worked backwards4 ,in this case heat passes from the refrigerator into the working substance1 which was at a lower temperature4 ,the working substance1 or gas1 is then compressed1 as the result of which operation it is heated to just above the temperature of the reservoir4 ,the heat it thus acquires is then given up to the reservoir4 ,in the direct ,carnot cycle1 therefore1 energy passes from a state of high potential to a state of low potential and work is done by the mechanism4 ,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 mechanism4 ,the ,carnot engine is thus perfectly reversible4 ,no energy is dissipated in its working4 ,it is1 of course1 a purely imaginary mechanism4 ,in the metabolism of the green plant carbon dioxide and water are taken into the tissues of the leaf and are transformed into starch4 ,but the energy of the compounds1 carbon dioxide and water1 is much less than that of the same compounds when built up into starch4 ,energy must therefore be derived from some source1 and this source is said to be the ether4 ,solar radiation is absorbed by the green leaf1 and this energy is employed to produce the chemical transformation4 ,just how this is effected we do not positively know1 in spite of much investigation4 ,it is possible that formaldehyde is formed from carbon dioxide and water1 polymerized1 and then converted into starch4 ,it is possible that the absorbed electro-magnetic vibrations are converted into electricity in the chlorophyll bodies of the leaf1 though when radiation is absorbed in physical experiments it is converted into heat4 ,we do not know just what are the steps in the transformation1 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 energy4 ,but the important thing to notice is1 that we have here a process closely analogous to that of a reversed ,carnot engine4 ,energy 7that of the carbon dioxide and water7 passes from a state of low potential to a state of high potential 7that of the energy of starch71 and work is done on the plant in producing this transformation4 ,work is not done by the green plant4 ,this statement is not1 of course1 quite rigidly true1 for a certain amount of mechanical work is done by the plant4 ,flowers open and close2 tendrils may move and clasp other objects2 there is a circulation of protoplasm in the plant cells1 and a circulation of sap in the vessels of stems1 etc4 ,also work is done against gravity in raising the tissues of the plant above the soil1 while work is also done by the roots in penetrating the soil4 ,but when compared with the work done by radiation in producing the chemical transformations referred to above1 these other expenditures of energy must be insignificant4 ,speaking generally1 then1 we may describe the green plant as a system in which available energy is accumulated in the form of chemical compounds of high potential4 ,it is1 further1 a system in which energy becomes transformed without doing mechanical work1 except to a trifling extent1 and in which there is no formation of heat1 or at least in which the quantity of heat dissipated is only perceptible during very restricted phases1 is relatively small during the other phases1 and tends to vanish4 ,let us now combine the processes of plant and animal2 we start with the latter4 ,in it we have a mechanism which does work4 ,the source of its energy is the potential chemical energy of its foodstuffs1 which latter reduce down to those substances known as proteids1 fats1 and carbohydrates4 ,the energy-value of these compounds is considerable1 that is to say1 if they are burned in a stream of oxygen a large quantity of heat is obtained from their combustion4 ,they are ingested by the animal1 broken down chemically1 and rearranged4 ,the proteids eaten by the animal 7say those of beef or mutton or wheat7 are acted upon by the enzymes of the alimentary canal and are decomposed into their immediate constituents1 amino-acids1 and then other enzymes rearrange these amino-acids so as to form proteid again1 but proteids of the same kinds as those characteristic of the tissues4 ,this decomposition and re-synthesis is carried out also with respect to the fats and carbohydrates ingested4 ,the result is that the food taken into the alimentary canal1 or at least a part of it1 is built up into the living substance of the animal's body4 ,the energy expended upon these processes of digestion and assimilation is probably inconsiderable4 ,during these processes the animal absorbs available chemical energy4 ,the energy thus taken into the animal is then transformed4 ,the major part of it appears as mechanical energy--that of bodily movement1 the movements of heart1 lungs1 blood1 etc4--and heat4 ,some part of it becomes nervous energy1 by which rather vague term we mean the energy involved in the propagation of nervous impulses4 ,some of it is used in glandular reactions1 in the formation of the digestive juices1 for instance4 ,the most of it1 however1 transforms to mechanical energy and heat4 ,just how these energy transformations are effected we do not know4 ,the heat is1 of course1 the result of chemical changes1 oxidations1 decompositions1 or changes of the same kind as that of the dilution of sulphuric acid by water1 but the mechanical energy appears to result directly from chemical change without the intermediation of heat4 ,we shall return to this point in a later chapter1 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 potential1 and that this difference of potential is represented by the work done and the heat generated4 ,the proteid1 fat1 and carbohydrate of the tissues represent the condition of high potential2 and the carbon dioxide1 the water1 and the urea1 into which these substances are transformed1 represent the condition of low potential4 ,let us suppose a ,carnot heat-engine in which the temperature of the reservoir of heat is 7say7 #abj;,c41 and that of the refrigerator #ej;,c4 ,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 #j;,c4 ,our animal organism may be compared with a ,carnot cycle2 its energy reservoir is the proteid1 fat1 and carbohydrate ingested1 and its refrigerator 7or energy sink7 is the carbon dioxide and urea excreted4 ,now the urea of the higher mammal becomes infected with certain bacteria1 which convert it into ammonium carbonate4 ,another species of bacteria converts the ammonia into nitrite1 and yet another turns the nitrite into nitrate4 ,the main process of the animal is therefore combined with several subsidiary ones4 ,carbohydrate1 fat1 proteid ,metabolism break down into of the animal ,carbon dioxide ,water ,urea------,urea ,metabolism of ,chemical urea bacteria ,energy at passes into high potential ammonium carbonate----ammonium metabolism carbonate of nitrifying bacteria oxidises to ,work done by nitrite----,nitrite ,metm4 of the system nitrifying oxidises bacteria to nitrate chemical energy at low potential ,the arrows show that energy is descending the incline indicated by a direct ,carnot cycle4 ,there is no more work to be obtained from the carbon dioxide and water excreted by the mammal1 but more work can be obtained from the urea when it is used by bacteria1 and 8ferments0 to ammonia4 ,work can again be obtained from the ammonia by bacteria1 which convert it into nitrite1 and yet again from the nitrite by other bacteria1 which convert it into nitrate4 ,the nitrate represents the energy-zero so far as the organisms considered are concerned4 ,other nitrogenous residues are contained in the urine of animals1 and several other excretory products may be formed4 ,but in all these cases we can easily find subsidiary energy-transformations effected by bacteria1 as in the above scheme4 ,this1 then1 is the positive1 or direct half1 of that reversible ,carnot cycle with which we are comparing life4 ,in it energy falls in potential 7or intensity1 or level71 and in this fall of potential transformations are produced--exhibit themselves1 is perhaps a better way of putting it4 ,we will consider these transformations later2 in the meantime it should be noted that in this fall of potential is a degradation of chemical energy4 ,compounds1 carbon dioxide1 water1 and nitrate are produced which are chemically inert4 ,it is no use to say that carbon dioxide may react with 7say7 glowing magnesium1 water with metallic sodium1 and nitrate with 7say7 glowing carbon4 ,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 carbon2 in which the metals would become inert oxides1 and the carbon would become dioxide4 ,the formation of these compounds represents a limit to energy-transformations4 ,note also that all these energy-transformations are conservative2 the total quantity remains unchanged throughout1 and is the same at the end as at the beginning4 ,but entropy has been augmented3 unavailable energy has increased at the expense of available energy4 ,consider now the indirect1 or reversed1 ,carnot cycle4 ,we begin with the inert matter1 resulting from the metabolism of the animal1 carbon dioxide1 water1 nitrate1 and a few more mineral substances4 ,we have the energy of solar radiation4 ,by virtue of the living chlorophyll plastid in the cells of the green plant1 this solar radiation uses the carbon dioxide and water as raw materials in the elaboration of starch4 ,at the same time it absorbs nitrate1 with some other inert mineral substances from the soil1 and takes these into its tissues4 ,the starch formed in the chlorophyll is converted into soluble sugar1 which circulates through the vessels of the plant and is associated with the nitrogenous salt in the elaboration of proteid4 ,proteid1 oils1 fats and resins1 and to a greater extent carbohydrates1 are thus built up by the plant and accumulate1 for mechanical work is not done by it1 nor is heat dissipated--or at least these processes occur to an insignificant extent4 ,metabolism -------------- are synthesised to-- ,carbon dioxide of the proteid ,water green fat ,nitrate plant carbohydrate ,chemical energy at -------------- ,chemical energy low potential ,work done on at high potential4 the system ,the 8working substance0 of our organic cycle has therefore returned to its original state4 ,we have considered the process of metabolism in two categories of organisms1 the typical animal and the green plant1 and we have combined these so as to obtain a picture of a reversible cycle of physico-chemical processes4 ,when we speak of the 8organism0 in the most general sense1 we mean that it exhibits these two modes of metabolism4 ,this is1 of course1 not the case in any actual organism which we can investigate1 or at least the typical modes of behaviour which characterise animal and plant life are not seen in any one individual4 ,but we find that there is no absolute distinction between the two kingdoms4 ,the plant may exhibit a mode of nutrition closely resembling that of the animal 7as in the insectivorous plants71 and it is possible that photo-synthetic process1 in the general sense1 may be present in the metabolism of some animals4 ,certain lower plants1 the zoospores of alg1 exhibit movements identical in character with those of lower animals4 ,at the base of both kingdoms are organisms1 the ,peridinians1 for instance1 which have much of the structure of the animal 7though cellulose is present in their skeleton71 which possess motile organs1 but which also possess a photo-synthetic apparatus1 and exhibit the typical plant mode of nutrition4 ,further1 there are symbiotic partnerships1 that is1 associations of plant and animal in one 8individual0 form 7as1 for instance1 among the lower worms1 ,echinoderms1 polyzoa1 molluscs1 and other groups of animals74 ,in these cases green algal cells1 capable of forming starch from carbon dioxide and water under the influence of light1 become intercalated among the tissues of the animal4 ,we find1 also1 that with regard to some fundamental characters1 plant and animal display close similarities3 the structure of the cell1 for example1 and the highly special mode of conjugation of the germ-nuclei in sexual reproduction4 ,we must regard all the distinctive characters of the plant as represented in the animal and vice versa4 ,why they have become specialised in different directions is a question that we discuss later4 ,the organism1 then1 in so far as we regard it as a physico-chemical mechanism1 as the theatre of energetic happenings1 exhibits the following general characters3-- 7#a7 ,it slowly accumulates available energy in the form of chemical compounds of high potential1 work being done upon it4 7#b7 ,it liberates this energy in relatively rapid1 controlled1 8explosive reactions10 transforming into movements carried out by a sensori-motor system of parts1 work being done by it4 7#c7 ,in all these transformations the amount of energy which is dissipated is relatively small1 and tends to vanish4 ,from the point of view1 then1 of energetic processes these are the characters of life1 using the term in the general sense indicated above4#af #af ,this is1 of course1 the argument of part of ,chapter ,,ii4 of ,bergson's ,creative ,evolution4 ,the reader will not find the essential differences between plants and animals stated so clearly anywhere else in biological literature4 ,is there an absolute distinction between the organic mechanism and the inorganic one8 ,let us note1 for the first time1 that the actual physico-chemical transformations themselves1 which we study in inorganic matter1 are identical with those which we study in the organism4 ,molecules of carbon dioxide1 water1 nitrate1 sodium chloride1 potassium chloride1 phosphate1 and so on1 are just the same in inert matter as in the organism4 ,chemical transformations1 such as the hydrolysis of starch1 the inversion of cane sugar1 or the splitting of a neutral fat1 are certainly just the same processes1 whether we carry them out in the glass vessels of the laboratory1 or observe them to proceed in the living tissues of the animal body4 ,the same molecular rearrangements1 and the same transfers of energy1 occur in both series of events4 ,this1 however1 is not the material of a distinction3 what we have to find is1 whether the direction of a group of physico-chemical reactions is the same in the organism and in a series of inorganic processes4 ,let us return to the ,carnot cycle4 ,this is a series of operations which occur in an imaginary mechanism in such a manner that the whole series can be easily reversed4 ,heat is supplied to the imaginary engine1 which then performs work and yields up its heat to a refrigerator4 ,work is then performed on the engine1 which thereupon takes heat from the refrigerator and returns it to the source4 ,the work done by the engine in the direct cycle is equal to the work done on it in the indirect cycle4 ,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 cycle4 ,but it is a purely imaginary mechanism1 and all experience shows not only that it has not been realised in practice1 but that it cannot so be realised4 ,if it could be realised1 we should show that the second law of thermo-dynamics is not physically true4 ,do the energy processes of life realise such a perfectly reversible cycle of operations8 ,in order to answer this question we must consider the fate of the energy which is absorbed in the plant metabolic cycle1 and that which is given out in the animal one4 ,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 manufactured8 ,does any of the energy of the animal which results from the metabolism of its body pass into the unavailable form--that is1 into a form in which it cannot be utilised by other organisms8 ,that is to say1 is energy dissipated by the organism8 ,undoubtedly it is to some extent1 but to a far less extent than in the inorganic train of processes4 ,some of the energy of solar radiation absorbed by the plant must become transformed1 by the friction of whatever movements occur1 into low-temperature heat1 and some quantity of heat1 however small1 is generated by the metabolism of the plant4 ,again1 some of the heat of the warm-blooded animal must be radiated into space1 or conducted away from its body2 and this energy becomes dissipated--let us assume1 at least1 that it is so dissipated in the physical sense4 ,probably also some quantity of heat is generated by the metabolism of the cold-blooded animal1 though this must be a very small proportion of the total energy transformed4 ,we see1 then1 that the distinction is one of degree1 though the difference between inorganic and organic energetic processes is very great in this respect2 so great that we must regard it as constituting a fundamental difference1 and as indicative of the limitation of the second law when extended to the functioning of the organism4 ,but we have also to consider the effect of the work done by the organism4 ,we consider the nature and meaning of the evolutionary process in a later chapter1 but in the meantime we may state this thesis3 that the process of evolution leads up to man and his activity4 ,it leads1 if we regard the process as a directed one2 but even if we regard it as a fortuitous process we still find that man1 far more than any other organism1 is the result of it4 ,all the facts of biology and history show that man dominates the organic world1 plant or animal2 that the whole trend of his activity is to eliminate whatever organisms are inimical1 and to foster those that are useful4 ,already1 during the brief period of his rational activity1 the wolf has disappeared from civilised lands while the dog has been produced4 ,species after species of hostile or harmful organisms have been1 or are being1 destroyed or changed1 while numerous other species have been preserved and altered for his benefit4 ,in the future we see an organic world subservient to him either entirely or to an enormous extent4 ,so also in the inorganic world4 ,rivers which formerly rushed down through rapids1 dissipating their energy of movement in waste irrecoverable heat1 now pour through turbines and water wheels1 generating electricity and accumulating available energy4 ,winds which 8naturally0 dissipated their mechanical energy in waste heat now propel ships and windmills4 ,tides1 with their incredibly great mechanical energy1 now simply warm up the crust of the earth by an infinitesimal fraction of a degree daily1 and produce heat which at once radiates into space4 ,who doubts that by and by this energy too will become accumulated for human use8 ,multitudes of chemical reactions were potential1 so to speak1 in the molecules of petroleum1 while the energy which might have produced them ran to waste4 ,but under human activity this energy became directed and made to produce chemical reactions formerly existing only in their possibility1 and all the substances of modern organic chemistry came into existence4 ,the energy1 then1 of human activity has been directed towards averting or retarding the progress towards dissipation1 or irrecoverable waste1 of cosmic energy--that of the sun's radiation1 and of the motions of earth and moon4 ,human activity has accumulated available energy4 ,the difference of water-level between ,niagara and the rapids below represents available mechanical energy4 ,a few years ago an enormous quantity of this energy became irredeemably lost in waste heat every twenty-four hours3 now it remains available for work2 and this quantity of work retained is enormously greater than is the human energy which was expended on erecting the water-power installation there4 ,the processes studied by physics and chemistry are therefore irreversible ones4 ,we can conceive a perfectly reversible process1 as in the ,carnot heat-engine1 but this is a purely intellectual conception1 formed as the limit to a series of operations which approximate closer and closer to an ideal reversibility4 ,it is a conception that has no physical reality--a guide to reasoning only4 ,on the other hand we see that all naturally occurring physical processes are irreversible and in their sum tend to complete degradation of energy4 ,mechanistic biology isolates physico-chemical processes in the functioning of the organism1 and sees that they conform to the law of dissipation1 as well as to that of the conservation of energy4 ,yet the organism as a whole1 that is1 life as a whole1 on the earth1 does not conform to the law of dissipation4 ,that which is true of the isolated processes into which physiology decomposes life is not true of life4 ,in all inorganic happenings energy becomes unavailable for the performance of work4 ,solar radiation falling on sea and land fritters itself away in waste irrecoverable heat1 but falling on the green plant accumulates in the form of available chemical energy4 ,the total result of life on the earth in the past has been the accumulation of enormous stores of energy in the shape of coal and other substances4 ,by its agency degradation has been retarded4 ,whenever1 says ,bergson1 energy descends the incline indicated by ,carnot's law1 and where a cause of inverse direction can retard the descent1 there we have life4 ,,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 organism4 ,we have seen that the first law of thermodynamics does so apply with all its exclusiveness4 ,the more carefully a physiological experiment is made2 the more closely do its results correspond with those which theory demands4 ,it is true that relatively few experimental investigations can be controlled in this way1 but in those that can be checked by calculation 7as1 for instance1 in the well-known calorimetric experiments7 everything tends to show that precisely the same quantities of matter and energy enter the body of an organism in the form of food-stuff1 that leave it as radiated and conducted heat1 as work done1 and as the potential chemical energy of the excretions4 ,even when we are unable 7as in most investigations7 to apply the test of correspondence with theory1 we have the conviction that the law of conservation holds with all its strictness4 ,then1 whenever it was possible to apply the methods of chemistry and physics to the study of the organism1 it was seen that the processes at work were chemical and physical4 ,the substance of the living body was seen to consist of a large 7though limited7 number of chemical compounds1 differing mainly from those which exist in inorganic nature in their greater complexity4 ,it was also seen that physico-chemical reactions occurred in living substance analogous with1 or quite similar to1 those which could be studied in non-living substance4 ,the conclusion1 then1 was irresistible that the life of the organism was merely a phase in the evolution of matter and energy1 and differed in no essential respect from the physico-chemical activities that could be observed in the non-living world4 ,these conclusions were stated so well by ,huxley in his famous lecture on 8,the physical basis of life10 over forty years ago1 that all subsequent utterances have been merely reiterations of this thesis in a less perfect form4 ,the existence of the matter of life1 ,huxley said1 depended on the pre-existence of certain chemical compounds--carbonic acid1 water1 and ammonia4 ,withdraw any one of them from the world and vital phenomena come to an end4 ,they are the antecedents of vegetable protoplasm1 just as the latter is the antecedent of animal protoplasm4 ,they are all lifeless substances1 but when brought together under certain conditions they give rise to the complex body called protoplasm2 and this protoplasm exhibits the phenomena of life4 ,there is no apparent break in the series of increasingly complex compounds between water1 carbon dioxide1 and ammonia1 on the one hand1 and protoplasm on the other4 ,we decide to call different kinds of matter carbon1 oxygen1 hydrogen1 and nitrogen and to speak of their activities as their physico-chemical properties4 ,why1 then1 should we speak otherwise of the activities of the substance protoplasm8 8,when hydrogen and oxygen are mixed in certain proportions and an electric spark is passed through them they disappear1 and a quantity of water1 equal in weight to the sum of their weights1 appears in their place4 ,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 it4444 ,we call these and many other phenomena1 the properties of water1 and we do not hesitate to believe that in some way they result from the properties of the component elements of the water4 ,we do not assume that a something called 8aquosity0 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 crystal1 or among the leaflets of the hoar frost40 8,is the case in any way changed when carbonic acid1 water1 and ammonia disappear1 and in their place1 under the influence of pre-existing protoplasm1 an equivalent weight of the matter of life makes its appearance80 8,it is true that there is no sort of parity between the properties of the components and the properties of the resultant4 ,but neither was there in the case of water4 ,it is also true that the influence of pre-existing protoplasm is something quite unintelligible4 ,but does anyone quite understand the modus operandi of an electric spark which traverses a mixture of oxygen and hydrogen8 ,what justification is there1 then1 for the assumption of the existence in the living matter of a something which has no representative or correlative in the non-living matter which gave rise to it80 ,all the investigations of over forty years leave nothing to be added to this statement of what1 in ,huxley's days1 was called materialistic biology4 ,it was a very unpopular statement to make then1 but it has become rather fashionable now4 ,let the reader compare it with all that has been spoken and written since #ahfi1 even with the utterances of the ,british ,association of the year #aiab1 and he will find that it expresses the point of view of mechanistic biology far better than all the subsequent restatements4 ,the only difference he will find is that the latter have become 7as ,william ,james has said about academic philosophies71 rather shop-soiled4 ,they have been reached down and shown so often to the enquiring public1 that each display has taken away something of their freshness4 ,illustration3 ,,fig4 #h4 ,now ,huxley's example leads up so well to the consideration of the differences between the chemical activities of the organism and those of inorganic matter that we may consider it in some detail4 ,what1 then1 is the difference between the explosion of a mixture of oxygen and hydrogen1 and the photo-synthesis of starch by the green plant8 ,in the case of the synthesis of water we have an example of an exothermic chemical reaction4 ,we are to think of the mixture of oxygen and hydrogen as existing in a condition of 8false equilibrium40 ,it may be compared with a weight resting on an inclined plane4 ,suppose that the plane is a sheet of smoothly polished glass1 and that the weight is a smooth block of glass4 ,by canting the plane more and more an angle will be found at which the slightest push starts the weight sliding down4 ,now in the case of the explosive mixture of oxygen and hydrogen we have a chemical analogue4 ,either the gases do not combine at all at the ordinary temperature or they combine 8infinitely slowly40 ,but the slightest impulse1 an electric spark requiring an almost infinitesimally small quantity of energy1 starts the combination of the gases1 and this continues until all is changed into water vapour4 ,in this reaction a large quantity of energy is liberated in the form of heat4 ,this heat becomes transformed into the kinetic energy of the water particles which condense from the steam formed in the explosion1 and these particles assume the temperature of their surroundings4 ,the energy which was potential in the explosive mixture1 and which was capable of doing work1 still exists as the kinetic energy of the water formed1 but it has become unavailable for any natural process of work4 ,we have seen what is the general character of the reaction series in the course of which carbon dioxide and water become starch2 and then this1 becoming first soluble1 and becoming associated with the ammonia or nitrate taken into the plant1 becomes protoplasm4 ,it is a reaction which differs from that just described1 in that available energy becomes absorbed and accumulated1 and retains the power of doing work4 ,it is not a reaction which can be initiated by an infinitesimal stimulus1 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 generated4 ,the first reaction is one which may take place by itself2#ag the other is one which requires a compensatory energy-transformation in order that it may happen4 ,in the first reaction energy is dissipated2 in the second one it is accumulated4 #ag ,it is no use saying that apart from the electric spark the combination would not take place1 for we do not know that the ,o and ,h of the mixture do not combine very slowly1 molecule by molecule1 so to speak4 ,at all events there is no functionality between the infinitesimal quantity of energy supplied by the spark1 and the energy which becomes kinetic in the explosion4 ,we are thus led to the consideration of the second principle of energetics and its limitations1 but before entering upon this discussion we must consider the nature of the activities of the organism4 ,by the term 8metabolism0 we understand the totality of the physico-chemical changes which occur in the living substance of the organism4 ,in physiological writings we usually find that two categories of metabolic changes are described3 7#a7 anabolic processes1 in the course of which simple chemical compounds possessing relatively little energy are built up into much more complex substances1 containing a relatively large quantity of available energy1 and therefore capable of doing work4 ,the transformations constituting an anabolic change must be accompanied by corresponding compensatory energy-transformations1 to account for the energy which becomes potential in the substances formed4 ,the formation of starch from carbon dioxide and water1 by the green plant1 is such an anabolic change1 and the compensatory energy-transformation is the absorption of radiation from the ether by the cells of the plant4 ,a further anabolic change in the plant organism is the formation of amido-substances from the ammonia or nitrate absorbed from the soil1 and from the soluble carbohydrates formed from the starch manufactured in the green cells4 ,the typical activities of the chlorophyll-containing organism are of this nature2 they are anabolic4 ,the organism may be a green land-plant2 a marine green1 red1 or brown alga2 a yellow-green diatom1 a yellow1 green1 red1 or brown peridinian or other holophytic protozoan2 an ascidian1 mollusc1 echinoderm1 polyzoan1 worm1 or coral containing 8symbiotic alg0 7that is the chlorophyll-containing cells of some plant organism which have become associated with the animal and incorporated in its tissues74 ,in all these cases the presence of this chlorophyllian substance confers on the organism the power of effecting the compensatory energy-transformation1 by the aid of which carbon dioxide and water are built up into starch4 ,what this transformation is1 and what are the steps by which the carbon dioxide and water become carbohydrate we do not exactly know4 ,solar radiation impinging upon an inorganic substance is partly reflected and partly absorbed4 ,the absorbed fraction may become transformed in such a way as to render the substance phosphorescent1 or it may transform into chemical energy1 as when light impinges on a photographic plate1 but as a general rule it is transformed into heat4 ,in the green plant1 however1 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 synthesised4 ,we must regard this power of absorbing radiation and utilising it in compensatory transformations as a general character of protoplasm4 ,it is true that it is now specialised in the cells containing the chlorophyll bodies1 but there are indications that it may be present in the tissues of the animal devoid of chlorophyll4 ,other anabolic transformations occur in the animal4 ,the food-stuffs which are absorbed from the intestine are substances which have undergone dissociations1 the nature of which is such as to render them capable of absorption and of reconstruction4 ,these anabolic changes in the higher animal are exceptional1 and their usefulness lies in the fact that by their means substances become capable of being transported by the tissue fluids of the body4 7#b7 ,katabolic changes in the animal body correspond in their frequency of occurrence to the anabolic changes of the plant organism4 ,in them complex chemical substances undergo transformation into relatively simple substances1 and the contained energy at the same time undergoes a parallel transformation1 passing into the form of heat and mechanical energy1 while a fraction becomes dissipated4 ,food-stuffs taken into the alimentary canal break down in this way1 but to a very limited extent4 ,proteids undergo dissociation or decomposition into amido-substances1 while fats are dissociated into fatty acids and glycerine4 ,doubtless energy is dissipated in these processes1 serving no other purpose but to heat the contents of the alimentary canal1 but this energy-transformation has not been worked out very completely and it is a question whether1 given a healthy animal and perfect food-stuffs1 any energy would necessarily be lost during the digestive processes4 ,the reactions involved in the latter do not belong to the category of chemical changes proceeding from the complex to the simple1 with a liberation of energy2 but appear to involve rather a rearrangement of the constituents of a complex molecule1 a process in which the contained energy need not undergo change in quantity4 ,these processes involve the action of enzymes4 ,enzymes play a great part in modern physiological theory and we must consider them in detail4 ,let us attach a concrete meaning to the general notion of enzyme-activity by considering the phenomena known as catalysis4 ,the metal platinum can be brought into a very fine stage of division when it is known as platinum black4 ,in this condition it brings about reactions in chemical mixtures or substances which would not otherwise occur3 a mixture of oxygen and hydrogen explodes when brought in contact with platinum black1 and a mixture of coal gas and air inflames1 a reaction which is made use of in the little gas-lighting apparatus which most people have seen4 ,if1 again1 a powerful electric current be passed between platinum wires which are a little distance apart1 and are immersed in water1 the metal becomes torn away from the points of the wire in the form of an impalpable powder1 colloidal platinum4 ,the liquid containing this colloid then has the power of setting up chemical changes in other substances1 changes which would not otherwise occur1 or1 at least1 would occur very slowly4 ,in general such catalysts1 platinum black or colloidal platinum for instance1 have the following characters3 7#a7 a small quantity is sufficient to cause change in a large 7theoretically an infinite7 quantity of the substance acted upon2 7#b7 the nature and quantity of the catalyst remain at the end the same1 as at the beginning of the reaction2 7#c7 a catalyst does not start a reaction in any other substance or substances1 it can only influence the rate at which this reaction may occur3 apparently it does1 in some cases1 start a reaction1 but in such cases we suppose that the latter proceeds so slowly as to be imperceptible2 7#d7 the final state of the reaction is not affected by the catalyst2 it depends only on the nature of the interacting substance or substances2 7#e7 the final state is not affected either by the nature or quantity of the catalyst3 it is the same if we employ different catalysts1 or a large or small quantity of the same catalyst4 ,finally1 it appears that the phenomena of catalysis are universal3 8,there is probably no kind of chemical reaction10 says ,ostwald1 8which cannot be influenced catalytically1 and there is no substance1 element1 or compound which cannot act as a catalyser40#ah #ah ,a statement of interest in view of the enormous number of 8ferments0 or enzymes discovered by physiologists4 ,it would appear that any tissue in any organism is capable of yielding an enzyme to modern investigation4 ,enzymes1 then1 are agents which are produced by the organism1 and which act by influencing 7accelerating or retarding7 chemical reactions4 ,an enzyme1 as such1 need not exist in a tissue2 it is there as a zymogen1 a substance which may become an enzyme when required4 ,an enzyme need not be active3 it may be necessary that it should be 8activated0 by a kinase1 another substance produced at the same time4 ,associated with many enzymes are anti-enzymes1 substances which undo what their corresponding enzymes have done4 ,finally some1 perhaps most1 enzymes are reversible1 that is1 if they produce a change in a certain substance they can also produce the opposite kind of change3 the meaning of this will become clearer a little later on4 ,we have spoken of enzymes as 8agents0 or 8substances10 but it is not at all certain that they are definite chemical compounds4 ,in the preparation of an enzyme what the bio-chemist obtains is a liquid1 a glycerine or other extract which possesses catalytic properties4 ,an actual catalytic substance1 like platinum black1 cannot be obtained from this liquid4 ,a white powder may be obtained1 but this usually proves to be proteid in composition2 it is not the actual enzyme itself but is the impurity associated with the latter4 ,now the very great number of enzymes 8isolated0 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 catalysts3 any tissue substance may influence the reactions that may possibly occur in other tissue substances4 ,but while pure chemistry has to deal with definitely known chemical compounds in the phenomena of catalysis1 this cannot be said to be the case with physiology in dealing with enzymes4 ,reasoning by analogy1 we may say that it is probable that enzymes are definite proteids1 or chemical substances allied to these1 but this has not been clearly demonstrated1 and it is possible that the phenomena of enzyme activity may belong to some other category of energy-transformations4 ,however this may be1 the conception is a useful one in describing the reactions of the organism1 and it may be illustrated by considering the digestion and absorption of fat in the mammalian intestine1 a process which appears to be better known than that of proteid digestion4 ,a neutral fat consists of an acid radicle1 oleic1 palmitic or stearic acids1 for instance1 united with glycerine4 ,the action of the pancreatic or intestinal enzymes is to dissociate this fatty salt4 ,let us write the formula of the latter as ,g ,f1 ,g being the glycerine base1 and ,f the fatty acid2 then ,g ,f ,g ,f which means that the enzyme can cause the neutral fat to dissociate into glycerine and fatty acid4 ,this action will go on until a state of equilibrium is attained1 in which there is a certain quantity of each of the radicles1 and a certain quantity of unchanged neutral fat1 the ratio of all these to each other depending on various things4 ,when this state of equilibrium is attained the enzyme does indeed go on splitting up more neutral fat1 but it is a reversible enzyme1 and it also causes the glycerine and fatty acid already split up to recombine1 forming neutral fat4 ,a condition is1 therefore1 reached in which the composition of the mixture remains constant4 ,now there is dissociated fat in the intestine after a meal1 but there is only neutral fat in the wall of the intestine4 ,the fat itself cannot pass through the cells forming the intestinal wall1 but the glycerine and fatty acid into which it is dissociated can so pass1 since they are soluble in the liquids of the intestine4 ,we suppose that the cells of the wall of the intestine also contain the fat-splitting ferment2 this ferment in the cells acts on the glycerine and fatty acid immediately they enter and recombines these radicles again into neutral fat1 the above equation now reading from right to left4 ,but after a time this reaction in the cells will also begin to reverse1 for the enzyme will begin to split up the synthesised neutral fat when the state of chemical equilibrium in the new conditions is attained4 ,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 liquids1 we are not sure4 ,at all events the lymph and blood after a meal containing much fat are crowded with minute fat globules4 ,but why are there no fatty acids or glycerine in the blood1 for the latter also contains lipase 7the fat-splitting enzyme78 ,the explanation is1 apparently1 that either an anti-enzyme is produced1 or that the enzyme passes into a zymoid condition4 ,why also does fat accumulate in the tissues8 ,here1 again1 the activity of the enzyme1 which from other considerations we may regard as being universally present almost everywhere in the body1 must be supposed to be arrested by some means4 ,the conception of a catalytic agent1 such as we can study in pure chemistry1 thus carries us a long way in our description of the processes of digestion1 absorption1 and assimilation4 ,we have applied it to the case of fat-digestion1 but very much the same general scheme might also apply to many other processes in the body4 ,obviously it enables us to describe these processes in terms of physico-chemical reactions1 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 kinase1 the operation of the anti-enzyme1 and the passage of the enzyme into the zymoid4 ,just why these things happen as they do we do not know1 yet the whole problem becomes shifted on to these reactions4 ,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 body4 ,the nature of these processes will probably be familiar to the reader1 nevertheless it may be useful to remind him that by diffusion we understand the passage of a liquid1 containing some substance in solution1 through a membrane2 and by osmosis the passage of a solvent 7but not of the substance dissolved in it7 through a 8semi-permeable membrane40 ,the molecules of the solvent 7water1 for instance7 pass through the membrane 7the wall of a capillary1 or lymphatic vessel71 but the molecules of the substance 7salt1 for instance7 dissolved in the solvent do not pass4 ,let us suppose that a strong solution of common salt in water is injected into the blood stream3 what happens is that osmosis takes place1 the water in the surrounding lymph spaces passing into the blood stream because the concentration of salt there is greater than it is in the lymph4 ,while this is happening1 the capillary walls are acting as semi-permeable membranes1 allowing the molecules of water to pass through but not the molecules of salt4 ,very soon1 however1 the process of osmosis becomes succeeded by one of diffusion1 and the salt molecules pass through the capillary wall into the lymph and are excreted4 ,illustration3 ,,fig4 #i4 ,undoubtedly the purely physical processes of diffusion and osmosis occur all over the animal body and are the means whereby food-materials1 secretory1 and excretory substances are transported from blood to lymph1 or vice versa1 from lymph to cell substance or to glandular cavities1 and so on4 ,but it is also the case that in very many processes the activity of the cells themselves plays an important part4 ,it may even be the case that a particular process1 after all physical agencies are taken into account1 reduces down to this action of the cells4 ,to understand this we must consider the mode of working of some well-known organ1 and the best possible example of such an organ1 considered as a mechanism1 is that of the sub-maxillary salivary gland of the mammal4 ,what1 then1 is this mechanism and how does it act8 ,the gland is a compound tubular one1 its internal cavity being prolonged into the duct which opens into the mouth4 ,the saliva prepared in the gland issues from this duct4 ,blood is carried to the gland by twigs of the facial artery1 and1 after circulating through it1 is carried away by factors of the jugular vein4 ,two nerves supply the gland3 one is the chorda tympani1 a branch of a cranial nerve1 and the other is a sympathetic nerve4 ,lymph also leaves the gland by a little vessel4 ,now suppose we have laid bare all this mechanism in a living animal and make experiments upon it4 ,if we stimulate the chorda tympani there is a copious flow of thin watery saliva1 but if we stimulate the sympathetic there is a less copious flow of thick viscid saliva4 ,why is this8 ,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 gland2 but that1 on the other hand1 the sympathetic contains fibres which constrict the arteries1 thus leading to a reduced flow of blood4 ,this accounts for the fact that 8chorda-saliva0 is abundant and thin1 while 8sympathetic-saliva0 is scarce and thick4 ,it was thought at one time that the chorda contained fibres which stimulated the gland to produce watery saliva1 while the sympathetic contained fibres which stimulated it to produce mucid saliva4 ,this1 however1 is not the case4 ,both nerves contain the same kind of secretory fibres3 their other fibres differ mainly in that they act differently on the arteries4 ,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-flow3 an abundant arterial circulation gave rise to abundant saliva1 a sparse flow to a sparse saliva4 ,undoubtedly the secretion depends on blood supply1 but not solely4 ,if it did1 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 vessels1 and the walls of the tubules into the cavity of the gland4 ,if this were the case1 then the liquid in the gland would be the same in composition and concentration as the liquid part of the blood--the plasma4 ,but it is really different in composition and it is not so concentrated4 ,now osmotic pressure--on the action of which so much is based--cannot help us1 for the liquid in the gland is less concentrated than that in the blood vessels1 so that water ought to pass from gland to blood instead of from blood into gland4 ,again1 if we tie the duct1 so that the saliva cannot escape1 secretion still goes on1 though the hydrostatic pressure of saliva in the cavity of the gland may be considerably greater than that of the liquid in the blood vessels4 ,yet again1 if we stop the blood flow by tying the artery1 secretion of saliva may still go on for a time4 ,therefore the only physical agencies we can think of do not explain the secretion4 ,the latter is actually the work of the individual cells1 stimulated by the nerves4 ,if the volume of the gland be measured just while it is being stimulated to secrete1 it will be found that the organ becomes smaller1 yet while it is being stimulated the blood-vessels are being dilated so that the volume of the whole structure ought to become greater4 ,obviously part of the substance of the gland is being emptied out through its duct as the secretion4 ,if we examine the cells of the gland in various states we see clearly that granules of some material1 different in nature from the substance of the protoplasm itself1 are being formed within them4 ,evidently these granules swell up during secretion and discharge their contents into the ducts4 ,further changes in the characters of the cell-substance1 and in the nucleus1 can be observed1 and all these indicate that the protoplasm of the cells1 as the result of stimulation1 elaborates certain substances2 that these substances are then washed out1 so to speak1 into the duct by the withdrawal of water from the cell2 and that thereafter the cell absorbs fresh nutritive material from the lymph which exudes from the blood vessels1 along with water4 ,the distinctive part of the whole train of processes is1 then1 this elaboration of material by the cells themselves2 while the concomitant changes in the calibre of the blood vessels and in the flow of blood and lymph are subsidiary ones4 ,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 pressure2 oxygen and nitrogen1 with other elements of course1 are withdrawn from the arterial blood stream for the purpose of the secretion1 and carbon dioxide and other substances are given off to the venous blood and lymph4 ,the problem thus is pushed back from the mechanical events occurring in the nervous and circulatory processes1 to the physico-chemical ones occurring in the cells of the gland tubules2 and it thus becomes much more obscure4 ,it is true that we can formulate a hypothesis which describes1 in a kind of way1 these intra-cellular metabolic changes1 in terms of physico-chemical reactions1 and1 without doubt1 reactions of this kind must occur within the cell4 ,but if we could test any such hypothesis as easily as the mechanical ones suggested1 should we find it any more self-sufficient8#ai #ai ,we have not referred to 8psychical secretion40 ,if we smell some very savoury substance our 8mouth waters10 that is1 secretion of saliva occurs4 ,if we even see some such substance the same secretion occurs4 ,all this is clear and can be 8explained0 mechanistically3 the stimulation of the olfactory or visual organs begins a kind of reflex process4 ,but if we even think about some very savoury morsel saliva may be secreted4 ,we must suppose now that our consciousness1 something which has nothing to do1 it must be noted1 with energy-changes in the body1 can react on the body4 ,if we show a dog an attractive bone it will secrete saliva2 if we show it again and again1 the same thing occurs4 ,but after certain such trials the dog will realise that he is being played with1 and the exhibition of the bone no longer evokes a flow of secretion4 ,why is this8 ,the whole process has now become more mysterious than ever4 ,irritability and contractility are general properties of the organism4 ,these properties are illustrated by the irritability of an ,amba or ,paramcium to stimuli of many kinds2 by the movements of the pseudopodia of the former animal1 or of the cilia of the latter2 by the nervous irritability of the higher animal1 and the contraction of its muscles when they are stimulated4 ,they are among the fundamental properties or functions of living protoplasm1 and their study is of paramount interest1 and carries us to the very centre of the problem of the activities of the organism4 ,naturally physiologists have never ceased to attempt to describe irritability and contractility in terms of physics1 but though we may be quite certain that the things that do occur in these phenomena are controlled physico-chemical reactions1 it must be remembered that what we positively know about their precise nature is exceedingly little4 ,what is the nature of a nervous impulse8 ,when a receptor organ is stimulated1 as1 for instance1 when light impinges on the cone cells of the retina1 or when the nerve-endings in a 8heat-spot0 in the skin are warmed1 or when the wires conveying an electric current are laid on a naked nerve1 an impulse is set up in the nerve proceeding from the place stimulated1 and we must suppose that approximately the same amount of energy moves along the nerve as was communicated to the receptor or the nerve itself by a stimulus of minimal strength4 ,how does it so move8 ,several facts of capital importance result from the experimental work4 7#a7 ,the impulse travels with a velocity variable within certain limits1 say from #h to #cj metres per second2 7#b7 it travels faster if the temperature is raised 7up to a certain limit72 7#c7 it is difficult to demonstrate that the passage of this impulse is accompanied by definite chemical changes in the nerve substance3 it is stated that carbon dioxide is produced1 but this is not certainly proved2 7#d7 an electric current is produced in the nerve as the result of stimulation2 7#e7 no heat is produced1 or at least the rise of temperature1 if it occurs1 is less than #j4jjjb ,c4 ,thus it is quite certain that physical changes accompany the propagation of the nerve-impulse1 for the latter has a certain velocity1 which depends on the temperature1 and an electric change also occurs in the substance of the nerve4 ,is this electric change the actual nerve impulse8 ,it is hardly likely1 since the velocity of the impulse is very much less than that of the propagation of an electric change through a conductor2 besides1 the passage of the impulse is not accompanied by a measurable heat evolution1 although the flow of electricity along a poor conductor must generate heat and dissipate energy4 ,is it a chemical change8 ,then we should be able to observe metabolism in the nerve substance--that is if the energy-change is a thermodynamic one--while it is not at all certain that metabolic changes do occur4 ,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 nerve4 ,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 7using the term 8explosion0 to connote chemical disintegrations rather than combustions74 ,if we imagine a long rod of dynamite1 or picric acid1 or a long strand of loosely-packed gun-cotton to be exploded by percussion at one end1 then a transmission of the chemical disintegration of any of these substances will pass along the rod1 etc41 with a velocity which will certainly vary with the physical condition of the material4 ,it would be a high velocity in a rod of dynamite1 or fused picric acid1 but a lower velocity in a loosely aggregated strand of gun-cotton1 or a trail of picric acid powder4 ,is this what happens in the nerve when an impulse travels along it8 ,obviously not1 since the substance of the nerve is not altered appreciably1 while that of the explosive substance passes into other chemical phases4 ,we might imagine1 then1 such a change in the nerve fibrils as that of a reversible transformation of some chemical constituent3-- 7#b7 7#a7 ---------------------------------------- --------------------- 3 a b 3 a b 3 a b 3 a b 3 a b 3 3 3 3 3 3 3 3 c d 3 c d 3 c d 3 c d 3 c d 3 ---------------------------------------- --------------------- ,let us imagine the substance of the fibril to be composed of1 or at least to contain1 the substances a b which dissociate reversibly into the substances c d4 ,at any moment1 and in any particular physical state1 as much of a and b pass into c and d as c and d pass into a and b4 ,there will be equilibrium4 ,but now let a stimulus alter the physical conditions3 prior to the stimulus the phase was am bn cp dr--the suffixes m1 n1 p1 r1 denoting the concentrations of a1 b1 c1 and d--but after the stimulus the phase may be am#a bn#a cp#a dr#a4 ,now the element of the nerve substance 7#a7 forms a system with the element 7#b74 ,the condition in 7#b7 is am bn cp dr1 and that of 7#a7 am#a bn#a cp#a dr#a1 but these two together now fall into a new state of equilibrium and this is transmitted along the whole nerve-fibril with a velocity which belongs to the order of magnitude of that of chemical changes4 ,if the stimulus remains constant 7a constant electric current for instance71 the new condition of equilibrium will be established throughout the whole length of the fibril and the nervous impulse will be a momentary one 7as it is in this case74 ,but if the stimulus is an intermittent one 7an interrupted electric current1 light-vibration1 sound-vibrations71 then in the intervals the former condition of equilibrium will become re-established and the nervous impulse will be intermittent 7as it is74 ,there would be no work done on the whole in the changes1 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 fibre1 or the cell of a secretory gland1 for instances4 ,there would1 probably1 be a certain dissipation of energy as in the case of the propagation of an electric impulse through a poor conductor1 but all our knowledge of the chemistry of the nerve fibre points to this amount of dissipation as tending to vanish4 ,something analogous to this may be expected to take place in a muscle fibre when it contracts2 except that1 of course1 energy is transformed in this case4 ,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 place4 ,certain positive results have1 of course1 been obtained by chemical and physical investigation of the contracting muscle3 carbon dioxide is given off to the lymph and blood stream1 and the amount of this is increased when an increased amount of work is done by the muscle2 heat is produced and this too increases with the work performed2 glycogen is used up1 and lactic acid is produced2 finally oxygen is required1 and more oxygen is required by an actively contracting muscle than by a quiescent one4 ,now the obvious hypothesis correlating all these facts is that the muscle substance is oxidised1 and that the heat so produced is transformed into mechanical energy4 8,we must assume10 says a recent book on physiology1 8that there is some mechanism in the muscle by means of which the energy liberated during the mechanical change is utilised in causing movement1 somewhat in the same way as the heat energy developed in a gas-engine is converted by a mechanism into mechanical movement40 ,now1 must we assume anything of the kind8 ,to begin with1 life goes on1 and mechanical energy is produced in many organisms living in a medium which contains no oxygen4 ,anaerobic organisms are fairly well known1 and we cannot suppose that in them energy is generated by the combustion of tissue substance in the inspired oxygen4 ,a muscle removed from a cold-blooded animal will continue to contract in an atmosphere containing no oxygen1 and it will continue to produce carbon dioxide4 ,it is true that the contractions soon cease1 even after continued stimulation under conditions excluding the fatigue of the muscle1 but do the contractions cease because the oxygen supply is cut off1 or because the muscle dies in these conditions8 ,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 produced4 ,we know that the carbon contained in the latter gas corresponds roughly with the carbon contained in the muscle substance which undergoes disintegration1 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 energy8 ,obviously not1 since we might equally well suppose that the complex metabolic substance of the muscle splits down into simpler substances and that in this transformation energy is generated4 ,suppose that these simpler substances are poisonous and that they must be removed as rapidly as formed4 ,the rle of the oxygen may be to oxidise them1 thus transforming them into carbon dioxide1 an innocuous substance which can be carried away quickly in the blood stream4 ,this line of thought1 according to which the rle of oxygen is an anti-poisonous one1 is held at the present day by some physiologists1 and many considerations appear to support it2 the existence of 8oxidases10 for instance1 enzymes which produce oxidations which would not otherwise occur in their absence4 ,such enzymes exist in very many tissues1 and they may1 apparently1 be present in an inactive form1 requiring the agency of a 8kinase0 before they are able to act4 ,the usual view among physiologists is that the muscle fibre is a thermodynamic apparatus transforming the heat generated during metabolism into mechanical energy4 ,how is this transformation effected8 ,it cannot be said that we have any one hypothesis more convincing than another4 ,it has been suggested that alterations of surface tension play a part1 or that the heat produced by oxidation causes the fibre to imbibe water and shorten4 ,engelmann has devised an artificial muscle consisting of a catgut string and an electrical current passing through a coil of wire1 and by means of this he has reproduced the phenomena of simple contraction and tetanus4 ,but it remains for future investigation to verify any one of these hypotheses4 ,when ,huxley published his ,physical ,basis of ,life1 probably few physiologists had any doubt that protoplasm was a definite chemical substance1 differing from other organic substances only by its much greater complexity4 ,but in #ahhj ,reinke and ,rodewald published the results of an analysis of the substance of a plant protoplasm and these appear to have demonstrated that the substance was really a mixture of a number of true chemical compounds and was not a single definite one4 ,now all of these substances might exist apart from protoplasm1 and in the lifeless form1 and a simple mixture of them could hardly bring forth vital reactions4 ,these results were followed by the morphological study of the cell--the discovery of the architecture of the nucleus1 and so on1 and so opinion began to turn to the hypothesis that the vital manifestations of protoplasm were the result of its structure4 ,microscopical examination of the cell appeared to disclose a definite arrangement1 the 8foam0 or 8froth0 of ,butschli1 for instance4 ,but1 again1 it was easily shown that the foam1 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 like4 ,artificial protoplasm and artificial ,amb 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 branches4 ,for instance1 one has only to shake up a little soapy water in a flask to see what resembles surprisingly the arrangement of certain kinds of connective tissues in the organism4 ,obviously these artificial phenomena have nothing to do with living substance4 ,yet if we grind up a living muscle with some sand in a mortar we do destroy something4 ,the muscle could be made to contract1 but after disintegration this power is lost4 ,we have certainly destroyed a structure1 or mechanism1 of some kind4 ,but1 again1 the paste of muscle substance and sand still possesses some kind of vital activity1 for with certain precautions it can be made to exhibit many of the phenomena of enzyme activity displayed by the intact muscle fibres1 or even the entire organism4 ,mechanical disintegration1 therefore1 abolishes some of the activities of the organism1 but not all of them4 ,if1 however1 we heat the muscle paste above a certain temperature1 the residue of vital phenomena exhibited by it are irreversibly removed1 so that heating destroys the mechanism4 ,this we can hardly imagine to be the case 7within ordinary limits of temperature at least7 with a physical mechanism1 but again a mechanism which is partly chemical might be so destroyed4 ,we see1 then1 that protoplasm possesses a mechanical structure1 but that all of its vital activities do not necessarily depend on this structure4 ,the full manifestation of these activities depends on the protoplasmic substance possessing a certain volume or mass1 and also on a certain chemical structure4 ,if living protoplasm has a structure1 and is not simply a mixture of chemical compounds1 what is it then8 ,two or three physico-chemical concepts are at the present time very much in evidence in this connection4 ,when the substances known as colloids were fully investigated by the chemists1 much attention was paid to them by the physiologists1 so that life was called 8the chemistry of the colloids10 just as after the investigation of the enzymes it was called the 8chemistry of the enzymes10 and when the discovery of the relative abundance of phosphorus in cell-nuclei and in the brain was discovered1 it was called the 8chemistry of phosphorus40 ,colloids 7e4g4 glue7 are substances that do not readily diffuse through certain membranes1 in opposition to crystalloids 7e4g4 solution of common salt7 which do readily so diffuse4 ,they form solutions which easily gelatinise reversibly1 that is1 can become liquid again 7glue72 or coagulate irreversibly1 that is1 cannot become liquid again 7albumen72 which have no definite saturation point2 which have a low osmotic pressure 7and derived properties71 etc42 and the molecules of which are compound ones consisting of combinations of the molecules of the substance with the molecules of the solvent1 or with each other1 that is1 they are molecular aggregates4 ,colloids pass insensibly into crystalloids on the one hand and into coarse suspensions 7water shaken up with fine mud1 for instance7 on the other4 ,we may replace the concept of a colloid by those of 8suspensoids0 and 8emulsoids40 ,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 solution1 if into large aggregates of molecules we have a suspension4 ,if the substance in the liquid is itself liquid1 the whole is called an emulsoid4 ,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 water1 when the drops of chloroform readily join together so that two layers of liquid 7chloroform and water7 form4 ,what we see1 then1 in protoplasm is a viscid substance possessing a structure of some kind1 and containing specialised protoplasmic bodies in its mass 7nuclei1 nucleoli1 granules of various kinds1 chlorophyll1 and other plastids1 etc474 ,it may contain or exhibit suspensoid or emulsoid parts or substances1 or it may contain truly crystalloid solutions4 ,these phases of its constituents are not fixed1 but pass into each other during its activity4 ,nothing that we know about it justifies us in speaking about a 8living chemical substance40 ,on analysis we find that it is a mixture of true chemical substances rather than a substance4 ,it is no use saying that in order to analyse it we must kill it1 for what we can observe in it without destroying its structure or activities indicates that it is chemically heterogeneous4 ,this is not a textbook of general physiology1 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 organism4 ,the question for our consideration is this3 do these results of physico-chemical analysis fully describe organic functioning8 ,dogmatic mechanism says 8yes0 without equivocation4 ,now it is clear1 from even the few typical examples that we have quoted1 that physiological analysis shows1 indeed1 a resolution of the activities of the organism into chemical and physical reactions4 ,how could it do otherwise8 ,how could chemical and physical methods of investigation yield anything else than chemical and physical results8 ,the fact that these methods can be applied to the study of the organism with consistent results shows that their application is valid2 that we are justified in seeing physico-chemical activities in life4 ,but are these results all that we have reason to expect8 ,we turn now to ,bergson's fertile comparison of the physiological analysis of the organism with the action of a cinematograph4 ,if we take a series of photographic snapshots of1 e4g41 a trotting horse and then superpose these pictures upon each other1 we produce all the semblance of the co-ordinated motions of the limbs of the animal4 ,yet all that is contained in the simulated motion is immobility4 ,from a succession of static conditions we appear to produce a flux4 ,yet if we could contract our duration of1 e4g41 a week1 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 more3 truly an illusion8 ,if1 again1 we reverse the direction of motion of the film1 we integrate our snapshots into something which is absolutely different from the reality which they at first represented2 and by such devices the illusions and paradoxical effects of the picture-house farces are made possible4 ,well1 then1 in the physiological analysis of the activity of the organism do we not do something very analogous to this8 ,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 once1 arbitrarily neglecting all the rest4 ,we find that the hydrostatic pressure of blood1 and lymph1 and secretion1 the osmotic pressure1 the diffusibility1 vaso-motor actions1 and other things must be investigated when considering the question of how the submaxillary gland secretes saliva4 ,one1 or as many as possible1 of these reactions are investigated at one time1 and then the results are pieced together--integrated--in order to reproduce the full activity of the whole indivisible process4 ,but in doing this do we not introduce something new--a direction or order of happening--into the elements of the dissociated activity of the organism8 ,each elemental process must occur at just the right time4 ,what right have we to say that the activity of the organism is made up of physico-chemical elements8 ,just as much as we have in saying that a curve is made up of infinitesimal straight lines4 ,let us adopt ,bergson's illustration1 with a non-essential modification4 ,illustration3 ,,fig4 #aj4 ,the curve #a-h is a line which we draw freehand with a single indivisible motion of the hand and arm and eye4 ,it is something unique and individualised1 in that no other curve ever drawn1 in a similar manner1 exactly resembles it4 ,let us investigate it mathematically4 ,we can select very small portions of it--elements we may call them--and each of these elements1 if it is small enough does not differ sensibly from a straight line4 ,let us produce each of these straight lines in both directions1 it is then a tangent to the curve1 and it does actually coincide with the curve at one mathematical point--the points #a-h in the figure4 ,the tangent then has something in common with the curve1 but would a series of infinitesimally small tangents reproduce the curve8 ,obviously not1 for the equations of the tangents would have the form ax b1 while that of the curve itself would be quite different1 containing x as powers of x1 or as transcendental functions of x4 ,in this investigation what we succeed in obtaining are the derivatives of the curve1 and to reproduce the latter from its elements we have to integrate the derivatives2 that is1 another operation differing in kind from our analytical one must be performed4 ,now in this illustration we have doubtless something more than an analogy with our physico-chemical analysis of life4 ,the activities of the organism do reduce to bio-chemical ones 7the elemental straight lines on the curve71 and each of these reactions has something in common with life 7it is tangent to life1 touching it at one point74 ,but if we attempt to reconstitute life from its physico-chemical derivatives we must integrate the latter1 and in doing so we over-pass the bounds of physics1 just as integrating a mathematical function we necessarily introduce the concept of the 8infinitely small40 ,the physico-chemical reactions into which we dissociate any vital function of the organism have1 then1 each of them1 something in common with the vital function4 ,but their mere sum is not the function4 ,to reproduce the latter we have to effect a co-ordination and give directions to these reactions4 ,in all physiological investigations we proceed a certain length with perfect success2 thus the elements1 so to speak1 of the function of the secretion of saliva are 7#a7 the blood-pressure1 7#b7 the hydrostatic pressure of the secretion in the lumina of the gland tubules1 7#c7 the diffusibility of the substances dissolved in the blood and lymph through the walls of these vessels1 7#d7 the osmotic pressure of the same substances1 and 7#e7 the stimulation of the gland cells by 8secretory nerve fires40 ,now the investigations carried out--and no part of the physiology of the mammal has been so patiently studied as the salivary gland--fail1 so far1 completely to describe the function in terms of these elements4 ,in the end we have to refer the secretion to intra-cellular processes1 and then we begin to invoke again processes of osmotic pressure1 diffusibility1 and so on with reference to the formation of the drops of secretion which we can see formed in the gland cells4 ,we are forced to the formulation of a logical hypothesis as to the nature of these intra-cellular processes1 and since much that goes on in the cell substance is1 so far1 beyond physico-chemical investigation1 our hypothesis will be as difficult to disprove as to verify4 99 99 99 99 99 ,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 hydrogen4 ,the lecture on the 8,physical ,basis of ,life0 was published in #ahfi2 in #aheb ,william ,thomson published his paper 8,on a ,universal ,tendency of ,nature to ,dissipation of ,energy10 and a year or two before that ,clausius had applied ,carnot's law to the kinetic theory of heat3 the second principle of energetics had therefore even then been exactly formulated1 but its significance for biological speculation had not been recognised by ,huxley1 any more than it has generally been recognised by most biologists since #ahfi4 ,what1 then1 does the comparison of ,huxley show8 ,clearly that the physical changes which occur in the explosion of a mixture of oxygen and hydrogen trend in a different direction from those which occur in the photo-synthesis of starch by a green plant4 ,generally speaking1 chemical activity1 that is1 the possibility of occurrence of chemical reactions1 is a case of the second law of energetics4 ,energy passes from a state of high to a state of low potential4 ,a chemical reaction will occur if this change of potential is possible4 ,in all such changes energy is dissipated4 ,what exactly does this mean8 ,it means that1 generally speaking1 the potential energy of chemical compounds tends to transform into kinetic energy2 while differences in the intensity factor of the kinetic energy of the bodies forming a system tend to become minimal4 ,in a mixture of oxygen and hydrogen there is energy of two kinds1 7#a7 potential energy due to the position of the molecules 7,o and ,h molecules are separated72 and 7#b7 kinetic energy of the molecules 7which are moving about in the masses of gas74 ,after the explosion the potential energy acquired in the separation of the molecules of ,o and ,h has disappeared 7the molecules having combined to form water71 but the kinetic energy has greatly increased1 since the explosion results in the formation of steam at high temperature4 ,but now this steam radiates off heat to adjacent bodies1 or becomes cooled by direct contact with the envelope which contains it4 ,the energy of the explosion is therefore distributed to the adjoining bodies1 and the temperature of the latter becomes raised4 ,but these again radiate and conduct heat to other bodies1 and in this way the heat generated becomes indefinitely diffused4 ,the general effect of all physico-chemical changes is therefore the generation of heat1 and then this heat tends to distribute itself throughout the whole system of bodies in which the physico-chemical changes occur4 ,the energy passes into the state of kinetic energy1 that is1 the motion of the molecules of the bodies to which the heat is communicated4 ,this molecular motion is least in solids1 greater in liquids1 and greatest in gases4 ,if solids1 liquids1 and gases are in contact1 forming complex systems1 the kinetic energy of their molecules becomes distributed in definite ways1 depending on the constants of the systems4 ,after this redistribution the kinetic energy of these molecules is unavailable for further energy transformations1 so that phenomena or change in the system ceases4 ,there is no longer effective physical diversity among the parts of the system4 ,we find that this conception of dissipation of energy cannot be applied to the organism1 at least not with the generality in which it applies to physical systems4 ,why8 ,not because the conception is unsound1 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 order4 ,the second law of energetics is subject to limitations1 and it is because it is applied to organic happenings without regard to these limitations that it does not describe the activities of the organism as well as it describes those of inorganic nature4 ,what1 then1 are these limitations8 ,we note in the first place that the laws of thermodynamics apply to bodies of a certain range of size2 or at least the possibility of mathematical investigation 7on which1 of course1 all depends7 is limited to 8differential elements0 of mass1 energy1 and time4 ,we cannot apply mathematical analysis to bodies1 or time-intervals of 8finite size10 since the methods of the differential and integral calculus would not strictly be applicable4 ,but molecules are so small 7#a cubic centimetre of a gas may contain about #e4d #ajai of them7 that even such a minute part of a body1 or liquid1 or gas as approximates to the infinitesimally small dimensions required by the calculus1 contains an enormous number of molecules4 ,obviously we cannot investigate the individual molecules4 ,even if experimental methods could be so applied1 such concepts as density1 pressure1 volume1 or temperature would have no meaning4 ,physics1 then1 is based on collections of molecules1 and the properties of a body are not those of a molecule of the same body4 ,such concepts as temperature and pressure are statistical ones1 and are applied to the mean properties of a large number of molecules4 ,illustration3 ,,fig4 #aa4 ,we can best illustrate this by considering ,maxwell's famous fiction of the 8sorting demons40 ,let us imagine a mass of gas contained in a vessel the walls of which do not conduct heat4 ,let there be a partition in this vessel also of non-conducting material1 and let there be an aperture in this partition greater in area than a molecule1 but smaller than the mean free path of a molecule4 ,now this mass of gas has a certain temperature which is proportional to the mean velocity of movement of the molecules4 ,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 outside1 nor can an inequality of temperature be produced in a mass of gas or liquid except under a similar condition4 ,but 8conceive a being10 says ,maxwell1 8whose faculties are so sharpened that he can follow every molecule in its course2 such a being1 whose attributes are still as essentially finite as our own1 would be able to do what is at present impossible to us40#bj ,for the temperature of the gas depends on the velocities of the molecules1 and in any part of the gas these velocities are very different4 ,suppose that the demon saw a molecule approach which was moving at a much greater velocity than the mean3 he would then open the door in the aperture and let it pass through from - to 4 ,on the other hand1 should a molecule moving at a velocity much less than the mean approach he would let it pass from to -4 ,in this way he would sort out molecules of high from those of low velocity4 ,but the collisions between the molecules in either division of the vessel would continually produce diversity of individual velocity1 and in this way the difference of temperature between and - would continually be increased4 ,heat would thus flow from a region of low to a region of high temperature without an equivalent amount of work being expended4 #bj ,impossible1 in the sense that while we are unable to 8abrogate0 a physical law1 ,maxwell's finite demon could1 although his faculties were similar in nature to ours4 ,now we must not introduce demonology into science1 so1 lest this fiction of ,maxwell's should savour of mysticism1 or something equally repugnant1 we shall state the idea involved in it in quite unexceptionable terms4 ,the conclusions of physics are founded on the assumption that we cannot control the motions of individual molecules4 ,in a mass of gas1 or liquid1 or in a solid1 the molecules are free to move and do move4 ,their individual velocities and free paths vary considerably from each other4 ,these motions and paths are un-co-ordinated--8helter-skelter0--if we like so to term them4 ,physics considers only the statistical mean velocities and free paths4 ,the irreversibility of physical phenomena1 the fact that energy tends to dissipate itself1 the second law of thermodynamics1 depend on the assumption that ,maxwell's demons exist only in imagination4 ,we must appeal to experience now4 ,there is no a priori reason why the phenomena of physics should be directed one way and not the other1 for it is possible to conceive a condition of our ,universe in which1 for instance1 solid iron would fuse when exposed to the atmosphere4 ,in such conditions organisms would grow backwards from old age to birth1 with conscious knowledge of the future but no recollections of the past4 ,experience shows1 however1 that phenomena do tend in one way--but this experience is that of experimental physics1 so that for the latter science ,maxwell's demons do not exist4 ,now physiology has borrowed from physics1 not only the experimental methods1 but also the fundamental concepts of thermodynamics4 ,the organism1 therefore 7so physiology must conclude71 cannot control the motions of individual molecules1 and so vital processes are irreversible4 ,but we have seen that the processes of terrestrial life as a whole are reversible1 or tend to reversibility4 ,we must therefore seek for evidence that the organism can control the1 otherwise1 un-co-ordinated motions of the individual molecules4 ,the ,brownian movement of very small particles of matter is so familiar to the biologist that we need not describe it4 ,it is doubtless due to the impact of the molecules of the liquid in which the particles are suspended4 ,groups of molecules travelling at velocities above the mean hit the particle now on one side1 and again on the other1 and so produce the peculiar trembling which ,brown thought was life4 ,now the particle must be below a certain size in order to be so affected4 ,are there organisms of this size8 ,undoubtedly there are1 for many bacilli show ,brownian movements1 while we have reasons for believing that ultra-microscopic organisms exist4 ,also1 on the mechanistic hypothesis there are 8biophors10 the size of which is of the same order as that of the molecules of the more complex organic compounds4 ,all these must be affected by the molecular impacts of the liquid in which they are suspended4 ,can they distinguish between the impacts of high-velocity molecules and those of mean-velocity ones1 and can they utilise the surplus energy of the former8 ,this has been suggested by the physicists4 ,in ,brownian movement1 says ,poincar1 8we can almost see ,maxwell's demons at work40 ,the suggestion is not merely a speculative one1 for it is well within the region of experiment4 ,to prove it experimentally we should only have to show that the temperature of a heat-insulated culture of prototrophic bacteria falls while the organisms multiply4 ,is it not strange that the biologists1 to whom the ,brownian movement is so familiar1 should have failed to see its possibly enormous significance8 ,is it not strange that the biologists1 to whom the distinction between the statistical and individual methods of investigation is so familiar1 should have failed to appreciate this distinction when it was made by the physicists8 ,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 take1 we should yet have failed to think of primitive organisms1 or even of the tissue elements in the bodies of the higher organisms1 as possessing also this power of directing physico-chemical processes8 ,,chapter ,,iv ,,the ,,vital ,,impetus ,two main conclusions emerge from the discussions of the last three chapters3 7#a7 that physiology encourages no notions as to a 8vital principle0 or force1 or form of energy peculiar to the organism2 and 7#b7 that although physiological analysis resolves the metabolism of the plant and animal body into physico-chemical reactions1 yet the direction taken by these is not that taken by corresponding reactions occurring in inorganic materials4 ,from these two main conclusions we have1 therefore1 to construct a conception of the organism which shall be other than that of a physico-chemical mechanism4 ,the ordinary person1 unacquainted with the results of physiological analysis1 and knowing only the general modes of functioning of the human organism1 has1 probably1 no doubt at all that it is 8animated0 by a principle or agency which has no counterpart in the inorganic world4 ,this is the 8natural0 conclusion1 and the other one1 that life is only an affair of physics and chemistry1 must appear altogether fanciful to anyone who knows no more than that the heart propels the blood1 that the latter is 8purified0 in the lungs1 that the stomach and liver secrete substances which digest the food1 and so on4 ,it is difficult for the modern student of biology1 saturated with notions of bio-chemical activities1 gels and sols and colloids and reversible enzymes and kinases and the like1 to realise that the belief in a vital agency is an intuitive one1 and that the mechanistic conception of life is only the result of the extension to biology of methods of investigation1 and not a legitimate conclusion from their results4 ,to the anatomist1 the embryologist1 and the naturalist1 as well as to the physicist unacquainted with the details of physiology1 no less than to the ordinary person this is perhaps by far the most general attitude of mind4 ,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 which1 for instance1 shape continents1 or deltas1 or river valleys4 ,and this conclusion would probably come with still greater force to the embryologist1 even though he still possessed a general knowledge of physiological science4 ,the mechanistic conception of life has1 without doubt1 been the result of the success of a method of analysis4 ,one sees clearly that just in proportion as physical and chemical sciences have been most prolific of discovery1 so physiology1 leaning upon them and borrowing their methods1 has been most progressive and mechanistic4 ,mechanistic hypotheses of the organism may all be traced back to ,descartes1 who built upon the work of ,galileo and ,harvey4 ,the anatomy of ,vesalius and his successors would have led to no such notions1 had not the discoveries of ,copernicus1 ,tycho1 and ,kepler shown men an universe actuated by mechanical law4 ,to a thinker like ,descartes1 at once the very type of philosopher and man of science1 ,harvey's discovery of the circulation of the blood must have suggested irresistibly the extension of mechanical law to the functioning of the human organism1 and it is significant that he made this extension without including a single chemical idea1 and yet produced a logical hypothesis of life as satisfactory and complete in its day as1 for instance1 the ,weismannian hypothesis of heredity has been in ours4 ,his hypothesis of the organism was purely mechanical4 ,it has been said that his organism was an automaton1 like the mechanical ,diana of the palace gardens which hid among the rose-bushes when the foot of a prying stranger pressed upon the springs hidden in the ground4 ,its functions were matters of hydraulics3 of heat1 and fluids1 and valves4 ,his physiology was ,galenic1 apart from ,harvey's discovery of the motion of the blood in a circuit1 for he did not accept the notion of the heart as a propulsive apparatus4 ,the food of the intestine was absorbed as chyle by the blood and carried to the liver1 where it became endued with the 8natural spirits10 and then passing to the heart it became charged with the 8vital spirits0 by virtue of the flame1 or innate heat1 of the heart1 and the action of the lungs4 ,this flame of the heart1 fed by the natural spirits1 expanded and rarefied the blood1 and the expansion of the fluid produced a motion1 which1 directed by the valves of the heart and great vessels1 became the circulation4 ,the more rarefied parts of the blood ascended to the brain1 and there1 in the ventricles1 became the 8animal spirits40 ,subtle and rarefied though they were1 these animal spirits were a fluid1 amenable to all the laws of hydro-dynamics4 ,this was contained in the cerebral ventricles1 and its flow was regulated just like the water in the pipes and fountains of the garden mechanisms4 ,from the brain it flowed through the nerves1 which were delicate tubes in communication with the ventricles1 and which were provided with valves2 and this outward flow corresponds to our modern efferent nervous impulse4 ,the afferent impulse was represented by the action of the axial threads contained in the nerve tubuli4 ,when a sensory surface was stimulated1 these threads became pulled1 and the pull1 acting on the wall of the cerebral ventricle1 caused a valve to open and allowed animal spirits to flow along the nerve to all the parts of the body supplied by the latter4 ,in the effector organs1 muscles or glands1 this influx of animal spirits produced motion or other effects4 ,this1 in brief1 was the physiology of ,descartes4 ,he spoiled it1 says ,huxley1 by his conception of the 8rational soul40 ,fearing the fate of ,galileo1 he introduced the soul into his philosophy of the organism as a sop to the ,cerberus of the ,church4 ,it was unworthy3 a sacrifice of the truth which he saw clearly4 ,is it likely that ,descartes deliberately made part of his philosophy antagonistic to the rest with the object of averting the censure of the ,church8 ,he was not a man likely to rush upon disaster1 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 truth4 ,the rational soul was something superadded to the bodily mechanism4 ,it was not a part of the body though it was placed in the pineal gland2 a part of the brain1 which by its sequestered situation and rich blood supply suggested itself as the seat of some important and mysterious function4 ,its existence was bound up with the integrity of the body1 and on the death of the latter the soul departed4 ,but the body did not die because the soul quitted it1 it had rather become an unfit habitation for the soul4 ,without the latter the functions of the healthy body might still proceed automatically1 and if the soul influenced action it actuated an existing mechanism1 and without that mechanism it could not act1 though the mechanism might act without the soul4 ,thought1 understanding1 feeling1 will1 imagination1 memory1 these were the prerogatives of the soul1 and not those of the automatic body4 ,but the movements of the latter1 even voluntary movements1 depended on a proper disposition of organs1 and without this they were wanting or imperfect4 ,thus to a thoroughgoing mechanism ,descartes joined a spiritualistic and immortal entity2 and this1 to the materialism of the middle of the nineteenth century1 was the blemish on his philosophy4 ,now of all men who have ever lived he is probably the one who has most profoundly influenced modern thought and investigation3 to us what he wrote seems strangely modern1 and this apparently arbitrary association of spiritualistic and materialistic elements in life seems almost the most modern thing in his writings4 ,being1 he said1 was indeed thought1 but how could he derive thought from his clockwork body1 with its valves and conduits and wires8 ,no more can we derive consciousness from the wave of molecular disturbance passing through afferent nerve and cerebral tracts4 ,we must account for all the energy of this disturbance1 from its origin in the receptor organ to its transformation into the wave of chemical reaction in the muscle1 and we must regard its transmission as a conservative process4 ,but how does the state of consciousness accompanying the passage through the cortex of this molecular disturbance come into existence8 ,none of the energy of the nerve disturbance has been transformed into consciousness3 the latter is not energy nor anything physical4 ,it is something concomitant with the physico-chemical events involved in a nervous process1 an 8epiphenomenon40 ,we have to imagine a 8parallelism0 between the mechanistic body and the mind4 ,but if we admit that consciousness may be an effective agency in our behaviour1 what is the difference between modern theories of physico-psychic parallelism and the ,cartesian theory of a rational soul in association with an automatic body8 ,descartes denied the existence in animals other than man of the rational soul2 the latter was not necessary4 ,but he1 like us1 must have been familiar with reflex actions and must have seen that consciousness was not invariably associated1 even in himself1 with bodily activity4 ,and he must have recognised the great distinction between the intelligent acting of man and the instinctive behaviour of the lower animals4 ,there was something in man that was not in the brute4 ,thus the first physiology1 borrowing its ideas and methods from the first physics1 was1 like the latter1 a mechanical science4 ,after ,galileo and ,torricelli came ,borelli with his purely mechanical conceptions of animal movement1 and of the blood circulation1 introducing even then mathematics into biology4 ,there was no chemistry in these speculations1 though ,basil ,valentine and ,paracelsus and ,van ,helmont had preceded ,descartes and ,borelli4 ,this chemistry was mystical1 and though chemical reactions had been studied in the organism1 they were supposed to be controlled by spiritual agencies1 the 8archei0 of the first bio-chemists4 ,but that notion was to disappear1 and with ,sylvius the conception of the animal body as a chemical mechanism arose4 ,all that was valuable in ,van ,helmont's chemistry was taken up by ,sylvius1 but in his mind the fermentations of the older chemists were sufficient in themselves without the mystical 8sensitive soul0 and 8archei40 ,with ,sylvius and ,mayow physiology became based upon chemical discovery and again became mechanistic1 and remained so until the time of ,stahl1 when chemical discovery attained for the time its greatest development4 ,the seventeenth century ended with the work of ,stahl4 ,it is well known to students of science how the views of this great chemist sterilised chemical investigation almost until the time of ,lavoisier4 ,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 one1 and it served as a working hypothesis for the chemists who immediately followed ,stahl4 ,it was1 of course1 a false hypothesis1 and retarded discovery to the extent that the greater part of the eighteenth century is a blank for chemistry1 when compared with the seventeenth and nineteenth centuries4 ,deprived therefore of the stimulus afforded by new physico-chemical methods of investigation1 physiology ceased to maintain the progress it had made during the previous century1 and the only great name of this period is that of von ,haller4 ,comparative anatomy1 and zoological exploration1 on the other hand1 made enormous advances1 and for these branches of biology the eighteenth century was the great period4 ,it was the period of the historic vitalistic views--vital principles1 and vital and formative forces4 ,stahl's teaching dominated physiology just as it did chemistry4 ,chemical and physical reactions occurred in the living body just as they did in non-living matter1 but they were controlled and modified by the soul1 or vital principle4 ,it has been said that ,stahl's vitalistic teaching retarded the progress of physiology1 but it does not seem clear that this was the case4 ,what did retard physiological discovery was the lack of progress made by chemistry and physics1 and this may have been the result of the ,stahlian phlogistic hypothesis4 ,however this may be1 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 physiology4 ,with the discoveries of ,lavoisier and his successors the latter science acquired new methods of research and the older working hypotheses were re-introduced4 ,there has been no recession from this position during the nineteenth century4 ,mechanistic biology culminated in the writings of ,huxley and ,max ,verworn and received a new accession of strength almost in our own day in the modern discoveries of physical chemistry2 and when physiology became truly a comparative science1 and embraced the lower invertebrates1 it became perhaps most mechanistic--witness the writings of ,jacques ,loeb4 ,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 processes4 ,the former deals essentially with the means of growth1 reproduction1 and so on4 ,we can no longer doubt that the changes which we can observe taking place in the organism1 either the developing embryo or the fully formed animal1 are1 in the long run1 physico-chemical changes2 and in ultimate analysis we cannot expect to find anything else than processes of this nature4 ,but physiological investigation has failed to provide anything more than this analysis4 ,if we watch the development of the egg of an animal into a larval form1 and continue to trace the metamorphosis of the larva into the perfect animal1 we cannot fail to conclude that1 beside the individual physico-chemical reactions which proceed1 there is also organisation4 ,the elementary processes must be integrated4 ,there must be a due order and succession in them4 ,in studying developmental processes1 in considering the developing organism as a whole1 we are impressed above all else with the notion that not only do physico-chemical reactions occur1 but that these are marshalled into place1 so to speak4 ,when we attempt to make a description of this integration of those ultimate processes which we can describe in terms of physical chemistry1 physiology fails us4 8,at present10 says ,morgan1 8we cannot 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 organism40 ,it is true that we can attempt to imagine a physico-chemical mechanism which is the organisation of the developing embryo2 but this must be a logically constructed mechanism1 not only incapable of experimental verification1 but which can also be demonstrated1 purely by physical arguments1 to be false4 ,this conclusion may1 without exaggeration1 be said to be that of modern experimental embryology4 ,there have always been 7in modern times7 two views as to the nature of the embryological process3 7#a7 that the egg contained the fully formed organism in a kind of rolled-up condition1 and that the process of development consisted merely in the unfolding 7evolution7 of this embryonic organism1 and in the increase in volume of its parts4 ,this was the hypothesis of preformation held in the beginning of embryological science4 ,it involved various consequences3 the limitation1 for instance1 of the duration of a species1 since each generation of female organisms contained in their ovaries all the future generations2 with other consequences which the preformationists did not hesitate to accept4 7#b7 ,the other view was the later one of epigenesis3 the egg was truly homogeneous and the embryo grew from it4 ,obviously the acceptance of this hypothesis led to vitalism1 and we find that it was abandoned just as soon as the embryologists recognised that physics provided a corpuscular theory of matter1 when a return was made to the preformation views of earlier times2 views which lent themselves to the construction of a mechanistic hypothesis of development4 ,illustration3 ,,fig4 #ab4 ,we may state very briefly the main facts of the development of a typical animal ovum1 such as that of the sea-urchin4 ,the fertilised ovum divides into two 7#b71 and then each of these blastomeres divides again in a plane perpendicular to the first division plane 7#c74 ,the third division plane is at right angles to the first two1 and it cuts off a tier of smaller blastomeres from the tops of the first four4 ,there are now 7#d7 two tiers of blastomeres1 a lower tier of large blastomeres and an upper tier of smaller ones4 ,this is the #h-;cell stage4 ,next1 each of these blastomeres divides in two simultaneously so that the embryo now consists of sixteen cells4 ,after this the divisions proceed with less regularity1 but after about ten divisions the embryo consists of about #ajjj cells 7#baj71 and these are arranged to form a hollow sphere consisting of a single layer of cells4 ,the latter are furnished with cilia1 and the whole embryo1 now known as the blastula1 can swim about by the movements of these cilia4 ,further development results in another larval form--the gastrula1 and yet another1 the pluteus larva4 ,after this the transformation into the fully formed sea-urchin occurs4 ,with various modifications this scheme represents the early development of a very large number of animals belonging to most groups4 ,if we study the process of cell-division we shall find it very complicated4 ,the ovum1 immediately after fertilisation1 consists of two main parts1 the nucleus and the cytoplasm4 ,illustration3 ,,fig4 #ac4 ,within the nucleus is a substance distinguishable from the rest2 it is distributed in granules and is called the chromatin 7#a74 ,when the cell is about to divide this chromatin becomes arranged in a long coiled thread 7#b71 and then 7#c7 this chromatic thread breaks into short rods called chromosomes4 ,two little granules now appear1 one at each end of the nucleus1 and very delicate threads1 the asters1 appear to pass from each of these bodies towards the chromosomes 7#d74 ,each of the latter then splits lengthways into two1 and a half chromosome appears to be drawn by the asters towards the poles of the nucleus4 ,the latter then divides 7#e7 and then the whole cell divides4 ,what thus1 in essence1 happens in nuclear divisions is that the chromatin of the nucleus is more or less accurately halved4 ,apparently this substance consists of very minute granules and the whole process is directed towards the splitting of each of these granules into two4 ,a half-granule then goes to each of the daughter nuclei4 ,every time the embryo divides this process is repeated4 ,thus each of the 7theoretically7 #ajbh cells of the blastula contains #a_/ajbhth of the substance of each chromatic granule in the fertilised ovum4 ,pfluger and ,roux 7in #ahhc and #ahhh respectively7 were the pioneers in the experimental study of the development of the ovum1 and the results of their work and that of their successors has1 more than anything else in biology1 modified and shaped our notions of the activities of the organism4 ,roux found1 or thought so at least1 that the first division of the frog's egg marked out the right and left halves of the body1 the one blastomere giving rise to the right half1 the other to the left half4 ,the next division1 which separates each of these blastomeres1 marked out the anterior and posterior parts of the embryo4 ,thus3-- ,illustration3 ,,fig4 #ad4--,the frog's egg in the #d-;blastomere stage seen from the top4 ,now in an experiment which has become classical ,roux succeeded in killing one of the blastomeres in the #b-;cell stage1 while the other remained alive4 ,the uninjured blastomere then continued to develop1 but it gave rise to a half-embryo only4 ,upon these experiments the ,roux-,weismann hypothesis of development--the 8,mosaik-,theorie0--was developed4 ,the lay reader will see how obviously the facts of nuclear division and the experimental results indicated above lend themselves to a mechanistic hypothesis4 ,notice that but for the physical conception of matter as made up of molecules and atoms the mosaic-theory would hardly have shaped itself in the minds of biologists4 ,but this notion of matter consisting of corpuscles must have suggested that the essential 8living material0 of the organism consisted also of corpuscles1 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 visible4 ,obviously the primordial ovum contained all the elements of the organisms into which it was going to develop4 ,but then in the process of division of the ovum all these chromatic granules are shared out among the cells1 and a really very pretty mechanism comes into existence for this purpose of distribution4 ,weismann built up his hypothesis of the germ-plasm upon the observations we have outlined4 ,the chromatic matter of the nucleus consists of elements called determinants1 the determinants themselves being composed of ultimate bodies called biophors4 ,each determinant possesses all the mechanism1 or factors1 necessary for the development of a part of the body3 there are determinants for muscles1 nerves1 connective tissues1 for the retina of the eye1 for hairs of each colour1 for the nails1 and so on4 ,all these determinants are contained in the chromatin of the nucleus of the egg1 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 part1 or organ1 or organ-system of the adult body4 ,the right blastomere1 for instance1 contains all the determinants for the right side of the frog's body1 those for the left side being contained in the left half4 ,the process of cell-division involved in the segmentation of the egg consists then in the orderly disintegration of this complex of determinants1 and in the marshalling into place of the isolated elements4 ,the cell body--the cytoplasm--carried out a very subordinate rle1 mainly that of nourishing the essential chromatic substance4 ,such was the ,roux-,weismann ,mosaic-theory of development in its pristine form4 ,it is clearly a preformation hypothesis4 ,it is true that the actual organism is not contained in the germ1 but all the parts of the latter1 even the colours of the eyes or hair1 are present in it in the form of the determinants4 ,obviously it involves a mechanism of almost incredible complexity4 ,but if we regard it as a working hypothesis of development this complexity of detail does not matter2 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 complexity4 ,but this is exactly what has not happened1 for all subsequent investigation has necessitated subsidiary hypothesis after hypothesis4 ,as a theory of development it has failed entirely4 ,if1 after one of the blastomeres in the frog's egg at the #b-;cell stage be killed1 the egg is then turned upside down1 the results of the experiment become totally different2 the uninjured blastomere develops into a whole embryo1 differing from the normal one chiefly in that it is smaller4 ,if the uninjured egg in the #b-;cell stage be turned upside down two whole embryos1 connected together in various ways1 develop4 ,in the frog's egg the two first blastomeres cannot be separated from each other without rupturing them1 but in the egg of the salamander they can be separated4 ,after this separation two perfect1 but small1 embryos develop4 ,in the egg of the newt a fine thread can be tied round the furrow formed by the first division4 ,if this ligature be tied loosely it does not affect development1 and then it can be seen that the median longitudinal plane of the embryo does not correspond1 except by chance1 with the first division plane4 ,if the ligature be tied tightly1 then each of the blastomeres gives rise to an entire embryo4 ,if it is tied in various places monsters of various types are produced4 ,therefore there is no segregation of the determinants in the first two blastomeres4 ,these results1 moreover1 are not exceptional1 for similar ones have been obtained with other animal embryos1 in fishes1 ,amphioxus1 ascidians1 medus1 and hydrozoa1 and in some cases even each of the first four blastomeres develops into an entire embryo when it is separated from the rest4 ,in the sea-urchin embryo the blastomeres can be shaken apart2 or by removing the calcium which is contained in sea water the blastomeres can easily be separated from each other4 ,it was then found by ,driesch that each of the blastomeres in the #af-;cell stage could develop into an entire embryo4 ,it is plain1 then1 that up to this stage at least there has been no segregation of the determinants4 ,upon the results of these experiments ,driesch based his first proof of vitalism4 ,let us suppose that there is a mechanism in the developing egg4 ,now the embryo which results from the latter sooner or later acquires a three-dimensional arrangement of parts3 head-end differs from tail-end1 dorsal surface differs from ventral surface1 and the parts differ on either side of the median plane4 ,the mechanism must1 therefore1 be one which acts in three dimensions1 anterior and posterior1 laterally1 and dorso-ventrally4 ,we may represent it by a diagram of three co-ordinate axes1 x1 y1 z2 x and y being in the plane of the paper1 and z at right angles to the plane of the paper4 ,now in the #b-;cell stage the same mechanism must be present1 for this stage develops normally into one entire embryo4 ,but since either of the blastomeres may develop into an entire embryo1 the mechanism must also be present in each of them1 and since in the #af-;cell stage each blastomere may develop an entire embryo1 it must be present in each of the sixteen blastomeres4 ,a three-dimensional mechanism is therefore capable of division down to certain limits4 ,illustration3 ,,fig4 #ae4 ,illustration3 ,,fig4 #af4 ,suppose now that we allow the sea-urchin egg to develop normally up to the blastula stage4 ,in this stage it is a hollow sphere1 the wall of which is a single layer of cells4 ,it is similar all round1 that is1 we cannot distinguish between top and bottom1 right and left1 anterior and posterior regions2 but since it develops into a larva in which all these distinctions become apparent very soon1 it must possess the three-dimensional mechanism1 since the activity of the developmental process is going to produce different structures in each direction4 ,now the blastula1 by very careful manipulation can be divided1 cut into parts with a sharp knife4 ,since it is similar all round the direction of the cut is purely a matter of chance4 ,it can be cut through along the planes #a #b1 #c #d1 #e #f1 #g #h1 for instance2 really there are an infinite number of planes along which the blastula can be cut into two separate parts1 and the direction of the plane is not a matter of choice1 but purely a matter of chance4 ,nevertheless1 each of the parts into which the larva is cut becomes an entire embryo4 ,for a time the partial blastula--approximately a hollow hemisphere in form--goes on developing as if it were going to become a partial embryo1 but soon the opening closes up and development becomes normal4 ,it does not matter even if the two parts into which it is divided are not alike in size2 provided that a part is not too small1 it will follow the ordinary course of development4 ,illustration3 ,,fig4 #ag4 ,suppose the blastula opened out on the flat1 like the ,mercator projection of a globe on a flat map4 ,suppose that a is a small element of it4 ,suppose that the rectangles b c d e1 ,f ,g ,h e1 ,i ,j c ,l1 ,m ,n ,o e1 and as many more as we care to make1 represent the pieces of the blastular wall separated by our operation--they all contain the element a1 but this is in a different position in each case4 ,there are really an infinite number of such parts of the blastula and a occupies an infinitely variable position in each of them4 ,this demonstration is very important1 so let us make it as clear as possible3 ,driesch's logical proof of vitalism may be stated as follows3-- ,the different parts of the blastula are going to become different parts of an embryo4 ,the part a1 occupying a definite position in the entire blastula1 is going to become a definite part1 having a definite position1 in the embryo2 ,but each partial blastula becomes an entire embryo and the same part a occupies a different position in each4 ,therefore any part of the blastula may become any part of the embryo4 ,now if a mechanism is involved1 it must1 according to our ideas of mechanism1 be one which is different in its parts1 for each part of it produces a different result from the others2 ,but since any part of the mechanism may produce any of the different results contained in the embryo1 every one of its parts must be similar to every other one4 ,that is1 all the parts of the mechanism are the same1 though the hypothesis requires that they should be different4 ,we conclude1 then1 that a mechanism such as we understand a mechanism to be in the physical sciences cannot be present in the developing ovum4 ,nevertheless1 an organisation1 using this term as an ill-defined one for the present1 must exist in the ovum1 or the system of undifferentiated cells into which the ovum divides1 during the first stages of segmentation4 ,in certain animals1 ,ctenophores 7,chun1 ,driesch1 and ,morgan71 and ,mollusca 7,crampton71 for instance1 separation of the blastomeres in the first stages of segmentation produces different results from those mentioned above4 ,in these cases the isolated blastomeres develop as partial embryos1 that is1 the latter are incomplete in certain respects1 and this incompleteness corresponds1 in a general way1 to the incompleteness of the part of the ovum undergoing development4 ,we have thus the apparently contradictory results3 7#a7 each of the first few blastomeres resulting from the first divisions of the ovum is similar to the entire ovum1 and develops like it2 and 7#b7 each of the first few blastomeres is different from the others1 and from the entire ovum1 and develops differently from the others1 and from the entire ovum4 ,let us try to construct a notion of what this organisation in the developing ovum must be4 ,in the #af-;blastomere stage of the sea-urchin egg we have a 8system0 of parts4 ,in the case of normal development each of these parts has a certain actual fate--it will form a part of the larva into which the embryo is going to develop3 ,it has1 as ,driesch says1 a prospective value4 ,but let the normal process be interfered with1 and then each of these parts does something else4 ,in the extreme case of interference1 when the blastomeres are separated from each other1 each blastomere1 instead of forming only a part of a larva1 forms a whole larva4 ,the prospective potency of the part1 that is its possible fate1 is greater than its prospective value4 ,normally it has a limited1 definite function in development1 but if necessary it may greatly exceed this function4 ,what any one blastomere in the system will become depends upon its position with regard to the other blastomeres4 ,when the egg of the frog is floating freely in water it lies in a certain position with the lighter part uppermost1 and then development is normal1 each of the two first blastomeres giving rise to a particular part of the body of the larva2 that is1 each of them is affected by the contact of the other and develops into whatever part of the normal embryo the other does not4 ,but let the egg in the #b-;cell stage be turned over and held so that the heavy part is uppermost3 the protoplasm then begins to rotate so as to bring the lighter part uppermost2 but the two blastomeres do not1 as a rule1 adjust themselves to the same extent1 and at the same rate1 and corresponding parts may fail to come into contact with each other4 ,lacking1 then1 the normal stimulus of the other part1 each blastomere begins to develop by itself1 and a double embryo is produced4 ,it is clear1 then1 both from this case and the last one1 that the actual fate of any one part of the system of blastomeres is a function of its position4 ,what it will become depends precisely on where it is situated with respect to the other parts4 ,driesch1 then1 calls the system of parts in such cases as the #b-;cell frog embryo1 or the #af-;cell sea-urchin embryo1 an equipotential system1 since each part is potentially able to do what any other part may do1 and what the whole system may do4 ,but in normal development each part has a definite fate and its activity is co-ordinated with that of all the other parts4 ,it is1 therefore1 an harmonious equipotential system1 each part acting in harmony1 and towards a definite result1 with all the others2 although if necessary it can take the place of any or all of the others4 ,such an harmonious equipotential system exists only at the beginning of the development of the egg4 ,it is represented by the #h-;cell stage of ,echinus but not by the #af-;cell stage1 since1 though the #a_/af-;blastomeres produce gastrul 7the first larval stage71 they do not produce plutei 7the second stage74 ,it is represented by the #d-;cell stage of ,amphioxus but not by the #h-;cell stage4 ,it is not exhibited even by the #b-;cell stage of the ,ctenophore egg4 ,what does this mean8 ,it means that the further development proceeds1 the less complete does the 8organisation0 inherent in any one part of the system become4 8,the ontogeny assumes more and more the character of a mosaic work as it proceeds0 7,wilson74 ,or perhaps it means1 and this is the better way of putting it1 that the 8organisation10 whatever it may be1 depends on size4 ,we see this very clearly in the experiment of cutting in two the blastula of the sea-urchin4 ,if the pieces are of approximately equal size each will form an entire ,pluteus larva1 but if one of them is below a certain limit of size it will not continue to develop4 ,the 8organisation10 therefore1 has a certain volume1 and this volume is much greater than that of any one of the cells of which the fragment exhibiting it is composed4 ,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 larva1 and still more enormously greater than the volume of a 8molecule0 of protoplasm4 ,now this association of 8organisation0 and size is of immense philosophical importance1 for it does away1 once and for all1 with the idea that the 8organisation0 is solely a series of chemical reactions4 ,if it were1 one cell of the blastula would contain it1 for on the mechanistic hypothesis one cell1 the egg-cell1 contains it1 and this cell can be divided innumerable times and still contain it4 ,the egg is a complex equipotential system 7,driesch71 which divides again and again throughout innumerable generations1 and still contains the 8organisation40 ,it is in vain that we attempt the misleading analogy of the 8mass action0 of physical chemistry1 to show that volume may influence chemical action4 ,in such a mass action what we have is this3-- ,aa ,bb ,cc ,dd the letters ,a1 ,b and ,c standing for chemical substances present1 and the letters a and b1 etc41 representing the active masses of these substances4 ,but variations in this active mass affect only the velocity of the reaction4 ,what we have to account for in our blastula experiments is the nature of the reaction1 and how can velocity or even nature of reaction affect form8 ,if we could show that the form of the crystals deposited from a solution in some reaction depended on the volume of the solution1 the analogy would be closer1 though even then the difficulties in pressing it would be so enormous as to render it futile to attempt to entertain it4 ,a chemical mechanism cannot1 then1 be imagined1 much less described1 and the only other mechanism so far suggested is the ,roux-,weismann one1 involving the disintegration of the determinants supposed to be present in the egg nucleus4 ,let us suppose 7in spite of the incredible difficulty in so doing7 that there is such a mechanism4 ,it must usher the nuclei containing the determinants of the embryonic structure into their places3 those for the formation of the nerve-centre go forward2 those for the mouth1 gut1 and anus go backwards and downwards2 those for the arms go forwards1 ventrally1 and posteriorly1 in a very definite way2 and those for the complicated skeleton are distributed in a variety of directions which defy description4 ,these nuclei are1 in short1 moved up and down1 right and left1 backwards and forwards1 and become built up into a complicated architecture4 ,suppose we prevent this4 ,suppose we compress the segmenting egg between glass plates so that the nuclei are compelled to distribute themselves in one plane only3 to form a flattened disc in which the only directions are right and left and anterior and posterior4 ,this has been done by ,driesch and others4 ,on the ,roux-,weismann original hypothesis a monstrous larva ought to result1 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 normally4 ,yet on releasing the pressure readjustment takes place4 ,new divisions occur so as to restore the normal form of larva4 ,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 disturbance4 ,let us remove some of the blastomeres4 ,on the original hypothesis the determinants for the structures which the nuclei of these blastomeres contained have been lost4 ,these structures should1 therefore1 be missing in the embryo4 ,but nothing of the sort is the result4 ,other nuclei divide and replace the lost ones1 and the embryo develops as in the normal mode4 ,the reply is that in addition to the determinants which were necessary for their own peculiar function1 these nuclei contained a reserve of all others4 ,on disturbance these determinants1 8latent0 in all other conditions1 became active and restituted the lost parts4 ,let us remove some organ from an adult organism4 ,the most remarkable experiment of this kind is the removal of the crystalline lens from the eye of the salamander4 ,now the lens of the eye develops from the primitive integument 7ectoderm7 of the head1 but the iris of the eye develops mainly from a part of the primitive brain4 ,after the operation a new lens is formed from the iris and not from the cornea4 ,therefore the highly specialised iris contains also determinants of other kinds4 ,does it contain those for itself and lens only1 or others8 ,if it contains many kinds1 then we conclude that even the definite adult structures contain determinants of many other kinds than their own1 that is1 reserve determinants are handed down in all cells capable of restitutive processes1 practically all the cells of the body4 ,or does it contain only its own and those of the lens8 ,then this highly artificial operation was anticipated1 an absurd hypothesis which need not be considered4 ,this particular mechanistic process 7and no other one is nearly so plausible7 crumbles away before attempts at verification1 and it survives only by the addition of subsidiary hypothesis after hypothesis4 ,in itself this demonstrates that it is an explanation incompetent to describe the facts4 ,what1 then1 is the 8organisation08 ,it is something elemental1 and we may just as well ask what is gravity1 or chemical energy1 or electric energy4 ,it cannot be said to be any of these things or any combination of them4 8,at present10 says a skilful and distinguished experimenter1 ,t4 ,h4 ,morgan1 8we 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 organism40 8,probably we shall never be able10 concludes ,morgan1 who is anything but a vitalist4 ,but does not this mean just that in biology we observe the working of factors which are not physico-chemical ones8 ,we have seen that the physiologist studies something very different from that which the embryologist or naturalist studies4 ,the former investigates a part of the animal1 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 once4 ,he adopts the methods of physical chemistry in his investigation and whatever results he obtains are necessarily of the same order4 ,inevitably1 from the mere nature of his method1 he can see1 in the organism1 only physico-chemical phenomena4 ,the embryologist1 on the other hand1 studies the organism as a whole and seeks to determine how definite forms are produced1 and how a change in the external conditions affects the assumption of these forms4 ,we have seen with what little success the attempts to relate embryological processes with physico-chemical ones alone have met4 ,in all studies of organic form mechanism has failed4 ,it is useless to attempt to press the analogies of crystalline form1 and the forms assumed in nature by dynamical geological agencies4 ,if the reader examines these analogies critically he will see that they are superficial only4 ,we seem1 however1 to see in those actions of the organism which are called 8tropistic0 or 8tactic10 reactions of a purely physico-chemical nature1 and starting with these as a basis a plausible theory of organic movements on a strictly mechanistic basis might be built up4#ba ,a 8tropism0 is the movement of a fixed organism with respect to a definitely directed external stimulus4 ,this movement may be that produced by growth of its parts1 or by the differential contraction or expansion of its parts4 ,a 8taxis0 we may call the motion of a freely-moving organism in response to the same directed stimuli4 ,the movements whereby a green plant turns towards the light are called heliotropic1 and those of its roots in the perpendicular direction are called geotropic4 ,the motion of the freely-moving larva of a barnacle1 for instance1 in swimming towards a source of light are called 8phototactic40 #ba ,many of ,jacques ,loeb's remarkable investigations point in this direction4 ,in all these cases we have to think of the stimulus as a 8field of energy0 in the sense in which physicists speak of electric1 or magnetic1 or electromagnetic1 or thermal1 or gravity fields4 ,in all these cases the factors affecting the movements of the organism are directed ones4 ,an electric field1 for instance1 7#a71 is produced by placing the electrodes of a galvanic cell at opposite extremities of a water-trough3 we imagine the electrons moving from one side of the trough to the other in parallel lines1 and in a certain direction4 ,a light field 7#b7 would be produced by the radiation of light travelling in straight lines through the water4 ,illustration3 ,,fig4 #ah4 ,the movements of the organism displaying a tropism or a taxis are not caused by the stimuli of the field1 but are only directed by it4 ,in the absence of these stimuli it would swim at random4 ,in a field1 however1 it will orientate itself in some direction with reference to the lines of force4 ,a 8positively phototactic0 animal swims towards the focus from which the light radiation emanates1 and a 8negatively phototactic0 one swims in the other direction4 ,on the theory of tropistic and tactic movements this orientation is produced by the differential stimulation of the opposite sides of the organism4 ,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 apex4 ,the animal possesses an elongated body1 with muscles beneath the integument1 and sensory nerve-endings in the latter4 ,its muscles are in a state of 8tone10 that is1 they are normally always slightly tense4 ,the incident rays of light affect the dermal sense-organs1 stimulating ganglionic centres and setting up efferent impulses which descend to the muscles4 ,let us suppose the animal is moving so that the longitudinal axis of its body is at an angle1 say of #de1 to the direction of the incident light3 one side of the body is therefore stimulated and the other is not4 ,the stimulation of the lighted side sets up efferent nerve impulses which descend to the muscles of this side and increase their tone 7or else the lack of stimulation of the other side produces impulses which inhibit the muscular tone1 or impulses which would otherwise preserve the tone cease in the absence of light stimulation74 ,in any case the muscles of the lighted side contract1 and the body of the caterpillar moves so that it sets itself parallel to the direction of the radiation4 ,both sides of the body are then equally stimulated and the animal moves towards the light4 ,the animal feeds and it then creeps back down the plant4 ,why does it do this8 ,because1 says ,loeb1 the act of feeding has reserved the 8sign0 of the taxis4 ,before1 when it was hungry1 it was positively phototactic1 but the act of feeding 7all at once1 it would appear1 before digestion and assimilation of the food itself7 has produced chemical substances in the muscles which cause the latter to relax in response to an impulse which previously produced contraction4 ,the nervous link is not1 of course1 a necessary one4 ,the stimulation by the energy of the field may affect the muscle substance directly1 or it may1 as in the case of a protozoan animal1 affect the general body protoplasm in the same way4 ,in the majority of cases1 however1 the orientation would be affected through the chain of sense-organ1 afferent nerve1 nerve centre1 efferent nerve1 and effector organ4 ,this is the chain of events which on this hypothesis causes a moth to fly into a flame1 or a sea-bird to dash itself against the lantern of a lighthouse4 ,a taxis is1 then1 an inevitable response by movement in a definite direction1 to a directed stimulus4 ,including also tropisms it may be admitted that the movement is a purposeful1 or at least1 a useful one in some cases1 as for instance the heliotropism and geotropism of the green plant4 ,if we admit that ,loeb's description of the feeding of the caterpillar1 as a tactic act1 is true1 we may also call this a useful act4 ,but in the majority of cases tropisms and tactes are acts which appear to be of no use to the organism4 ,the invasion of a part of the body which is irritated by a poison 7as in inflammation7 by leucocytes1 is useful to the body itself1 but we must regard the leucocytes as organisms1 and their tactic motion leads to their destruction1 and so also with other analogous acts4 ,just because of this we find difficulty in accounting for their origin in terms of natural selection4 ,this does not matter so much1 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 plants1 galvano-taxis1 the chemico-taxic movements of bacteria and leucocytes1 and some other analogous cases1 perhaps1 are these exceptions4 ,it can hardly be doubted that the extension of the concept to cover the motions of many invertebrates1 and even some vertebrate actions1 by ,loeb and his school is a straining after generality which has not been justified4 ,the hypothesis1 as ,loeb has stated it1 is evidently almost certainly a logical one and was obviously elaborated as a protest against the anthropomorphism which saw in the flying of a moth into a flame the expression of an emotion2 or in the movements of a caterpillar on a green shrub the expression of hunger and satiety and of the inherited experience of the animal2 or in the avoidance by a ,paramcium of a drop of acid the emotion of dislike of the feeling of pain4 ,well1 let it be granted that this is so1 and that the protest was a useful one1 for it is obviously impossible that these notions as to the causes of the movements can be verified3 does it improve matters to take refuge in an hypothesis which is just as purely physico-chemical dogmatism as the other is anthropomorphism8 ,but the former hypothesis is at all events one which is susceptible of experimental verification and in this lies its usefulness1 inasmuch as it has stimulated investigation4 ,it is evident1 however1 that this verification has not yet been made4 ,the differential afferent impulses set up by the energy-field2 the increases or inhibition of muscular tone2 the presence of photo-sensitive substances in the tissues of tactically acting lower animals2 the change of velocity of chemical reaction1 in these cases1 which ought to follow stimulation--all these things could be verified if they possess reality4 ,yet it is only indirect proofs1 capable perhaps of other interpretations1 and not direct experimental ones1 which have so far been adduced in favour of a general theory of tropisms4 ,moreover1 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 cases4 ,this observer studied the acting of the organisms themselves and not the beginning and end of the series1 and he shows that the behaviour of the organisms is far more obviously described by saying that it adopts a method of 8trial and error40 ,let us suppose a number of infusoria 7,paramcium7 in a film of water1 at one part of which is a drop of acetic acid slowly diffusing out into the surrounding medium4 ,there is a zone of changing concentrations round the drop3 if we draw imaginary contours through the points where the concentration is approximately the same 7the concentric rings in the diagram71 and then draw straight lines normal to these rings 7the radial lines7 we can construct a 8field0 analogous to an electric or magnetic field4 ,the animal on approaching the field ought to orientate itself and take the direction of the 8lines of force40 ,it does not1 however1 behave in this way1 but only enters the field at random4 ,having entered1 it remains within a part where the concentration is within certain limits4 ,if it approaches the margin of this limited field it stops1 swims backwards1 revolves round its own axis1 and then turns to the aboral side2 and it repeats this series of movements whenever it approaches 7by random7 a region where the concentration is too high1 or one where it is too low4 ,in this1 and other organisms we see then what ,jennings has called a typical 8avoiding reaction10 the precise nature of which depends on the 8motor-system0 of the animal4 ,its general movements are random ones1 but having found a region of 8optimum conditions0 7conditions which are most suitable in its particular physiological state71 it remains there4 ,illustration3 ,,fig4 #ai4 ,suppose 7what indeed repeatedly happens7 that an extensive 8bed0 of young mussels forms on a part of the sea bottom4 ,in a short time the bed becomes populated by a shoal of small plaice feeding greedily on the little shellfish4 ,in their peregrinations the fishes must repeatedly pass out beyond the borders of this feeding-ground4 ,usually1 however1 they will return1 for failing to find the food they like they swim about in variable directions and so re-enter the shellfish bed4 ,suppose 7this was really a fine experiment made by ,yerkes7 a crab is confined in a box from which two paths lead out but only one of which leads to the water4 ,the animal runs about at random1 finds the wrong path1 retraces it1 tries again and again1 and then finds the right path and gets back to the water4 ,if the experiment is repeated the animal finds the right path again with rather less trouble1 and after many trials it ends by finding it at once on every repetition of the experiment4 ,all this discussion of concrete cases leads up to our consideration of the modes of acting in the higher organisms4 ,on the strictly mechanistic manner of thinking the actions of the organism in general are based on reactions of the tactic kind--inevitable reactions the nature of which is determined1 and which follow a stimulus with a certainty often fatal to the organism displaying them4 ,accepting these tactic reactions as1 in general1 truly descriptive of the behaviour of the organism1 we can build up a theory of instincts4 ,in their simplest form instincts are reflexes--tactic movements4 ,in their more complex forms they are concatenated reflexes1 or tactes4 ,a complicated instinctive action is one consisting of many individual actions1 each of which is the stimulus for the next one2 or1 of course1 it may also be complex in the sense that several simple reactions proceed simultaneously1 upon simultaneous stimulation of different receptors4 ,now the extension of all this to movements of a 8higher0 grade is obvious4 ,let us note in the first place1 that the stimuli so far considered in all the examples quoted are simple elemental ones4 ,there are1 of course1 relatively few such stimuli3 gravity1 conducted heat 7the kinetic energy of material bodies71 radiated heat 7the energy of the ether71 electric energy1 chemical energy1 and mechanical contact or pressure 7including atmospheric vibrations74 ,in all these cases we have a definite1 measurable1 physical quantity1 with which we must relate a definite response in the form of a definite measurable1 physico-chemical reaction4 ,there should be a functionality between the stimulus and response1 a definite1 quantitative energy-transformation4 ,to take a concrete example1 a certain quantity of light energy falling upon the receptor organs of ,loeb's caterpillar ought to transform into another quantity of 8nervous energy10 and this travelling in an analogous way to a 8wave of explosion0 ought to transform into an energy quantity of some kind1 which initiates another 8wave of explosion0 in the muscle substance4 ,all these transformations must be quantitative ones1 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 substance of the latter4 ,nothing less than this is required to demonstrate the purely physical nature of a reaction1 on the part of the organism1 to an external stimulus4 ,it may safely be said that physiological investigation has not yielded anything even approximating to such an experimental demonstration4 ,what are the stimuli to the actions of a higher organism8 ,it is true that their elements are energies such as we have indicated1 but these energies are integrated to form individualised stimuli 7,driesch74 ,the stimulus in an experimentally studied taxis is1 perhaps1 a field of parallel pencils of light rays of definite wave length2 but in the action of a man1 or a dog say1 the stimulus is an immensely complicated disturbance of the ether1 producing an image upon the retina of the animal4 ,a sound stimulus employed in an investigation may be the relatively simple atmospheric disturbance produced by the sustained note of a syren or violin-string2 but the stimulus in listening to an orchestra may consist of dozens of notes1 with all their harmonies1 sounding simultaneously at the rate perhaps of some hundred or two in the minute4 ,all these are integrated by the trained listener1 and one or two false ones among the multitude may entirely spoil the effect of the execution4 ,surely there is here something more than a mere difference in degree4 ,more important still is the strict functionality between stimulus and action that the theory of tactic responses imposes on itself4 ,putting this very precisely 7but no more precisely than the theory demands71 we say that ,sigma,a f7x1 y1 z71 that is1 the series of actions ,sigma,a 7the dependent variable7 is a mathematical function of the independent variables x1 y1 z4 ,now is there anything like this functionality between the acting of the higher animal and the stimulus8 ,evidently there is not4 ,we recognise someone whom we know very well by any one of a hundred different characters1 mannerisms of walk1 speech1 dress1 etc4 ,he or she is the same person1 whether seen close at hand1 or afar off1 or sideways1 or in any one of almost infinitely different attitudes1 and we respond to each of these very different physical stimuli by the same reaction of recognition3 pleasure1 dislike1 avoidance1 greeting1 or whatever it may be4 ,to a sportsman shooting wild game the stimulus may be some almost imperceptible tint or shading in cover of some kind1 differing so little from its environment as hardly at all to be seen1 yet1 to his experience1 upon this almost infinitesimal variation of stimulus depends his action with all its consequences4 ,in ,driesch's example two polyglot friends met and one says to the other1 8,my brother is seriously ill10 or 8,mon frre est sverment malade10 or 8mein ,bruder ist ernstlich erkrankt40 ,here the physical stimulus is fundamentally different in each case1 but the reaction--the expressions of sympathy and concern1 the discussions of mutual arrangements1 etc41 are absolutely the same4 ,or let the one friend say to the other1 8,my mother is seriously ill10 and in spite of the very insignificant difference between the consonantal sound br in this sentence and the corresponding sound m in the other ,english sentence1 the reaction1 that is1 the subsequent conversation1 and the arrangements between the two friends may be entirely different4 ,putting this argument in abstract form we may say1 generally1 that two stimuli1 which are1 in the physical sense1 entirely different from each other1 may produce absolutely the same series of reactions2 and conversely two stimuli differing from each other in quite an insignificant degree may produce entirely different reactions4 ,it is also easy to see1 by analysis of the antecedents to the actions of the intelligent animal1 that these stimuli are1 in the majority of cases1 not elemental physical agencies1 but individualised and integrated groupings of these agencies2 and that the animal reacts1 not to their mathematical sum1 as it should do on a purely mechanistic hypothesis of action1 but to the typical wholes which are expressed in these groupings4#bb #bb ,thus to the ordinary woman the sight of a cow in the middle of a country road produces a certain definite feeling of apprehension1 which is always the same although the optical image of the animal differs remarkably in different adventures4 ,it is no answer to this argument to say that it is not the actual atmospheric vibrations 7in the case of the conversation71 nor the optical image 7in the case of the recognition of a friend71 which are the true stimuli1 but rather the mental conditions1 or states of consciousness1 aroused by these physical agencies4 ,if we are to adopt a strictly mechanistic method of explaining actions1 such a method as that indicated by ,loeb's hypothesis of the purely tactic behaviour of his caterpillars1 then these atmospheric vibrations and optical images are most undoubtedly the true stimuli1 and the reactions must be functions of them in the mathematical sense4 ,but since this strict functionality does not exist in any behaviour-reaction closely analysed1 we must grant at once that it is1 indeed1 not the physical series of events that determines the actual response1 but truly the conscious state immediately succeeding to these physical sense-impressions4 ,now let us see to what conclusions this admission leads us4 ,between the external stimulus 7the atmospheric undulations impinging on the auditory membranes1 or the light radiations impinging on the retin7 and the behaviour-reaction something intervenes4 ,this is the individual history of the organism1 the 8associative memory0 of ,jacques ,loeb1 the 8physiological state0 of ,jennings1 the 8historical basis of reacting0 7historische ,reaktionsbasis7 of ,driesch1 or the 8duration0 of ,bergson4 ,the last concept is the most subtle and adequate one and we shall adopt it4 ,the physical stimulus1 then1 leads to a state of consciousness1 a perception1 and this is succeeded by the action4 ,what is the perception8 ,there may be no perception in a reflex action2 there is none in a taxis4#bc ,these kinds of reaction follow inevitably from the nature of the stimulus--depend upon the latter1 in fact2 but we cannot fail to observe that the intelligent behaviour of the higher animal involves choice between alternative kinds of action4 ,the perception1 then1 is this choice1 or it is intimately associated with it4 ,but it is something more than the choice of one among many kinds of response4 ,the whole past experience of the animal enters into the perception1 or at least all that part of the past experience which illuminates1 in any way1 the present situation4 ,what the intelligent animal does in response to a stimulus depends not only on the stimulus but on all the stimuli that it has received in its past1 and on all the effects of all those stimuli4 ,into the perception that intervenes between the external stimulus1 then1 and the action by which the animal responds what we usually call its memory enters4 ,its duration is really the something which is changed by the stimulus1 and which then leads to the behaviour-reaction4 #bc ,we do not find this explicitly stated in this way in mechanistic biological writings4 ,none the less it is implied1 and is the legitimate conclusion from the arguments used4 ,duration1 then1 is memory1 but it is more than memory as we usually think of this quality4 ,the past endures in us in the form of 8motor habits10 and when we recall it we may act over again those motor events4 ,careful introspection will readily convince the reader that in recalling a conversation he is really speaking inaudibly1 setting in motion the nerves and muscles of his vocal mechanisms4 ,actions that have been learned endure2 in some way cerebral and spinal tracts and connections become established and persist3 undoubtedly when a cerebral lesion destroys or impairs memory it is these physical nerve tracts and cells that become affected4 ,but in addition to this we have pure memory 7,bergson's 8souvenir pur074 ,what1 for instance1 is the visual image of some thing seen in the past1 which most people can form1 but pure recollection8#bd #bd ,a visual image may1 of course1 be something that has never been actually seen4 ,but then its elements have had actual perceptual existence in the past4 ,all the past experience of the organism--all its perceptions1 and all the actions it has performed--endures1 either as motor habits or mechanisms1 or as pure memories4 ,all this need not be present in its consciousness2 the motor habits would not1 of course1 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 organisations4 ,out of this past it would select all that was connected in any way with the actions which were possible to it in the present4 ,it would recall all actions previously performed which resembled the one provisionally decided upon2 but recalling also the other circumstances associated with those past actions1 it would discover something which would lead it to modify that provisional action4 ,now in describing the whole behaviour of the acting organism in this way are we doing any more than simply expressing in more precise terms the 8commonsense0 notions of the ordinary person8 ,the latter would sum up all this discussion by saying that what he would do in any set of circumstance depended not only on the circumstances themselves but upon his experience4 ,physiology shows us as clearly as possible that in the stimulation of a receptor organ1 the propagation of a nervous impulse along an afferent nerve1 the transmission of this impulse through the cord or brain1 or both--in the propagation again of the impulse through an efferent nerve and the transformation of this impulse into a releasing agency1 setting free the energy potential in the muscle substance--that in all this there can be nothing more than physico-chemical energy-transformations4 ,all this is clear and certain4 ,but why should the same afferent stimuli1 entering the central nervous system at different times by the same avenues1 and in the same manner1 traverse different tracts1 and issue along different efferent nerves1 producing different results8 ,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 organs8 ,it is because these stimuli lead to perceptions which fuse with1 and become part of the duration of1 the organism4 ,and the response then becomes a response not to the physical stimulus1 but to the duration modified in this way4 ,can we conceive of any physical mechanism in which the duration of the organism accumulates8 ,can we think of any way in which memories are stored in the central nervous system8 ,when we say 8stored10 it is our ingrained habit of thinking in terms of space and number that makes us regard memories as laid by somewhere1 in the way we file papers in a cabinet1 or store specimens in a museum4 ,supposing perceptions are stored in this way1 we think of them as stored or recorded in the same way as a conversation is recorded and stored in a phonograph4 ,the phonograph can reproduce the conversation just as it was received1 but what we make use of when we utilise our experience is obviously the elements of that experience1 selected and re-integrated as we require them4 ,there must1 then1 be something like an analysis of our perceptions1 a dissociation of these into simple constituents1 and a means of restoring and recording these constituents in such a way that they can be recombined in any order1 and again made to enter into our consciousness4 ,it is quite possible to imagine such a mechanism4 ,let us suppose that an efferent impulse enters the cerebral cortex via any one axon3 there is a perfect labyrinth of paths along which the impulse may travel4 ,everywhere in the central nervous system we come upon interruptions of nervous paths formed by inter-digitating arborescent formations4 ,the twigs of these arborescences do not1 apparently1 come into actual contact with each other and the impulse leaps across the gap between them4 ,this gap is1 of course1 exceedingly narrow1 and one can almost speak of it as a membrane1 since it must be occupied by some organised substance4 ,it has been called the synaptic membrane4 ,let us suppose that a stimulus of a certain nature passes through the synapse1 modifying it physico-chemically as it passes4 ,thereafter a stimulus of similar nature will tend to pass across this particular synapse1 the resistance of the latter having been decreased4 ,it will thus tend to travel by a definite tract through the central nervous system4 ,now the latter we may regard in a kind of way as a very complicated switchboard1 the function of which is to place any one stimulus 7or series of stimuli7 out of many in connection with any one motor#be mechanism 7or series of mechanisms7 out of many4 ,a motor habit1 or path1 is then established and will persist4 #be ,or more generally effector mechanism4 ,this enables us to include reactions1 such as secretory ones1 which are not motor4 ,such a conception is clear and reasonable in principle1 and all work on nervous physiology tends to show that it is a good working hypothesis4 ,we cannot read modern books without feeling that immense advances will be made by its aid4 ,but the complexity of the brain of the higher vertebrate is so incredibly great1 and the difficulties of imagining the nature of the necessary physico-chemical reactions in the synapses1 and elsewhere1 are so immense that experimental verification may be impossible4 ,and all that we have said applies to a single elemental stimulus1 yet in any common action the stimulus is a synthesis of almost innumerable simple ones1 while the response is also a synthesis4 ,the optical image of almost any object contains a very great number of tints and colours differing almost imperceptibly3 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 image4 ,the motor responses consist of a multitude of delicately adjusted and co-ordinated muscular contractions and relaxations4 ,if we are to accept a mechanistic hypothesis of action1 of this kind1 and which includes only such processes as are suggested above1 it is not enough that a logical description1 consistent in itself1 and consistent with physico-chemical knowledge1 should be formulated4 ,the mere statement of such an hypothesis does not carry us far4 ,if it is1 in essence1 mechanistic1 it must be capable of experimental verification in detail4 ,even if it were verified experimentally it would still leave untouched the problem of consciousness4 ,all that we have considered are series of physico-chemical energy-transformations4 ,how1 then1 does consciousness arise8 ,we cannot even imagine its association in a functional sense with the train of events forming an afferent impulse4 ,in some form or other mechanism must assume a dualism--a parallelism of physical and psychical processes4 ,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 8causes0 in any physical sense of the latter4 ,consciousness follows cerebral energy-transformations as a parallel 8epiphenomenon40 ,at once we leave the province of mechanism1 and how can we remain content with such a limitation of our descriptions8 ,and if we conclude1 as we seem obliged to do1 that consciousness is an affective agency in modifying our responses to external stimuli1 does not this in itself show that our concept of behaviour as a purely physico-chemical process is insufficient in its exclusiveness8 ,we return to a consideration of the main results of experimental embryology in a later chapter1 but let us notice here what is the direction in which these results1 and those of the analysis of instinctive and intelligent action1 carry us4 ,it is towards the conclusion that physico-chemical processes in the organism are only the means whereby the latter develops1 and grows1 and functions1 and acts4 ,in the analysis of these processes we see nothing but the reactions studied in physical chemistry2 but whenever we consider the organism as a whole we seem to see a co-ordination1 or a control or a direction of these physico-chemical processes4 ,ngeli has said that in the development of the embryo every cell acts as it if knew what every other cell were doing4 ,there is a kind of autonomy in the developing embryo1 or regenerating organism1 such that the normal1 typical form and structure comes into existence even when unforeseen interference with the usual course of development has been attempted3 in this case the physico-chemical reactions which proceed in the normal train of events proceed in some other way1 and the new direction is imposed on the developing embryo by the organisation which we have to regard as inherent in it4 ,this same direction and autonomy must be recognised in the behaviour of the adult organism as a whole4 ,what is it8 ,we attempt to think of it as an impetus which is conferred upon the physico-chemical reactions which are the manifestations of the life of the organism4 ,it is the lan vital of ,bergson1 or the entelechy of ,driesch4 ,what is included in these concepts we consider in the last chapter of this book2 and before so doing it will be necessary to consider the organism from another point of view1 that of its mutability when it is regarded as one member of a series of generations4 ,,chapter ,v ,,the ,,individual ,,and ,,the ,,species ,what is an individual organism8 ,a ,protozoan1 such as an ,amba or a ,paramcium1 is a single cell3 it is an aggregate of physical and chemical parts1 nucleus1 cytoplasm1 etc41 and no one of these parts can be removed if the organism is to continue to live4 ,the cell can be mutilated to some extent1 but1 in general1 its life depends on the integrity of its essential structures1 and it cannot be divided without ceasing to be what it was4 ,it contains the minimum number of parts which are necessary for continued organic existence4 ,such an organism as a ,hydra consists of an aggregate of cells which are not all of the same kind4 ,the outer layer1 or ectoderm1 is sensory and protective1 and contains organs of aggression2 while the inner layer consists of cells which subserve the functions of digestion and assimilation4 ,all these parts are1 in general1 necessary for the life of the ,hydra4 ,they can be mutilated2 the animal can be cut into two parts1 and each of these parts may regenerate1 by growth1 the part that was removed4 ,yet the existence of ectoderm and endoderm1 in a certain minimum of mass1 is necessary for this regeneration4 ,the higher animal1 or ,metazoon1 is therefore an aggregate of cells1 each of which is equivalent to the individual ,protozoon2 but these cells are not all alike--that is1 there is differentiation of tissues in the multicellular organism4 ,again1 the ,clenterates provide examples of animals which are aggregates of parts1 each of which is the morphological equivalent of a single ,hydra4 ,such an animal as a ,siphonophore1 for instance1 consists of zooids1 and each of these units has the essential structure of a ,hydra4 ,but the zooids are not all alike3 some of them subserve the function of locomotion1 others of aggression1 others of digestion and assimilation1 and so on4 ,here1 again1 the whole organism may be mutilated2 parts may be removed and regeneration may occur2 but1 as a ,siphonophore1 all of the different zooids must be present if the characteristic functioning of the animal is to continue4 ,the ,protozoon is1 therefore1 an individual of the first order1 the ,hydra an individual of the second order1 and the ,siphonophore an individual of the third order4 ,some such conception of degrees of individuality will probably be regarded as satisfactory by most zoologists1 yet consideration will show that it is very inadequate4 ,many unicellular plants and animals may consist of a number of cells1 which are all alike4 ,the ,diatoms and ,peridinians reproduce by the division of their cell bodies and nuclei1 and the parts thus formed may remain in connection with each other4 ,a ,diatom may consist of one cell1 or it may consist of a variable number of such connected together by filaments1 or in other ways2 and the dissociation of such a series may occur without interfering in any way with the functioning of the parts separated4 ,a ,tapeworm consists of a 8head0 or scolex1 containing a central nervous mass and organs of fixation2 and organically continuous with this is a series of segments or proglottides4 ,these proglottides are formed continuously from the posterior part of the scolex1 and they may remain in connection with each other1 and with the central nervous system and some other organs which are concentrated in the scolex4 ,nevertheless1 each proglottis contains a complete set of reproductive organs2 it has locomotory organs so that it can move about1 and can fix itself to any surface into which it comes in contact4 ,it can lead1 for a considerable time1 at least1 an independent existence apart from that of the scolex and the other proglottides with which it was originally in continuity4 ,in the majority of ,polyzoa1 the common ,sea-,mat1 for instance1 the organism consists of a very large number of polypes or zooids1 each of which secretes an investment of some kind round itself1 but all of which may be connected together by a common flesh4 ,in many ,zoophytes there is essentially the same structure4 ,in ,corals there are very numerous zooids1 each of which lives in a calcareous calyx secreted by itself4 ,polyzoa1 ,zoophytes1 and ,corals are individuals of the third order1 and we might regard the tapeworm strobila--the scolex with its chain of proglottides--as belonging also to the same category4 ,nevertheless1 a part of a ,polyzoan or ,hydrozoan colony1 or a proglottis from a tapeworm1 may become detached1 when it will continue to live and reproduce and exhibit all the characteristic functioning of the species to which it belonged4 ,such an animal as a ,hydra1 or a ,planarian or ,chtopod worm1 or a starfish1 may be cut into several pieces1 and provided that each of these pieces exceeds a certain minimum of mass1 it will regenerate the whole structure of the organism of which it formed a part4 ,in the developing embryo of the ,sea-urchin the eight-cell stage may be treated so that the blastomeres may come apart from each other3 each of them will then begin to segment again and will reproduce the typical larval ,sea-urchin4 ,the parasitic flat-worm1 known as the liver-fluke1 produces larv which develop to form other larv called redi4 ,each redia normally develops into another larval form1 called a cercaria1 which finally develops into the adult worm4 ,but in certain circumstances each redia may divide and reproduce a number of daughter-redi1 and there may even be several generations of these larv4 ,in many lower animals buds may be formed from almost any part of the body1 and each of these buds may reproduce the entire organism4 ,in plants the entire organism may be grown from a very restricted part or cutting4 ,thus the individual1 whether of the first1 second1 or third order1 may be divided without necessarily ceasing to be what it was4 ,regeneration of fragments detached from the fully developed adult body so as to form complete organisms does not1 in general1 occur among the higher animals1 nor1 as a general rule1 does reproduction by bud-formation occur4 ,when such animals reproduce1 an ovum develops to form a large mass of cells1 which later on become differentiated to form the tissues and organs of the adult body4 ,but a relatively small number of the undifferentiated cells persists in the ovaries of the females1 or in the testes of the males1 and each of these cells may again develop and reproduce the organism4 ,there is apparently no limit to this process3 any animal ovum may become divided successively so that an infinite geometrical series is produced1 and in every term of this series all the potentialities of the first one are contained4 ,the physical concept of individuality--that which cannot be divided1 or which may not be divided without ceasing to be what it was--such individuality as the chemical molecule possesses cannot be applied to the organism4 ,any definition that involves the idea of materiality fails4 ,obviously the notion of the individual most commonly met with in zoological writings--that it is the product of the development of a single ovum--fails1 for1 logically applied1 it would regard the entire progeny of the ovum1 that is1 all the organisms belonging to the species1 as the individual4 ,it is clear that the difficulties of the concept arise from our attempt to identify the life of the organism with the material constellation in which this life is manifested4 ,in the course of generation after generation the ovum becomes divided and grows and is again divided1 and so on without apparent limit4 ,but if we assume that the 8organisation0 or 8entelechy0 is material and is capable of this infinite divisibility without impairment of its attributes1 do we not extend to matter a property which belongs only to the concepts dealt with by mathematics8 ,the discussion of individuality with regard to the organism1 considered as a morphological entity1 is1 indeed1 rather a formal one1 and it is valuable only in so far as it has for its object the establishment of the most convenient terminology4 ,nevertheless1 the notion of organic individuality is clear to us though it is a notion felt intuitively and incapable of analysis4 ,we see in nature animals like ourselves1 and we do not doubt that each of them is an entity isolated from the rest of the universe1 and to which the rest of the universe is relative4 ,we ourselves are primarily centres of action4 ,motion1 or change of position with respect to some object apart from ourselves in nature1 is only relative1 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 own4 ,but the motion of our own body is something felt or experienced intuitively1 something absolute4 ,as we move1 the universe1 our universe rather--that is1 all that we act upon1 actually or in our contemplation--contracts in one direction and expands in another4 ,we feel ourselves to be apart from it although we may1 to some extent1 control it4 ,we have no doubt that the higher animals have this feeling of isolation from1 and relation to1 an universe which is something apart from themselves2 though1 of course1 the attempt to demonstrate this leads to all the kinds of difficulties suggested in our attempt to discuss individuality4 ,it is a conviction so strongly felt that we have no doubt about it4 ,the organic individual we may then describe as an isolated1 autonomic constellation of physico-chemical parts capable of indefinite growth or reproduction4#bf #bf ,the description is1 of course1 only a convenient one4 ,the notion of individuality1 as it is expressed in the earlier part of this paragraph1 is an intuitively felt1 or subjective1 one4 ,it is best called personality4 ,what is reproduction8 ,it is organic growth by dissociation accompanied in the higher organisms by differentiation and reintegration4 ,to make this statement clear1 we must now consider the phenomena of reproduction in the lower and higher organisms4 ,we know purely physical growth4 ,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 grow1 and there is no apparent limit to the mass which it may attain4 ,such giant crystals may be grown in the laboratory or they may be found in rock masses4 ,growth here is a process of accretion in which a particular form is maintained4 ,form in inorganic nature may be essential or accidental4 ,accidental forms are such as are partially the result of a very great number of small and un-co-ordinated causes3 the form of an island or a mountain suffering erosion1 or the shape of a river valley or delta1 or the arrangement of the stones forming a moraine at the side of a glacier4 ,essential forms are such as are assumed as the result of the operation of one or a few co-ordinated causes1 and such are the forms of crystals4 ,they are invariable1 or they vary within very small limits about an invariable mean form4 ,the form of a crystal depends on the structure of the molecules of the chemical substance from which it is produced4 ,we cannot1 of course1 speak of the shape of a molecule1 but we know that the atoms of which it is composed have certain positions in space relative to each other--positions which are conceptualised in the structural formul of the chemists4 ,in the solution1 or mother-liquor1 these molecules move freely among each other1 but in the crystal they become locked together and their motions are restricted4 ,the shape of the crystal depends on the way in which the molecules are locked together1 or on the way in which they are arranged4 ,a cube may be built up by the arrangement of a number of very small cubes3 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 space4 ,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 is1 by the accretion of elements of essentially similar form4 ,in every cube 7or crystal7 of this infinite number the geometrical form would be the same1 and if we were to measure any one side of any cube of this series we should find that the total surface would always be a definite function of the length of this side4 ,the mass of a cube would also be a function of such a measurement3 it would be al#c1 a being a constant depending on the unit of mass and on the specific weight of the substance of which the crystal was composed4 ,if we take a series of crystals of increasing size1 this relation holds for every one of them3 ,m al#c1 ,m being the mass1 a the constant referred to above1 and l1 the independent variable1 being any one length of a side of the crystal4 ,if the organism grows by accretion in the same way as does a crystal1 this relation ought also to hold in all the exclusiveness with which we expect it to hold in the growth of a crystal4 ,but it does not so grow4 ,its growth is something essentially different1 and none of the superficial analogies so prevalent nowadays ought to obscure this difference4 ,the organism may grow by accretion1 thus layers of calcareous matter may be added to the outside of a membrane bone from the investing periosteum1 or it may grow by the deposition of matter within the actual cell bodies1 7the process of growth by intussusception of the plant physiologists74 ,but the extent of growth by accretion is strictly limited in all organisms3 for each there is a maximal mass determined by the nature of the animal or plant1 and this mass is that of the unicellular organism itself1 or that of the cells of which the multi-cellular organism is composed4 ,there may also be growth by accretion in the case of the formation of skeletal structures1 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 substance we shall see that accretion ceases when the mass characteristic of the cells has been attained1 when growth by dissociation begins4 ,the cell then divides1 and each of the parts into which it has divided grows to the limiting size1 and division again occurs4 ,this is what happens in the case of the growth of the ,sea-urchin egg to form the larva1 or blastula4 ,the ovum segments into two blastomeres1 each of which then grows to a certain extent1 and again segments into two blastomeres4 ,after the completion of ten divisions there are about #ajjj cells which are arranged so as to form a hollow ball--the blastula4 ,illustration3 ,,fig4 #bj4--,the ,sea-urchin ,gastrula larva in section4 ,differentiation is now set up4 ,in the blastula stage all the cells are alike1 actually and potentially4 ,but soon one part of the hollow ball of cells becomes pushed inwards1 and the cells of this inturned layer become different from those of the external layer1 while cells of a third kind appear in the space between the external and internal layers4 ,this is the process of differentiation leading to the development of the various tissues--protective1 sensory1 digestive1 skeletal1 etc4 ,the cells still continue to divide and grow to their maximal size1 but when the process of differentiation begins1 the cells which are formed are not quite the same as those from which they originated4 ,finally1 however1 when the rudiments of all the tissues of the adult body have been laid down1 the cells begin to produce daughter-cells of only one kind4 ,growth of the embryo consists1 therefore1 of the dissociation or division of the substance of the ovum and blastomeres1 followed by a gradually increasing differentiation of the cells so produced4 ,reintegration proceeds all the time4 ,blastula and gastrula larv are really organisms capable of leading an independent existence--that is1 they are autonomous entities or individuals4 ,the activities of the parts of which they are composed--ectodermal locomotory cells1 ectodermal sensory cells1 endodermal assimilatory cells1 and so on1 must be co-ordinated4 ,the cells are in organic material continuity with each other1 and events which occur in any one of them affect all the rest4 ,impressions made upon the sensory cells are transmitted to the locomotory cells1 and food-material assimilated by the assimilatory cells is distributed to all the others4 ,at all stages the growing embryo is an organic unity4 ,the more fully it is developed1 the greater the morphological complexity of the organism1 and the more numerous its activities1 the greater is the differentiation2 but the greater also is the co-ordination of the organs and tissues4 ,in the higher animals this co-ordination and integration of activities is effected 7mainly7 by the central and peripheral nervous systems1 but specially differentiated nervous cells are not necessary for this purpose4 ,differentiation during growth is therefore necessarily accompanied by reintegration of the parts dissociated and differentiated4#bg #bg ,societies and civilisations1 the associations of bees and ants1 or the ,modern ,state1 obviously exhibit this differentiation4 ,it is morphological and functional in the case of the ,arthropods1 since individuals performing different duties are modified in form4 ,it is functional only in the case of human societies4 ,integration of the activities of the individuals in both kinds of societies is effected by inter-communication3 articulate symbols in the case of the lower animals1 language in the case of man4 ,if the concept of 8orders of individuality0 were anything more than a convenient1 though artificial1 analysis of naturally integral entities1 we might speak of the ideal state or the insect society as a 8fourth order of individuality40 ,in the process of organic growth the relation between mass and form no longer holds in all the exactness with which it applies to the growth of the crystal4 ,we might spend a lifetime growing tablets of cane-sugar1 but in all cases we should find that the mass of any crystal was proportional to the cube of a length of a diameter3 there would be a strict relation between mass and geometrical form4 ,but this strict relation does not hold in the case of a series of organisms belonging to the same species but differing in size4 ,if we measure1 for instance1 the lengths of a great number of fishes of the same species1 we should find that we must describe the law of growth1 not by the simple equation ,m al#c1 but by an empirically evaluated expression of the form ,m a bl cl#b dl#c 444 and that the constants in this equation would vary with the species studied and with the conditions in which it is living--that is1 the organism changes in form as it increases in size4 ,this is inconceivable in the case of purely physical growth by the accretion of molecules1 and we find again that the characters of the organism depend not only on what it is but also upon what it has been--that is1 upon its duration4 ,growth1 then1 in plants and animals implies variability in form1 in general cumulative variability1 leading to an indefinite departure from the typical form4 ,the organism1 therefore1 does not grow simply by the accretion of material1 but1 having attained a certain limit of size1 it divides or reproduces4 ,in the lowest plants and animals this process of division is simple3 either the organism 7unicellular or multicellular7 divides itself into two approximately equal parts or it divides into a number of such parts4 ,the first process is represented by the reproduction of a bacterium or an ,amba1 or by the division of a ,planarian worm2 the second is represented by the division 7in many ,protozoa1 for instance7 of the whole organism into a number of spores4 ,fundamentally the two processes are alike3 the simple1 binary division of the ,bacterium is followed at once by growth by accretion1 while in brood-formation 7the cases of multiple division7 the parent cell divides1 and then each of the daughter-cells divide1 and so on for several generations4 ,after the completion of these divisions the brood-cells grow by accretion to their normal size4 ,it is meaningless1 in the light of our previous discussion1 to say that the individuality of the mother-cell 8is merged in that of the daughter-cells40 ,but we may believe that a ,paramcium possesses some degree of consciousness4 ,does it possess personality--that is1 the feeling of isolation from the rest of the universe1 and the feeling of oneness with its own past-memory or conscious duration8 ,if so1 its personality1 when it divides1 becomes one with that of its daughter-cells4 ,or is its personality and conscious past that also of its sister-cells1 and also that of the no longer existent mother-cell1 and the cell of which this in its turn was a part8 ,we must remember that such an organism as a ,paramcium shows in its behaviour most of the signs of intelligence2 that the parts into which it divides when it reproduces are equally developed2 and that the process of division may not interrupt the conscious duration of either part4 ,is there a common personality1 or oneness of consciousness1 of all the organisms of this kind which are descended from the same individual8 ,reproduction by division1 simple or multiple1 does not proceed indefinitely in the case of the unicellular organisms4 ,sooner or later there is a limit1 and the cell is then no longer able to continue dividing4 ,conjugation then occurs in one of many modes4 ,essentially two organisms come into contact and their nuclei fuse1 or rather some of the material of one nucleus is transferred to the other4 ,the cells then separate and reproduction by division begins again4 ,this is not necessarily sexual reproduction3 it is the conjugation of essentially similar morphological entities4 ,if two conjugating ,paramcia possessed distinct personalities we might imagine a merging or addition of two conscious durations or memories4 ,sexuality1 however1 includes less than this4 ,in this mode of reproduction the conjugating bodies are not organisms in the usual sense1 but rather modified organisms or highly modified parts of organisms4 ,in some lower plants the conjugating cells may be modified with respect to the cells characteristic of the organism1 but they may be approximately equal in size4 ,but in the multicellular plant and animal1 in general1 the conjugates are cells detached from the parental body1 and differing chiefly from the cells of the latter in that they show a lack of differentiation4 ,one of these cells1 that detached from the paternal body1 is the spermatozoon 7in the case of the animal71 or the pollen cell 7in the case of the plant74 ,it is much smaller than the sexual cell detached from the maternal body3 this is the ovum in the case of the animal1 or the oosphere in the case of the plant4 ,in general the ovum is a relatively large cell1 since it contains abundant cytoplasm1 which may also be loaded with yolk or other reserve food material4 ,the spermatozoon is very much smaller and consists of a nucleus with a minimal mass of cytoplasm4 ,the ovum is1 in general1 immobile2 the spermatozoon is generally highly mobile4 ,the essential process in the sexual reproduction of the unicellular organisms is therefore the conjugation of the organisms themselves4 ,in multicellular organisms1 modified cells--the germ-cells--become detached from the bodies of the parents1 and these cells conjugate4 ,in many lower plants and animals phases of sexual and asexual reproduction alternate1 thus ,paramcium reproduces by simple division1 but at intervals conjugation occurs4 ,in plants sporophytic and gametophytic generations alternate1 the sporophyte reproducing by multiple division--that is1 by the formation of spores1 and the gametophyte reproducing by the formation of germ-cells4 ,there are few organisms--possibly none--in which continued asexual reproduction by simple or multiple division1 spore-formation1 bud-formation1 etc41 can proceed without limit4 ,in the great majority of cases investigated asexual reproduction becomes feeble after a time and then ceases1 and it has been held that the stimulus of conjugation of the cells1 or that of sexual reproduction1 is necessary for its renewal4 ,in such cases the organism is said to have become 8senescent10 and 8rejuvenescence0 by some means becomes necessary4 ,as a general rule rejuvenescence is effected by the interchange of nuclear matter between two conjugating organisms1 but it may be effected by rest1 or by a change of environment1 or by the supply of some unusual food-material to the liquid in which the dividing organism is contained4 ,thus1 if various materials be added to the water inhabited by a dividing ,paramcium1 the ,protozoon may continue to reproduce by simple division for at least two thousand generations4 ,we must remember1 however1 that 8senescence0 and 8rejuvenescence0 are only words2 what is the essential nature of the changes denoted by them we do not know4 ,in sexual reproduction1 as it occurs in the great majority of plants and animals1 the ovum1 or female germ-cell1 is fertilised or 8activated0 by the male germ-cell4 ,but this activation by the spermatozoon is not necessary1 for the ovum itself is capable of division and development to form a complete organism4 ,this occurs in the cases of natural parthenogenesis among insects and some other animals1 where the ovum proceeds1 without fertilisation1 to segmentation and development4 ,in some lower plants1 where the size of the male and female germ-cells is nearly equal1 either of them may undergo parthenogenetic development3 in such cases we cannot1 of course1 properly speak of sexual differentiation4 ,in the cases of organisms normally reproducing sexually1 the stimulus to development is afforded by the entrance into the ovum of the spermatozoon--that is1 by the mixture of the male and female germ-plasms2 but in some animals this stimulus may be replaced by the addition to the water in which they are living of certain chemical substances4 ,this is the process of artificial parthenogenesis first studied by ,loeb in the case of the eggs of the ,sea-urchin2 and its analysis suggests that the spermatozoon conveys some substance into the egg1 and that this substance initiates segmentation by setting up a train of chemical reactions4 ,what these reactions are exactly1 and what is the process of 8formative stimulation0 by the spermatozoon1 we do not know4 ,it is quite certain1 however1 that much more than this process of formative stimulation is involved in the fertilisation of the egg by the spermatozoon4 ,the mixture of the male and female germ-plasms resulting from conjugation confers upon the embryo the characters of both the parents and of their ancestries4 ,in an unicellular organism the 8body0 consists of a single cell containing a nucleus4 ,the extra-nuclear part of the cell--the cytoplasm--is modified in various ways3 thus it may possess flagella1 or cilia1 so that it may be actively locomotory4 ,it is at once a receptor apparatus1 susceptible to changes in the medium in which it lives1 and it is also an effector apparatus1 capable of transforming stimuli received into motor impulses4 ,it may be able to accumulate available energy by making use of the energy of radiation in the synthesis of carbohydrate and proteid from the inorganic substances in solution in the water in which it lives2 and it is also able to expend this energy in controlled movements4 ,all the characteristics of life1 in fact1 are exhibited by the unicellular organism1 the differentiation of the cytoplasm corresponding functionally to the differentiation of the tissues of the multicellular animal or plant4 ,in the latter the organs1 organ-systems1 and tissues are composed of differentiated cells4 ,development consists essentially of a process of cell-formation by simple division1 and at the end of this process of segmentation various rudiments 7,anlagen7 are established4 ,the older embryologists sought to recognise the formation of three 8germ-layers0 in most groups of animals3 these were the outer layer or ectoderm1 the middle layer or mesoderm1 and the internal layer or endoderm4 ,the ectoderm1 it was held1 gave rise to the integument1 the central and peripheral nervous systems1 and the sensory organs4 ,the mesoderm gave rise to the musculature and skeleton1 the excretory organs1 and some other tissues4 ,the endoderm gave rise mainly to the alimentary canal and its glands4 ,the 8,gastrea-,theory0 of ,haeckel sought to recognise a similar larval form1 or 8,gastrea10 in the development of most multicellular animals1 and much ingenuity of argument was required for the establishment of this homology4 ,the newer embryology recognises the difficulties implied in the application1 in all its exclusiveness1 of the ,gastrea-theory to the higher phyla of multicellular animals2 so that nowadays it has been necessary to abandon the notion of the metazoan animal as being built up from these three primary germ-layers4 ,at the conclusion of segmentation1 then1 the embryo consists of a mass of cells similar to each other in structure1 but differing in fate and in potency4 ,some of these cells are destined to give rise to the integument1 the nervous system1 and the sense-organs2 others become the skeleton and musculature2 and others again the organs of digestion1 assimilation1 and excretion4 ,a primary arrangement of these groups of cells into three layers is indeed set up in many cases of development1 but it is plain that this arrangement is far from being an universal one4 ,modern embryology shows in the clearest possible manner that at the end of segmentation the embryo consists of a group of cells each of which has normally a different fate in subsequent development4 ,what precisely each cell will become depends on its position with regard to the others4 ,but each cell is capable of becoming more than it normally becomes3 its potency is greater than its actual fate4 ,if the normal course of development is interrupted1 a cell1 which would usually have given rise to a part of the skeleton1 may give rise to a part of the alimentary canal4 ,the cells of the developing embryo are autonomous4 ,in the normal course of development most of the cells existing at the end of segmentation give rise to the 8body0 of the organism1 undergoing differentiation as they so develop4 ,but a few embryonic cells persist without structural modification throughout the development of the animal4 ,they divide and grow and become greater in number1 but remain unchanged in other respects4 ,these cells become the essential reproductive organs1 or gonads1 of the adult animal--that is1 the ovaries of the female and the testes of the male4 ,in the females of the higher animals 7the mammals1 and perhaps some of the ,arthropods7 these cells only divide and grow during the early stages of development1 and long before the beginning of adult life the number of ova in the gonads has become fixed4 ,in all males1 and in the females of most animals1 however1 the reproductive cells appear to be capable of unlimited multiplication4 ,the essential cells of the gonads1 the ovarian mother-cells or the sperm mother-cells1 constitute the germ-plasm4 ,in modern1 speculative1 biological literature the term germ-plasm is1 however1 restricted to the chromatic material in the nuclei of the reproductive cells1 the cytoplasm being regarded as non-essential for the transmission of the hereditary qualities of the organism4 ,it seems clear1 however1 that this distinction between the cytoplasm and the chromatic matter of the nucleus is not always a valid one1 so that it is best to speak of the whole cell as constituting the germ-plasm4 ,the embryonic cells1 therefore1 have different fates3 some of them become transformed during development into the body or soma1 and others remain unmodified throughout life as the germ4 ,the soma enters into intimate relationships with the environment2 it is affected by the vicissitudes of the latter2 and it may actively respond to them4 ,the germ-cells may possibly migrate through the body1 perhaps1 it has been suggested1 developing fatally and irresponsibly into the mysterious1 malignant tumours of adult life4 ,normally1 however1 they remain segregated in the reproductive glands1 secluded from the outer environment4 ,their activities are inherent in themselves1 are rhythmic1 and become functional only on the assumption by the soma of the phase of sexual maturity4 ,from the point of the species the soma is only the envelope of the germ-cells4 ,it is affected by every change of the environment1 and being usually cumulatively affected by the latter it becomes at length an unfit envelope4 ,somatic death then follows as a natural consummation1 but the germ-cells are1 in a sense1 immortal in that they remain capable of indefinite growth by division4 ,in the sexual reproduction of the higher organism a part of the germ-plasm becomes detached1 undergoes growth1 and develops into an organism exhibiting the parental organisation4 ,but in the development of the offspring1 part of the germ-plasm received from the parent persists unchanged1 is transmitted to another generation1 and so on without apparent limit4 ,something is transmitted from parent to offspring4 ,this something we regard as a cell exhibiting a definite chemical and physical structure2 but while the germ-cell differs in certain respects from an ordinary somatic cell1 these structural and chemical differences are insignificant when they are compared with the differences in the potentialities of the cells4 ,the somatic cells are1 in general1 capable of reproducing only the general character of the tissues of which they form part4 ,some of them1 the cells of the grey matter of the central nervous system1 for instance1 appear to be incapable of division and growth4 ,but again the facts of regeneration appear to point to the possession by the somatic cells of more than this restricted power of reproducing the tissues of which they form part3 to this extent the regeneration experiments tend to remove the essential distinction between the somatic and germinal cells4 ,neglecting these results in the meantime1 we see that the germ-cells contain within themselves the potentiality of reproducing the entire organism in all its specificity4 ,that which is transmitted from the parent to the offspring is the parental organisation in all its specificity2 and to say that this organisation is a material thing is1 of course1 to state a hypothesis1 not a fact of observation4 ,this transmission of a specific form and mode of behaviour from generation to generation is what a hypothesis of heredity attempts to explain--that is1 to describe in the simplest possible terms1 making use of the concepts of physical science4 8,twelve years ago10 says ,jacques ,loeb1 8the field of heredity was the stamping ground for the rhetorician and metaphysician2 it is to-day perhaps the most exact and rationalistic part of biology1 where facts cannot only be predicted qualitatively1 but also quantitatively40 ,let the reader examine for himself the meagre array of facts on which this apotheosis of mechanistic biology is based4 ,two modern hypotheses of heredity demand attention--,weismann's hypothesis of the continuity of the germ-plasm1 and ,semon's 8,mnemic0 hypothesis4 ,in the latter it is assumed that the basis of heredity is the unconscious memory of the organism3 modes of functioning are 8remembered0 by the germ-plasm and are transmitted4 ,this notion presents many points of similarity to that which we consider later on1 so that it need only be mentioned here4 ,weismann's hypothesis--like ,darwin's hypothesis of ,pangenesis--is a corpuscular one1 and has obviously been suggested by the modern development of the concepts of molecules and atoms in the physical sciences4 ,it supposes that that which is handed down is a material substance of a definite chemical and physical structure4 ,this is not the germ-cell1 nor even the nucleus of the latter1 but a certain material contained in the nucleus4 ,the latter contains protein substances containing a greater proportion of phosphoric acid than does the cytoplasm of the cells in general2 these proteins are known as nucleo-proteins1 though our knowledge of their chemical structure is1 so far1 not very exact4 ,it is not1 however1 these that are the germ-plasm1 but a substance in the nucleus which becomes visible when the cell is killed in certain ways1 and which becomes stained by certain basic dyes4 ,it is distinguished by this character alone and on that account is loosely called 8chromatin40 ,this substance ,weismann identifies as 8the material basis of inheritance40 ,when a cell divides1 a very complex train of events usually occurs4 ,this process of 8,mitosis0 exhibits many variations of detail1 and without actual demonstration it is rather difficult to explain clearly4 ,but its essential feature is evidently the exact halving of all the structures in the cell which is about to divide4 ,in the ordinary cell which is not going to divide immediately1 the chromatin is diffused throughout the nucleus as very numerous fine granules1 recognised only by their staining reactions4 ,they may be concentrated at some part of the nucleus1 so that a division through a plane of geometrical symmetry of the cell would not1 in general1 exactly halve the chromatin4 ,prior to division1 therefore1 this substance becomes aggregated as granules lying along a convoluted filament of a substance called 8linin10 which is characterised principally by the fact that it does not stain with the dyes that stain the chromatin4 ,the filament breaks up into short rods1 called ,chromosomes1 and these rods become arranged in the equator of the nucleus4 ,the rods then split longitudinally1 and one-half of each moves towards one pole of the nucleus1 the other half moving towards the other pole4 ,various other modifications of the cell and nucleus occur concomitantly with these changes1 but the essential thing that happens seems to be the halving of all the structures of the cell1 and this is the simplest explanation of the phenomena of mitotic cell division4 ,two daughter-cells are then formed by the division of the mother-cell1 and each of these daughter-cells receives one-half of each of the chromatin granules that were contained in the mother-cell4 ,the chromosomes1 or 8,idants10 are seen to consist of discrete granules1 and these are 7generally7 the bodies known as the 8,ids40 ,the id cannot be resolved by the microscope into any smaller structures3 it lies on the limits of aided vision2 but the hypothesis assumes that it is composed of parts called 8,determinants10 and the determinants are further supposed to consist of 8,biophors40 ,the biophors are the ultimate organic units or elements1 and they are of the same order of magnitude as chemical molecules4 ,we must suppose them to be more complex than a protein molecule1 and the latter contains many hundreds 7at least7 of chemical atoms4 ,now it is possible to calculate the number of atoms contained in a particle of the same size as the id3 such a calculation may be made by different methods1 all of them yielding concordant results4 ,this calculated number of atoms may be less than that which we must suppose to be present in the biophors1 of which the hypothetical id is composed6#bh #bh 8,but10 says ,weismann1 referring to an objection of this nature1 8it should rather be asked whether the size of the atoms and molecules is a fact1 and not rather the very questionable result of an uncertain method of investigation40 ,the id is supposed to contain all the potentialities of the completely developed organism4 ,it is composed of a definite number of determinants1 each of the latter being a 8factor0 for some definite1 material constituent of the adult body4 ,there would be a determinant for each kind of cell in the retina of the eye1 one for the lens1 one for the cornea 7or rather for each kind of tissue in the latter71 one for each kind of pigment in the choroid and iris1 and so on2 every particular kind of tissue in the body would be represented by a determinant4 ,thus packed away in a particle which lies just on the limits of microscopic vision are representatives of all those parts of the body which are chemically and physically individualised1 each of these hypothetical 8factors0 being a very complex assemblage of chemical atoms4 ,in development the determinants become separated from each other1 so that whatever parts of the body are formed by the first two blastomeres are represented by determinants which are contained in those cells1 and which are sifted out from each other and segregated4 ,as development proceeds this process of sifting becomes finer and finer1 until when the rudiments of each kind of tissue have been laid down a cell contains only one kind of determinant4 ,this consists of biophors of a special kind1 and the latter then migrate out from the chromatin into the cytoplasm of the cells in which they are contained1 and proceed to build up the particular kind of tissue required4 ,the nucleus of the germ-cell is thus a mixture of incredible complexity1 but in addition to this material mixture there must exist in it the means for the arrangement of the determinants in the positions relative to each other occupied by the adult organs and tissues4 ,a mechanism of unimaginable complexity would be required for this purpose1 and it must be a mechanism involving only known chemical and physical factors4 ,it is safe to say that absolutely no hint as to the nature of this mechanism is contained in the hypothesis4 ,the determinants must be able to grow by reproduction1 or by the accretion of new biophors1 since in each generation new germ-cells are formed4 ,if we say that they grow by reproduction in the sense that an organism grows by reproduction1 we beg the question of their means of formation4 ,do they grow by the addition of similar substances in the way that a crystal grows8 ,if so1 the molecules of which they are composed must exist in the lymph stream bathing the germ-cells--that is1 the biophors themselves must already exist in this liquid1 for if we suppose that the biophors are able to divide and grow by making use of the protein substances which we know are present in the lymph stream1 then we confer upon these bodies all the properties of the fully developed organism4 ,if they are present in the blood1 then the composition of the latter must be one of inconceivable complexity1 since it must contain as many substances as there are distinct tissues in the animal body4 ,we know1 of course1 that this is not the case4 ,how1 then1 are the biophors reproduced8 ,we must leave this field of unbridled speculation 7which cannot surely be 8the most exact and rationalistic part of biology407 ,what the study of the reproduction of the organism does show is that something--which we call the specific organisation--is handed down from parent to offspring1 and that this something may possess a high degree of stability4 ,no apparent change of significance can be observed in the very numerous generation of organisms 7the #bjjj generations of ,paramcium1 for instance1 which were bred by ,woodruff7 which can be produced by experimental breeding4 ,some species of animals--the ,brachiopod ,lingula1 for instance--have persisted unchanged since ,palozoic times4 ,throughout the incredibly numerous generations represented by this animal series1 the specific organisation must have been transmitted in an almost absolutely unchanged condition4 ,the germ-plasm is therefore continuous from generation to generation1 and it possesses an exceedingly great degree of constancy of character4 ,this conception of the continuity and stability of the specific organisation is the feature of value in ,weismannism1 and all that we know of the phenomena of heredity confirms it4 ,but it is pure speculation to regard the organisation as an aggregate of chemically distinct substances1 or if we say that this speculation is rather a working hypothesis1 then it must justify itself by leading us back again to the results of experience4 ,it is1 however1 not quite accurate to say that the organisation persists unchanged from generation to generation4 ,the offspring is similar to the parent--that is1 the organisation has been transmitted unchanged4 ,but the offspring also differs just a little from the parent--that is to say1 the organisation is modified by each transmission4 ,in these two statements we formulate in the simplest manner the law of organic variability4 ,organisms may obviously be arranged in categories in such a way that the individuals in any one category resemble each other more closely than they resemble the individuals belonging to another category4 ,we may1 by experimental breeding1 produce an assemblage of organisms all of which have had a common ancestor1 or a pair of ancestors4 ,now the individuals composing such an assemblage would exhibit a close resemblance to each other1 such a resemblance as our categories of naturally occurring organisms are seen to exhibit4 ,we should also find that the individuals of our naturally occurring assemblage would be able to interbreed among themselves1 just as in the case of the experimentally produced population4 ,it may be concluded1 then1 that the naturally occurring population is also the product of a pair of ancestors4 ,this inter-fertility1 as well as the close morphological resemblance of the individuals1 are the facts on which the hypothesis of the common origin and unity of the assemblage1 or species1 is formed4 ,the morphological resemblance between the individuals1 either in the natural or the artificial populations1 is not absolute4 ,if we take any single character capable of measurement we shall find that it is variable from organism to organism4 ,this important concept of organic variability may be made more clear by a concrete example4 ,examination of a large number of cockle shells taken from the same restricted part of the sea-shore1 and therefore belonging presumably to the same race1 will show that the number of the radiating ridges on the shell varies from #ai to #bg1 and that the ratio of the length to the depth of the shell also varies from #a 3 #j4ei to #a 3 #j4he4 ,in the former case the most common number of ridges is #bc1 and in the latter case the most common ratio of length to depth is #a 3 #j4ga4 ,these are the characteristic or modal values of the morphological characters in question1 and the other or less commonly occurring values are distributed symmetrically on either side of the mean or modal value1 forming 8frequency distributions40#bi ,the value of the first character changes by unity in any distribution3 obviously there cannot be a fraction of a ridge2 and this kind of variation is called 8discontinuous40 ,the value of the second character may change imperceptibly1 and it is therefore called 8continuous10 a term which is not strictly accurate1 since in applying it we assume that the numerical difference between two variates may be less than any finite number1 however small4 ,in this assumption we postulate for biology the distinctive mathematical concept of infinite divisibility4 #bi ,see ,appendix1 p4 #cej4 ,the difference from the mode1 or mean1 with respect to a definite character in a fully grown organism may be due to the direct action of the environment1 in the sense in which we have regarded the environment as influencing the organism2 or it may be due to the changes in the organism resulting from the increased or decreased use of some of its parts4 ,the conditions with regard to nutrition1 for instance1 will not be the same for all the individuals composing a cluster of mussels growing on the sea-bottom4 ,those in the interior of the cluster do not receive so abundant a supply of sea-water as those on the outside of the cluster2 and since the amount of food received by any individual depends on the quantity of water streaming over it in unit time1 we shall find that the internally situated individuals will be stunted or dwarfed1 while those on the outside will be well grown4 ,such variations are acquired ones1 but even when we allow for them1 even if we take care that all the organisms studied live under conditions which are as nearly uniform as possible1 there will still be some degree of variability4 ,we cannot be sure that this absolute uniformity ever exists2 and the notion of the environment of an organism may be extended so as to include the medium in which embryonic development took place1 and even the parental body which formed the environment for the germ-cells from which embryonic development began4 ,but it is probably the case that even with an uniform environment1 or with one in which the differences were insignificant1 variability would still exist4 ,the variations that might be observed in such a case would belong to two kinds--8fluctuating variations10 and 8mutations40 ,illustration3 ,,fig4 #ba4 ,whether the variations observed in a population of organisms are fluctuations or mutations can only be determined by experiment4 ,let us suppose that we are dealing with a human population1 and that the variation studied is that of stature4 ,let the men with statures considerably over the mean value marry the women who are correspondingly tall1 then it will be found that the children from these unions will1 when grown up1 exhibit a stature which is greater than that of the whole population1 but not so great as that of their parents--that is1 regression towards the mean of the whole population takes place4 ,this is shown in the above diagram1 where the lines above and below the mean one indicate the proportion 7relative to the value or frequency of the mean7 of people of each grade of stature4 ,the latter is proportional to the distance from the mean measured along the vertical line1 distances below this line indicating statures below the mean1 and vice versa4 ,if1 on the other hand1 the men and women with statures considerably below the mean marry1 their children will ultimately exhibit statures which are greater than that of their parents1 but which are less than that of the whole population4 ,regression again occurs1 but in the opposite direction1 and such a case would be represented by the above diagram reversed4 ,continued selection of this kind would lead to an immediate increase in the mean stature 7or the opposite1 if the 8sign0 of the selection were reversed7 in one or two generations1 but after that the amount of change would be very small1 while if the selection were to cease the race produced would slowly revert to the mean1 which is characteristic of the whole population from which it arose4 ,it is very important to grasp this result of the practical and theoretical study of heredity--the selection of the ordinary variations shown by a general population leads at once to a small change in the mean value of the character which is selected1 but continued selection thereafter makes very little difference to this result1 while the race slowly reverts to the value of that from which it arose on the cessation of the selection4 ,races which 8breed true0 do1 of course1 exist2 thus the mean height of the ,galloway peasant is greater than that of the ,welsh4 ,in the cases of 8pure races0--that is1 races which breed true with respect to one or more characters1 we have to deal with another kind of variation1 one which shows no tendency to revert to the value from which it arose4 ,let the observed variability of stature in a human population be represented by the frequency distribution ,a1 and let the individuals at ,n--that is1 those in which the stature was greater than the mean by the deviation ,,on--intermarry4 ,it might then happen that the variability of the offspring of these unions would be represented by the frequency distribution ,b1 in which the value of the mean is also that of the stock1 at ,n1 from which the race originated4 ,it does not matter now from what variants in ,b a progeny of the third generation arises3 the mean height of the latter will be that of the pure race4 ,in this case the individuals from which the pure race originated 7those at ,n in ,a7 have exhibited a mutation4 ,the stature of the individuals of this new race will continue to exhibit fluctuating variations1 and the range of this variability may be as much as that of the stock from which it arose1 but the mean stature of the new race will continue to be that of the original mutants4 ,illustration3 ,,fig4 #bb4 ,it is well known that de ,vries himself considered fluctuating variations and mutations as something quite different4 ,the former he considered as nothing new1 only as augmentations or diminutions of something previously existing2 and he regarded fluctuations as due to the action of the environment1 following in their distribution the laws of chance4#cj ,mutations1 on the other hand1 were something quite new4 ,now future analysis of variability will not1 we think1 bear out the validity of this distinction4 ,it is far more likely that a fluctuation is a variation which is the result of some causes the action of which is variable4 7,we are regarding variability now as subject to 8causation0 in the physical sense1 for only by so regarding it can we attempt its analysis74 ,as a rule this process results in a fluctuation1 but if its extent1 or degree of operation1 exceeds a certain 8critical value0 a mutation is produced4 ,we may1 following the example of the physicists1 illustrate this by a 8model40 #cj ,see ,appendix1 p4 #cea4 ,illustration3 ,,fig4 #bc4 ,this model is a modification of ,galton's illustration of the degrees of stability of a species4 ,it is a disc of wood rolling on its periphery4 ,we divide it into sectors1 and the arcs ab1 cd1 ef1 and gh have all the same radius1 #aj1 #bj1 #cj1 and #dj4 ,then we flatten the sectors bc1 de1 fg1 and ha1 so that their radii are greater than are those of the other arcs4 ,now let us cause the disc to roll about the point #h as a centre4 ,it will oscillate backwards and forwards about a mean position #h4 ,let us think of these oscillations as fluctuations4 ,suppose1 however1 that we cause the disc to roll a little more violently1 so that it oscillates until either of the points #c or #d are perpendicularly beneath the centre ,o4 ,in either of these positions the disc is in a condition of 8unstable equilibrium10 and an infinitesimal increase in the extent of an oscillation will cause it to roll beyond the points #c or #d4 ,but if it does pass either of these critical points it will begin to oscillate about either of the new centres #e or #g1 thus rolling on one of the arcs1 ha or de4 ,this assumption of a new condition of stability we may compare with the formation of a mutation4 ,all this is merely a conceptual physical model of a process about which we know nothing at all4 ,it is meant to illustrate the view that the organisation of a plant or animal is not something absolutely fixed and invariable4 ,the organism in respect of each recognisable and measurable character oscillates about a point of stability1 that is to say exhibits fluctuating variations about the mean value of this character4 ,if the stability of the organisation is upset1 so that it oscillates1 or fluctuates about a new centre1 that is1 if the variations deviate in either direction from a new 8type0 or mean1 a mutation has been established4 ,a mutation is not1 therefore1 necessarily a large departure from 8normality40 ,it is not necessarily a 8discontinuous variation10 nor a 8sport0 nor a 8freak40 ,it is essentially a shifting of the mean position about which the variations exhibited by the organism fluctuate4 ,such a mutation will1 in general1 involve the creation of an 8elementary species40 ,we have considered only one character1 say stature1 in the above discussion1 but it generally happens that the assumption of a new centre of stability involves all the characters of the mutating organism4 ,an elementary species therefore differs a little in respect of all its characters from the species from which it arose1 or from the other elementary species near which it is situated4 ,this is what we do usually find in the cases of the 8races10 or 8local varieties10 of any one common species of plant or animal4 ,that we do not recognise that most1 or perhaps all1 of the species known to systematic biology are really composed of such local races is merely because such results involve an amount of close investigation such as has not generally been possible except in the few cases studied with the object of proving such variability2 or in the case of those species which are studied with great attention to detail because of their economic importance4 ,thus the herrings of ,north ,european seas can be divided into such races1 and it is possible for a person possessing great familiarity with these fishes to identify the various races or elementary species--that is1 to name the locality from which the fish were taken--by considering the characteristics in respect of which the herrings of one part of the sea differ from those of other parts4 ,the term 8variety0 has rather a different connotation in systematic biology from that which is included by the term 8elementary species40 ,the meaning of the latter is simple and clear4 ,two or more elementary species are assemblages of organisms1 in each of which assemblages the mean positions about which the various characters fluctuate is different4 ,the term 8variety0 cannot so easily be defined4 ,the progeny of two different species 7in the sense of the term as it is usually applied by systematists7 may be called a hybrid variety of one or other of the parent species4 ,in the case of the ordinary species of zoology such a hybrid would1 in general1 be infertile1 or if it did produce offspring these would be infertile4 ,in the case of ordinarily bred offspring from parents of the same species a large deviation from the parental characters might be a malformation1 or the result of some irregularity of development4 ,an 8atavistic0 variation we may regard as the reappearance of some character present in a more or less remote ancestor4 ,thus dogfishes and skates are no doubt descended from some elasmobranch fish which possessed an anterior dorsal fin4 ,this fin persists in the dog-fishes1 but has been lost in the skates and rays4 ,yet it may appear in the latter fishes as an atavistic variation4 ,in a variety 7following de ,vries' analysis7 a character which disappears is not really lost3 it is only suppressed1 and it still exists in a latent form4 ,some flowers are coloured1 for instance1 but there may be varieties in the species to which they belong in which the flowers are colourless4 ,it may not be quite correct1 in the physical sense1 to say that the colour has been lost1 but we may put it in this way4 ,these flowers are then coloured and colourless varieties of the same species4 ,colour or lack of colour is not1 however1 fixed in the variety1 for the individual plant bearing colourless flowers also bears in its organisation the potentiality of producing coloured flowers4 ,the petals of a flower may be smooth or covered with hairs1 and in the same stock both of these varieties may occur4 ,but we must not speak of the presence or absence of hairs as constituting a difference of kind3 the smooth-petalled flowers might be regarded as containing the epidermal rudiments of hairs4 ,so also coloured and colourless flowers may be regarded as containing the same kinds of pigment1 but these pigments are mixed in different proportions4 ,such a view enables us to look upon these contrasting characters in the same way as we look upon fluctuating variations1 that is1 as quantitative differences in the value of the same character4 ,such a suppression of a character is not really a loss4 ,an organism belonging to an elementary species in which1 say1 monochromatic flowers are usually produced may produce flowers which are striped4 ,the progeny of the plant may still produce monochromatic flowers1 but we must think of it as also possessing the potentiality of producing striped flowers4 ,in the terminology of ,mendelism the characters are dominant and recessive ones4 ,in discussing ,mendelian varieties we consider the manner in which two contrasting characters--one present in the male parent and one in the female--are transmitted to the offspring4 ,the characters in question may be the tallness of the male parent and the contrasting shortness of the female2 or the brown eyes of the male and the blue eyes of the female2 or the brown skin of the female parent and the white skin of the male one4 ,these characters may be inherited in two ways3 either they may be blended or they may remain distinct in the offspring4 ,the children of the brown mother and the white father are usually coloured in some tint intermediate between those of the parents4 ,the mulatto hybrid is fertile with either of the parent races1 and again the offspring may take a tint intermediate between those of the parents1 and so on through a number of generations4 ,but somewhere in this series the concealed or recessive brown colour may appear in all its completeness1 showing that it has been present in the organisations of all the intervening generations4 ,the progeny of a tall male parent and a short female parent are not1 in general1 intermediate in stature between the parents2 some of them may be tall and others short4 ,the children of a brown-eyed mother and a blue-eyed father do not usually have eyes in which the colours of the parental eyes are blended3 they are blue-eyed or brown-eyed4 ,the contrasting characters are spoken of as dominant and recessive3 if tallness is transmitted to offspring1 which may nevertheless produce dwarf offspring1 the latter character is said to be recessive to tallness4 ,the contrasting characters of the parents therefore remain distinct in the progeny1 some of the latter exhibiting the one character and some the other2 while it may happen that the one character or the other may be segregated1 so that it only appears in1 and is transmitted by1 the offspring4 ,there are numerical relationships between the numbers of the offspring in which the contrasting characters appear4 ,obviously1 tallness and dwarfness are not characters which differ in quality3 they are different degrees of the same thing4 ,brown eyes and blue eyes are not necessarily different in quality1 for we may think of the same kinds of pigment as being present in the iris but mixed in different proportions4 ,but the terminology of this branch of biology appears to suggest that the contrasting characters are1 each of them1 something quite different from the other3 there are 8factors0 for 8tallness10 8dwarfness10 for blue eyes and brown eyes1 and so on4 ,these qualities are called 8unit-characters10 and they are supposed to possess much the same individuality in the germ-plasm as the 8radicles0 of the chemist possess in a compound4 ,sodium chloride1 for instance1 is not a blend of sodium and chlorine3 the two kinds of atoms do not fuse together but are held together merely4 ,the analogy is1 however1 very imperfect1 for in the chemical molecule the characters are not those of either of the constituents but something quite different1 whereas in the ,mendelian cross the characters remain distinct1 but one of them is patent while the other is latent4 ,in the molecule1 however1 the atoms are regarded by the chemist as lying beside each other in certain positions1 and the ,mendelian factors are also spoken of as if they lay side by side in the germ-plasm4 ,this terminology is useful1 perhaps necessary1 in the work of investigation1 but we must not forget that it symbolises1 rather than describes1 the results of experiment4 ,if the factors are identified with certain morphological structures in the nuclei of the germ-cells1 obviously all the objections that may be urged against the ,weismannian hypothesis as an hypothesis of development apply also to the ,mendelian hypotheses as descriptions of a physical process of the transmission of morphological characters4 ,it should clearly be understood what is implied in the construction of such a hypothesis4 ,certain processes are observed to take place when a somatic cell divides3 these processes we have regarded as having for their object the exact division of all the parts of the cell into two halves4 ,this process of somatic cell division is modified when a germ cell divides prior to maturation 7the process fitting it to become fertilised74 ,then the cell nucleus divides into four daughter-nuclei4 ,one of these remains in the cell substance which is to become the ovum1 and the other three1 each of them invested in a minimal quantity of cytoplasm1 are eliminated as the 8polar bodies40 ,also the number of chromosomes in the mother-cell becomes halved1 so that the mature ovum1 or spermatozoon1 possesses only one-half of the number of chromosomes which are present in the ordinary somatic cell4 ,now let the reader puzzle out for himself what may be meant by this behaviour of the germ cells1 and he will certainly see that several interpretations are possible4 ,but suppose that the chromatin consists of an incredibly large number of bodies differing in chemical structure from each other1 and occupying definite positions with regard to each other2 and suppose that there is a mechanism of unimaginable complexity in the cell capable of rejecting some of these chemically individualised parts1 and of 8assembling0 or arranging the others in much the same way as an engineer assembles the parts of a dynamo when he completes the machine4 ,then we may regard the hypothetical discrete bodies which form the hypothetical nuclear architecture as the material carriers of ,mendelian characters4 ,it is strange that the correspondence of such a logically constructed mechanism with the effects which it would produce if it existed should be regarded as a proof that it does exist1 yet biological speculation has actually made use of such an argument4 8,it seems exceedingly unlikely that a mechanism so exactly adapted to bring it0 7the separation from each other of the ,mendelian material 8factors0 of inheritance7 8about should be found in every developing germ cell if it had no connection with the segregation of characters that is observed in experimental breeding40 ,put quite plainly this argument is as follows3 there is a certain segregation to be seen in experimental breeding1 and certain processes may be observed to occur in the developing germ cell4 ,add to these processes many others logically conceivable1 and add to the observed material structure of the cell another structure also logically conceivable4 ,then the assumed mechanism and structure is 8exactly adapted0 to produce the effects which are to be explained4 ,therefore the mechanism and structure do actually exist6 ,that which renders the son similar to the father--the specific organisation--is undoubtedly very stable1 and it may persist in the face of a variable environment4 ,but now and then the son differs from the father4 ,the differences may be 8accidental0 and may not be transmitted further--then we have to deal with an unstable fluctuation2 or the differences may be permanent--then we have to deal with a stable mutation4 ,what 8produces0 a mutation8 ,a change of the environment1 it may be said3 if so1 the mutation is an active change or adaptation of the organism to a change in its surroundings1 and this adaptation is a permanent one and is transmitted4 ,or the mutation may be a spontaneous change of functioning4 ,if this disturbance of the stability of the organisation is general1 if it affects all the characters of the organism1 we have to deal with the establishment of a new elementary species4 ,but if the disturbance affects only one1 or a few characters1 then we need not recognise that a new elementary species has come into existence4 ,men and women remain men and women 7in their morphology71 although some time or other among the brown eyes characteristic of a race blue eyes may have appeared4 ,the result of the disturbance1 in this case1 has been to cause one1 or a few1 of the characters that fluctuate to surpass their limits of stability4 ,the idea of the elementary species is a clear and simple one4 ,it is a group of organisms connected by ties of blood relationship3 all have descended from one pair of ancestors4 ,the individuals exhibit certain characters1 all of which are variable4 ,this variability is not cumulative2 in generation after generation the individuals of the species display variations which fluctuate round the same mean values4 ,two or more elementary species may have had the same origin--a common ancestor or ancestors--but the organisms in one species exhibit characters which1 although similar in nature to those of the other species1 yet fluctuate about different mean values4 ,this is not the 8species0 of the systematic biologist4 ,the ,linnean or systematic species is a concept which is much more difficult to define3 it is a concept indeed which has not any clear and definite meaning1 in actual practice4 ,we often forget how very young the science of systematic biology is1 and how intimately its progress has been dependent on that of human invention and industrial enterprise4 ,physics and mathematics might be studied in a monastic cell1 but the study of systematic biology can only be carried on when we have ships and other means of travelling--the means1 in short1 of collecting the animals and plants inhabiting all the parts of the earth's surface4 ,until a comparatively few years ago the fauna and flora of great tracts of land and sea were almost unknown3 even now our knowledge of the life of many parts of the earth is scanty and inaccurate4 ,systematic biology has therefore had to collect and describe the organisms of the earth1 and in so doing it has set up the ,linnean species of plants and animals4 ,these we may describe as1 in the main1 categories of morphological structures4 ,the older and more familiar species are clearly defined in this respect3 such are cats and dogs1 rabbits1 tigers1 herrings1 lobsters1 oysters1 and so on3 the individuals in each of these categories are clearly marked out with respect to their morphology1 and the limits of the categories are clearly defined4 ,in all of them the specific organisation has attained a high degree of stability so that the individuals 8breed true to type02 and it has also attained a high degree of specialisation1 so that it does not fuse with other organisations4 ,yet1 in the majority of the systematic species of biology1 this criterion of specific individuality--this recognition of the isolation of the species from other species--cannot be applied4 ,very many species have been described from a few specimens only1 many from only one4 ,how does a systematist recognise that an organism with which he is dealing has not already been classified8 ,it differs from all other organisms most like it1 that is1 he cannot identify it with any known specific description4 ,but the differences may be very small1 and if he had a number of specimens of the species most nearly resembling it he might find that these differences were less than the limits of variation in this most closely allied species1 and he would then relegate it to this category4 ,but if he has to compare his specimen with the 8type0 one1 that is1 the only existing specimen on which the species of comparison was founded1 the test would be unavailable4 ,the question to be answered is this3 are the difference or differences to be regarded as fluctuations1 or are they of 8specific rank08 ,now certainly many systematists of great experience possess this power of judgment1 though they might be embarrassed by having to state clearly what were the grounds on which their judgment was based4 ,but on the other hand hosts of species have been made by workers who did not possess this quality of judgment2 and even with the great systematists of biology confusion has originated4 ,slowly1 very slowly1 the organic world is becoming better known1 and this confusion is disappearing4 ,the species1 then1 whether it is the systematic group of the biological systems1 or the elementary species based on the study of variability and inheritance1 is an intellectual construction3 an artifice designed to facilitate our description of nature4 ,this is clearly the case with the higher orders of groups in classifications3 genera1 families1 orders1 classes1 and phyla express logical relationships1 or describe in a hypothetical form our notions of an evolutionary process4 ,but species1 it may be said1 have an actual reality3 there are no genera in nature1 only species4 ,these categories of organisms really exist2 they have individuality1 a certain kind of organic unity1 inasmuch as the individuals composing them have descended from a common ancestor4 ,yet just as much may be said of genera1 families1 and the other groupings4 ,one species originates from another by a process of transmutation3 a genus is a group of species which have all had a common origin2 a family is a similarly related group of genera1 and so on4 ,the higher categories of biological science are intended to introduce order and simplification into the confusion and richness of nature as we observe it1 but obviously the concept of the species has the same practical object4 ,must we then say that there are no species in nature1 only individuals8 ,if so1 we are at once embarrassed by the difficulty of forming a clear notion of what is meant by organic individuality4 ,does it not indicate that life on the earth is really integral1 and that our analysis of its forms--species1 genera1 families1 and so on--are only convenient ways of dealing actively with all its richness8 ,systematic biology is a very matter-of-fact occupation1 and one is surprised to find upon reflection how he1 in his handling of the concepts of the science1 follows the methods of ancient philosophy4 ,in classical metaphysical systems mutability was an illusion4 ,behind the confusion and change given to sensation there is something that is immutable and eternal4 ,if there is change there is something that changes2 or1 at least there ought to be something that changes when it is perceived through the mists of sensation1 just as the image of a well-known object on the horizon wavers and is distorted by refraction4 ,this immutable reality is the ,form or ,essence of the ,platonic ,idea3 that which is in some way degraded by its projection into materiality1 so that we become aware of it only through our imperfect organs of sense4 ,we do not see the ,form itself1 but its quality rather1 the ,form with something added or something taken away from it4 ,the ,form itself is only a phase in a process of transmutation4 ,everything that exists in time flows or passes into something else4 ,but it is not a momentary or instantaneous view of the flux that we see1 but rather a certain aspect of the reality that flows1 that in some way expresses the nature of the transmutation from one ,form into another4 ,the sculptor represents the motion of a man running by symbolising in one attitude all the actions of body and limbs2 so that from our actual1 sensible experience or intuition of the movement of the runner we see in the rigid marble all the plasticity of life4 ,the instantaneous photograph shows us a momentary fixed attitude of the runner--an attitude which is strange and unfamiliar4 ,the ,idea does not1 then1 represent a moment of becoming like the photograph1 but rather a typical or essential phase of the process of transmutation1 just as the sculptor represents in immobile form the characteristic leap forward of the runner4 ,just as our intuitive knowledge of the actions of our own bodies enables us to read into the characteristic attitude represented in the marble all the other attitudes of the series of movements1 so our experience enables us to expand the formal moment of becoming into the action which it symbolises4 ,this action has a purpose1 an intention or design which was contemplated before it began4 ,there is therefore the threefold meaning in the ,platonic ,idea3 7#a7 an immutable and essential ,form of which we perceive only the quality2 7#b7 the characteristic phase in the transmutation of this ,form into some other one2 and 7#c7 the design or intention of the transmutation4 ,this was1 as ,bergson says1 the natural metaphysics of the intellect4 ,it was1 in reality1 the 8practical0 way of introducing order and simplification into the confusion of the sensible world--all that is presented to us by our intuitions4 ,and in the effort to reduce to order the welter of the organic world biology has followed the same method1 so that it represents the species with the threefold significance of the ,platonic ,idea4 ,that which is expressed in the term species is an assemblage of organisms each of which is defined by an essential form and an essential mode of behaviour--the characters indicated in the specific diagnosis4 ,but organisms are variable1 their specific characters fluctuate round a mean1 and in saying this we suggest that there is something which varies--there ought to be an essential form from which the observed forms of the individuals deviate1 something invariable which nevertheless varies accidentally4 ,this is 7#a7 the quality of the specific idea4 ,so also we never do actually observe the essential individual2 what we do see is the embryo1 or the young and sexually immature organism1 or the sexually mature one1 or the senescent one3 there is continual change from the time of birth to that of senile decay4 ,this confusion is unmanageable1 and for it we substitute the characteristic form and functioning1 and that phase in the life-history of the organism which suggests all that the previous phases have led up to1 and all that subsequent phases take away4 ,thus there is contained in our idea of the species 7#b7 the notion of a typical moment in an individual transformation4 ,it is not a 8snap-shot0 of some moment in the life-history that we make3 in identifying a larval form as some species of animal we are identifying it with all the other phases of the life-history4 ,since we accept the doctrine of transformism1 the specific idea also includes that of an evolutionary process4 ,for the organic world is a flux of becoming1 and species are only moments in this becoming4 ,it does not help us to reflect that if the hypothesis of evolution by mutations is true the process is a discontinuous one3 mutability is the result of periods of immutability during which the change was germinating1 so to speak4 ,in this flux of becoming we seize moments at which the specific form flashes out--not as instantaneous views of the flux1 but as aspects of it which suggest the steps1 the morphological processes1 by which the transmutation of the species has been effected4 ,thus our specific idea represents not only a phase of becoming in an individual life-history1 but also a phase of becoming in an evolutionary history4 ,whether we consider this evolutionary movement as the working out of a ,creative ,thought1 or as the development of elements assembled together by design1 or as the results of the action of a mechanism working by itself1 we must suppose that underlying it there is design1 or purpose1 or determinism4 ,all is given1 therefore1 and our comparison between the metaphysical ,platonic ,idea and the modern concept of the species becomes complete4 ,,chapter ,,vi ,,transformism ,the species is therefore a group of organisms all of which exhibit the same morphological characters4 ,this sameness is not absolute1 for the individuals composing the species may vary from each other with respect to any one character4 ,but the range of these variations is limited4 ,they fluctuate about an imaginary mean value which remains constant in the case of a species which is not undergoing selection1 and is therefore nearly the same throughout a series of generations4 ,the formal characters which we regard as diagnostic of the species are these imaginary mean ones4 ,it is possible to breed from stock a very great number of animals1 all of which are connected by a tie of blood-relationship1 that is1 all have descended from the same ancestor or ancestors4 ,such an assemblage of animals would resemble those assemblages living in the wild which we call species1 in that a certain morphological similarity would be exhibited by all the individuals4 ,if the breeding were conducted so as to avoid selection1 the range of variability would be very much the same as that observed in the wild race4 ,the two groups of animals--that bred artificially1 and that observed in natural conditions--would be very much alike1 and it is impossible to resist the conclusion that the natural race1 like the artificial one1 is a family in the human sense1 that is1 all the individuals composing it are connected together by a tie of common descent4 ,let us extend this reasoning to categories of organisms of higher orders than species4 ,we can associate together groups of species in the same way that we associate together the individuals of the same species4 ,there are certain morphological characters which are common to all the species in the category1 but there are also differences between specific group and specific group1 and these differences may be regarded as variations from the generic morphological type4 ,all the ,cats1 for instance1 have certain characters in common3 fully retractile claws1 a certain kind of dentition1 certain cranial characters1 and so on4 ,we postulate a feline type of structure1 and we then regard the characters displayed by the cat1 lion1 tiger1 leopard1 etc41 as deviations from this feline morphological type4 ,thus we establish the ,family ,felid4 ,but again we find that the ,felid together with the ,canid1 and many other species of animals1 also display common characters1 dental and osteological chiefly1 and we express this resemblance by assembling all these families in one ,order1 the ,carnivora4 ,the ,carnivores1 however1 are only one large group of ,quadrupeds3 there are many others1 such as the ,rodents1 ,ungulates1 ,cetacea1 etc41 and all of these possess common characters4 ,in all of them the integument is provided with hairs1 or other similarly developed structures2 all breathe by means of a diaphragm2 in all1 the young are nourished by suckling the mamm of the mother2 and all develop on a placenta4 ,we therefore group them all in the ,class ,mammalia4 ,now the ,mammals possess an internal skeleton of which the most fundamental part is an axial rod--the notochord--developing to form a vertebral column2 and this notochordal skeleton is also possessed by the ,birds1 ,reptiles1 ,amphibia1 and ,fishes4 ,there are also some smaller groups in which the notochord is present but does not develop to form segmented vertebr4 ,including these1 we are able to form a large category of animals--the ,chordata--and this phylum is sharply distinguished from all other cognate groups4 ,all animals and plants may be classified in a similar way4 ,insects1 ,spiders1 and ,crustacea1 for instance1 are all animals in which the body is jointed1 each joint or segment being typically provided with a pair of jointed appendages or limbs4 ,because of this similarity of fundamental structure we include all these animals1 with some others1 in one phylum1 the ,arthropoda4 ,so also with the rest of the animal kingdom1 and similar methods may be extended to the classification of the plants4 ,a few small groups in each of the kingdoms are difficult to classify1 but it has been possible to arrange most living organisms in a small number of sub-kingdoms or phyla1 and even to attempt to trace relationships between these various categories4 ,the mere systematic description of the organic world would have resulted in such a reasoned classification apart altogether from any notions of an evolutionary process4 ,but the classification1 originally a conventional way of making a list of organisms1 would at once suggest morphological similarities4 ,it would suggest that all the ,cats were ,carnivores1 that all the ,carnivores were ,mammals1 and that all the ,mammals were ,chordates4 ,it would suggest that all ,wasps were ,hymenoptera1 that all ,hymenoptera were ,insects1 and that all ,insects were ,arthropods4 ,it would establish a host of logical relations between animals of all kinds4 ,it would show us a number of groups of animals separated from each other by morphological dissimilarities4 ,but let us also consider all those animals which lived in the past of the earth1 and the remains of which are found in the rocks as fossils4 ,including all the forms of life known to ,palontology1 we should find that the dissimilarities between the various groups would tend to disappear4 ,the gaps between existing ,birds and ,reptiles1 for instance1 would become partially bridged4 ,palontology would also supplement morphology in another way4 ,the study of the structure of animals leads us to describe them as 8higher0 and 8lower0--higher in the sense of a greater complexity of structure4 ,thus the body of a ,carnivore is more complex than that of a ,fish1 inasmuch as it possesses the homologues of the truly piscine gills1 but it also possesses a four-chambered heart instead of a two-chambered one2 and it possesses the mammalian lungs1 diaphragm1 and placenta1 structures which are not present in the ,fish4 ,now1 so far as its imperfect materials go1 palontology shows us that the higher forms of life appeared on the earth at a later date than did the lower forms4 ,the remains of ,mammals1 for instance1 are first found in rocks which are younger than 7that is1 they are superposed upon7 those rocks in which ,reptiles first appear2 and so also ,reptiles appear later in the rock series than do ,fishes4 ,palontology thus adds to the logical order suggested by morphology a chronological order of this nature3 higher1 or more complex forms of life appeared at a later date in the history of the earth than did lower or less complex ones4 ,a parallel chronological sequence would also be suggested by the results of embryology4 ,this branch of biology shows us that all animals pass through a series of stages in their individual development1 or ontogeny4 ,the earlier stages represent a simple type of structure1 usually a hollow ball of cells1 but as development proceeds1 the structure of the embryo becomes more and more complex4 ,the process of development is continuous in many animals1 but in others 7perhaps in most7 larval stages appear1 that is1 development is interrupted1 and the animal may lead for a time an independent existence similar to that of the fully developed form4 ,often these larval stages suggest types of structure lower than that of the fully developed animal into which they transform4 ,even if larval stages may not appear in the ontogeny1 it is very often the case that the developing embryo exhibits traces1 or at least reminiscences1 of the types of morphology characteristic of the animals which are lower or less complex than itself2 thus the piscine gills appear during the development of the tailed ,amphibian1 and even in that of the ,mammal1 and then vanish1 or are converted into organs of another kind4 ,the individual thus passes through a series of developmental stages of increasing complexity3 it repeats1 in its ontogeny1 the palontological sequence in a distorted and abbreviated form4 ,it is true that the evidence afforded by palontology is very meagre4 ,the preservation of the remains of organisms in the stratified rocks is a very haphazard process1 and it depends for its success on a series of conditions that are not always present4 ,as the surface of the earth becomes better known1 our knowledge of the life of the past will become fuller1 but there can be little doubt that whole series of organisms must have existed in the past1 and that no recognisable traces of these are known to us4 ,there is also no doubt that the sequences indicated by palontology are very incomplete3 they are obscured and shortened by many conditions4 ,the earlier embryologists entertained hopes that the study of embryology would reveal the direction of the evolutionary process in many groups of animals3 if the organism repeats in its ontogeny the series of stages through which it passed in its phylogenetic development1 then a close study of the embryological process ought to disclose these stages4 ,although these hopes have not been realised1 there is yet sufficient truth in the doctrine of recapitulation to enable us to state that there is a rough parallelism between the palontological and embryological sequences4 ,we therefore state a plausible hypothesis when we assert that different species may be related to each other in the same way that the individuals of the same species are related1 that is1 by a tie of blood-relationship2 and that different genera1 families1 orders1 and so on are also so related4 ,morphological studies enable us to arrange numbers of species in such a way that series1 in each of which there is an increasing specialisation of structure1 are formed4 ,both palontology and embryology show1 to some extent at least1 that these stages of ever-increasing specialisation of structure occurred one after the other4 ,now1 stated briefly and baldly as we have put it1 this argument may not appear to the general reader to possess much force1 but it is almost impossible to over-state the strength of the appeal which it makes to the student of biology4 ,to such a one a belief in a process of transformism will appear to be inseparable from a reasoned description of the facts of the science4 ,but it would be no more than a belief1 not even a hypothesis1 if we did not attempt to verify it experimentally4 ,it is merely logical relationships that we establish1 and the chronological succession of forms of life1 higher forms succeeding lower ones1 does not itself do more than suggest an evolutionary process4 ,all that we have said is compatible with a belief in a process of special creation4 ,but if we cling to such a belief1 if we suppose that the organisms inhabiting the earth1 now and in the past1 are the manifestations of a ,creative ,thought1 we must still accept the notion of logical and chronological relationships between all these forms of life4 ,if we permit ourselves to speculate on the working of the ,creative ,thought1 we seem to recognise that the ideas of the different species must have generated each other1 and that the genesis of living things must have occurred in some such order as is indicated by a scientific hypothesis of transformism4 ,an evolutionary process must have occurred somewhere1 but the kinships so established between organisms would be logical and not material ones4 ,science must not1 of course1 describe the mode of origin of species in this way4 ,so long as it investigates living things by the same methods which it uses in the investigation of inorganic things1 it must hold that the concepts of physical science are also adequate for the description of organic nature4 ,it must assume that matter and energy and natural law are given2 and that1 even in the conditions of our world1 life must have originated from lifeless matter2 must have shaped itself1 and undergone the transformations that are suggested by the results of biology4 ,it must assume1 in spite of the formidable difficulties that the assumption encounters1 that cosmic physical processes are reversible and cyclical2 and that worlds and solar systems are born1 evolve1 and decay again4 ,every stage in such a cosmic process1 as well as every stage in the evolution of living things1 must have been inevitably determined by the stages preceding it4 ,such a mechanistic explanation must assume that a superhuman intellect1 but still a finite intellect like our own1 such a calculator as that imagined by ,laplace or ,du ,bois-,reymond1 would be able to deduce any state of the world1 or universal system1 from any other state1 by means of an immense system of differential equations4 ,it would be able1 as ,huxley says1 to calculate the fauna of ,great ,britain from a knowledge of the properties of the primitive nebulosity with as much certainty as we can say what will be the fate of a man's breath on a frosty day4 ,such a fine notion as that of an universal mathematics must ever remain as the ideal towards which science strives to approximate4 ,or we may suppose that a plan or design has been superposed on nature1 is immanent in matter and energy1 and works itself out1 so to speak4 ,such a teleological explanation of inorganic and organic evolution inevitably forces itself upon us if we reject the notion of radical mechanism4 ,we think of an universal system of matter and energies as consisting of elements which1 when assembled together1 interact in a certain way1 and with results which are definite and calculable4 ,the assembling together of the elements of the system would be the result of the previous phases of the system4 ,that is radical mechanism4 ,but let us think of the elements of the system as being differently assembled--thus involving the idea of an agency1 external to the system1 which rearranges them--then the same energies inherent in this system1 as in that previously imagined1 will also work out by themselves4 ,but the result will be different1 and will depend on the manner in which the elements were originally arranged4 ,that would be radical finalism4 ,science must reject this notion as it rejects that of special creation1 since it introduces indeterminism into the evolutionary process4 ,it must regard the organism and its environment as a physico-chemical system studied from without4 ,it must avoid all attempts to acquire an intuitive knowledge of the actions of the organism1 for the latter1 and the things which environ it1 are only bodies moving in nature4 ,in the systems studied by it time must be the independent variable1 and there must be a strict functionality between the parts of the organism and the parts of the reacting environment1 so that any change in the one must necessarily be dependent on a change in the other4 ,such a system and series of interactions is that which is described in a mechanistic hypothesis of transformism4 ,all this is indeed suggested to ordinary and aided methods of observation4 ,the plant or animal acts upon1 and is acted on by1 the environment1 though it is usually the modification of the organism to which we attend4 ,a man's face becomes reddened by wind and sun and rain2 manual labour roughens his hands and develops callosities2 in the summer he sweats and loses heat2 in the winter the blood-vessels of his skin contract and heat is economised4 ,in the winter months the fur of many animals becomes more luxuriant and may change in colour4 ,fishes which inhabit lightly coloured sand are lightly pigmented1 but their skins become dark when they move on to darkly coloured sea-bottoms2 prawns which are brown when they live on brown weed1 become green when they are placed on green weed4 ,birds migrate into warmer countries1 and vice versa1 when the seasons change4 ,such are instances of the adaptations of the morphology and functioning of organisms consequent on changes of environment4 ,what is an adaptation8 ,the term plays a great part in biological speculation1 but it is often used in a loose and inaccurate manner1 and not always in the same sense4 ,it suggests that the organism is contained by the environment1 and that its form becomes adapted to that of the latter1 just as the metal which the ironfounder pours into the mould takes the form of the cavity in the sand4 8,we see once more how plastic is the organism in the grasp of its environment0--such a quotation from morphological literature is perhaps a typical one4 ,over and over again this passive change in the organism as the result of the action of something rigid which presses upon it is what is understood by an adaptation4 ,no doubt the organism may be so affected1 and often the change which it experiences is of the same order as the environmental change4 ,in the winter many animals become sluggish and may hibernate2 their heart-beats slow down2 their respiratory movements become less frequent1 and generally the rate of metabolism1 that is the rapidity with which chemical reactions proceed in their tissues1 becomes lessened4 ,all these changes become reversed in sign when the temperature again rises4 ,the time of year at which a fish spawns depends on the nature of the previous season4 ,the rate of development of the egg of a cold-blooded animal varies with the temperature4 ,the quantity of starch formed in a green leaf depends on certain variables--the intensity of light1 the temperature1 and the quantity of carbonic acid contained in the medium in which it is placed4 ,in all these cases the rate at which certain metabolic processes go on in the body of an organism varies according to the conditions of the environment4 ,in general they are cases of van't ,hoff's law1 that is1 the rapidity at which a chemical reaction proceeds varies according to the temperature4 ,they are changes of functioning passively experienced by the organism as the result of environmental changes1 and we must clearly distinguish between them and such changes as are the result of some activity or effort on the part of the organism4 ,a flounder which lives in a river migrates out to sea when the first of the winter snows melt and flood the estuary with ice-cold water4 ,brown or striped prawns living on brown or striped weeds become green when they are placed on green weed1 changing their pigmentation to match that of the alga4 ,a kitten brought up in a cold-storage warehouse develops a sleeker and more luxuriant coat than does its sister reared in a well-warmed house4 ,an animal which recovers from diphtheria forms an antitoxin which enables it to resist1 for a time at least1 repeated infection4 ,a man who goes exploring in polar seas puts on warmer clothing than he wears in the tropics4 ,it is not necessary that an environmental change should occur in order that an adaptation should be evoked1 for the organism may react actively and purposefully to a change in itself4 ,the athlete acquires by running or rowing a more powerful heart2 the blacksmith develops more muscular shoulders and arms2 and the professional pianist more supple wrists and fingers4 ,if one kidney is removed by operation1 or if one lung becomes diseased1 the organ on the other side of the body becomes hypertrophied4 ,aphasia1 which is due to a lesion in the unilateral speech-centre1 may pass away if the previously unused centre on the other side of the brain should become functionally active4 ,in general1 the continued use of an organ leads to its increase in size and efficiency1 and conversely disuse leads to a decrease of size and even to atrophy4 ,the essence of an adaptation is that it is an active1 purposeful change of behaviour1 or functioning1 or morphology1 by which the organism responds to some change in its physical environment1 or to some other change in its own behaviour1 or functioning1 or morphology4 ,it is also a change which remains as a permanent character in the organisation of the animal exhibiting it4 ,it does not matter even if the change of behaviour is one which is willed in response to some change of environment actually experienced1 or whether it anticipates some change that is foreseen4 ,a changed mode of behaviour adapted intelligently leaves1 at the least1 a memory which becomes a permanent part of the consciousness of the animal1 and may influence its future actions2 or if it is evoked by a process of education it must involve the establishment of a 8motor habit40 ,the education of a singer sets up1 in the cortex and lower centres of the brain1 a nervous mechanism which controls and co-ordinates the muscles of the chest and larynx1 and which did not exist prior to the process of education4 ,adaptations are therefore acquired changes of some kind or other by means of which the organism is able to exert a greater degree of mastery over its environment1 including in the latter both the inert matter of inorganic nature and the other organisms with which the animal competes4 ,they are acquirements because of which the organism deviates from the morphological structure characteristic of the species to which it belongs4 ,do they affect the entire organisation of the animal exhibiting them1 that is1 may an acquired change of structure be so fundamental that it affects not only the body of the animal in which it occurs but also the progeny of this animal8 ,let us suppose that this is the case2 let us suppose that quite a large proportion of all the individuals of a species inhabiting a restricted part of the earth's surface acquire the same change of character simultaneously and that they transmit this deviation of structure to their progeny4 ,then we should have an adequate means whereby the specific type becomes modified--a means of transformism4 ,this is the hypothesis which is associated with the name of ,lamarck1 and its essential postulate is that characters which are acquired by an organism during its own lifetime are transmitted to its offspring4 ,it seems reasonable to suppose that this transmission of acquired characters should occur--how reasonable we should note when we see that de ,vries tacitly assumes that fluctuating variations due to the action of the environment may be inherited by the offspring of organisms which exhibit them4 ,that transmutation of species might occur in this way was a popular and widespread belief in ,england and ,germany throughout the greater part of the nineteenth century2 and it was a belief entertained by ,darwin himself1 and confidently1 and even dogmatically affirmed at one time by the majority of biologists in both countries4 ,how was it1 then1 that a very general change of opinion with regard to this question occurred both in ,england and ,germany during the last two decades of the last century8 ,certainly many botanists and zoologists continued to adhere to the older hypothesis1 and most physiologists still do not appear to make any clear distinction between morphological characters which are inherited and those which are acquired2 but the majority of biologists did not hesitate to conclude that not only was the transmission of acquired characters an unproved conjecture1 but that it was even theoretically inconceivable4 ,at the beginning of the nineteenth century this belief had almost become a doctrine dogmatically asserted1 and one cannot fail to notice a tone of irritation and impatience on the part of the spokesmen of zoology when the contrary opinions are expressed4 8,nature10 says ,sir ,e4 ,ray ,lankester1 87and there's an end of it7 does not use acquired characters in the making and sustaining of species for the very simple reason that she cannot do so40 ,there can be little doubt that the interrogation of nature with regard to this question was not a very thorough process4 ,the dogmatic denial of the transmission of acquired characters was not the result of exhaustive experiment and observation1 but was due rather to the very general acceptance in ,england and ,germany of ,darwin's hypothesis of the transmutation of species by means of natural selection1 and of ,weismann's hypothesis of the continuity of the germ-plasm4 ,the newer hypothesis of transmutation was one which seemed adequate to account for the diversity of forms of life1 so that it was unnecessary to invoke the older one2 though ,darwin himself admitted that the individual acquirement of structural modifications might be a factor in the evolutionary process2 and for more than twenty years after the publication of the 8,origin of ,species0 ,lamarck's hypothesis was not strenuously denied by naturalists4 ,early in the 'eighties1 however1 ,weismann published his book on the germ-plasm1 and the brilliancy and constructive ability of the speculations contained in this remarkable work1 as well as the analogies which they suggested between organic and inorganic phenomena1 compelled the attention of biologists4 ,the essential parts of ,weismann's hypothesis1 as it was first presented to the world1 are as follows3 very early in the evolution of living from non-living matter many kinds of life-substance came into existence4 ,these were chemical compounds of great complexity1 able to accumulate and expend energy1 and capable of indefinite growth and reproduction4 ,they were able to exist in an environment which was hostile to them and which tended always to their dissolution1 and which was able to modify their nature and their manner of reacting1 though it could not destroy them4 ,these elementary life-substances were very different from those which we know in the world of to-day4 ,they were naked protoplasmic aggregates1 undifferentiated into cellular or nuclear plasmata1 much less into somatic and germinal tissues4 ,all of their parts were similar1 or rather their substance was homogeneous4 ,but even with the evolution of the unicellular organism a profound change was initiated1 for henceforth one part of the living entity1 the nucleus1 became charged with the function of reproduction1 although it still continued to exercise general control over the functions of the extra-nuclear part of the cell4 ,when the multi-cellular plant and animal became evolved1 the heterogeneity of the parts of the organism became greater still4 ,all the cells of the metazoan animal do indeed contain nuclei1 but these structures are only the functional centres of the cells3 some of the latter are sensory1 others motor1 others assimilatory1 others excretory1 and so on4 ,only in the nuclei which form the essential parts of the reproductive organs does the reproductive function persist in all its entire potentiality3 there only does the protoplasm retain all the properties which were possessed by the primitive life-substance before it became heterogeneous1 that is1 before nucleus and cytoplasm evolved4 ,when part of the primitive life-substance became secluded in a nuclear envelope1 it became1 to that extent1 shielded from the action of the physical environment1 and when the organism became composed of multicellular tissues this seclusion became more complete4 ,clothed in the garments of the flesh1 it was henceforth protected from the shocks of the environment1 and it became the immutable germ-plasm4 ,but for a very long time before this evolution of tissues the naked life-substance had been exposed to the action of external physical agencies1 and it had been modified by these into very numerous forms of protoplasmic matter4 ,when multicellular plants and animals had been evolved there were1 therefore1 not one1 but many kinds of life-substance in existence1 and these have persisted until to-day as the unchanging germ-plasmata of the existing organisms4 ,the ,weismannian hypothesis of to-day1 supported and amplified1 as it is1 by subsidiary hypotheses1 does not make the same appeal to the student as did the pristine and altogether attractive speculation of thirty years ago4 ,the analogy which it then presented with the matured chemical theory of matter must have been almost irresistible4 ,just as the indefinitely numerous compounds of chemistry are only the permutations and combinations of some of eighty-odd different kinds of matter1 so all the forms of life are combinations and permutations of some of the many different kinds of life-substance which came into existence before the evolution of the multicellular organism4 ,and just as the chemical elements were regarded 7in #ahhc7 as immutable things1 preserving their individuality even when they were associated together as compounds1 so ,weismann and his followers looked upon the different kinds of life-substance contained in the chromatic matter of the nucleus as immutable and immortal living entities4 ,associated together in indefinitely numerous ways by sexual conjugation1 they may build up indefinitely variable living structures1 but they remain individualised and lying side by side in the germ-plasmata of organisms1 just as the atoms were supposed to lie side by side in the chemical molecule of the inorganic compound4#ca #ca ,we know now that this statement is not quite accurate4 ,if these speculations were true1 a change of morphology or functioning1 acquired by the body1 or somatoplasm1 could not possibly be transmitted to the progeny of the organism1 for by hypothesis the germ-plasm cannot be affected by external changes1 and it is only the germ-plasm contained in the spermatozoon of the male parent1 or in the ovum of the female1 that shapes and builds the body of the offspring4 ,as if this were not enough1 ,weismann and his followers argued that the transmissibility of a somatic change to the germ was inconceivable4 ,why8 ,because the germ-cells are apparently simple3 they are only semi-fluid protoplasmic cell bodies and nuclei1 not differing appreciably from the cell bodies and nuclei of the somatoplasm 7by hypothesis1 it should be noted1 the difference is profound74 ,there are no structural connections--no nerves1 for instance--which join together the cells of the bodily tissues with the parts of the germ and transmit changes in the former to the latter4 ,how1 then1 could a somatic change affect the germ so that when the latter developed into an organism this particular change became reproduced8 ,now this may have seemed a conclusive argument in #ahhc1 but is it so conclusive to-day8 ,we know that the cells and tissues are not isolated particles1 but that all are connected together by protoplasmic filaments4 ,we know that specialised nervous tissues are not necessary for the transmission of an impulse from a sensory to a motor surface1 but that such an impulse may be transmitted by undifferentiated protoplasm4 ,we know that nerve-cells and nerve-fibres are not structurally continuous with each other but that the impulse leaps across gaps1 so to speak4 ,we know that events that occur in one part of the body of the mammal may affect other parts by means of the liberation of a chemical substance1 or hormone1 into the blood stream4 ,it would be strange indeed if a logical hypothesis capable of accounting for the transmission of a particular change from the soma to the germ could not be elaborated4 ,but acquired characters were not really transmitted after all4 ,so those who clung to ,weismannism argued--an unnecessary task surely if this transmissibility were inconceivable4 ,we cannot discuss the evidence here1 and it is unnecessary that we should do so1 since it is all considered in the popular books on heredity4 ,there is an apparent consensus of opinion in these books which should not influence the reader unfamiliar with zoological literature1 nor obscure the fact that many zoologists and botanists accept the opposite conclusion4 ,the discussion is all very tiresome1 but we may glean some results of positive value from it4 ,it is unquestionable that very few conclusive and adequate investigations have been made3 one cannot help noticing that the literature contains an amount of controversy out of all proportion to the amount of sound experimental and observational work actually carried out4 ,most of the experiments deal with the consideration of traumatic lesions or mutilations1 and it seems to be proved that such defects are not transmitted1 or at least are very rarely transmitted4 ,the tails of kittens have been cut off2 the ears of terrier-dogs have been lopped2 and the feet and waists of ,chinese and ,european ladies have been compressed1 and all throughout very numerous generations1 yet these defects are not transmitted from parent to offspring4 ,this kind of evidence forms the bulk of that which orthodox zoological opinion has adduced in favour of the belief in the non-inheritability of acquired characters1 but does it all really matter8 ,what might be transmitted is a useful1 purposeful modification of morphology1 or functioning1 or behaviour1 induced by the environment throughout a number of generations--an adaptation rather than a harmful lesion4 ,there is little conclusive evidence that such adaptations are inherited1 though anyone who carefully studies the evidence in existence will not be likely to say that they are certainly not transmitted4 ,does1 for instance1 the blacksmith transmit his muscular shoulders and arms to his sons1 or the pianiste her supple wrists and fingers to her daughters8 ,there are no observations and experiments in the literature worthy of the importance attaching to the question at issue4 ,it should be noted also that the germ-plasm is certainly not the immutable substance that the hypothesis originally postulated4 ,changes in the outer physical environment may certainly affect it2 thus the larv bred from animals which live in abnormal physical conditions 7temperature1 moisture1 etc47 may differ morphologically from the larv bred from animals belonging to the same species but living in a normal environment4 ,the latter must therefore react on the germ-plasm1 but the environment formed by the bodily tissues which surround the germ-cells may also so react3 thus the germ-cells may be affected by such bodily changes as differences in the supply of nutritive matter1 for instance4 ,the offspring may deviate from the parental structure as the result of structural modifications acquired by the parent during its own lifetime1 and1 even if the filial deviation were not of the same nature as the parental modification1 its inheritance would be an adequate cause of some degree of transmutation4 ,it is1 however1 certainly difficult to prove that organisms transmit to their progeny the same kinds of deviation from the specific structure that they themselves acquire as the result of the action of the environment4 ,even if they did transmit such acquired deviations1 it does not seem clear that this kind of inheritance alone would be a sufficient cause of the diversity of forms of life that we do actually observe in nature4 ,change of morphology would indeed occur1 but we should expect to find insensible gradations of form and not individualised species4 ,let us suppose that ,lamarckian inheritance acts for a considerable time on two or three originally distinct species inhabiting an isolated tract of land1 and let us suppose that we investigate the variations occurring among all the organisms which are accessible to our observation with respect to some one variable character4 ,the diagram ,a represents what would seem to be the result of this process of transmutation4 ,the numbers along the horizontal line are proportional to their distance from o1 the origin1 and represent the magnitude of the variation considered2 and the height of the vertical lines represents the number of organisms exhibiting each degree of variation4 ,we should expect to find that all the variations were equally frequent in their occurrence1 but this is not what a study of variability in such a case as we have supposed--that of the animals inhabiting an isolated part of land--does actually indicate4 ,what we should find would be the conditions represented by the diagram ,b4 ,there would be two or more modes1 that is1 values of the variable character which are represented by a greater number of individuals than any other value of the variation4 ,the environmental conditions favour the individuals displaying this variation to a greater extent than they favour the rest4 ,illustration3 ,,fig4 #bd4 ,that is to say1 the environment selects some kinds of variations among the many that are exhibited1 and this is1 of course1 the essential feature of the hypothesis of the transmutation of species by means of natural selection of variable characters4 ,organisms enter the world differently endowed with the power of acting on the medium in which they live1 or on the environment consisting of their fellow-organisms4 ,those that are most favourably endowed live longest and have a more numerous progeny than those that are less favourably endowed1 and they transmit this favourable endowment to their offspring4 ,among the progeny of the progeny there may be some in which the favourable variation is still more favourable than it was when it first appeared4 ,thus the variations which are selected increase in amount4 ,elimination of the weakest occurs4 ,the idea is eminently clear and simple1 and possesses a great degree of generality3 it is self-evident1 says ,driesch1 meaning that it cannot be refuted1 for it was certainly not clearly obvious to the naturalists before ,darwin and ,wallace4 ,but1 unless we choose to be dogmatic1 we can hardly claim that it is an all-sufficient cause for the evolutionary process1 and it is useless to attempt to minimise the difficulties of the hypothesis4 ,it is not easy to make it account for the origin of instincts or tropisms1 or for restitutions and regenerations of lost parts1 or for the appearance of the first non-functional rudiments of organs which later become functional and useful4 ,it is1 indeed1 possible to devise plausible hypotheses accounting for all these things in terms of natural selection1 but each such subsidiary hypothesis loads the original one and weakens it to that extent4 ,natural selection does not1 of course1 induce or evoke variations2 these are given to its activity1 and they are the material on which it operates4 ,what1 then1 is the nature of the deviations from the specific types of morphology that are selected or eliminated8 ,not those induced by the environment1 and transmitted in their nature and direction to the progeny of the organisms first displaying them4 ,it is not unproved that such variations do occur1 and it is even probable that they do occur4 ,but we may conclude that the frequency of their occurrence is not great enough to afford sufficient material for natural selection4 ,it is also clear that the ordinarily occurring variations that we observe in any large group of organisms collected at random are not alone the material for selection2 for we have seen that experimental breeding from such variations does not lead to the establishment of a stable race or 8variety40 ,nevertheless some effect is produced1 and this may be accounted for by supposing that the observed variations are really of two kinds--fluctuating variations1 which are not inherited1 and mutations1 which are inherited4 ,the small observed effect is due to the selection of the mutations alone3 it is a real effect of selection1 an undoubted transmutation of the specific form1 but experimental and statistical investigations seem to show that selection from the variations that we usually observe is too slow a process to account for the existing forms of life4 ,natural selection acts1 therefore1 on mutations4 ,now it seems that we are forced to recognise the existence of two categories of mutations1 7#a7 those stable modifications of an 8unit-character0 which we term 8,mendelian characters10 and 7#b7 those groups of stable modifications to which de ,vries applied the term mutations4 ,it seems at first difficult to see how permanent modifications of the specific form can be brought about by the transmission of ,mendelian characters1 for these characters are always transmitted in pairs4 ,let us take a concrete case--that of a man who has six fingers on his right hand1 and let us suppose that this was a real1 spontaneously appearing character or mutation which had not previously occurred in the ancestry of the man4 ,two contrasting characters would then be transmitted1 7#a7 the normal five-fingered hand1 and 7#b7 the six-fingered hand4 ,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 individual1 but one of them is always latent or recessive4 ,there would1 however1 be individuals in which only one of the characters would be present--either the normal or abnormal number of digits1 but intermarriage with individuals belonging to the other pure strain would immediately lead again to the transmission of the contrasting characters1 or allelomorphs1 although marriage with an individual belonging to the same pure strain would carry on the normal or abnormal unmixed character into another generation4 ,but if the possession of six fingers conveyed an undoubted advantage1 and if natural selection did really act in civilised man as regards the transmission of morphological characters1 then a stable variety 7,homo sapiens hexadactylus1 let us say7 might be produced by its agency4 ,the mutations 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 variations displayed by organisms in general3 but since only one or two characters appear to be subject to this mode of transmission1 the process would be so slow as to be inadmissible as an exclusive cause of evolution4 ,if we assume that de ,vries' mutations are the material on which selection works1 this difficulty is immediately removed1 for we now have to deal with groups of stable deviations3 not one or two1 but all the characters of the organism appear to share in the mutability4 ,but another difficulty now arises4 ,a species of plant or animal may have got along very well with its ordinary structural endowment1 and then a number of individuals begin to mutate4 ,some of the deviations from the specific type may be of real advantage1 but others may not3 we can1 indeed1 imagine an in-co-ordination between the mutating parts or organs which would be fatal to the animal2 on the other hand1 there might be complete co-ordination1 with the result that great advantage might be conferred upon the individual4 ,it is easy to see how co-ordination of mutating parts is absolutely essential4 ,an animal which preserves its existence by successful avoidance of its enemies would not be greatly benefited by a more transparent crystalline lens if the vitreous humour of its eye were slightly opaque2 and even if all the parts of the eye were perfectly co-ordinated1 increased acuity of vision would not greatly help it if its limbs were not able to respond all the more quickly to the more acute sensation4 ,un-co-ordinated mutations would therefore tend to become eliminated1 while co-ordinated ones would become selected and would become the characters of new species4 ,we must now ask why some groups of variations are co-ordinated while others are not1 and it is here that we encounter the most formidable of the difficulties of any hypothesis of transformism which depends on the concept of natural selection4 ,if we assume that the environment induces the appearance of variations1 it seems to follow that these variations are likely to be co-ordinated1 but we then invoke the principle of the acquirement of characters and their transmission by heredity4 ,if1 on the other hand1 we assume that variations appear spontaneously1 and quite irresponsibly1 so to speak1 in the germ-plasm of the organism1 the selection1 or elimination1 by the environment will not occur until the co-ordinated or un-co-ordinated variations appear4 ,it is far more likely that a large number of simultaneously appearing variations will be un-co-ordinated than that they will be co-ordinated4 ,merely as a matter of probability the progressive modification of a species will take place slowly--too slowly to account for what we see4 ,two examples will make it easier to appreciate this difficulty4 ,evolution has undoubtedly proceeded in definite directions4 ,there are two dominant groups of fishes1 the ,teleosts and the ,elasmobranchs1 and both must have originated from a common stock4 ,all the characters in each kind of fish must have been useful 7since they were selected71 and all must have been modifications of the characters of the common stock4 ,the latter became modified along two main lines1 or directions1 which are indicated by the characters of the existing ,teleosts and ,elasmobranchs4 ,the whole skeleton1 the gills1 the circulatory system1 and the brain differ in certain respects in these groups4 ,therefore a modification of the brain in the primitive ,elasmobranchs was associated with a modification of the cranium1 and therefore with the jaw-apparatus1 and so with the branchial skeleton and the gills1 and therefore also with the heart1 and so on4 ,suppose that the evolutionary process included ten useful and co-ordinated variations--not an unlikely hypothesis--and suppose that each of these ten useful variations was associated with nineteen useless ones4 ,the chance that any one of them did occur was therefore one in twenty2 and if they all occurred independently1 that is1 if the occurrence of any one of them was compatible with the occurrence of any other one1 or of all the others1 then the chance that all the ten variations occurred simultaneously was #bj-aj that is1 one in the number #bj followed by #aj cyphers1 a rather great improbability4 ,most biological students are familiar with the similarity of the so-called eye of the mollusc ,pecten and that of the vertebrate4 ,the resemblance is one of general structure3 in each of these organs there is a camera obscura1 a transparent cornea1 and behind that a crystalline lens4 ,on the posterior wall of the camera there is a receptor organ1 or retina1 and this is composed of several layers of nervous elements4 ,the actual nerve-endings are on the surface of the retina1 which is turned away from the light1 that is1 the optic nerve runs towards the anterior surface of the retina1 and then its fibres turn backwards4 ,this 8inversion of the retinal layers0 occurs in all vertebrate animals1 but it is exceptional in the invertebrates4 ,the above general description applies equally well to the eye of the vertebrate and to that of ,pecten4 ,let us admit that these mantle organs in ,pecten are eyes1 for there is no conclusive experimental evidence that they really are visual organs1 and plausible reasoning suggests that they may subserve other functions4 ,let us assume that the minute structure of the ,pecten eye is similar to that of the vertebrate1 and that its development is also similar3 as a matter of fact both histology and embryology are different4 ,then we have to explain1 on the principles of natural selection1 the parallel evolution of similar structures along independent lines of descent2 for mollusc and vertebrate have certainly been evolved from some very remote common ancestor in which the eye could not have been more than a simple pigment spot with a special nerve termination behind it4 ,in each case the organ was formed by a very great number of serially occurring variations1 yet these two sets of variations must have been the same at each stage in two independently occurring processes4 ,on any reasonable assumption as to the number of co-ordinated variations required1 and their chances of occurrence1 the mathematical improbability that these two series of variations did occur is so great as to amount to impossibility so far as our theory of transformism is concerned4 ,natural selection could not1 therefore1 have produced these two organs4 ,this argument of ,bergson's fails1 of course1 in the particular instance chosen by him1 but this is because the case is an unfortunate one4 ,probably a morphologist could find a very much better case of convergent evolution--the parallelism between the teeth of some ,marsupials and some ,rodents1 for instance4 ,if detailed histological and embryological investigation should show a similarity of structure and development1 in such compared organs ,bergson's argument would retain all its force4 ,we should then have to assume that there was a directing agency1 or tendency in the organism1 co-ordinating1 or perhaps actually producing1 variations4 ,mechanistic biology can suggest no means whereby simultaneously occurring variations are co-ordinated3 let us therefore think of these variations as occurring independently of each other1 and let us ignore the difficulty of the infrequency of occurrence of suitably co-ordinated variations4 ,variations are exhibited by the evolving organism1 and the selection of co-ordinated series is the work of the environment4 ,but the environment is merely a passive agency1 and it has to confer direction on the innumerable variations presented to it by the organism1 rejecting most but selecting some4 ,let us think of the environment1 says a critic of ,bergson1 as a blank wall against which numerous jets of sand are being projected4 ,the jets scatter as they approach the wall3 each of them represents the variations displayed by some organ or organ-system of an animal4 ,let us think of a pattern drawn on the wall in some kind of adhesive substance3 where the wall is blank the sand would strike1 but would fall off again1 but it would adhere to the parts covered by the adhesive paint4 ,the sand grains strike the wall from all sides1 that is1 their directions are un-co-ordinated4 ,the wall is passive1 yet a pattern is imprinted upon it4 ,from passivity and un-co-ordination come symmetry and order4 ,this argument withstands superficial examination1 but to accept it is truly to be 8fooled by a metaphor40 ,for what is the pattern on the wall8 ,it is the environment1 says the critic4 ,but what is the environment8 ,inevitably we think of it as something that makes or moulds the organism1 a way of regarding it that drags after it all the confusion of thought implied in the above analogy4 ,clearly the environment is made by the organism4 ,its form1 that is1 space1 is only the mode of motion possible to the organism2 it is clear that whether the space perceived by an organism is one-1 two-1 or three-dimensional1 space depends upon its mode of motion4 ,its universe is whatever it can act upon1 actually or in contemplation4 ,atoms and molecules1 planets and suns are its environment because it can in some measure act upon these bodies1 or at least they can be made useful to it4 ,chloroform or saccharine1 or methyl-blue and all the dye-stuffs prepared from coal-tar by the chemists1 are part of our environment because we have made them4 ,they existed only in potentiality prior to the development of organic chemistry4 ,they were possible1 but man had to assemble their elements before they became actual4 ,in making them1 he conferred direction on inorganic reactions4 ,surely the organism itself selects the variations of structure and functioning that are exhibited by itself4 ,if we hesitate to say that these modifications are creations1 let us say that they are permutations of elements of structure1 and that they were potential in the organisation of the creature exhibiting them4 ,they occur in the latter if we must not say that they are produced4 ,if they are detrimental1 the organism is the less able to live and reproduce1 and if it does reproduce1 its progeny are subject to the same disability4 ,if1 as is usual1 they simply do not matter1 they may or may not affect the direction of evolution4 ,if they are of advantage1 that is1 if they confer increased mastery over the environment1 over the inert things with which the organism comes into contact1 the latter enlarges its universe or environment1 lives longer1 and transmits to its progeny its increased powers of action4 ,indefinite increase of power over inert matter is potential in living things1 and variation converts this potentiality into actuality4 ,this discussion is all very formal1 but two conclusions emerge from it3 7#a7 the insufficiency of the mechanistic hypotheses of transformism to account for all the diversity of life that has appeared on the earth during the limited period of time which physics allows for the evolutionary process4 ,there does not appear to be any possibility of meeting this objection if we continue to adhere to the hypothesis of transformism already discussed3 it faces us at every turn in our discussion4 ,how great a part is played1 for instance1 by 8pure chance0 in the elimination of individual organisms during the struggle for existence6 ,let us think of a shoal of sprats on which sea-birds are feeding3 it is chance which determines whether the birds prey on one part of the shoal rather than another4 ,or let us think of the millions of young fishes that are left stranded on the sea-shore by the receding tide3 it is chance that determines whether an individual fish will be left stranded in a shallow sandpool which dries up under the sun's rays1 rather than in a deeper one that retains its water until the tide next flows over it4 ,it is no use to urge that there is no such thing as 8pure chance10 and that what we so speak of is only the summation of a multitude of small independent causes4 ,let us grant this1 and it still follows that the alternative of life or death to multitudes of organisms depends not upon their adaptability but upon minute un-co-ordinated causes which have nothing to do with their morphology or behaviour4 ,these are instances among many others which will occur to the field naturalist3 they shorten still further the time available for natural selection in the shaping of species1 for they reduce the material on which this factor operates4 ,the other result of our discussion is to indicate that the problem of transformism of species is in reality the problem of organic variability4 ,let us assume that all the hypotheses of evolution are true3 that the environment may induce changes of morphology and functioning in animals and plants1 and that these changes themselves--the actual acquirements themselves1 that is--are transmissible by heredity4 ,let us assume that the germ-cells may be affected by the environment1 either the outer physical environment1 or the inner somatic environment1 and that mutations may thus arise4 ,let us assume that mutations may be selected in some way1 so that specific discontinuities of structure--8individualised0 categories of organisms1 or species--may thus come into existence4 ,even then transformism is still as great a problem as ever1 for the question of the mode of origin of these variations or modifications still presses for solution4 ,the simplest possible cases that we can think of present the most formidable difficulties4 ,the muscles of the shoulders and arms of the blacksmith become bigger and stronger as the result of his activity4 ,why8 ,we say that the increased katabolism of the tissues causes a greater output of carbonic acid and other excretory substances1 and that these stimulate certain cerebral centres1 which in turn accelerate the rate of action of the heart and respiratory organs4 ,an increased flow of nutritive matter and oxygen then traverses the blood-vessels in the muscles of the shoulders and arms1 and the latter grow4 ,probably processes of this kind do occur1 but to say that they do is not to give any real explanation of the hypertrophy of the musculature of the man's body1 for what essentially occurs is the division of the nuclei and the formation of new muscle fibres4 ,how precisely does an increased supply of nutritive matter cause these nuclei to divide and grow8 ,this is a relatively simple example of the adaptability of a single tissue-system to a change in the general bodily activity1 that is to say it is a variation of structure induced by an environmental change4 ,in most cases1 however1 the variations of structure that form the starting-points of transmutation processes cannot clearly be related to environmental changes4 ,some fishes produce very great numbers of ova in single broods--a female ling1 for instance1 is said to spawn annually some eighteen millions of eggs4 ,if we examine these ova we shall find that there is considerable variation in the diameter and in other measureable characters4 ,we may attempt to correlate these deviations from the mean characters with environmental differences4 ,all the eggs 8mature10 that is1 they absorb water and swell1 while various parts1 such as the yolk1 undergo chemical changes1 during the month or so before the fish spawns4 ,this process of maturation takes place in the closed ovarian sac2 and the eggs lie practically free in this sac1 and are bathed in a fluid which exudes from the blood-vessels in its walls4 ,it may indeed be the case that there are variations in the composition of this fluid in the different parts of the sac2 but these variations cannot be great2 the fluid is not really a nutritive one2 and the process of maturation is not hurried4 ,we can hardly believe that the differences in morphology are due to these minute environmental differences4 ,we may indeed say that we do not really study the germ cells when we measure the diameter of the egg or investigate any other measurable character1 for the real germ-plasm is the chromatic matter of the nucleus4 ,but this obviously begs the whole question3 all the parts of the egg that are accessible to observation do vary1 and ought we to conclude that the parts which are not accessible do not vary8 ,they must vary3 the germ-plasm of each egg must be different from that of all the others1 for the organisms which develop from these germs show inheritable differences4 ,further1 can we contend that such minute environmental differences as we have indicated affect the germ-plasm8 ,is it so susceptible to external changes8 ,a high degree of stability of the germ-plasm is postulated in the mechanistic hypothesis that we have considered1 and indeed everything indicates that the specific organisation is very stable4 ,can it then be upset by such minute differences in the somatic environment8 ,but the germ-plasm is not really simple1 says ,weismann2 it is a complex mixture of ancestral germ-plasms4 ,the individual fish that we were considering arose from an aggregate of determinants1 and half of these determinants were received from the male parent and half from the female one4 ,but each of these parents also arose from a similar aggregate of determinants1 which again were received from both parents1 and so on throughout the ancestry of the fish4 ,it is true that the germ-plasms contributed by the ancestors were not quite different1 but they differed to some extent4 ,then there must have been as many permutations of determinants in the ovum from which the fish developed as there were permutations of characters in the eighteen millions of ova produced by it4 ,does not the hypothesis collapse by its own weight8 ,it could only have been such difficulties as are here suggested that led ,weismann to formulate his hypothesis of germinal selection4 ,all those eighteen millions of eggs arose from the division of relatively few germ cells4 ,each of these original cells contained the specific assemblage of determinants1 and the elements of the latter are of course the biophors4 ,the biophors1 it will be remembered1 are either very complex chemical molecules1 or aggregates of such4 ,when the germ cells of the germinal epithelium divide to form those cells which are going to become the ova1 the biophors must divide and grow to their former size1 and again divide--it is really a chemical hypothesis that we are stating1 though we have to employ language which seems to do violence to all sound chemical notions6 ,now while the biophors were dividing and growing they were 8competing0 for the food matter which was in the liquid bathing them1 and some got less1 while others got more than the average quantity4 ,in this way their characters became different1 so that the eggs1 on the attainment of maturity1 became different from each other4 ,now1 apart altogether from the impossibility of applying any test as to the objective reality of this hypothesis1 it must be rejected1 for it confers on bodies which belong to the order of molecules properties which are really those of aggregates of molecules4 ,the typical properties of a gas1 for instance1 are not the properties of the molecules of which the gas is composed1 but are statistical properties exhibited by aggregates of molecules4 ,on the hypothesis of germinal selection the properties of the animals which develop from the biophors are extended to the biophors themselves4 ,it was surely a desperate plight which evoked this notion6 ,it is1 as ,william ,james said about ,mr ,bradley's intellectualism1 mechanism in extremis6 ,we seem forced to the conclusion--and this is the result to which all this discussion is intended to approximate--that variations1 heritable variations at least1 arise spontaneously4 ,that is1 there are organic differences which have no causes1 a conclusion against which all our habits of reasoning rebel4 ,yet it may be possible to argue that the problem of the causes of variations is really a pseudo-problem after all1 and that there is no logical reason why we should be compelled to postulate such causes4 ,when we think of organic variability1 do we not think1 surreptitiously it may be1 of something that varies1 that is1 something that ought to be immutable but which is compelled to deviate8 ,but what is given to our observation is simply the variations among organisms4 ,let us think of the crude minting machines of ,tudor times which produced coins which were not very similar in weight and design4 ,from that time onward minting machines have continually been improved1 each successive engine turning out coins more and more alike in every respect1 so that we now possess machines which stamp out sovereigns as nearly as possible identical with each other4 ,yet they are not quite alike1 and this is because the action of the engine1 in all its operations1 is not invariably the same4 ,in imagination1 however1 we make a minting machine which does work perfectly1 and turns out coins absolutely alike1 but this ideal engine is only the conceptual limit to a series of machines each of which is more nearly perfect than was the last one4 ,it is unlikely that matter possesses the rigidity and homogeneity which would enable us to obtain this perfect identity of result2 nevertheless this identity has a very obvious utility1 and we strive after it1 so that the result of our activity is the conception of a perfect mechanism1 and of products which are identical4 ,we assume that the reasons why our early and cruder machines were imperfect are also the reasons why our later and more perfect ones do not produce the results that we desire4 ,we are artisans first of all1 and then philosophers1 and so we extend this ingrained mechanism of the intellect into our speculations4 ,to the biologist the organism is a mechanism which1 in reproduction1 ought to turn out perfect replicas of itself4 ,it does not do so4 ,now1 if biology shows us anything1 it shows us that living matter is essentially 8labile10 that is1 something fluent1 while lifeless matter is essentially rigid1 or nearly so4 ,yet1 ignoring this difference1 we expect from the organism that identity of result and operation that we conceptualise1 but do not actually obtain from the artificial machine4 ,we regard the organism1 not only as a mechanism like the minting machine1 but as the conceptual limit to a series of mechanisms4 ,the reproductive apparatus of our fish does not turn out ova which are identical1 but which differ from each other4 ,some of this variation1 we say1 is due to the action of the environment2 and some of it is due to the condition that each ovum receives a slightly different legacy of characters from the multitude of ancestors4 ,the rest we conceive as due to the imperfect working of the reproductive machinery4 ,it is useful that science should so regard the working of the organism1 for in the search for the causes of variation our analysis of the phenomena of life becomes more penetrating4 ,but does any result of investigation or reasoning justify us in assuming1 as a matter of pure speculation1 that deviations from the specific type of structure are physically determined in all their extent8 ,have we not just as much justification for the belief that these deviations are truly spontaneous1 and that they arise de novo8 ,so we approach1 from the point of view of experimental biology1 ,bergson's idea of ,creative ,evolution4 ,,chapter ,,vii ,,the ,,meaning ,,of ,,evolution ,apart from experimental investigation1 the results of comparative anatomy1 even if they are amplified by those of comparative embryology1 and even if they include fossil as well as living organisms1 do no more than suggest the occurrence of an evolutionary process4 ,it is in vain that we attempt a demonstration of transmutation of forms of life by showing that a similarity of structure is to be observed in all animals belonging to the same group4 ,we may show successfully that the skeleton of the limbs and limb-girdles of vertebrate animals is anatomically the same series of parts1 whether it be the arms and legs of man1 or the wings and legs of birds1 or the pectoral and pelvic fins of fishes3 such homologies as these were indeed suggested by the medival comparative anatomists apart altogether from any notions as to an evolutionary process4 ,we may show that the simplicity of the skeleton of the head of man is apparent only1 and that in it are to be traced most of the anatomical elements that enter into the skull and visceral arches of the fish2 and that fusions and losses and translocations of parts have occurred and can be made to account for the observed differences of form4 ,all this might just as easily be explained by assuming a process of special creation1 or the gradual development of a plan or design4 ,just as ,god made ,eve from a superfluous rib taken from the body of her husband1 so ,he may have formed the auditory ossicles of the higher vertebrate from those parts of the visceral arches of the lower forms which had become superfluous in the construction of the more highly organised creature4 ,however much the language of evolution may force itself on biology1 it does no more than symbolise the results of anatomy and embryology1 and provide a convenient framework on which these may be arranged4 ,but if1 as all modern experimental work shows1 the form of the organism is1 in the long run1 the result of its interaction with the environment2 if1 as indeed we see1 this form is not an immutable one1 but a stage in a flux2 and if deviations from it may occur with all the appearance of spontaneity1 then it would appear that the observed facts of comparative anatomy and embryology are capable of only one explanation4 ,they represent the results of an evolutionary process1 and the relationships that morphological studies indicate are no longer merely logical1 but really material ones4 ,we can now endeavour to utilise these results in the attempt to trace the directions taken by the process of evolution4 ,in so doing we set up the schemes of phylogeny4 ,we divide all organisms into plants and animals1 and then we subdivide each of these kingdoms of life into a small number of sub-kingdoms1 in each of which we set up classes1 orders1 families1 genera1 and species4 ,but our classification is no longer merely a formal arrangement whereby we introduce order into the confusion of naturally occurring things4 ,it is now a 8family tree10 and from it we attempt to deduce the descent of any one of the members represented in it4 ,the sub-kingdoms1 or phyla1 of organisms are the primary groups in this evolutionary classification4 ,we divide all animals into about nine of these phyla--the ,protozoa or unicellular organisms2 the ,porifera or sponges2 the ,clenterates1 a group which includes all such organisms as ,zoophytes1 ,corals1 ,sea-,anemones1 and 8,jelly-fishes02 the ,platyhelminth worms1 that is the ,tapeworms1 ,trematodes1 and some other structurally similar animals which live freely in nature2 the ,annelids1 a rather heterogeneous assemblage of creatures which includes all those animals commonly called worms2 the ,echinoderms1 which are the ,star-fishes1 ,sea-,urchins1 and ,feather-,stars found in the sea2 the ,molluscs1 that is the animals of which the ,oyster1 the ,periwinkle1 the ,garden-,slug and the ,octopus are good examples2 the ,arthropods1 which include the ,crustacea1 the ,insects1 and the ,spiders2 and lastly the ,vertebrates4 ,any such classification we naturally endeavour to make as complete a one as possible1 but round the bases of the larger groups there cling small groups of organisms the precise relationships of which are doubtful4 ,yet1 on the whole1 these sub-kingdoms of organisms represent clearly the main directions along which the present complexity of animal structure has been evolved4 ,there is an essential structure which we endeavour to assign to all the animals of each phylum1 and which is different from the structure of the animals belonging to all other phyla4 ,the ,protozoa1 which for the present we regard as animals1 are organisms the bodies of which consist of single cells4 ,these cells may become aggregated into colonies1 but they may as well exist apart from each other4 ,they may be enclosed in limy1 siliceous1 or cellulose skeletons or shells1 or they may possess limy or siliceous spicules in their tissues--these parts are non-essential1 and the schematic ,protozoan is a cell containing a single nucleus1 and capable of independent existence4 ,the ,porifera1 and all the other phyla1 include organisms the bodies of which are made up of aggregates of cells4 ,in the ,porifera the cells1 which are specially modified in structure1 are arranged to form the internal walls of a 8sponge-work0 the cavities of which open to the outside by series of pores through which water is circulated4 ,the bodies of the ,clenterates are typically sacs formed by a double wall of cells--endoderm and ectoderm4 ,this sac opens to the exterior by a single opening1 or mouth1 surrounded by a circlet of tentacles1 and its cavity is the only one contained in the body of the animal4 ,the ,platyhelminth worms are animals the bodies of which are also composed of ectodermal and endodermal tissues1 between which is intercalated another mesodermal tissue4 ,they have a single digestive sac or alimentary canal opening to the exterior by means of a mouth only2 and they all possess a complex1 hermaphrodite1 reproductive apparatus4 ,in all the other phyla there are also three principal layers or kinds of tissue1 but in addition to the cavity of the alimentary canal there is also a body cavity1 or clom1 which is contained in the mesodermal tissues4 ,the ,echinoderms are such clomate animals1 but the alimentary canal now opens to the exterior by means of both mouth and anus2 there are separate systems of vessels through which water and blood circulate2 the blood-vascular system of vessels is closed to the exterior1 the water-vascular system being open2 and the integument is armed by means of calcareous spines or plates4 ,the ,annelids are animals with cylindrically shaped bodies1 segmented so as to form numerous joints4 ,each segment bears spines or hairs or appendages of some sort1 and also contains a separate nerve-centre4 ,the alimentary canal opens externally by a mouth and anus1 and there is a spacious body cavity4 ,the ,molluscs are unsegmented animals4 ,the dorsal part of their bodies contains the viscera1 and is protected by a shell2 while the ventral part is modified for the purpose of locomotion4 ,a fold of integument hangs down all round the body and encloses a cavity in which the gills are contained4 ,the ,arthropods are segmented animals4 ,the body is armed by a calcareous carapace or shell which forms the exo-skeleton4 ,each bodily segment bears a pair of jointed appendages1 and also contains a separate nerve-centre4 ,the whole series of ganglia are connected together by means of a nerve-cord1 and the nervous system lies ventral to the alimentary canal4 ,the ,vertebrata are also segmented animals1 but the segmentation is not apparent externally4 ,the skeleton is an internal one1 and is built up round an axial rod or notochord4 ,the nervous system is situated dorsally to the alimentary canal4 ,there are two pairs of limbs4 ,thus we set up an essential or schematic structure characteristic of each phylum4 ,these schemata have no real existence3 they are morphological types from which the actual bodily structure of the animals in each phylum may be deduced4 ,they represent the minimum of parts which must be present in order that an animal may be placed in the phylum to which we assume that it may belong4 ,but these anatomical parts need not actually be present in the fully developed organism3 thus there are ,crustacea in which the body is not segmented1 and in which neither calcareous exo-skeleton nor jointed appendages are present2 and there are ,vertebrata in which the limbs may be absent4 ,but in such cases we require evidence that the essential anatomical characters which are absent in the fully developed animal have appeared at some stage in its ontogeny1 and this evidence is usually available4 ,or if embryological evidence cannot be obtained1 we require proof that the animal can be traced backwards in time1 by means of other characters1 to some form in which the missing structures reappear4 ,the schemata are thus the generalised or conceptual morphology of the phyla4 ,they are not the morphology of an individual organism1 but they include the morphology of the race4 ,they are1 ,bergson says1 themes on which innumerable variations have been constructed4 ,structural elements may be suppressed1 as when the notochord disappears in the development of the individual ,tunicate1 though it is present in the larva4 ,or elements may disappear and become replaced by other structures1 as when the true molluscan gills are lost in the ,nudibranchs and are replaced by the respiratory plumes4 ,they may be reduced to vestiges1 as in the case of the 8pen0 of the ,squids1 or the 8cuttlebone0 of the cuttlefish1 remnants of the domed shell of the primitive mollusc2 or in the appendix vermiformis of the human being1 a remnant of the voluminous ccum of the herbivorous animal4 ,structures which were originally distinct may coalesce1 as when the greater number of the primitively distinct segments of the thorax of the crustacean fuse to form the 8body0 of the crab2 or when the segmental ganglia of the same animal fuse together to form the great thoracic nerve-centre4 ,the form and situation of a structure may vary within wide limits3 thus the digestive cavity of some ,clenterates may be a simple sac1 as in the ,hydra1 but it may be partially subdivided by numerous mesenteries as in the zooid of the ,corals2 or the simple tubular alimentary canal in some ,platyhelminth worms may be bifurcated in others1 triple-branched in others again1 or even provided with numerous lateral branches1 as in the more specialised species in the group4 ,organs originally simple may undergo progressive modification3 thus the eye of a mollusc may be a simple integumentary cavity in the floor of which there are some simple nerve-endings1 and some black pigment2 or this cavity may close up so as to form a sac1 and the anterior part of the sac may become transparent so as to form a cornea4 ,behind the cornea a lens may be formed1 and the simple terminal twigs of the nerve-endings may become a many-layered retina of great complexity of structure4 ,in the lowest ,chordates the central part of the blood-vascular system is a simple contractile vessel1 but this becomes the two-chambered heart of the fish1 the three-chambered heart of the reptile1 or the powerful four-chambered heart of the warm-blooded animal4 ,anatomical elements may change in function2 thus parts of the visceral skeleton in the fish may become the ossicles of the middle ear in the ,reptiles and ,mammals2 while its swim-bladder may possibly be represented in the higher vertebrates by the lungs4 ,thus there may be suppression of parts leading to entire disappearance or to mere vestiges of the original morphology4 ,a structure degenerating through disuse may become removed from its typical relations with other structures and may acquire altogether new ones4 ,or its increasing importance may lead to its hypertrophy and to increased complexity of structure1 and perhaps to the inclusion of new anatomical elements1 or to the incorporation of other parts1 the function of which may originally have been quite different4 ,in all sorts of ways organs and organ-systems may become anatomically different as the result of adaptive modifications1 or indirectly as non-adaptive modifications induced by the adaptive modifications of adjacent parts4 ,it is the task of comparative anatomy to trace these changes of morphology1 aided by the study of embryology and by the comparison of the structure of the parts of fossil animals4 ,regarding the process of transformism as proved by experiments and observations in breeding and heredity1 the naturalist endeavours to trace the lines along which evolution has proceeded from the results of morphological investigations4 ,such results cannot have more than a very limited value1 and it is often the case that several interpretations of morphological results are equally probable4 ,we may conclude that the existing ,teleost and ,elasmobranch fishes are descended from a common stock which no longer exists2 we may similarly conclude that the ,birds and ,reptiles are closely allied1 more so than either group is to the ,mammals2 and we may conclude that the ,primates--the group of ,mammals to which ,man belongs--is descended from some group allied to the existing ,ungulates or ,insectivores1 while the ,mammals themselves may have come down from some group of vertebrates related to both the ,amphibia and the ,reptiles4 ,but as to the nature of the animals which combined the characters of the ,birds and ,reptiles1 or of the ,reptiles and ,amphibia1 we know nothing4 ,palontology1 if its results were more numerous than they are1 would afford us the material for the discovery of these 8missing links10 and there can be no doubt that as the world becomes better known our knowledge of palontological stages in the history of existing groups will become more complete1 so that we may1 in time1 possess an actual historical record of the phylogeny of the main groups of animals4 ,but it is remarkable that while the results of comparative anatomy and embryology1 aided by those of palontology1 enable us to trace back short series of stages in the evolutionary process1 they still show us gaps at all the places where lines of descent ought to converge4 ,they show us1 for instance1 that the oldest ,birds known were decidedly reptilian in their morphology1 but they do not show us an animal which was neither ,bird nor ,reptile1 but from which both groups of ,vertebrata have descended2 and this is almost always the case in our hypothetical schemes of phylogeny4 ,morphology has continually to postulate the existence of 8annectant0 forms1 8,archi-,mollusc10 8,protosaurian10 8,protochordate10 etc43 hypothetical animals which combine the characters of those which lie near the bases of diverging lines of descent4 ,there is nothing to guide us in the construction of these annectant forms except the progressive simplicity of structure indicated in the morphological and palontological series4 ,the earlier ,birds had teeth1 for instance1 and so have the ,reptiles1 therefore the annectant form had teeth1 and it was an animal combining the schematic morphology of both ,birds and ,reptiles4 ,but just according to the value which we attach to one morphological character rather than another1 so will the structure of the annectant form differ4 ,is1 for instance1 the alimentary canal of the ,vertebrate the most fundamental and conservative part of its morphology3 that is1 is it the structure which has been most resistant to change in the course of the evolutionary process8 ,then we may regard the ,vertebrates as having descended from some animal which was closely related to the ,annelid worms4 ,or is the nervous system the most conservative part of the ,vertebrate anatomy8 ,if so1 we may trace back the main ,chordate stem to animals which included among their characters those of the most primitive ,arthropods4 ,in the one case the annectant form joins together the ,vertebrate and ,annelid stems1 but in the other case it would join together the ,vertebrate and ,arthropod stems1 a conclusion which a rigid application of the results of morphology would seem to make the more probable one4 ,illustration3 ,,fig4 #be4 ,but1 however this may be1 we must not fail to notice that annectant forms--8,archi-,mollusc10 8,protosaurian10 8,protochordate10 and the like1 are only fictions which we base on the precise importance that we attach to one part of the essential morphology of a group of animals rather than another4 ,these hypothetical animals1 and the genealogical schemes or phylogenies of which they form the roots1 are conventional summaries of the results of comparative anatomy1 this term being used to include the anatomy of the developing animal and that of extinct forms4 ,so long as we do not possess a representative series of the fossil remains of the animals which have existed in the past1 all schemes of descent founded on the comparison of the parts or the organs of living animals1 or on the comparison of stages of development1 must possess doubtful value when they profess to indicate the direction taken by evolution4 ,their true value lies rather in the way they epitomise our knowledge of morphology1 and in the incentive which they give to sustained and minute investigation of the structure of animals4 ,illustration3 ,,fig4 #bf4 ,why did ,haeckel's 8,gastrea-,theorie0 gain the acceptance that it did during the latter part of the nineteenth century8 ,it correlated a great number of facts1 in that it postulated a general uniformity of structure in the early developmental stages of very many animals belonging to widely separated groups4 ,in all of these the ovum segments into a mass of cells1 which then become arranged as a hollow ball 7,a74 ,one side of this ball becomes pushed in so that the inner part of the hollow sphere becomes opposed to the inner wall of the upper part4 ,thus a little sac1 consisting of two layers of cells1 ectoderm and endoderm1 and opening to the outside by an aperture1 the blastopore1 is formed 7,b74 ,this is essentially the anatomy of the schematic ,clenterate animal--,hydra1 for instance1 strongly suggests it4 ,suppose now that the lips of the blastopore fuse together at one place so that there are two openings into the cavity of the gastrula instead of one2 and suppose that the spherical organism elongates so as to form a cylinder1 the elongation involving the fused part of the blastoporic region4 ,then we obviously have a worm-like animal with an alimentary canal1 a mouth and an anus 7,c74 ,suppose further that an additional layer of cells becomes formed between the endoderm and ectoderm by proliferation from one of these tissues1 and suppose that this becomes double and that a cavity appears between the two sheets of cells forming this middle layer3 this cavity becomes the body cavity or clom 7,d74 ,now such blastula and gastrula stages appear in the ontogeny of animals belonging to widely different groups1 and such a formation of the middle layer1 or mesoblast1 and of the mesoblastic or clomic cavities also actually occurs4 ,let us assume therefore that all multicellular animals have descended from a primitive ,gastrea-form essentially similar in morphology to the gastrula larva2 and let us assume that all clomate animals have descended from a form in which a third layer of cells1 or mesoblast1 became intercalated between the other two4 ,these two assumptions are the bases of the classic phylogenies of the last century2 all ,clenterate animals have descended from a ,gastrea-form1 and all animals higher than the ,clenterates have been evolved from a three-layered form4 ,implied in this hypothesis is also a third one1 that the ,gastrea-stage of evolution possesses such a degree of stability that it has persisted1 though in an obscure condition it may be1 in the development of nearly all multicellular animals4 ,the triple germinal layers1 endoderm1 ectoderm1 and mesoderm1 which first became distinct from each other in the primitive clomate animal1 also acquired a high degree of stability1 and they have been transmitted by heredity to all animals higher than ,clenterates4 ,the ,gastrea and the three germinal layers are therefore to be sought for in the developmental stages of all the higher animals1 and they have usually been found4 ,let it be admitted that they may make a transient appearance--that they may be obscured in many ways1 still they ought to be there4 ,the ,gastrea-,theorie ceased to be useful1 as a means of description1 or a working hypothesis of investigation1 after the rise of experimental embryology4 ,it could not be proved that the process of development by gastrulation and the cleavage of a mesodermal layer are so very conservative that they have persisted throughout the greater part of the evolution of the animal world1 yet without this proof it could not be contended that the veiled gastrula of the developing frog's egg1 for instance1 is related genetically to the gastrula of the ,echinoderm larva4 ,what experimental embryology does indicate is that the formation of gastrula and 7in most groups7 the three germinal layers are only the means of morphogenesis4 ,in the division of the ovum1 and the arrangement of the cells to form the organ-rudiments1 the formation of the gastrula and the mesoderm are in general the line of least resistance in the process of development4 ,if they do not appear1 or are difficult to recognise in the ontogeny of a group of animals1 it is not a sound method to assume their presence in an abbreviated or distorted form1 postulating that they ought to be present1 having been transmitted by heredity4 ,physical conditions undoubtedly influence developmental processes and there is no reason for assuming that all ontogenetic processes were originally the same4 ,if we do not strain the facts of our descriptions of organic nature1 and if we do not build on unprovable conjectures1 all that morphology certainly shows us is that the evolutionary process has led to the establishment of some dozen or so great groups of organisms1 each with appended smaller groups more or less closely related to them4 ,whether these greater lines of descent are to be represented1 as they usually are1 as branches springing from a single stem1 or whether they are truly collateral1 each evolved independently of all the others1 is a question which is not to be solved merely by the methods of comparative anatomy or embryology4 ,the widely different1 and equally probable1 phylogenies of the past indicate that data for the solution of such a problem do not exist1 not just yet at all events4 ,what we may discuss with greater advantage is the question as to which of the great subdivisions of life represents the main results of the evolution of complex organic entities from the simple living substances in which we suppose life first became materialised on our earth4 ,what activities and structural forms represent the main manifestations of the evolutionary process8 ,that is to say1 what great groups of organisms are the dominant ones on the earth8 ,greater or less degrees of dominance are indicated by the extent to which a group of organisms is distributed on the earth1 by its abundance1 and by the period of time during which it can be recognised in the fossil condition4 ,ubiquitous distribution implies a high degree of adaptability3 a group of organisms inhabiting land and sea and atmosphere is obviously one in which the morphological structure has been elastic enough to admit of the development of various modes of locomotion2 and the limbs may be either the appendages of a terrestrial animal1 or the fins1 or other swimming organs1 of an aquatic creature1 or the wings of one adapted for flight4 ,dominance in this respect implies mobility and activity1 and a relatively highly developed nervous system2 it implies the development of organs specialised for prehension1 that is1 for the capture of food2 and it also implies a high degree of adaptability to widely different physical conditions1 to temperature changes1 for instance4 ,dominance in geological time means also this great adaptability to changes in climatic conditions1 and the development of means of distribution sufficient to overcome extensive physical changes on the surface of the earth4 ,a terrestrial species might become isolated by the formation of a mountain range1 or the submergence of the land adjacent to that which it inhabited1 and some widely distributed species of plants and insects must have been able to traverse oceanic areas4 ,the abundance of a group obviously implies great powers of reproduction1 the ability to withstand physical changes1 and the ability to resist competition with other predatory creatures4 ,dominance1 in short1 means that the organism possesses in high degree the inherent powers of reproduction2 and also those activities which enable it to respond by adaptations of morphology1 functioning1 and behaviour1 to environmental changes4 ,these environmental changes are those which must have been experienced during lengthy geological periods1 and also those experienced by the organism in its attempt continually to enlarge its area of distribution4 ,if we make a broad survey of the animal world we shall find that dominance in these respects has been acquired by three great groups of organisms1 7#a7 the ,bacteria1 7#b7 the chlorophyllian organisms1 7#c7 the ,arthropods1 and 7#d7 the ,vertebrates4 ,in each case the threefold condition of wide distribution over all the earth1 both in fresh and marine water areas1 on the land and in the atmosphere2 of existence throughout the greater part of geological time2 and of ability to withstand environmental change1 are satisfied4 ,the bacteria are known to have existed in the carboniferous period4 ,at the present time their distribution on the earth is universal3 no part of the land surface1 and no water masses1 either marine or lacustrine--no matter how unsuitable they may be for the life of more highly organised creatures--are untenanted by bacteria4 ,they are able to withstand extremes of temperature1 or of salinity1 which would be fatal to the multicellular plant or animal4 ,parasitism is a mode of life which they exhibit in a more manifold degree than do any other organisms4 ,the upper regions of the atmosphere are the only parts of the earth and its envelopes which they do not inhabit4 ,the chlorophyllian organisms include those unicellular plants and animals--the distinction becomes obscure with regard to these organisms--which are pigmented blue1 green1 brown1 or red owing to the existence in the cells of chlorophyll1 or of some substance allied to this compound1 and they include1 of course1 the green plants4 ,like the ,bacteria their distribution is world-wide1 extending over land and sea and fresh-water areas2 and it is restricted mainly by the distribution of sunlight1 and by a lower limit of temperature4 ,the ,marine ,alg1 the ,diatoms1 the ,peridinians1 and other chlorophyll-containing organisms appear to inhabit all parts of the world ocean1 certainly within a depth of about twenty to fifty fathoms from the surface of the sea4 ,green plants inhabit the land everywhere except within polar areas1 the tops of high mountains1 and over areas desert by reason of lack of water1 or by the presence of mineral substances4 ,these conditions--temperature1 light1 soil1 etc4--do not appear to limit the distribution of the ,arthropods and ,vertebrates4 ,we find both kinds of animals in the deepest oceanic abysses 7deep-sea fishes and ,crustacea71 in polar land and sea regions 7,man1 some ,insects1 ,crustacea1 and ,birds71 as well as in desert areas and on the summits of the loftiest mountains4 ,the ,ants share the subsoil with the ,bacteria4 ,birds and ,insects conquer the atmosphere by their activity and not1 like the ,bacteria1 merely by being blown about4 ,crustaceans such as the ,copepoda have much the same distribution in the sea as the ,insects have in the atmosphere1 while ,isopods and ,amphipods are a parallel1 so far as the sea bottom is concerned1 to the ,spiders1 ,millipedes1 and ,ants on the land4 ,fishes are distributed throughout all depths1 and in almost all physical conditions in the sea4 ,some species of marine ,mammalia and ,birds are quite cosmopolitan except that they are restricted to the upper layers of the ocean4 ,land ,mammals are subject to the same restrictions as are the green plants1 being unable to survive in desert and polar areas4 ,the only parts of the sea which are not inhabited by ,arthropods and ,vertebrates are those limited deep strata of water 7as in the case of the deeper layers of the ,black ,sea7 where there are accumulations of poisonous chemical substances in solution4 ,but the ,bacteria inhabit even these regions4 ,green plants1 ,arthropods1 and ,vertebrates appear as fossils in almost every part of the stratified rocks4 ,the ,trilobites represent the end of a long evolutionary process1 and the same is to be said of the first fishes found in ,silurian rocks1 so that these groups of animals must have existed in the geological periods represented by those remains of rocks which are older than the earliest fossiliferous ones4 ,plant remains are present in ,silurian rocks1 but there can be no doubt that ,ferns and other chlorophyllian organisms must have been in existence long before this time4 ,we can hardly suppose that the ,bacteria found in the ,carboniferous rocks first appeared at this time in the earth's history3 like the other great groups of life they probably had a prolonged history prior to that date of the geological formations in which they are first to be recognised4 ,our dominant groups of organisms may therefore be traced back almost to the very beginnings of life on the earth4 ,dominance1 such as we have defined it1 cannot be said to have been attained by any other of the sub-kingdoms of life4 ,clenterates and sponges appear to have existed throughout the whole period during which the remains of organisms are to be traced in the rocks1 but they have always been exclusively aquatic animals and they are very sparsely distributed in fresh water regions4 ,echinoderms are also a very old group1 but they were more abundant in the past than they are now1 and they appear to have been an exclusively marine group of animals4 ,molluscs have existed since the beginnings of stratified deposits and they are both aquatic and terrestrial animals1 but they belong predominantly to the sea4 ,they have always been relatively sluggish and inactive animals1 with the exceptions of the great ,squids and ,cuttlefishes1 but fortunately for the other inhabitants of the sea these formidable creatures appear to possess restricted powers of reproduction1 and they have never been very abundant4 ,all the smaller groups of animals are restricted in their distribution3 the flat-worms occur sparingly both on the land and in the sea1 and they attain their highest development as parasites in the bodies of other animals4 ,annelid worms1 ,gephyrea1 ,nemertine worms1 ,polyzoa1 ,rotifers1 etc41 are all groups of animals occurring mainly in fresh and sea water and none of them is abundant4 ,related to most of the great phyla are smaller groups3 the extinct ,trilobites1 ,eurypterids1 etc41 in relation to the ,arthropoda2 the group represented now by ,peripatus in relation to the ,arthropods and ,annelids2 the ,enteropneusta and some other creatures which appear to possess affinities with the ,echinoderms and ,chordates2 and the extinct ,ostracoderms1 which appear to have been related to either the ,arthropods or ,vertebrates1 or to both4 ,all these smaller groups of animals we must regard as representing sidepaths taken by the evolutionary process--paths which have either ended blindly1 as in the case of those groups which have become extinct1 or which we can still trace in the existing remnants of groups which were formerly more abundant than they are now4 ,only among the existing ,bacteria1 chlorophyllian organisms1 ,arthropods1 and ,vertebrates has the vital impetus found its most complete manifestation1 and we may even narrow down the main path that evolution has taken to certain groups in each of these phyla4 ,some of the ,bacteria--those which are exclusively parasitic in the bodies of the warm-blooded animals--have adopted a most specialised mode of life1 and may even be said to exist only with difficulty1 since the healthy animal is able to destroy them4 ,only those ,bacteria living in the open or upon the dead tissues of plants and animals have attained to real dominance4 ,some green plants1 like the ,ferns1 are far less abundant now than they were in the past2 while the ,fungi and some other saprophytic and parasitic plants have specialised in much the same way as have the parasitic worms1 and are restricted in their distribution4 ,marine ,alg are confined to a relatively narrow selvedge of sea round the land margin4 ,the great trees1 the grasses1 and the microscopic green plants such as the ,diatoms and ,peridinians1 represent the truly dominant organisms in the vegetable kingdom4 ,on the side of the ,arthropods and ,vertebrates there have been many unsuccessful lines of evolution3 the ,trilobites1 for instance1 in the former group2 and the armoured ,ganoid fishes1 the armed ,reptiles1 the volant ,reptiles1 and the giant ,saurians and ,mammals among the ,vertebrates4 ,among the existing ,arthropods and ,vertebrates there are some smaller groups which persist1 so to speak1 only with difficulty4 ,such are the ,spiders1 ,mites1 and ,scorpions among the ,arthropods2 and the ,tunicates1 the ,dipnoan fishes1 the tailed ,amphibians1 many ,reptiles1 and the volant ,mammals among the ,chordates3 such are1 of course1 only instances of the less successful lines of evolution in these phyla4 ,the dominant ,arthropods and ,vertebrates are the ,crustacea1 the ,hymenopterous ,insects1 the ,teleost and ,elasmobranch fishes1 and the terrestrial ,mammals4 ,the earth belongs to ,man1 to the social and solitary ,ants1 ,wasps and ,bees1 the marine ,crustacea1 the ,teleost fishes1 the ,trees1 ,grasses1 and unicellular ,diatoms and ,peridinians1 and to the putrefactive and prototrophic ,bacteria4 ,these are the organisms in which life has attained its fullest manifestations1 and has been most successful in its mastery over inert matter4 ,in what kinds of activity and morphology1 then1 has the vital impetus found most complete expression8 ,we see at once that in relation to energetic processes life has followed two divergent lines--animal and vegetable4 ,there is no absolute distinction between the energy-transformations which proceed in the living plant and animal--we return to this point later on--but we may trace an unmistakable difference in tendency1 that is1 in the direction taken by evolution4 ,this difference we have already considered in an earlier chapter1 but we may illustrate it by considering a lifeless earth1 and also one tenanted only by plants1 or animals1 or by both4 ,in a lifeless earth all energetic processes would tend continually toward a condition of stability4 ,the crust of the earth1 that is1 the part known to us by direct observation1 is made up of rocks and the remains of rocks2 materials consisting of compounds of oxygen1 silicon1 iron1 aluminium1 sodium1 potassium1 calcium1 and so on4 ,they are substances which would be stable but for the eroding action of water1 the gases of the atmosphere1 and volcanic activity4 ,but as volcanic activity tends always toward cessation1 the oxygen of the atmosphere would gradually disappear1 first by its combination with oxidisable substances1 and second by its combination with the nitrogen of the atmosphere under the influence of electric discharges4 ,carbon dioxide would either combine with materials in the rocks1 or would remain in the atmosphere along with nitrogen and other inert gases in a stable condition4 ,water1 moved by the tides and winds1 would gradually plane down the surface of the land1 unless along with other gases it would gradually become dissipated into outer space4 ,we see1 then1 that the materials of the earth tend to fall into stable combinations1 and that they approximate toward conditions in which potential chemical energy becomes reduced to a minimum1 the whole energy possessed by matter being that of the motions of the molecules1 that is1 kinetic energy unavailable for transformations of any kind4 ,it would be an earth devoid of phenomena4 ,vegetable life alone would be possible only for a time on an earth such as we know it at present4 ,the green plant depends for its existence on the presence in the soil of mineral substances such as salts of nitric acid and of ammonia1 and on the presence of water and carbon dioxide in the atmosphere4 ,the chlorophyllian apparatus is essentially a mechanism whereby these substances become built up into carbohydrates1 like starch and sugar2 hydrocarbons1 like resins and oils2 and proteids4 ,the energy necessary for these syntheses is obtained from solar radiation through the agency of the chlorophyll plastids4 ,the green plant would depend for its supply of nitrate or ammonia on the combination of the nitrogen of the atmosphere with oxygen1 or on the exhalations from volcanoes1 and these are irreversible processes which tend continually toward cessation4 ,the plant requires also carbon dioxide and the amount of this substance in the atmosphere is very limited1 while the only inorganic source from which it can be renewed seems to be volcanic activity3 this substance also would tend to disappear4 ,a time would therefore come when plant life on the earth would cease to be possible because of the disappearance of the materials on which it depends2 but while it did exist its result would be the accumulation of chemical compounds of high potential energy4 ,the result of the metabolism of the plant is the formation of such compounds as cellulose from woody tissues and shed leaves1 of other plant carbohydrates1 of oils and resins1 and of proteids4 ,in the absence of bacteria such substances would persist unchanged3 even in an earth tenanted by bacteria such products as oils1 lignite1 peat1 coal1 etc41 have been able to accumulate throughout geological time4 ,the tendency of plant life is therefore toward the accumulation of compounds of high potential energy1 and this process also is irreversible4 ,bacterial activity would1 of itself1 make continued plant life possible on the earth4 ,the essential characters of these organisms are their ability to bring about the most varied energy-transformations4 ,from our present point of view bacteria may be divided into paratrophic1 metatrophic1 and prototrophic forms4 ,paratrophic bacteria are those which live as parasites within the living tissues of plants and animals3 this mode of life is obligatory1 and these organisms are unable to live in the open4 ,the result of their activity is the breaking down of protoplasmic substance4 ,metatrophic bacteria are those that produce putrefaction and fermentation of organic compounds4 ,they may be parasitic in their mode of life1 but most of them live in soil1 in water1 and in the cavities of the animal body--the mouth1 alimentary canal1 nose1 and vagina4 ,proteids are decomposed by them into simple chemical compounds such as amido-acids1 and then these substances1 along with carbohydrates1 are fermented so as ultimately to form water1 carbonic acid1 and salts of nitric acid4 ,these bacteria obtain their energy from the conversion of chemical compounds of high potential energy into compounds of low potential energy4 ,prototrophic bacteria are never parasites1 nor do they live in the cavities of the bodies of animals3 they always live in the open4 ,they carry on still further the action of the putrefactive bacteria by converting ammonia into nitrous acid1 and nitrous acid into nitric acid4 ,others reverse this series of changes by reducing nitric acid to nitrous acid1 nitrous acid to ammonia1 and ammonia to free nitrogen4 ,others again oxidise sulphuretted hydrogen to sulphuric acid1 others ferrous hydrate to ferric hydrate1 while it has recently been shown that some bacteria are apparently able to oxidise the carbon of coal to carbonic acid4 ,some are able to oxidise the free nitrogen of the atmosphere into nitrous and nitric acids4 ,how precisely the energy necessary for these transformations is obtained is not at all clearly understood1 and it may be possible that some of the prototrophic bacteria obtain their energy by making use of the un-co-ordinated kinetic energy of the medium in which they live4 ,from our point of view the net result of the activity of the predominant species of bacteria which inhabit the earth is that they reverse the processes which are the manifestations of the metabolism of plants and animals4 ,the result of the metabolism of plants is the accumulation of stores of high potential compounds such as carbohydrates1 and the depletion of the terrestrial stores of carbon dioxide and other materials necessary for the continued existence of the plants themselves4 ,the result of the metabolism of the bacteria is the break-down of this accumulation of such compounds as carbohydrates1 and the replenishing of the stores of carbon dioxide and nitrogenous mineral substance on which the plant depends4 ,if bacteria are present1 the life process becomes a reversible one4 ,plant life and bacterial life are thus complementary to each other1 for1 on the whole1 the energetic processes of the green plant proceed in the opposite direction to those of the bacteria4 ,an organic world consisting of green plants and bacteria would therefore be one capable of permanent existence4 ,now1 so far1 we need only consider these various kinds of organisms as living protoplasmic substances in which energy-transformations of different types proceed4 ,the bacterium is simply a cell containing a nucleus1 and the green plant need only be a nucleated cell containing a chlorophyll plastid3 this is1 indeed1 all that it is in the case of a ,diatom or a ,peridinian4 ,the morphology of the green plant is only accessory to the chlorophyllian apparatus4 ,neglecting the reproductive apparatus1 the higher green plant consists essentially of the chlorophyllian cells in the parenchyma of the leaf1 for roots and stomata are only organs for the absorption of water and mineral salts from the soil and carbon dioxide from the atmosphere2 while the tissues of the trunk1 stems1 and branches are1 in the main1 apparatus for the conduction of these raw materials through the body of the plant1 and1 of course1 the nutritive substances into which they are elaborated4 ,all the innumerable variations of form in the plant 7apart from the structure of the flower or other reproductive organ7 are adaptations which provide for the absorption and distribution of these substances2 or for the mechanical support of the plant body2 or are non-adaptive variations1 pure luxuries1 so to speak4 ,more than this is represented by the structure of the animal body1 but we must first of all consider the points of difference between plant and animal regarded merely as apparatus in which energy-transformations occur4 ,in the green plant energy is accumulated in the form of high potential chemical compounds1 but in the animal energy is expended4 ,inorganic mineral substances are built up by the plant into carbohydrate1 proteid1 and fat or oil1 but in the animal body carbohydrate1 proteid1 and fat are dissociated into water1 carbonic acid1 and urea 7or some other nitrogenous excretory substance72 and the urea or other analogous substance is broken down by bacteria into nitrate1 water1 and carbon dioxide4 ,the metabolic activities of the animal are said to be 8analytic0 or destructive1 while those of the plant are said to be 8synthetic0 or constructive1 but these contrasting terms hardly describe accurately the essential nature of the activities of the two kinds of organisms4 ,what further constitutes 8animality08 ,it is purposeful mobility1 and the energy-transformations that occur are the means whereby this mobility is attained4 ,the plant is essentially immobile1 for such movements as the turning of leaves toward the light1 the down-growth of roots1 the up-growth of stems1 the twining of tendrils round supporting objects1 and the opening and closing of flowers are only the movements of parts of the plant organism4 ,they are constant1 directed responses to external stimuli--real tropisms--and the extension of this kind of response so as to describe in general the movements of animals is only an instance of the insufficient analysis of facts4 ,the movements of the typical green plant are therefore movements of its parts1 they are few in number1 they belong to a few simple types1 and they are evoked by simple external physical changes in the medium4 ,the movements of the typical animal are movements of the organism as a whole2 they are infinitely varied in their nature2 they are evoked by individualised stimuli and they are continually being modified by the experience of the organism4 ,the bodily structure of the animal is the means whereby this purposeful mobility is attained and the energy-transformations directed2 and the greater and more varied the movements of the animal1 the more complex is its structure4 ,in respect of the manner in which the energy-transformations are effected1 that is1 in respect of the material means whereby energy falls from a state of high potential to a state of low potential1 the morphology of the animal is similar to that of the plant1 that is1 the energy-transformations are the functions of nucleated cells4 ,but in the plant the kinetic energy of solar radiation passes into the potential energy of chemical compounds which become stored in the body of the plant2 while in the animal the potential energy of ingested chemical compounds passes into the kinetic energy of the movements of the animal itself4 ,how exactly it moves1 how this kinetic energy is employed is determined by the sensori-motor system4 ,it is the existence of the sensori-motor system that makes the animal an animal4 ,what1 then1 is the sensori-motor system8 ,it is the skeleton and muscles1 that is1 the organs of locomotion1 aggression1 prehension1 and mastication2 the peripheral sensory and motor nerves2 and the central nervous system or brain4 ,the skeleton of an animal1 whether it be the carapace or exoskeleton of a crustacean1 or the vertebral column1 limb-girdles1 and limb-bones of a vertebrate1 is a rigid and fixed series of supports to which the muscles are attached4 ,organs of locomotion are1 for instance1 the appendages of a crustacean1 the wings of a bird or insect1 the tail and fins of a fish1 or the limbs of a vertebrate4 ,organs of aggression are the mandibles of a spider or blood-sucking fly1 the chelate claws of a crab or lobster1 the jaws of a fish1 or the claws and teeth of a terrestrial vertebrate4 ,organs of prehension and mastication are in the main also those of aggression4 ,all these parts consist of modified skeletal structures1 teeth1 claws1 etc41 attached to muscles which originate in the rigid parts of the skeleton4 ,when we speak of the movements of an animal we speak of the motions of such parts as we have mentioned2 other parts do indeed move--the heart pulsates1 the lungs dilate and contract1 and the blood and other fluids circulate through closed vessels2 but these are movements of the parts of the animal1 and are comparable rather with those movements of the plant organism that we have considered4 ,they are not to be regarded as examples of the mobility of the animal in the sense of the exercise of its sensori-motor system4 ,a central and peripheral nervous system is1 of course1 bound up with a motor system4 ,receptor organs1 eyes1 olfactory1 auditory1 tactile organs of sense1 and so on1 are the means whereby the animal is affected by changes in its environment--it need not be cognisant of1 or become aware of1 or perceive these impressions on its receptor organs4 ,these stimuli are transmitted along the sensory1 or afferent1 nerves to the central nervous system3 this is the way in4 ,the effector nervous organs are the motor plates1 that is1 the nervous structures in the muscles in which the nerves terminate4 ,the motor nerves are the efferent paths1 the way out from the central nervous system4 ,the central nervous system is essentially the organ for the integration of the activities of the whole body4 ,it is the 8seat of multitudinous synapses10 a description which better than any other applies to the morphology of the brain of the vertebrate animal4 ,we have already considered what is meant by the term 8reflex action10 it is the series of processes which occur when a 8reflex arc0 becomes functionally active4 ,a reflex arc consists of 7#a7 a receptor organ1 say a tactile corpuscle in the skin2 7#b7 an afferent nerve fibre2 7#c7 a nerve cell in the brain or spinal cord2 7#d7 an efferent nerve fibre2 and 7#e7 an effector nerve organ1 say a motor plate in a muscle fibre4 ,the series of processes involved in a reflex action consist of the stimulation of the receptor organ1 the passage of the afferent impulse into the brain or cord1 the passage of the impulse through a series of cells in the nerve centre forming a synapse1 the transmission of the impulse through the efferent nerve fibre into the effector organ in the muscle and the stimulation of the latter to an act of contraction4 ,this is a purely schematic description of the structures and processes forming a reflex action and arc3 in reality the path both into and out from the central nervous system is interrupted again and again1 and at each place of interruption there are alternative paths4 ,the interruptions occur at the synapses4 ,at a synapse the nervous impulse passes through an arborescence of fine nervous twigs1 into which the fibre breaks up1 into a similar arborescence1 and these two arborescences are not in actual physical contact3 the impulse leaps over a gap4 ,at numerous places in both brain and cord there are alternative synapses and at these places the impulse may travel in more than one direction4 ,the brain and cord are a switch-board of unimaginable complexity1 so that an efferent impulse entering it from1 say1 the eye1 can be shunted on to one nerve path after another1 so that it may affect any muscle in the whole body4 ,this is no fiction3 it may actually be the case4 ,in normal respiration a centre in the hind-brain is stimulated to rhythmical activity by the presence of carbon dioxide in the blood1 and from it efferent impulses originate which stimulate the muscles of the chest wall and diaphragm4 ,but in the distress of asphyxia every muscle of the body may be stimulated to activity in the effort to accelerate the oxygenation of the blood1 and these are not spasmodic movements of the muscles of limbs1 etc41 but purposeful contractions having for their object the increased intake of air into the lungs4 ,the central nervous system is1 therefore1 a switch-board--so mechanistic physiology teaches1 neglecting any idea of an operator4 ,but the whole trend of modern investigation is to show that every increase of specialisation in the evolution of the higher animal adds to the complexity of this nervous apparatus by increasing the number of alternative paths that an impulse originating anywhere in the body may take before it issues from the brain or spinal cord4 ,yet with all this increase of complexity it is nevertheless the case that in the higher animal the various parts of the central and peripheral nervous system are more and more integrated1 so that in the actions of the animal it becomes more and more the organism as a whole that acts4 ,all other organs in the animal body--excepting always the reproductive apparatus--are accessory to the sensori-motor system4 ,the alimentary canal and its glands dissolve the food-stuffs ingested2 the metabolic organs1 that is1 the cells of the wall of the intestine1 the liver1 etc41 transform these ingested proteids1 fats1 and carbohydrates of the food into the proteids1 fats1 and carbohydrates of the animal itself2 the heart1 blood1 and lymph vessels carry this food material to the muscles and nervous organs2 the respiratory organs absorb oxygen which is distributed throughout the body in the blood stream2 the excretory organs1 that is1 the lungs1 skin1 and kidneys1 remove noxious materials like carbonic acid and urea1 or its precursors2 and purposeful changes of functioning of all these organs are brought about by changes in motor activity4 ,round the sensori-motor system all the rest of the structure of the animal body is built up4 ,what we see clearly in the evolution of the animal body is the progressive increase of activity of the sensori-motor system4 ,the animal becomes more and more mobile4 ,it is in this way that dominance has been attained and all the directions of structural evolution in the past that have not tended in this direction have been unsuccessful1 irreversible1 evolutionary processes4 ,great size has not succeeded in the animal kingdom1 and so the gigantic reptiles and mammals of the secondary and tertiary periods have become extinct4 ,defence against enemies by the development of dermal armour has not succeeded1 and so the ,dinosaurs1 and other armed animals of the ,tertiary ,age have also become extinct4 ,the transformation of the fore limbs of the reptile into wings1 or the legs of the mammal into flappers1 did not succeed1 because all the rest of the structure of these animals had become adapted to locomotion on dry land1 and the change of structure had become too profound to be modified3 so the ,pterodactyls passed away1 as the whales of our own period are also passing4 ,only in the lightly boned1 feathered bird1 with the possibility of the development of powerful pectoral muscles1 did indefinite possibilities of flight reside2 and only in the fish1 with the concomitant evolution of gills1 the reduction of a minimum of the mass of the alimentary canal and its glands1 and the conversion of most of the muscles of the body into organs actuating the tail fin1 was the completeness of adaptation to aquatic life realised4 ,mobility1 a bodily structure capable of indefinitely varied movements1 and a nervous system by the aid of which any part of the body might become linked to any other part--these were the structural adaptations that have been successful alike in ,arthropod and ,vertebrate4 ,there were apparently two main types of structure by means of which this mobility and elasticity could be attained1 the ,arthropod type and the ,vertebrate type4 ,there seems little to choose between them if we had to select one of them in order to obtain a highly mobile organic mechanism4 ,arthropod and ,vertebrate seem to be equally complex if we take account of difference in size and the additional bodily mechanism that great size must involve4 ,certainly the musculature of the ,vertebrate is more complex than in the ,arthropod4 ,but greater weight must require larger and more powerful muscles if the same degree of mobility relative to the size of the animal is to be attained1 and this more complex musculature must carry with it a more complex brain4 ,it must also be concomitant with a more massive skeleton1 for rigid supports for the muscles must be present in the mechanism4 ,why are there no great insects or crustaceans8 ,mr ,wells has suggested in one of his novels the formidability of a wasp two feet long6 ,such a creature would indeed be more dreadful than any predatory bird that we know if its activity were also that of the wasps that we know1 just as a ,copepod as large as a shark would be a more formidable animal than the fish4 ,it seems possible that the reason for the smaller size of the ,vertebrate is to be found in the nature of the skeleton4 ,powerful muscles would require a very strong and thick carapace1 and this would attain a mass in a very large insect or crustacean which would require too much energy for its rapid transport4 ,a rigid exoskeleton like that of an ,arthropod also means that growth must take place by a process of ecdysis1 that is1 the animal grows only during the periods when it casts its shell2 and the necessity of this process of ecdysis must be a formidable disadvantage in the case of a very large animal1 if indeed it would be possible at all4 ,thus the ,arthropod developing an exoskeleton must remain small1 and this smallness1 fortunately for the ,vertebrate1 has made it the less formidable animal4 ,it was an accident of evolution that the ,arthropods developed an exoskeleton instead of an endoskeleton4 ,undoubtedly the internal skeleton of the ,vertebrates1 with its light1 hollow1 cancellated bones1 was mechanically the best means for the attachment of muscles4 ,it made possible a greater degree of freedom of movement of the parts of the body1 greater variety and plasticity of action1 and it removed1 to some extent1 the limit of size and the embarrassing discontinuity of growth by ecdysis1 with all the dangers that this involves4 ,above all1 it led to the increased complexity of the central nervous system1 since this became bound up with the increasing variety of bodily movement4 ,in the evolution of the dominant groups of organisms we see1 then1 the development of several tendencies4 ,first1 that tendency which seems to offer the greatest contrast to the universal tendency displayed in inorganic processes1 the dissipation of energy4 ,the plant organism is essentially a system in which energy is accumulated in the potential form4 ,then1 in the animal kingdom we see that the main tendency of evolution has been the development of systems in which energy becomes expended in infinitely varied movements4 ,it may seem1 on superficial examination1 that in the animal mode of metabolism energy is dissipated as it is in inorganic processes2 and this is the conclusion that we should reach if we considered the actions1 and the results of the actions1 of the lower animals only1 that is1 animals lower than man4 ,we return to this point later on1 but in the meantime it is to be noted that the fundamental division of organisms is that founded upon their activities as energy-transformers1 that is1 into plants and animals4 ,within each of these kingdoms of organisms structural evolution has occurred3 the unicellular green plant has evolved along very numerous lines1 each of them characterised by a different type of morphological structure4 ,the unicellular animal has also evolved in a similar way with the result that the present phyla have become established4 ,looking at these great groups of animals1 we see that two of them have attained dominance by the development along different lines of a sensori-motor system4 ,here we see another fundamental difference between the plant and animal organism1 but one which is a consequence of the difference that exists between the two kingdoms in respect of the energy-transformations carried out by them4 ,the plant is characterised by immobility1 the animal by mobility4 ,immobility implies unconsciousness1 mobility consciousness1 and this physical difference is the third one which we can establish between the plant and the animal4 ,now few physiologists are likely to accept this distinction as one which has any real objective meaning4 ,consciousness is not a concept to be dealt with in any process of reasoning1 it is not even something felt in the way in which we speak of the feelings of pain1 or light1 or hunger3 these are all states of our consciousness4 ,the difference in ourselves1 says ,ladd1 when we are sunk in sound dreamless sleep1 and when we are in full waking activity1 that is consciousness4 ,if we reason about organisms and their activities as we do about inorganic things we have no right to speak about consciousness1 for outside our own ,ego it has no existence4 ,the acting animal is only a body1 or a system of bodies1 moving in nature1 and all its activities are to be described by a system of generalised force and position co-ordinates with reference to some arbitrarily chosen point of space4 8,this animal machine10 says a zoologist1 writing about instinct1 8which ,i call my wife1 exhibits certain facial contortions and emits certain articulate sounds which correspond with those emitted by myself when ,i have a headache1 but ,i have no right to say that she has a headache40 ,this kind of argument does not appear to be capable of refutation except1 perhaps1 by the domestic conflicts which it would usually evoke if applied in such cases as that quoted4 ,in a description of nature by the methods and symbolism of science we see only systems of molecules in motion1 and in those systems which we describe as organisms the motions are only more complex than they are in inorganic systems4 ,such is the method of science1 as irrefutable in the study of the organism as we know that it is false4 ,valid in pure speculation according to the methods of the intellect it would nevertheless be absurd in the everyday affairs of common civilised life and the scientific man who applies it in his writing would nevertheless hesitate to apply it in the affairs of his own household4 ,we must recognise that our knowledge that other beings like ourselves1 as well as animals lower in organisation than ourselves1 are consciously acting organisms is intuitive knowledge1 attainable because of community of organisation3 our intuitive knowledge of the behaviour and feelings of our own brothers and sisters is greater than our knowledge of other men and women2 and we can1 by intuition1 place ourselves within the consciousness of an intelligent dog to a greater extent than in the case of other animals4 ,this knowledge of the consciousness of other animals is not scientific knowledge and it is unattainable and unprovable by reasoning or methods of scientific observation4 ,it is a conviction in itself incapable of analysis or proof1 but yet a conviction on which we confidently base most of our dealings with our fellow-creatures1 and which is justified by our experience4 ,it is nevertheless a scientific hypothesis of much the same validity as many other scientific hypotheses4 ,we cannot bring ourselves to doubt that other men and women are consciously acting organisms1 however impossible it may be to adduce scientific reason for the faith that is in us4 ,we cannot doubt that a compass needle which 8responds0 by turning one or other of its poles towards us according as we push forwards one or other of the poles of a magnet is an unconscious piece of metal1 though we find it impossible to say why this belief possesses such conviction4 ,from this to the movements of the typical green plant is only a step4 ,the turning of a green leaf towards the source of light1 or the downward movement of a root into the soil1 are responses to external stimuli which exhibit most of the inevitability of response of the magnet4 ,they are 8tropisms03 the plant leaf is obliged to turn towards the light so that the latter strikes against its surface perpendicularly1 and the root must grow downwards because gravity acts along vertical lines4 ,but suppose that reflex actions are tropistic3 suppose1 for instance1 that the moth is bound to fly into the candle flame because the light stimulates both sides of its body equally and this orientates it and guides it towards the direction from which the stimulus proceeds4 ,complex actions1 in the higher animal1 on this view are chains of reflexes1 and the acting must be unconscious and inevitable1 just as the turning of the magnet or green leaf are unconscious movements4 ,therefore the actions of our fellow-creatures are unconscious and automatic1 a conclusion toward which the whole tendency of mechanistic physiology forces us4 ,yet we know that the conclusion cannot be true4 ,between the obligatory reaction of the compass needle to the magnet1 or the analogous heliotropism and geotropism of the plant organism1 and the infinitely variable responses of the higher animal toward changes in its environment1 consciousness must come into existence4 ,it is absent in the inorganic system and the typical green plant2 it is dim in the sedentary sea-anemone or mollusc2 it becomes brighter in the freely moving ,arthropod or fish2 and it is most intense in man4 ,this1 it must be admitted1 is only a belief1 but accepting it as such we may attempt to support it by showing a parallelism of stages of structural complexity and actions4 ,the sensori-motor system is absent in the green plant2 it is simple in the extreme in the sea-anemone2 and it is rudimentary or vestigial in the sedentary mollusc4 ,it becomes more complex in the ,arthropod or fish1 and it is developed to the greatest degree in ourselves4 ,if we now examine our own mental states1 with their corresponding conditions of bodily activity1 we see as clearly as possible that our consciousness waxes and wanes with our activities4 ,it is absent in normal sleep1 when bodily activity in the real sense ceases almost absolutely1 when the cerebral cortex becomes inactive1 and when the only movements performed are those truly automatic ones of parts of the body which are analogous to the movements of the plant organism4 ,such movements are the rhythmic ones of the heart and lungs1 the movements of the blood1 and so on1 in general the movements leading to constructive metabolism4 ,consciousness is most intense in difficult unfamiliar actions3 the lad learning to row2 the child learning scales on the piano1 or the fingering of the violin2 the engineer assembling together the parts of a new machine2 or the artist engaged on a picture4 ,in each of these cases the worker is acutely conscious1 in a deliberative manner1 of his own bodily actions4 ,but with the habitual exercise of these movements1 and with the ease and facility with which they are performed1 consciousness that they are being performed fades towards nothingness4 ,what does this mean but that degrees of consciousness are parallel to degrees of complexity of deliberated and purposeful bodily movements or actions8 ,or degrees of consciousness are also parallel to the attempt of the organism to perform these actions4 ,what is pain1 the most acutely felt of all our mental states8 ,it is1 ,bergson says1 the consciousness of the persistent and unsuccessful effort of the tissues to respond purposefully to a persistently renewed stimulus4 ,but complex actions require for their performance systems of skeletal and muscular parts capable of moving in the most varied ways1 and a system of afferent and efferent nerves with all their connections in the central nervous system3 that is1 a sensori-motor system4 ,therefore just as the sensori-motor system is more or less complex so1 in general1 is consciousness more or less acute4 ,yet in the same organism consciousness is the more or less acute as the actions which it performs are more or less familiar4 ,the pianist who plays scales as a matter of exercise carries out most complex movements of hands and wrists unconsciously and without effort1 but to play an unfamiliar composition for the first time without error involves attention of the highest degree4 ,a girl who counts the sheets of paper coming from a machine seizes a handful in one hand1 and drops a separate sheet between every two fingers of the other hand1 repeating this most difficult operation with great rapidity1 and counting the handfuls of sheets accurately while thinking and talking deliberately about some other matter4 ,at the beginning of her work these actions were clumsily performed and facility was only attained by sustained attention to the movements of the hands1 yet with experience they become unconsciously performed4 ,complex movements of the body and limbs and digits1 involving the co-ordinated activity of numerous muscles1 nerves1 and nerve centres1 are performed at first only after a high degree of conscious effort1 but with each repetition of the series of movements the animal ceases to be aware of them1 or at least of their difficulty4 ,in the higher animals there are1 therefore1 two categories of actions1 7#a7 those unfamiliar actions which are difficult1 and in the performance of which the animal becomes conscious of complex muscular activities2 and 7#b7 those habitual actions which have become easy by dint of repetition1 and the performance of which is unattended by conscious effort4 ,analysis of our own activities reveals these two categories of actions1 and we have no doubt whatever that the higher animals have the same feelings of difficulty and effort in the one case1 and of lack of conscious effort in the other4 ,the difference is one of those which separate instinctive from intelligent activities4 ,now we hesitate to attempt the discussion of this much-controverted question of the distinction between instinct and intelligence3 after reading much that has been said as to the nature of this difference1 one rises with the uncomfortable impression that the time is not yet ripe for its discussion1 and that the problem is still one far more for the naturalist than for the psychologist4 ,reliable data are still urgently required4 ,yet it is a question which we cannot fail to consider4 ,the typical plant differs from the typical animal in that a sensori-motor system has been evolved in the one but not in the other2 and among the animals in which this system is developed to a high degree the activities which involve its exercise differ in their form4 ,actions of a stereotyped pattern characterise the behaviour of the higher ,invertebrate1 while in the higher ,vertebrate all that we see indicates that the behaviour is the result of deliberation1 and that the actions performed are not stereotyped but differ infinitely in their patterns4 ,just as clearly as differences in morphology differentiate ,arthropod from ,vertebrate1 so also do differences in the mode of activity of the sensori-motor system mark divergent lines of evolution culminating in the ,hymenopterous ,insect on the one hand and in ,man on the other4 ,what is the essential difference between an action performed instinctively and one performed intelligently8 ,it is not that the animal is unaware of its activity in the first case and not in the second2 however much we tend to 8explain0 organic activity in terms of inorganic reactions1 we do not really believe that the instinctively acting wasp is a pure automaton1 while admitting that the schoolgirl is acutely conscious of her own multifarious activities4 ,it is not that the instinctive action displays a 8finish10 or perfection of technique1 that the deliberative action lacks3 the comb built by the wasp is not more perfect in its way than is the doorway constructed by a skilled mason1 or the 8buttonholes0 stitched by a seamstress4 ,it is not that instinctive actions are so absolutely stereotyped1 as is sometimes assumed1 while intelligent actions grow more perfect in their result by repetition3 the work of the insect or bird is often faulty and it is improved by practice4 ,the most obvious difference is that the instinctive action is effective the very first time it is performed1 while the intelligent action only becomes effective after it has been attempted several times1 or very many times1 according to its difficulty4 ,the flight of the young swallow is effective inasmuch as it sustains the bird in the air1 but it is also an exceedingly difficult series of muscular efforts which is at first clumsily performed and which becomes more perfect by repetition4 ,but the flight of an aeroplane1 even now after years of experiment1 is not always effective1 and exhibits at its best all the imperfections of the flight of the young swallow4 ,yet can we doubt that in time it will exhibit all the ease and certainty and finish of the flight of the bird8 ,the typical intelligently performed action is the action of a tool1 or of a part of the body which is used for some other purpose than that which is indicated by its immediate evolutionary history1 or by its previous use4 ,the typical instinctively performed action is always the action of a bodily organ1 the structure and immediate evolutionary history of which indicates that it originated as an adaptation for the performance of these particular actions1 or category of actions4 ,here it seems to us that we find the distinction between the two kinds of bodily activity2 and the distinction is one which depends for its validity on our notions as to what a tool is4 ,an implement made by man is a piece of inert matter fashioned in order that it may be used for a definite preconceived purpose4 ,it has an existence as a definite specific object apart from its use2 and its exercise by the man who made it and its existence in nature are two different things4 ,its use must be learned1 and the results obtained by its employment become more perfect with every repetition of its use4 ,but the mandibles of an insect are implements purposefully adapted for some action or series of actions1 just as the pincers of the blacksmith are so adapted4 ,they are1 however1 implements which are part of the organisation of the animal using them--organised tools--and it does not seem as if we ought to think of them1 and of their shape and nature1 as something apart from their exercise4 ,must we think of an animal as having to learn how to use any part of its body8 ,if so1 then the problem of instinct remains with us in all its historic obscurity4 ,but if we think of the existence of a bodily tool as something inseparable from the functioning of the tool1 the problem becomes less obscure1 or at least it can be stated in terms of some other problems which we have already considered4 ,we do actually think of bodily parts or organs as material structures quite apart from the consideration of their functions3 it is the distinction between morphology and physiology--an altogether artificial one4 ,an animal1 for the morphologist1 is a complex of skeleton1 muscles1 nerves1 glands1 and so on2 and it does not matter whether it is contained in a jar of methylated spirit or is running about in a cage4 ,for the physiologist it is 8something happening02 but is it not really both things1 and are not the structure and the functioning only two convenient1 but arbitrary1 aspects from which we consider the organism8 ,we ought not to think of diaphragm and lungs apart from the movements of these organs1 and we do not say that the first breath drawn by the newly-born mammal is an instinctive action1 involving the use of inborn bodily tools--the diaphragm1 lungs1 etc4 ,we ought not to think of the lips and mouth and pharynx of the young baby apart from the actions of suckling the mamm of its mother1 but usually we say that this action is an instinctive one4 ,where does the ordinary functioning of an organ end and its instinctive functioning begin8 ,are the muscular actions of the lobster when it frees its body and appendages from the carapace during the act of ecdysis instinctive ones8 ,most zoologists would say that they are not1 any more than the movements of the maxillipedes in respiration are instinctive ones1 yet they probably would not hesitate to say that the action of the 8soft0 lobster in creeping into a rock crevice is instinctive4 ,does a young child really 8learn0 to walk8 ,it is more likely that the actions of walking are potential in its limbs and that they become actual when all the connections of nerve tracts and centres in its brain and spinal cord become established4 ,what is the difference between the acquirement of the ability to walk and to write8 ,the latter series of actions are unfamiliar combinations of nervous and muscular activities which are no part of the organisation of the young child2 while the former are simply the result of the complete functional development of certain nervous and muscular apparatus4 ,it seems difficult1 then1 to express clearly what is the essential difference between instinctive and intelligent behaviour2 and it is doubtless the case that reasoned experiments and observations are still too few to enable us to make sound deductions4 ,but it certainly seems as if we ought to think of instinctive actions as having evolved concomitantly with the structure of the organs which effect them3 they are those inheritable adaptations of behaviour which are bound up with--are indeed the same things as--inheritable adaptations of structure4 ,in performing them the instinctively acting animal is doubtless aware of its own activity1 but we must think of this awareness as being of much the same nature as our consciousness of the automatic activities of our own bodies--the rhythmic activities of the heart and respiratory organs1 or the actions of our arms and legs in walking1 for instance4 ,it is knowledge of the inborn ability of the organisms to use an inborn bodily tool4 ,in the intelligent action we certainly see something different from this4 ,the organ or organ-system which carries out such an action functions in a manner which is different from that for which it was evolved3 the action is the conscious adaptation of the organ for some form of activity new to it1 and this acquirement of activity seems to be non-inheritable--at least it is non-inheritable in the sense in which we speak of acquired characters being non-inherited4 ,it is accompanied1 while it is being acquired1 by a consciousness which is deliberative1 and is different from that awareness of its own activity which accompanies the acting of the instinctive animal--the knowledge that it is acting in an effective manner4 ,it does not seem as if the animal in so acting is aware of the relation of the bodily tool to the object on which it is acting4 ,but intelligence seems to imply more than this3 it implies the knowledge of the organism that some parts of its body bear certain relations to the parts of the environment on which they are acting1 and that these relations are variable ones and may be the objects of conscious choice4 ,,chapter ,,viii ,,the ,,organic ,,and ,,the ,,inorganic ,it is convenient that we should express the results of biological investigation in schemes of classification1 for only in this way can we reduce the apparent chaos of naturally occurring organic things to order1 and state our knowledge in such a way that it can easily be communicated to others4 ,but we must always remember that the classifications of systematic biology are conceptual arrangements1 depending for their precise nature on the point of view taken by their authors4 ,the clear-cut distinctions that apparently separate phylum from phylum1 class from class1 order from order1 and so on1 do not really exist4 ,there are no such categories of organisms in nature as genera1 families1 and the higher groupings4 ,all that we can say exist naturally are the species1 since all the organisms composing each of these groups are related together by ties of blood-relationship1 and all are isolated from the organisms composing other species by physiological dissimilarities which render the plants or animals of one species infertile with those of any other4 ,such would doubtless have been the opinion of most botanists and zoologists prior to the work of de ,vries1 but we must now recognise that the systematic1 or ,linnean1 species of the nineteenth century was just as artificial a category as were the genera and families4 ,our arrangements of plants and animals into systematic species and the higher groupings are therefore convenient ways of symbolising the results of morphological and physiological investigations1 although they also indicate the main directions taken by the evolutionary process1 but the manner in which they are stated in taxonomic schemes is always a more or less formal one4 ,there are no absolute distinctions between group and group1 even between the animals and the plants4 ,there is nothing1 for instance1 in the morphology of a ,diatom to indicate that it belongs to the vegetable kingdom1 or in that of a ,radiolarian1 to indicate that it is an animal4 ,peridinians are either plants or animals according to the general argument1 or the point of view of the author who writes about them4 ,even a study of the energy-transformations that are effected in the living substance of these lower organisms does not afford an absolute distinction3 synthetic metabolic processes in which energy passes into the potential condition may be carried out in animals1 while many plants--the saprophytic fungi1 or the insectivorous plants1 for instances--may effect analytic energy-transformations of essentially the same nature as those exhibited in the typical mode of animal metabolism4 ,motility and the possession of a sensori-motor system do not afford the means of making a sharply drawn line of division between plants and animals4 ,potential energy passes into the condition of kinetic energy in the typical animal1 and this kinetic energy is directed by the sensori-motor system4 ,but some lower unicellular plants are motile1 and they possess the rudiments of a sensori-motor system in the flagella by which their movements are effected4 ,on the other hand1 the sensori-motor system has become vestigial in many animal parasites--in the ,crustacean ,sacculina1 for instance1 which is parasitic on some ,crabs4 ,the possession of consciousness1 in so far as we can say that other animals than ourselves possess it1 is no distinction between the two kingdoms of life4 ,consciousness1 judged by the degree of development of motility1 must be supposed to be absent or very dim in the extreme cases of parasitism attained by some animals2 on the other hand1 we may assume that it is present1 to some extent at least1 in the highly motile zoospores of the ,alg4 ,thus some lower organisms1 the ,peridinians and the algal spores1 exhibit all the characters which we utilise in separating animals from plants--the chlorophyllian apparatus1 by means of which the kinetic energy of solar radiation becomes transformed into the potential energy of organic chemical compounds2 the apparatus of receptor and motile organs1 by means of which the potential energy of stored chemical compounds passes into the kinetic energy of bodily movements2 and the existence 7so far as we can say that it exists in organisms other than ourselves7 of some degree of consciousness4 ,neither do those morphological schemata which we construct as diagnostic of phyla1 or classes1 or orders1 etc41 separate these groups from each other so clearly and unequivocally as our classifications suggest4 ,it might seem for instance that the presence or absence of a notochord would sharply distinguish between the vertebrate and invertebrate1 but structures which suggest in their development the true notochordal skeleton of the typical vertebrate animal are to be traced in animals which exhibit few or none of the characters which we regard as diagnostic of the ,vertebrate4 ,typical ,arthropods and typical ,vertebrates seem to be distinct from each other1 but the extinct ,ostracoderms of ,silurian times may have been animals which possessed an internal axial skeleton1 and which were also armed by a heavy dermal exo-skeleton4 ,it is a hypothesis of considerable plausibility that they really were ,arthropods1 on the other hand they are usually regarded as ,vertebrates4 ,so also with most other phyla3 the morphological characters which absolutely distinguish between one group and others are very few indeed1 and the small appended groups that lie about the bases of these larger groups may present one or other of the characters of several phyla4 ,looking at the morphology of the animal kingdom in a general kind of way1 one does indeed see that a certain structural plan is characteristic of the organisms belonging to each of the great phyla1 while more detailed structural plans may be said to be characteristic of the sub-groups4 ,but minute morphological and embryological investigation reduces almost to nothing the characters which are absolutely diagnostic of these various groups4 ,no more than the nature of the energy-transformations1 and the essential morphology1 does the behaviour of animals afford us the means of setting up absolute distinctions between group and group4 ,really tropistic behaviour is exhibited by the movements of the stems1 roots1 and leaves of green plants1 or in the movements of ,bacteria1 and perhaps some unicellular animals4 ,typically instinctive behaviour is exhibited by the individuals of societies of ,insects and by many solitary-living animals belonging to this class2 and typically intelligent behaviour is exhibited by the acting of the higher ,mammalia4 ,yet there is undoubtedly much that is truly instinctive in the behaviour of ,man1 and something of the same nature as his intelligence seems to inhere in the instinctively-acting mammal or insect3 how else could an instinctive action become capable of improvement8 ,we cannot doubt that intelligence is manifested by a dog or by much that we see in the behaviour of ants4 ,no rigid distinctions between tropisms1 such as we have mentioned above1 and the reflexes that may be taken to constitute instinctive behaviour1 can be established4 ,minute analysis1 such as that carried out by ,jennings on the swimming movements of the ,protozoa1 leaves us quite in doubt as to how these modes of behaviour are most properly to be described2 and all the controversy as to the nature of tropisms1 reflexes1 instinct1 and intelligence surely indicates that these modes of behaviour have something that is common to all of them1 and that no clear and certain distinction can be said to separate one from the other4 ,even those psychic processes which we call intellectual do not seem to be different in kind from some that we attribute to the lower animals3 the ,protozoan ,paramcium studied by ,jennings1 or the crabs1 crayfishes1 and starfishes studied by ,yerkes and others really learn to perform actions1 but this learning is said to be the result of a process of 8trial and error40 ,the animal tries one series of movements and finds that it fails1 tries another and another with a similar result1 and in the end finds one that is effective4 ,this is remembered1 and when the same problem again confronts the animal it is solved after fewer trials1 and finally1 after experience1 the end-result is attained at once without previous trials4 ,now many of what we call truly intellectual processes are certainly processes of precisely this nature4 ,hypothesis after hypothesis occurs to the scientific man 7or to the detective1 or to the engineer confronted with some exceptional difficulty71 and one after another is tested by actual trial1 or by a process of reasoning 7which is really the rapid and formal resuming of previous experience71 until a hypothesis verifiable1 or a priori verifiable1 is found4 ,what1 for instance1 are our mathematical methods of integrating a function1 or working a long division sum1 but methods of scientific 8guessing10 and verification of the hypotheses so made8 ,they are truly instances of the method of trial and error practised by the lower animals4 ,all the above amounts to saying that there is a community of energetic processes1 of morphology1 and of behaviour in animals and plants4 8,protoplasm0 is the same1 or much the same chemical aggregate1 whether it is contained in the cells of animals or plants4 ,the cell1 with its nucleus1 chromatic architecture1 cell-inclusions1 and cell-wall1 is essentially the same structure in all organisms4 ,the complex and specialised process of nuclear division in tissue growth1 or the series of events which constitute the acts of fertilisation of the ovum or its plant correlative1 are the same all through the organic world4 ,the sensori-motor system--receptor organ1 nerve-fibre and cell1 and effector-motor organ--is the same all through the animal kingdom4 ,alimentary canal and glands1 enzymes1 excretory tubules1 contractile blood-vascular apparatus--all these are structures which are functionally the same1 which are built on essentially the same morphological plan4 ,life1 whether it is the life of plant or animal1 makes use of the same material means of perpetuating itself on the earth and avoiding the descent of matter towards complete inertia4 ,absolute dissimilarities1 dissimilarities such as those between atoms of hydrogen and oxygen1 or between a point and a straight line1 or between rest and motion1 do not exist between the different categories of entities that make up the organic world4 ,yet differences do exist1 and must we conclude that because these differences are not absolute ones1 because they are differences of degree1 and not of kind1 they are not essential1 are not differences at all8 ,must we say1 for instance1 that although an animal is a much more efficient machine than a gas-engine 7in the sense of efficiency as understood by the engineer71 there is really no difference between them1 that they are both thermo-dynamic mechanisms1 since in both energy is dissipated8 ,ought we to say that1 because the last steps in the formation of urea in the animal body are synthetic ones1 there is really no difference between the nature of the energy-transformations that occur in the animal and the plant modes of metabolism8 ,ought we to say that1 because a dog may sometimes act intelligently and a man instinctively1 psychically they are similarly-behaving organisms8 ,surely this amounts to saying that1 because things are not absolutely different1 they are the same2 and surely the mode of reasoning is a vicious one6 ,what we clearly see in the different kinds of organisms--in the metabolically constructive plant and the metabolically destructive animal2 or in the instinctively-acting ,arthropod and the intelligently-acting ,mammal--is the progressive development of different tendencies4 ,if the green plant is1 in its essence1 the same kind of physico-chemical constellation as is the animal1 yet the tendency of its evolution has been that more and more it has acquired the habit1 or the power1 of using solar radiation to combine together carbon dioxide1 water1 and nitrogenous inorganic salts to form proteid and carbohydrate substances4 ,on the other hand1 the tendency of the animal has been more and more to absorb into its own tissues the proteid and carbohydrates synthesised by the green plant1 and then to break these substances down into carbon dioxide and water1 and less and less to effect such syntheses as are effected by the plant4 ,even if the ,annelid worm1 the ,arthropod1 and the ,vertebrate were1 at the origin of their ancestries1 animals which were very like each other in the morphological sense2 even if there are some ,arthropods which are very like ,annelids1 and some ,annelids which might very easily be imagined to become transformed into ,vertebrates1 and some extinct ,arthropods which may after all have been ,vertebrates1 yet it is the case that the tendencies of the evolution of each of these groups have been very different4 ,all the while the ,vertebrate tended more and more to develop a rigid axial rod or notochord1 becoming later a jointed vertebral column1 and a soft1 pliable1 exo-skeleton2 while the ,arthropod tended more and more to develop a rigid exo-skeleton1 and to remain soft in its axial parts4 ,even if these two tendencies may not have been fully realised1 is it not the case that they are really different things8 ,the evolutionary process has therefore been1 in its essence1 the development1 or unfolding1 of tendencies originally one4 ,what is the evolutionary process8 ,it is usually regarded as a progress from organic simplicity towards organic complexity4 ,yet if we think about it as a physical process we cannot say that any one stage is any more simple or complex than any other stage4 ,let us compare organic evolution with the process of inorganic evolution1 as1 of course1 we are compelled to do if we regard the former process as a physico-chemical one4 ,assume1 then1 that the nebular hypothesis of ,kant and ,laplace is true--it will make no difference to our argument even if this hypothesis is not true1 and it is more easily understood than any other hypothesis of planetary evolution4 ,originally all the materials composing our solar system existed in the form of a gaseous nebula possessing a slow rotatory motion of its own4 ,it does not matter that the silicates1 carbonates1 oxides1 and all other mineral substances that we now know existed then in the form of chemical elements1 or the precursors of chemical elements3 all the material bodies now present in the solar system were present in the original nebula4 ,the energy of this nebula consisted of the potential energy represented by the separation of atoms which later on became combined together1 and of the kinetic energy of motion of these atoms2 and this material and energy1 together with the other cosmic bodies radiating energy to it and those bodies receiving the energy which it lost by its own radiation1 constituted a system1 in the sense of the term as it is employed by the physicists4 ,now1 in the process of cosmic evolution this system became transformed1 because it was continually losing energy by radiation4 ,as it cooled1 the mean free paths of its atoms and molecules became less and less1 and finally condensation to the liquid and then to the solid condition occurred4 ,the parts of the nebula continually gravitated together1 so that it became smaller and smaller while its rotatory motion became greater4 ,finally1 mechanical strains became set up in its mass as the consequence of the increased velocity of rotation1 and disruption occurred with the formation of the sun1 the planets1 and the satellites4 ,there was no increase of complexity of the system4 ,at any moment of time its elements1 that is1 the chemical atoms composing it and the energy of these atoms1 was the same as at any other moment of time4 ,heat-energy may have been radiated from one part of the system--the heated nebula--to some other part of the system--the other cosmic bodies absorbing this radiation1 but the total energy of the system remained the same4 ,the chemical atoms may have combined together to form molecules and compounds1 and their energy of position may have become the energy of motion1 but the ultimate materials were still the same4 ,what happened during the cooling and contraction of the nebula was a rearrangement of the elements of the system1 that is1 of the atoms and their energies4 ,at any moment of time the condition of the system was an inevitable consequence of the condition at the moment immediately preceding this1 and a strict functionality1 in the mathematical sense1 existed between the two conditions4 ,it was not more complex in the later stage than in the earlier one--it was merely different4 ,stages of evolution were really phases in a transforming system of matter and energies4 ,if we choose to regard organic evolution as a similar process of physico-chemical transformation1 we must also regard the totality of life on our earth1 with all the inorganic materials which interact with organic things1 and with all the energies1 cosmic and terrestrial1 which also so interact1 as a system in the physical sense4 ,we are now compelled to think about this system in the same way as we thought about the cosmic one1 that is1 we must postulate that a rigid mathematical functionality existed between any two conditions of it1 and that the latter condition was inevitably determined by the former one4 ,we must think of the system as at all times composed of the same elements4 ,in its later condition life may have been manifested in a greater mass of material substance than in its earlier conditions1 but this increase of mass was only the increase of one part of the system at the expense of another part4 ,at all times1 then1 the constitution of the system was the same1 and different stages of the evolutionary process have only been different phases1 or arrangements1 of the same elements4 ,at no time was the organic world any more or less complex than at any other time4 ,in its 8primitive0 condition all was given4 ,mechanistic biology does not1 of course1 hesitate to accept this view of the evolutionary process4 ,the 8,laplacian mind0 must have been able to calculate what would be the condition of the system at any phase1 knowing the positions of all the atoms or molecules in the original nebula1 and the velocities and directions of motions of all these atoms or molecules4 ,just as 7in ,huxley's illustration7 a physicist is able to calculate what will be the fate of a man's breath on a frosty day1 so the ,laplacian mind must have been able to predict the fauna and flora of the world in the year #aiac from a complete knowledge of the material nature and energetic properties of the nebula from which it arose4 ,we cannot fail to see1 on reflection1 to what this view of the nature of the evolutionary process leads us4 ,the primitive world-nebula was a system of parts which had extension in space4 ,materially it consisted of atoms isolated from each other by space1 and energetically it consisted of the movements of these atoms1 and of the energy of their positions with regard to each other4 ,no two atoms could occupy the same space--they mutually excluded each other3 this is what we mean by saying that the original--and every other--state of the system was a state of material things or elements spatially extended4 ,therefore1 if the physical analogy is consistently to be retained1 the organic system undergoing evolution was a system of elements which at any moment whatever were spatially extended4 ,it was really a system of atoms or molecules possessing kinetic energy of motion1 or potential energy of position--molecules which lay outside each other1 and energies which were really the movements or positions of these molecules1 and which therefore lay outside each other in the same sense4 ,the evolution of the individual organism must be a process of the same kind4 ,like cosmic and phylogenetic evolution1 it is apparently a progress from the simple to the complex4 ,a minute fragment of protoplasmic matter1 homogeneous in composition1 or apparently so1 grows and differentiates1 becoming the complex structure of the adult organism4 ,here the system in the physical sense is the fertilised ovum1 the oxygen and nutritive matter which have become incorporated with it1 and the physical environment with which these things interact4 ,all these elements existed in that phase of the system which contained among its parts the fertilised ovum1 as well as in that phase which contained the fully developed organism4 ,complex by comparison with the fertilised ovum and its environment as the adult animal and its environment may seem to be1 it is only a different phase of the same system4 ,further1 all the parts that form the tissues of the adult1 and all their motions1 are spatially extended1 and are only rearrangements of the molecules and of the motions of the molecules that were actually present in the system in its initial phase4 ,speculation along these lines has led to all the results of ,weismannism4 ,all the parts of the adult organism are really present in the fertilised ovum and the nutritive matter which is to build up the fully developed animal1 not in potentiality it must be noted1 but actually present in the spatially extended condition4 ,it is true that the hypothesis only requires that the determinants of the adult organs and tissues1 and of the adult qualities1 should be present in the ovum2 but since the energies necessary for the separation of these determinants1 and for their arrangement and growth in mass1 must also be present in the initial phase of the system1 it is evident that the hypothesis implies that all the material structure of the animal is present in the spatially extended form in the initial phase of the system4 ,just as the adult animal is a manifoldness of material parts and energies that possess extension1 so also is the undifferentiated embryo and its material environment an extensive manifoldness4 ,we cannot otherwise conceive it if we are to retain the mechanistic view of the development of the individual organism4 ,let us think of the process of organic evolution in another way by comparing it with the mathematical process by which we form the permutations and combinations of a number of different things4 ,individual development is termed the assumption of a mosaic structure1 that is1 all the parts of the adult are assumed to be present in the embryo1 but in a sort of 8jumbled-up0 condition4 ,as development proceeds1 these parts become sorted out and arranged in a pattern which continually becomes more and more distinct4 ,much the same process of arrangement and segregation must be assumed to have occurred during the process of racial evolution3 the parts of the 8primitive0 life-substance1 with all the parts of the physical environment which become incorporated with it during its evolution1 must have become segregated and arranged so as to form the existing species of plants and animals4 ,a permutation1 then1 of the separate things a1 b1 c--x1 y1 z1 is an arrangement of all these things3 obviously there are a very great number of ways in which the letters of the alphabet may be arranged1 #bf6 in all4 ,but we may take some of the letters and arrange them in different ways3 the selections a1 b1 c1 d1 can be arranged in #d6 ways b1 c1 d1 e1 also in #d6 ways1 and so on4 ,thus by a process of dissociation and arrangement of a certain number of elements1 a very great number of different things--things which consist of elements spatially extended--can be obtained4 ,the group of things1 a1 b1 c1 d--x1 y1 z1 was an extensive manifoldness1 since it was formed by juxtaposing in space the separate units of which it is composed4 ,yet it is an unitary thing1 for it is a different thing from the group1 b1 c1 a--x1 y1 z4 ,it is also a multiplicity1 for it can be transformed into every one of the #bf6 permutations1 and broken up into the selections of some of the separate things of which it is composed1 and of the permutations of the things taken in each of these selections4 ,in a way these arrangements exist in the group a1 b1 c--x1 y1 z1 and yet the group itself possesses no other actual extended existence than the group of things that it is4 ,it is an intensive multiplicity or manifoldness in that the potentiality of all the arrangements exists in it but not in the spatially extended condition4 ,it is a multiplicity only when we associate with it the mental operations by which we conceive of its dissociation and rearrangement4 ,by reason of these mental operations the intensive multiplicity of the group becomes the extensive multiplicity of its arrangements4 ,this appears to be the only really philosophical way in which we can attempt to picture to ourselves the processes of individual and racial evolution4 ,the 8primitive0 life-substance1 or the undifferentiated ovum1 each of them with its environment1 was an intensive manifoldness1 a multiplicity of distinct things or qualities which co-existed1 and which were not separate each from other in that they occupied different compartments of space1 but which interpenetrated each other4 ,this notion of distinct things co-existing in time1 yet occupying the same space1 is not at all a difficult one4 ,our consciousness is such a multiplicity of states or qualities all in one4 ,the idea of a group of figures has a very real existence for the sculptor1 and he may visualise it with almost all the appearance of reality that the actual1 material piece of statuary possesses4 ,in his mind it is a real manifold existence1 which nevertheless does not occupy the three-dimensional space which the marble fills4 ,the musical notes ,c1 ,f1 ,a1 ,c1 heard in arpeggio1 are things which possess real existence1 but which are extended in time1 and when we think of these separate sounds we lay them alongside each other in our mind in an empty1 homogeneous medium which seems to be all that we think of as space4 ,yet the same notes heard simultaneously as a chord are not extended4 ,they interpenetrate each other1 but yet they are distinct things1 since on hearing the chord we can recognise the notes composing it4 ,as an arpeggio the notes are an extensive manifoldness1 but as a chord they are an intensive manifoldness4 ,the mechanistic biology of the latter part of the nineteenth century based itself on the methods and concepts of physics1 and it was therefore compelled to assume that the manifoldness of the 8primitive0 life-substance--the 8,biophorid0 of ,weismann and his followers--or that of the fertilised ovum1 was a manifoldness that had spatial extension4 ,all the systems studied by physics were aggregates of elements1 or parts1 that had such extension3 the sun1 with its attendant planets and satellites1 was a system of bodies isolated from each other in space4 ,even the atmosphere1 or the sea1 media which to our unaided senses appear to be homogeneous1 are really media consisting of discrete bodies1 or molecules1 which are not actually in contact with each other1 but which are separated from each other by empty space4 ,chemical compounds were assemblages of molecules1 molecules were assemblages of atoms1 and the atoms themselves were either simple or were composed of corpuscles1 or still smaller bodies4 ,this mode of analysis was forced upon the human mind by formal logic and geometry1 and it was apparently the only method of acquiring mastery over nature4 ,yet there were difficulties1 appreciated no less by the philosophical physicists than by the writers on formal philosophy4 ,how could bodies1 or molecules1 or atoms that were separated from each other act upon each other8 ,the molecule ,a could only act upon the molecule ,b if there were some particles between them which could convey the impulse or attraction1 but then we must suppose that there were other particles between these intermediate ones1 and so on ad infinitum1 otherwise how could a body act1 that is1 really exist1 where it was not8 ,in other words1 how could there be action at a distance8 ,how1 for instance1 could the atoms of the earth attract those of the moon with a force sufficient to break a steel rope of #djj miles in diameter8 ,physics had therefore to invent the ether of space1 not only to account for interstellar or interplanetary gravitation and other modes of radiant energy1 but also to account for the interaction of the atoms or molecules which make up chemical compounds4 ,in our own day atoms have ceased to be the limits to the subdivision of things3 they are composed of electrons1 but the electrons are entities separated from each other by empty space4 ,they are not1 however1 the ultimate limits of subdivision of matter1 as the atoms were supposed to be by the chemistry of the early part of the last century1 but are regarded as 8singularities0 in an universal continuous medium or ether4 ,it is of no moment that we are unable to describe the ether in terms of our former concepts of matter and energy1 or at least that we can only so describe it in such a way that it is represented by negative qualities3 we are compelled to postulate its existence in order to avoid philosophical confusion4 ,the universe is therefore a continuum1 and an atom or any other body exists wherever it can act4 ,the atoms of a fixed star1 so far away that we can only represent its distance in billions of miles1 are nevertheless on our earth as well as at the point of space which we regard as their astronomical position1 for the light emitted by them acts on our retinas4 ,the universe is an unitary thing in that it is a continuous medium or substance in the philosophic sense1 but it is also a multiplicity in that singularities or conditions of this medium pervade each other throughout space4 ,such seem to be the conclusions towards which the later physics forces us1 and it is interesting to reflect how different biological speculation might have been had it been formulated now instead of half a century ago6 ,why has a process of evolution occurred at all8 ,why is it that tendencies that might have co-existed1 that indeed do co-exist to some extent1 have become separate from each other8 ,it is possible to conceive of an organism which contains chlorophyll1 and which might therefore synthesise carbohydrate and proteid from inorganic substances1 but which might also contain a sensori-motor system1 and which might therefore expend the energy so obtained in regulated movements4 ,to a certain extent such organisms combining the plant and animal modes of metabolism do exist among the ,protista4 ,yet1 the effect of the evolutionary process has been more and more to dissociate the plant and animal modes of metabolism until the typical animal is quite unable to make use of carbon dioxide and water as materials to be synthesised1 while the typical plant has lost all power of motion except the tropistic movements of its roots1 leaves1 and stems4 ,instinctive and intelligent behaviour coexist in many animals1 yet the tendency of man1 most highly intelligent of all1 is more and more to act intellectually2 while the opposing tendency1 that is1 to act instinctively1 has been evolved in the ,hymenoptera4 ,it seems as if such contrasting methods of transforming energy1 or of acting1 were incompatible with each other1 and yet it is clear that they are not really incompatible1 for they may co-exist4 ,but it does seem clear that each of these contrasting tendencies cannot be manifested to the fullest extent if it is accompanied by the other4 ,that is to say1 life is limited in its power over inert matter4 ,manifested in the same material constellation1 it cannot both use solar radiation to build up substances of high potential energy and then break down these substances so as to obtain kinetic energy of movement4 ,now we see clearly that life on our earth is indeed limited to a very restricted range of physical conditions4 ,when we think of the mass of the earth we are surprised to find what an insignificant fraction of all this matter displays vital phenomena4 ,the surface of the land is clothed with a layer of vegetation1 luxuriant and abundant as we see it when we walk through a tropical forest1 but which is really a film of inconceivable tenuity when we compare its thickness with the diameter of the globe4 ,even the whole surface of the land is not so clothed with vegetation1 for polar regions and the tops of high mountains are almost lifeless1 while desert tracts may be absolutely so4 ,the lower strata of the atmosphere are inhabited by birds1 insects1 and bacteria1 but the total mass of these is infinitesimal when compared with the total mass of the gases of which the atmosphere is composed4 ,even the sea1 which we regard as rich in life1 is not really so3 estimates of the luxuriance of planktonic life are really misleading1 for although a single drop of water may contain some hundreds of organisms1 the mass of these is exceedingly small and is usually expressed as one or two parts per million4 ,all this means that life has difficulty in manifesting itself in material forms4 ,whether it be simply a mode of interaction of some complex chemical substances with a relatively simple physico-chemical environment--the mechanistic view--or whether it be an impetus or agency which is neither physical nor chemical1 but which acts through physical and chemical elements--the vitalistic view1--life is capable of acting on terrestrial materials to a very limited extent4 ,acting through all the tendencies which we see to exist in it1 life may be1 so to speak1 diluted2 but by being concentrated in one or a few of them it becomes more effective4 ,the dissociation of this bundle of tendencies which we call life is therefore the meaning of the evolutionary process4 ,ontogenetic development1 says ,roux1 is the production of a visible manifoldness4 ,it cannot be said that this cautious description of the developmental process has been apprehended by those who expound the dogmas of mechanistic biology4 ,development is indeed the production of a diversity1 but this diversity is only a phase of a preceding diversity1 a rearrangement of spatially extended pre-existing elements4 ,how else could the developing embryo and its material environment be regarded as a system of physico-chemical elements1 capable of study by the methods of experimental and mathematical physics1 except by regarding it as a system passing through phases each of which is a necessary consequence of the preceding one1 and each of which contained the same elements separated from each other in space8 ,let us think of water occupying a vessel at a high temperature and continually cooling4 ,the states of this system are 7#a7 the gaseous state in which the molecules of the water are moving at a high velocity and are a relatively considerable distance apart1 and in which they are incessantly colliding with each other and with the walls of the vessel2 7#b7 the state of the system consisting of the separate phases1 liquid water and gaseous steam in contact with it2 and 7#c7 the solid phase1 in which the molecular motions almost1 or quite1 cease4 ,here the progress of the system through its phases leads to physical diversity and then again to physical homogeneity4 ,but the diversity of the different phases is in a sense an apparent one only3 any single phase1 or at least those which involve the passage of the system from the gaseous to the liquid phases1 and vice versa1 can be represented by van der ,waal's general equation1 ,,rt 7p a_/v#b7 7v - b74 ,does anything in modern biological investigation1 except1 of course1 the speculations of non-physical physiologists1 suggest that an ontogenetic process can be represented in such a manner8 ,are the arbitrary 8stages0 of the embryologists--the ovum1 blastula1 gastrula1 etc41 phases in a system in the above sense1 the only sense in which the process can be regarded as capable of physico-chemical analysis8 ,what precisely is the embryo at the close of the process of segmentation8 ,it is an harmonious equipotential system1 that is to say1 an assemblage of discrete organic parts or cells1 each of which has all the potentialities that every one of the others has4 ,any cell in the blastula may become a cell1 or a series of such1 in any part of the gastrula or pluteus larva4 ,this is what the parts are in potentiality1 but actually their individual fates are different4 ,the system is an harmonious one1 and each of its parts1 although able to do whatever any other part can do1 yet does one thing only3 it becomes an endoderm cell1 or an ectodermal cell1 or a part of the skeleton1 and so on2 what it does depends on its position with regard to the other cells4 ,an extensive manifoldness or diversity is produced1 but this was not the consequence of a preceding extensive manifoldness1 for in the preceding stage all the parts of the system were the same4 ,the manifoldness of the ovum or blastula--that potential manifoldness which became actual in development--must be an intensive manifoldness1 and admitting this we must abandon the comparison of the ontogenetic 7and1 of course1 phylogenetic7 processes with the phases of a physico-chemical system in process of transformation4 ,evolution is the transformation of an intensive into an extensive manifoldness4 ,more than this--much more than this--must be the difference between the transforming systems of physics and the evolving systems of biology4 ,there is a quality1 or sense1 or direction in all naturally occurring inorganic processes which is not like that of organic evolutionary processes4 ,we return now to the consideration of the second law of thermodynamics1 for only in this way can we approach the notion of the vital impetus4 ,if an energy-transformation occurs in inorganic nature1 that is to say1 if anything happens1 the transformation occurs or the thing happens because there were diversities in the system in which it occurred4 ,the condition for inorganic happening is that there must have been differences of energy in the different parts of the system3 in the most general sense there must have been diversity of the elements4 ,but with the transformation this diversity disappears1 or tends to disappear1 and it cannot be restored--that is1 differences of energy cannot again be established unless by a compensatory energy-transformation2 that is1 energy must be expended on the system from without by some external agency4 ,whatever else physics shows us it shows us an unitary universe1 that is1 an universe in which anything that happens affects1 to some extent1 all the other parts4 ,therefore the diminution of diversities1 or energy-differences1 is something that cannot be undone1 or compensated1 for there is nothing without the universe4#cb ,everything that happens in our universe reduces the possibility of further happening4 ,we desire1 at the risk of reiteration1 that this principle of energetics should be perfectly clear3 inorganic happening1 of whatever kind it may be1 is a case or consequence of the second law of energetics--is the second law itself in a sense4 ,all energy-transformations occur because energy-differences are being diminished1 because diversities are being abolished4 ,this is the sense1 or quality1 or direction of inorganic phenomena4 #cb ,it is assumed that the universe is a finite one4 ,if it were infinite the whole discussion becomes meaningless1 and we must give up this and other problems4 ,it is not the direction of organic evolution4 ,in the development of the individual organism what we most clearly see is the progressive increase of diversity of the parts4 ,in phylogenetic evolution one1 or a few1 simple morphological forms of life have become1 and are becoming1 indefinitely numerous morphological forms4 ,diversity is continually increasing4 ,if we cling to the mechanistic view of life1 we must suppose that the diversity of the fully developed organism1 or that of the organic world with all its species1 was also the diversity of the fertilised ovum or that of the primitive life-substance in another phase4 ,then we commit ourselves to all the crudities of modern speculations on heredity4 ,with this increasing diversity of form there is a concomitant segregation of energy4 ,we see as clearly as possible that the tendency of all inorganic happening is the transformation of potential into kinetic energy1 and the equal distribution of this kinetic energy throughout all the parts of the system in which the happening occurred4 ,on the other hand1 the tendency of organic happening is the transformation of kinetic energy into potential energy1 7#a7 in the stores of chemical compounds which result from the metabolism of the green plants1 and which are capable of yielding energy again2 and 7#b7 in the results of the instinctive or intelligent activities of the animal's organism4 ,the first result of organic evolution is clearly to be traced and needs no further explanation1 the second is apparent on reflection1 but is perhaps not clearly apprehended in all its significance by the student of biology and physics4 ,organic evolution is the process which has had1 or is having1 for its tendency the development of the putrefactive and fermentation bacteria1 the chlorophyllian organisms1 the ,arthropods1 and man and other mammals4 ,all that we have said has been futile if this teleological description of the evolutionary process has not been clearly suggested4 ,the indefinitely numerous forms of life that have appeared on the earth in the past1 and are now appearing1 seem to be experiments most of which have been unsuccessful4 ,only in the organisms mentioned1 organisms which are complementary in their metabolic activities1 has life been successful in manifesting itself in activities which are compensatory to those of inorganic nature4 ,the energy which is dissipated in the radiation of the cooling sun is again made potential in the form of the carbohydrates1 synthesised from water and carbon dioxide by the agency of the chlorophyllian organisms1 and this energy accumulates4 ,it is employed by the instinctive and intelligent animal1 in that it is used as food and converted into bodily energy1 which can then be utilised for any purpose that is contemplated4 ,these plant substances taken in by the animal as sources of energy are broken down into excretory substances1 which are further broken down by the metabolic activity of the fermentation and putrefaction bacteria1 and become the substances used as foods by the chlorophyllian organisms4 ,if the activities of man were only those of undirected or misapplied muscular movements 7as indeed most of his activities have so far been71 then cosmic energy would truly be dissipated after it had become the energy of organisms4 ,but does not all the history of man point to his ever-increasing activity in the conquest over nature1 that is1 the effort to hoard and employ natural sources of energy1 and to arrest its tendency towards dissipation8 ,it must be admitted that the past history of human civilisation has been almost entirely that of the irresponsible exploitation of natural resources--for it has been founded on the thoughtless and wasteful utilisation of energy which was made potential by the plant and animal organisms of the past4 ,man1 the hunter1 maintained himself and multiplied by the destruction of other animals or plants1 or by the mere collection and utilisation of naturally occurring fruits and other plant-substances4 ,during historic times the bison and other animals have almost become extinct owing to his ruthless activity1 just as in our own days the whale1 sole1 and turbot are disappearing before the activity of the machine-aided fisherman4 ,industrial man has been successful with his factories and railroads and steamships1 and his electrical power and transport1 only because he has been able to utilise the stores of energy contained in the coal and oil accumulated in the rocks of the earth4 ,the progress of civilisation has been a progress rendered possible by discovery and invention1 and by the application of the knowledge so obtained to the practical things of human life1 but in this speculation and its application two different things are indicated4 ,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 activity2 but the object of the 8entrepreneur0 or 8organiser0 or the 8captain of industry0 has been to employ these results of thought to the irresponsible exploitation and the selfish depletion of natural sources of energy4 ,just as the bison and other animals have disappeared or are disappearing before the hunter and fisherman1 so the stores of coal and oil are disappearing before the activities of commerce4 ,it has been said that the triumphs of industrialism are only the triumphs of the scientific childhood of our race4 ,human effort has so far only contributed to the general dissipation of natural energy4 ,yet just as man1 the hunter1 has been succeeded by man1 the agriculturalist1 so this irresponsible depletion of natural wealth must be succeeded by the endeavour to retard1 and not to accelerate1 the degradation of energy4 ,plants and animals which were simply killed by primitive man are now sown and harvested1 or cultivated and bred2 so that the energy of solar radiation1 which formerly ran to waste1 so to speak1 is now being fixed by the metabolic activity of the green plants of our crops and harvests4 ,rainfall and winds1 tides and rivers1 all represent energy primarily derived from solar radiation and from the orbital and rotatory motions of the earth and moon4 ,this energy even now is almost entirely dissipated as waste1 irrecoverable1 low-temperature heat2 but more and more as our stores of coal and oil are being depleted1 the attention of men is being directed to these sources of kinetic energy4 ,waterwheels and windmills1 and the more effective mechanisms that must be evolved from these primitive motors1 will capture this waste energy and convert it into the kinetic energy of machines serviceable to man1 or into the potential energy of chemical compounds capable of storage and future utilisation4 ,the study of radio-activity has made us acquainted with the enormous stores of potential energy locked up in the atoms1 and if it ever should become possible to utilise this by the disintegration of these particles1 the downward trend of natural energetic processes will further be retarded4 ,life1 when we regard it from the point of view of energetics1 appears therefore as a tendency which is opposed to that which we see to be characteristic of inorganic processes4 ,the direction of the latter is towards the conversion of potential into kinetic energy1 and the equal distribution of the latter throughout all the parts of the universe4 ,the direction of the tendency which we call life is towards the conversion of kinetic into potential energy1 or towards the establishment and maintenance of differences of kinetic energy1 whereby the latter remains available for the performance of work4 ,in general terms1 the effect of the movement which we call inorganic is towards the abolition of diversities1 while that which we call life is towards the maintenance of diversities4 ,they are movements which are opposite in their direction4 ,what is cosmic evolution8 ,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 of stages1 each phase of the series being marked by a progressive decrease of diversity1 that is1 by some degradation of energy4 ,two main series of hypotheses accounting for the present condition of the universe seem to have been the result of physical investigation3 7#a7 the origin of discrete solar and planetary bodies by a process of condensation of a gaseous nebular substance2 and 7#b7 the origin of the same systems by aggregations of meteoric dust4 ,plausible as is the nebular hypothesis on first consideration1 it fails when it is subjected to minute analysis4 ,what is a gaseous nebula8 ,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 states4 ,but it has been pointed out that we cannot be certain that the gaseous nebul known to astronomy are hot1 or even that they gravitate4 ,the great nebula in ,orion1 it is stated1 is at an enormous distance from us1 and making a minimal estimate of this distance the volume of the nebula must still be incredibly great4 ,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 own4 ,assuming that all this matter is contained in the great nebula in ,orion 7and obviously only a small portion of it can be so contained71 we find on calculation that the 8gas0 so formed would be much less dense than even the trace of gas contained in a high vacuum artificially produced4#cc ,how1 then1 can we speak of such a body as this nebula as an extended mass of hot gas1 cooling and gravitating as it loses heat8 #cc ,its density would be #a_/7eh #ajh7th that of our atmosphere4 ,even on the other hypotheses1 those of the formation of discrete suns and planets by the aggregation of meteoric dust1 and the compensatory dispersal of such dust by radiation pressure1 apparently insurmountable difficulties arise4 ,all such hypotheses as we have indicated assume material substance and modes of energy-transformation similar to those that we study in laboratory processes1 and all such hypotheses involve the notion of the degradation of energy4 ,so long as we suppose that all cosmic processes are transformations of extended systems of material substances we must assume that energy is dissipated at every stage of the transformation1 and whenever we assume this we admit that the processes are irreversible ones1 and that the material universe as a whole tends towards a condition of inertia4 ,yet this1 we see1 cannot be true1 for the universe teems with diversity4 ,is the progress towards the ultimate state of inertia an asymptotic one1 as ,ward suggests8 ,this does not help us1 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 developed4 ,somewhere or other1 it has been said1 the second law of thermodynamics must be evaded in our universe4 ,how can it be evaded8 ,that movement or progress which we call inorganic is a movement of energy-transformations in one direction--towards their cessation4 ,it is a movement which we can easily reverse in imagination4 ,a cigarette consumed by a smoker represents the downfall of energy3 the cellulose and oils of the tobacco burn with the liberation of heat1 and the formation of water1 carbon dioxide1 and some soot2 and this is what happens when potential energy contained in an organised substance becomes converted into kinetic energy4 ,now1 the opposite process can clearly be conceived--it can even be pictured4 ,if we make a kinematographic record of the smoking of the cigarette and then reverse the direction of motion of the film1 we shall see the particles of soot recombining to form the substance of the cigarette1 and we can imagine the concomitant combination of the water1 carbon dioxide1 and other substances formed during the combustion with the absorption of kinetic energy4 ,this is not a mere analogy1 for the same reversal of ordinary chemical happening occurs whenever a green plant builds up starch from the water and carbon dioxide of the atmosphere and it also occurs whenever a chemical synthesis of an 8organic0 compound1 like that of urea by ,whler1 or that of the sugars by ,fischer1 is brought about in the laboratory4 ,in all such syntheses the experimenter reverses the direction of inorganic chemical happening4 ,he may cause endothermic chemical reactions1 reactions accompanied by the absorption of available energy1 to take place1 and in these kinetic energy becomes transformed into potential energy4 ,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 conclusion4 ,sugar is built up in the cells of the green plant from the inorganic compounds1 water1 and carbon dioxide1 and is therefore a compound prepared by life--that of the plant organism4 ,but sugar may also be built up in the laboratory from inorganic compounds1 which may further have been synthesised by the chemist from their elements4 ,does this destroy the distinction between compounds formed by the agency of the organism and those formed by inorganic agencies8 ,obviously it does not1 for in the green plant the sugar was formed as the result of the vital agency of the living chlorophyllian cell1 while in the laboratory it was built up because of the intelligence of the experimenter4 ,apart from this intelligence or vital agency1 the series of chemical transformations beginning with the elements carbon1 oxygen1 and hydrogen1 and ending with the substance sugar1 would not have occurred4 ,we have no right to say1 therefore1 that such syntheses destroy the distinction between the organic and the inorganic4 ,what they do indicate is the distinction between the tendency expressed by the second law of thermo-dynamics 7inorganic processes71 and those that occur as the result of direction conferred upon processes taken as a whole1 either by the vital agency of the living cell1 or by the intelligence of man 7vital processes74 ,the direction1 therefore1 that may be conferred on a series of physico-chemical processes is what we must understand by the 8vital impetus0 of ,bergson1 or the 8entelechy0 of ,driesch4 ,it must be admitted that it is difficult to describe more precisely than we have done above what is meant by these terms4 ,it is with very much the same embarrassment that is experienced by the physicist when he has to apply the concepts of mass and inertia1 in their eighteenth-century meaning1 to his description of an universe in terms of electro-magnetic theory1 that we seek to describe the modern concept of entelechy4 ,yet the physicist has had to make this step forward1 and the same adventure awaits the biologist if the speculative side of his science is to make further progress1 and if he is disinclined to make his science an appendage of physics and chemistry4 ,entelechy does not correspond to the eighteenth-century notion of a 8vital force10 or to the 8soul0 of ,descartes1 as the writer of a book on evolutionary biology seems to suggest4 ,it is a concept which is forced upon us mainly because of the failure of mechanistic hypotheses of the organism4 ,if our physical analysis of the behaviour of the developing embryo1 or the evolving race or stock1 or the activities of the organism in the midst of an ever-changing environment1 or even the reactions of the functioning gland1 fail1 then we seem to be forced to postulate an elemental agency in nature manifesting itself in the phenomena of the organism1 but not in those of inorganic nature4 ,this argument per ignorantium possesses little force to many minds3 it makes little appeal to the thinker1 or the critic1 or the general reader1 but it is almost impossible to over-estimate the appeal which it makes to the investigator1 as his experience of the phenomena of the organism increases1 and as he feels more and more the difficulty of describing in terms of the concepts of physics the activities of the living animal4 ,we may1 however1 attempt to illustrate mainly by analogy what is meant by ,driesch's entelechia1 a more precise concept than is ,bergson's lan vital4 ,we return to the consideration of the behaviour of the embryo at the close of the process of segmentation4 ,the organism at this stage consists of a number of cells organically in continuity with each other1 either by actual protoplasmic filaments or by the apposition of parts of their surfaces1 thus constituting 8semi-permeable0 membranes4 ,these cells are all similar to each other1 both structurally and functionally4 ,it does not matter that modern 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 blastomeres2 and it does not matter that these hypotheses are compelled to assume that a part of the original germ-plasm remains intact1 being destined to form the gonads of the adult animal4 ,these are hypotheses invented to account for the differentiation of the embryo in terms of eighteenth-century physics and chemistry1 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 segmentation4 ,further1 it is certainly the case that any one cell of the early embryo can give rise to any part of the larva4 ,the segmented embryo is therefore a system of parts1 all of which are potentially similar to each other4 ,but actually each of these parts has a different fate in the process of the development of the larva1 and this fate depends on what is the fate of the adjacent cells4 ,there is also a plan or design in the development of the embryo--that is1 a very definite structure results from this process--and each of the cells shares in the evolution of this design4 ,the system of cells is therefore an harmonious equipotential system4 ,the cells themselves are not the ultimate parts of this system1 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 compounds1 but we must never forget that it is the dead cell which we thus subject to analysis1 and not a living organism4 ,let us call these supposed chemical constituents of the living cells the elements of the system2 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 8homogeneous0 manner very like the distribution which is effected on shuffling a pack of cards4 ,but as differentiation proceeds1 the elements of this system become unequally distributed1 and the diversity becomes greater and greater1 attaining its maximum when the definitive tissues and organs of the adult become established1 just as at the close of a game of bridge the cards acquire a particular arrangement indicative of a very definite plan which was present in the minds of the players shortly after the game began4 ,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 other1 and by the reaction of the environment4 ,but1 given a homogeneous arrangement of elements capable of interacting with each other1 then only one final phase can be supposed to be produced4 ,a mixture of sulphur1 carbon dust1 copper and iron filings raised suddenly to a high temperature will only interact in one way1 and the final phase of the system will depend on the composition of the mixture1 on the temperature1 and on the conduction of heat into the mixture in the initial stage of heating4 ,a mixture of chloroform and water shaken up in a bottle is at first a 8homogeneous0 mixture of the particles of the two substances1 but under the influence of gravity the liquids separate from each other and form two distinct layers1 each of which will contain in solution some of the other liquid4 ,a homogeneous mixture of different substances therefore becomes a heterogeneous arrangement in the inorganic system1 as in the organic one1 but while we can predict the former one we cannot predict the latter4 ,we can express the result of the combination of the elements of the inorganic mixture as something that depends on chemical and physical potentials1 but this is quite impossible in the case of the development of the embryonic system4 ,it is not only that our knowledge of the developmental process is imperfect3 the distinction between the two processes of differentiation is a fundamental one4 ,a change in the conditions under which the inorganic system differentiates leads of necessity to a different final phase1 but a change in the conditions under which the embryo develops need have no such effect4 ,if some unforeseen occurrence takes place--some artificial interference with the process of segmentation1 which could never have been experienced in the racial history of the organism--a regulation by the parts of the embryo occurs1 and the final phase of development may be the same as if no interference had been experienced4 ,that which is operating in the development of the embryo is something that is permitting1 or suspending1 or arranging physico-chemical reactions4 ,let us think of the developing embryo merely as an aggregation of substances contained in an inorganic medium3 the segmented frog's egg floating on the water at the surface of a pond is an example4 ,as an inorganic system its fate is determined4 ,autolysis of the substances in the cells will occur and the proteids will break down with the formation of amido-bodies1 while other chemical changes1 strictly predictable if our knowledge of organic chemistry were more complete than it is1 would also occur4 ,putrefactive and fermentative bacteria will attack the proteids1 fats1 and carbohydrates1 and in the end our aggregation of chemical substances will become an aggregation of much simpler compounds--water1 carbon dioxide1 marsh gas1 sulphuretted hydrogen1 phosphoretted hydrogen1 ammonia1 nitrates1 etc41 all of which will dissolve in the water of the pond1 or will diffuse into the adjacent atmosphere4 ,but in the living embryo this is not what occurs3 an entirely different1 and much more complex1 arrangement of the chemical substances originally present in the segmented egg1 or at least a physical and chemical re-arrangement1 is brought about4 ,the entelechy of the developing embryo prevents some reactions from occurring and directs the energy which is potential in the system towards the performance of other reactions4 ,two analogies1 suggested by ,driesch1 will perhaps make the rle of entelechy more clear4 ,a workman1 a heap of bricks1 some mortar1 some food1 and some oxygen constitute a system in the physico-chemical sense4 ,from his heap of bricks and mortar the workman may build one of several different kinds of small house1 or he may perhaps construct several walls without any definite arrangement1 or he may merely convert one 8disorderly0 heap of bricks and mortar into another 8disorderly0 heap4 ,in the same way a man1 a case of movable types1 some food1 and some oxygen constitute another system4 ,the initial phase of this system consists of the compositor1 his food1 and some fifty-odd boxes of types1 each of which contains a large number of similar elements4 ,a final phase of the system may be the arrangement of the types to form an epic poem1 or a series of dramatic criticisms1 or a meaningless jumble of correctly spelt words4 ,in all these cases the same amount of energy was expended3 the bricklayer used up the same quantity of food and oxygen and excreted the same quantities of water1 carbon dioxide1 and urea1 whether he made a house1 or a small chimney1 or a heap of bricks without architectural arrangement4 ,the system of bricks and mortar acquired during the process of differentiation a gradually increasing complexity2 while in the case of the type-setting the diversity of arrangement acquired in the final phases may be of a very high order4 ,yet the intelligent mind of the worker remained in either case unchanged4 ,let us consider further a man walking along the ties1 or sleepers1 of a railway track4 ,the ties are at variable distances apart1 so that the steps of the walker must vary in length1 being sometimes closer together1 sometimes further apart4 ,the mean step has a definite length and requires the expenditure of a certain amount of energy1 and the condition that the man takes sometimes 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 length1 for the additional energy that is required for the long steps is saved from the short ones4 ,that which operates here is the power of regulation exercised by the walker regarded as a mechanism4 ,there is no purely inorganic process precisely similar to this4 ,it might be thought that the governor of a steam engine did very much the same thing1 admitting more steam into the cylinder when the load on the engine increases1 and vice versa4 ,but the governor is a mechanism designed to compensate for variations that are given in advance4 ,in the case of the man walking on the railway track1 entelechy operates by suspending energetic happening 7the muscular contractions of the short steps7 when necessary1 and allowing it to proceed when necessary4 ,entelechy itself1 whatever it may be1 need not be affected by these regulations4 ,the organism is therefore an aggregation of chemical substances arranged in a typical manner4 ,these substances possess energy in the potential form1 capable of undergoing transformation so that they may give rise to other chemical substances--secretions1 for instance--or to energy in the kinetic form1 that is1 the movements of muscles4 ,in the resting organism these transformations do not take place3 the energy remains potential1 so that chemical happening is suspended4 ,in the unfertilised ovum1 for instance1 nothing happens although all the potentialities of segmentation are contained in the cell4 ,if reactions did occur in consequence of the chemical potentials contained in the substances of the cells1 the progress of these would be such as to lead to the formation of substances in which potential energy was minimal1 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 changes4 ,this is not what happens in the differentiation of the ovum3 the developing cell forms new substances from those of its inorganic medium similar to the substances of which it is already composed1 and then these substances become arranged to produce the specific form of the organism into which the ovum is about to develop4 ,all hypotheses which attempt to describe the functioning of the differentiating ovum1 or the functioning organism1 in terms of the physical concepts of matter and energy alone1 fail on being subjected to close analysis4 ,the manifestations of the life of the organism are1 it is said1 particular 8energy-forms10 of the same order as light1 heat1 chemical and electrical energy1 etc4 ,all these energy-forms are 8concatenated10 that is1 each can be converted into any of the others4 ,a particular frequency of the vibration of the ether can be converted into a movement of the molecules of a material body1 and so become heat1 while chemical energy may become converted into electrical energy1 or vice versa1 and so on4 ,it is said that life may be merely a transformation of some 8energy-form0 known to us3 the potential energy of food may be converted into 8biotic energy10 and this may then manifest itself in the characteristic behaviour of the organism4 ,this is the method of physical science4 ,energy continually disappears from our knowledge3 the mechanical energy which was employed to carry a weight to the top of a hill1 or that which raises a pendulum to the highest point of its swing1 apparently disappears4 ,if we pass a current of electricity through water1 energy disappears1 for it requires more current to pass through water than through a piece of metal of the same section4 ,in these and similar cases physics invents potential energies in order to preserve the validity of the law of conservation4 ,the kinetic energy of the weight1 or that of the swinging pendulum1 becomes the potential energy of the weight resting at the top of the hill1 or that of the bob of the pendulum at its highest point1 while the electrical energy that has apparently been lost becomes the potential energy of the changed positions of the molecules of oxygen and hydrogen4 ,this assumption that the visible kinetic energy of motion becomes converted into the invisible potential energy of position is justified by our experience1 for 7neglecting dissipation7 we can recover this lost energy1 in its original quantity1 from the condition of the bodies which became changed physically when the kinetic energy disappeared4 ,apply the same method to the phenomena of the organism and suppose that the chemical potential energy of the food consumed becomes converted into the kinetic energy of motion of the parts of the body3 we are justified in this assumption by the results of physiology4 ,but then some of this chemical energy undergoes a transformation of quite another kind and becomes the 8biotic energy10 which is apparently that which is in us which enables us to perform regulations1 or establishes that condition which we call consciousness4 ,we cannot say exactly what this 8biotic energy0 is1 or what are the steps by which the energy of food becomes converted into it2 but no more can we say what is electrical energy1 nor what are the steps by which chemical energy becomes converted into it4 ,thus our ignorance of the precise nature of the energy-transformations of inorganic things--an ignorance which is all the while disappearing--becomes the excuse for a comparison of these with vital transformations1 and for the assumption that there is a fundamental similarity in the two kinds of happening4 ,less is assumed in the assumption of an entelechian agency than in assuming that the manifestations of life are the consequences of a vital 8energy-form10 different from inorganic forms1 though belonging to the same order1 inasmuch as it may be concatenated with these inorganic energy-forms4 ,we need not suppose that a particular kind of transformation occurs only in the sphere of the organic3 all that we need assume is that1 by some agency inherent in the activities of the organism1 chemical reactions that would occur if the constellation of parts were an inorganic one are suspended4 ,nothing unfamiliar to physical science is involved in this assumption4 ,hydrogen and chlorine1 gases that combine together when mixed with the production of heat and light1 may be mixed under conditions such that the combination may be delayed for an indefinite time4 ,iron which dissolves in nitric acid may nevertheless be brought into the 8passive0 form when it remains in contact with the re-agent but is not dissolved by it4 ,enzymes which are in contact with the walls of the alimentary canal do not dissolve these membranes so long as the tissues are alive1 and they do not dissolve the food stuff until they have been 8activated40 ,oxygen which is contained in the tissues does not oxidise the tissue substances until an enzyme or a catalase has exerted its influence4 ,more and more1 as physiology has become more searching in its study of the functions of the animal1 has it sought to explain the metabolic processes by assuming the intervention of enzymes1 until the number of these substances has become legion1 and much of the original simplicity of the notion of ferment-activity has been lost4 ,but why do not these enzymes1 if they are always present in the tissues1 always act8 ,they must be activated1 says modern physiology2 that is1 the enzyme really exists in the tissues as a 8zymogen0 or a substance which is not1 but which may become1 an enzyme2 or they exist as 8zymoids10 that is1 substances which appear to be chemically enzymes1 but which must be activated by 8kinases0 before they can become functional4 ,undoubtedly it is along these lines that physiology is making advances1 has increased our knowledge of the activities of the animal1 and is conferring on the physician greater power of combating disease2 but the hypotheses of the activity of the enzymes is obviously one which has been based on the results of the physico-chemical investigation of inorganic reactions1 and it has taken the precise form it has because of the attempted analogy of many metabolic processes with catalytic processes4 ,why do the inert zymoids become activated by the kinases just when they are required by the general economy of the whole organism8 ,we do know that kinases are produced by the entrance of digested food into certain parts of the alimentary canal1 and that these kinases are carried in the blood stream to other parts where they activate the zymoids already there4 ,but of the nature of the machinery by means of which all this is effected physiology gives us no hint1 and it is an assumption that the mechanism involved is a purely physico-chemical one4 ,suppose we say that the entelechy of the organism possesses the power of suspending the activation of the enzyme1 that is to say1 of arresting the drop of chemical potential involved in the process of the hydrolysis of 7say7 a proteid4 ,when this process of hydrolysis is necessary in the interest of the organism entelechy can then institute the reaction which it has itself suspended3 all this is in accord with the law of conservation4 ,entelechy does not cause chemical reactions to occur which are 8impossible03 it could not1 for instance1 cause sulphuric acid and an alkaline phosphate to react with the formation of hydrochloric acid4 ,but chemical reactions which are possible may be suspended1 and suspended reactions may then become actual when this is necessary in the interest of the organism4 ,entelechy is therefore not energy1 nor any particular form of energy-transformation1 and in its operations energy is neither used nor dissipated4 ,in all that it does the law of conservation holds with all the rigidity with which we imagine it to hold in purely inorganic happening--at least we need not assume that it does not hold--and this is the essential difference between the entelechian manifestations and the manifestations of the 8vital0 or 8biotic0 forces or energies of the historic systems of vitalism4 ,it is essentially arrangement1 or order of happening1 and it is therefore a non-energetic agency4 ,the workman who may build half-a-dozen zigzag walls1 or an archway1 or a small house1 from the same materials and with the expenditure of the same quantity of energy1 is indeed an energetical agent1 but he is more than that4 ,he is a physico-chemical system in which any one phase is not determined by the preceding phase4 ,different results may arise from the same initial arrangement of materials and energies1 and this is because the system contains more than the material and energetical elements4 ,it contains the intelligence or entelechy of the workman4 ,what is this entelechy8 ,sooner of later in all our speculation on organic happening we must cross the arbitrary line which divides the space of our concepts from the non-spatial--the intensive from the extensive4 ,just as the physicists have left materiality behind them in their speculations and treatment of the phenomena of radiation1 so biology must attempt to trace back the materiality of the organism to something which is immaterial4 ,just as physics has now abandoned the idea of matter as something which consists of discrete particles1 or atoms1 having extension in space1 and which therefore exclude each other1 so biology must seek the origin of living things1 not in the hypothetical 8biophorid10 or other ultimate living material particles1 but in the intensive manifoldness of entelechy4 ,there is a manifoldness in the potentiality which the simple and homogeneous ovum possesses of becoming the heterogeneous adult organism4 ,this manifoldness1 says the mechanistic biologist1 consists of a manifoldness of extended material units1 the determinants of ,weismann1 and the organisation that arranges these units--what is this organisation8 ,it cannot be a three-dimensional machinery1 as all close analysis of the facts of development and regulation shows4 ,it is then something that is intensive1 something which is not in space1 but which acts into space1 and the result of which is manifested in spatial material arrangements and activities4 ,vague and incomprehensible as is this concept of the activities of the organisms1 it is only vague and incomprehensible because we have been accustomed to express all chemical and physical happening in terms of the fundamental concepts of matter and energy1 and the science of the last two centuries has left us with a terminology which applies strictly to operations in which only these concepts are involved4 ,but if1 as all minute analysis of vital phenomena shows1 the search for the antecedents of some energetic1 material1 extended system of elements in a preceding energetical1 material1 extended system of elements only leads to confusion and contradictions1 then this concept of an agency which is neither energetic1 nor material1 nor spatial must be formulated4 ,entelechy1 then1 is not energy1 but rather the arrangement and co-ordination of energetic processes4 ,it is not something that is extended in space1 but something which acts into space4 ,it is not material1 but it manifests itself in material changes4 ,it is a manifoldness1 or organisation1 but the manifoldness is an intensive one4 ,compare this definition with the notion of the ether of space now accepted by the mathematical physicists1 and it will be seen that our speculations are similar to those of the physicists1 and1 like them1 the test of their reality and usefulness is to be justified pragmatically4 99 99 99 99 99 ,we may now attempt a formal description of the organism based on the discussions of the previous chapters4#cd #cd ,this description is largely an expansion of ,driesch's 8,analytical definition of the individual living organism40 ,the reader should note also that it includes the ,bergsonian idea of duration1 and that of the organism as a typical phase in an evolutionary flux1 as parts of the description4 ,the organism is a typical constellation of physico-chemical parts or elements4 ,that is to say1 it is an object in nature possessing a definite form1 which is the result of the arrangement of its tissues4 ,each tissue is again an arrangement of cells1 and each cell is a complex of chemical substances4 ,the organism therefore resembles1 so far as our definition goes1 an inorganic crystal4 ,but it is the typical organism that we are considering1 and this is a pure conception1 for our typical organism does not occur in nature4 ,the organisms that are accessible to our observation are constellations of physico-chemical parts1 but these constellations tend continually to deviate from the conceptual arrangement4 ,progressive variation from the type is something that distinguishes the organic constellation from the inorganic one4 ,the organism is an entity in which energy-transformations of a particular nature are effected4 ,these transformations raise energy from a state of low1 to a state of high potential4 ,this is the general tendency of terrestrial life1 and it is expressed most fully in the metabolism of the green plant4 ,the energy-transformations that are effected here are those in which the kinetic energy of radiation is employed to build up chemical compounds of high potential1 from inorganic substances incapable in themselves of undergoing further transformations4 ,the general tendency of all inorganic transformations is towards inertia4 ,in them energy is not destroyed1 but it is dissipated3 it becomes uniformly distributed throughout material bodies as the un-co-ordinated motions of the molecules of which those bodies are composed1 and it ceases to be available for further transformations4 ,the green plant reverses this transformation1 and accumulates energy in the form of chemical compounds of high potential4 ,inorganic processes are those in which available energy becomes unavailable1 and this unavailable energy can only become available again if a compensatory energy-transformation is effected4 ,life is that which effects these compensatory energy-transformations4 ,the organism is a constellation capable of indefinite growth by dissociation4 ,that is to say1 it is a constellation which reproduces itself in all its specificity4 ,growth consists in the separation from the organism of a part1 or reproductive cell1 which divides 7or dissociates7 repeatedly1 each dissociated part growing again in mass by the addition of substances similar to its own1 but which are taken from a medium dissimilar in composition to itself4 ,the aggregate of parts so formed then differentiates so that the constellation is reproduced in all its specificity4 ,there is nothing precisely similar to this in inorganic happening4 ,the growth of a crystal consists simply of the accretion of elements similar in nature to those of the growing body1 and there is no differentiation4 ,the organism exhibits autonomy4 ,it is a constellation which persists in the midst of an ever-changing environment1 and the typical organic form remains the same1 although the material of which it is composed undergoes continual change4 ,there are inorganic entities which resemble the organism in this respect3 the form of a cyclone or atmospheric disturbance1 for instance1 remains the same even though the air of which it is composed is continually changed4 ,but the form of the organism does not vary strictly with the changes in the environment in which it is placed1 for it may respond to an environmental change by a regulation1 or compensatory change in form or functioning1 the effect of which is to maintain the constellation in all its specificity4 ,the regulation is not a complete or perfect one1 for environmental changes do1 to some extent1 produce changes in the organic constellation1 but there is no functionality between the environmental change and the organic response4 ,in inorganic happening a change in one part of a transforming system necessarily determines the nature and extent of the changes that occur in the other parts of the system4 ,the organism is a centre of continuous action4 ,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 animals4 ,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 inorganic4 ,an inorganic system which transforms energy is either one which tends continually towards stability1 or it is a machine made by man for a definite purpose1 and it is therefore a system involving a teleological idea4 ,an organic centre of action is one in which energy-transformations proceed without cessation4 ,in the plant organism the energy-transformations represent1 with the exception of the reproductive processes1 the whole activity of the organism4 ,in the animal organism they are accessory to regulated and purposeful motile activity1 that is1 muscular action4 ,the object of this muscular activity varies with the stage of evolution attained by the animal4 ,its sole object in the lower animal is that of individual or racial preservation4 ,living in an organic and inorganic environment which is always hostile and tends continually towards its destruction1 the whole activity of the organism is directed to the attempt to master this environment3 it struggles for its individual existence1 and that of its offspring4 ,the activities of man are also these1 but they are more than these1 for1 knowing that physical processes tend continually towards inertia1 he seeks to control these processes1 and to preserve the instability of nature on which the possibility of further becoming depends4 ,the activity of the organism1 whether it be the energy-transformations of the plant or the motile activities of the animal1 are directed and regulated activities4 ,the activity of the organism is not a functional activity in the sense that the activity of a dynamo is a function of the nature of the machine1 and of the nature and quantity of the energy supplied to it4 ,the nature of the activity of the organism is regulated autonomously by purposes which it 8wills0 to carry out4 ,the organism is a phase in an evolutionary flux4 ,categories of organisms--varieties1 species1 genera1 etc4--are fictions4 ,they are arbitrary definitions designed to facilitate our description of nature4 ,they are types or ideas4 ,in constructing them we follow the method of the intellect1 and we represent by immobility that which is essentially mobile and flows4 ,between the fertilised egg and the senile organism there is absolute continuity4 ,our description of the individual organism is a description of it at a typical moment of its life-history1 and this description includes all that has led up to1 as well as all that will fall away from1 the morphology at this particular typical moment4 ,even then the arbitrarily defined organism is only a phase4 ,in defining it we arrest1 not only the individual1 but also the racial1 evolutionary flux4 ,the specific morphology is that of a typical moment in a racial flux4 ,leading up to it at this moment are all the variations that have joined it with its ancestry1 and leading away from it will be all the variations that will convert it into its descendants4 ,the individual and racial developments are true evolutions4 ,they are the unfolding of an organisation which was not expressed in a system of material particles or elements interacting with each other1 and with the elements of the environment1 but which we must seek in an intensive1 non-spatial manifoldness4 ,in the evolutionary flux the changes are non-functional ones1 that is to say1 any phase1 whether it be one in an individual or a racial development1 is not merely a rearrangement of the elements of the preceding phases1 as in the case of a transforming system of material particles and energies4 ,there is inherent1 spontaneous variability4 ,the organism endures4 ,that is1 all its activities persist and become part of its organisation4 ,it does not matter whether or not we decide that characters which are acquired are transmitted1 nor does it matter whether or not we conclude that the environment is the cause of these acquirements4 ,some time or other in the individual or racial history new characters arise by the activity of the organism itself1 and these characters either persist in an individual or in a race4 ,they endure4 ,all its activities1 even its thoughts1 persist and form the experience of the animal--an experience which continually modifies its conduct4 ,in man those true acquirements1 the results of education and of investigation1 persist as written language1 or as tradition1 even if they are not inherited4 ,duration is not time4 ,the mathematician does not employ1 in his investigations1 intervals of duration4 ,when he relates something which is happening now to something which happened some time ago he employs the differential co-efficient dy_/dx1 so that the interval between the two occurrences becomes an 8infinitesimal0 one4 ,when the astronomer predicts events that will happen some years hence1 or describes those that happened some years ago1 he is really describing things that are all there at once1 so to speak1 things which are given4 ,if we unfold a fan1 stick by stick1 we see the separate members in succession1 but they are all there1 and we can1 if we like1 see them all at once4 ,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 other4 ,things become extended in time as they become extended in space4 ,whether occurrences capable of analysis by the methods of physics are what we call past or future occurrences1 they are all given1 in that each of them is only a phase of the others4 ,duration belongs to the organism4 ,the past is known because all that has occurred to the organism still persists in its organisation4 ,the future is unknown because it has still to be made4 ,duration is therefore a vector--something having direction1 and the organism progresses out of the past into the future4 ,it grows older but not younger4 99 99 99 99 99 ,such appears to be the nature of life4 ,can we discuss the problem of its origin8 ,did life originate on our earth8 ,we must first consider what we mean when we speak of an origin4 ,the organic world of the present moment1 with all its environment--that is to say1 the totality of organisms on the earth1 with all the materials which they can utilise in any way1 the energy of radiation from which they ultimately derive their energy1 and all the parts of the cosmos which interact with them--constitute a system in the physical sense4 ,the present condition of the organic world1 that is1 the kinds and numbers of organisms1 and their distribution1 and the distribution of the materials which they can utilise1 and the quantity and nature of the energy which is available to them1 are the present phase of this system4 ,all the conditions of life in the past1 that is to say1 the kinds1 and numbers1 and distribution of organisms1 and the quantity and nature of their environment at any time1 together formed phases of this system4 ,if there was a time when life1 as we know it1 did not exist1 then the materials and the energies1 which were antecedent to life when it did appear1 were also a phase of the system4 ,on a strictly mechanistic hypothesis there could be no origin3 there could only be a transformation of a system which was already in existence4 ,all that exists to-day was given then4 ,when1 therefore1 we speak of the origin of life from non-living materials we mean simply a transformation of those materials and energies4 ,there was a time1 it is said1 when life could not exist on the earth4 ,for the organism is essentially that aggregate of chemical compounds which we call protoplasm1 and this cannot exist at temperatures higher than #ajj ,c41 and it cannot function at temperatures lower than #j ,c4 ,it requires carbon dioxide1 and ammonia or nitrate1 as the materials for its constructive metabolism1 and there was a time when these compounds could not exist1 for they must have been dissociated by the heat of the gaseous nebula from which our earth originated4 ,the organism requires energy in the form of solar radiation of a particular frequency of vibration1 and there was a time when the sun's radiation was different from what it is now4 ,therefore life did not exist then4 ,even if we believe that life came to the earth as germs1 which existed previously in outer cosmic space1 this belief does not solve the problem1 which simply becomes transferred from our earth to some other cosmic body4 ,but life1 as we know it1 makes use of the materials and the energies which are available to it in the conditions in which it exists4 ,the plant organism obtains its energy from solar radiation because this is the most abundant source of terrestrial energy4 ,the human eye is most susceptible to light of a particular frequency of wave-length1 but this is the radiation that is most abundant in the light of the sun4 ,does this not mean that the organism has merely adapted itself to the material and energetic conditions in which it exists8 ,does it necessarily mean that because the conditions were very different life could not exist8 ,protoplasm could not exist at a temperature of several thousand degrees ,centigrade1 but does that mean that life1 which on any hypothesis of mechanism must be described in terms of energy1 could not exist in these conditions8 ,it must have had an origin1 says ,weismann1 because it has an end4 ,organic things are destroyed1 inasmuch as they disintegrate into inorganic things4 ,organisms die4 ,thus the organic process comes to an end1 and because it comes to an end it must have a beginning4 ,spontaneous generation of life is thus1 for ,weismann1 a 8logical necessity40 ,need this logical necessity exist8 ,the argument clearly implies that life is a reversible process4 ,organic things become inorganic1 and therefore inorganic things must become organic things4 ,the first statement is a fact of our experience1 but the second one would only be logically true if we were to postulate that the process of life1 whatever it may be1 is a reversible process4 ,but we must not postulate this if we are to hold to a physico-chemical mechanism1 for it is a fundamental result of physical investigation that all inorganic processes are irreversible3 reversible inorganic processes are only the limits to irreversible ones4 ,physical processes go only in one way1 and that organic substance is destroyed to the extent that it becomes inorganic is a particular case of this irreversible physical tendency4 ,now the mechanism of ,weismann must base itself on the concepts of physics and chemistry1 and it must postulate the origin of life from non-living substances4 ,why8 ,because life is a reversible process1 that is1 it exhibits a tendency which does not exist in inorganic processes4 ,clearly the logic is faulty6 ,and must we conclude that life has an end8 ,weismann himself suggests that nothing in the results of biology indicates that physical death is a necessity3 it is rather an adaptation4 ,the soma1 or body1 is the envelope of the germ-plasm1 and exposed as it is to the vicissitudes of an environment which is always hostile1 it becomes at length an unfit envelope4 ,but with the reproductive act the germ-plasm acquires a new soma1 and it is no longer necessary that the former one should continue to exist as an unfit envelope4 ,physical death therefore occurs as an adaptation serving for the best interests of the race4 ,the organism need not die1 for the germ-plasm may be a physical continuum throughout innumerable generations4 ,somatic death is only a destructive metabolism3 it is a catastrophic metabolism1 if we like4 ,we may legitimately discuss such problems as the origin of the protoplasm of the prototrophic organism1 or that of the chlorophyll-containing cell1 or that of the nerve-cell4 ,on the mechanistic view each of these conditions is a phase of a transforming physico-chemical system1 and it is within the scope of the methods of physical science to investigate the nature of these transformations4 ,but if the argument of this book is sound1 then the problem of the origin of life1 as it is usually stated1 is only a pseudo-problem2 we may as usefully discuss the origin of the second law of thermo-dynamics6 ,if life is not only energy but also the direction and co-ordination of energies2 if it is a tendency of the same order1 but of a different direction1 from the tendency of inorganic processes1 all that biology can usefully do is to inquire into the manner in which this tendency is manifested in material things and energy-transformations4 ,but the tendency itself is something elemental4 ,,appendix ,,mathematical ,,and ,,physical ,,notions#ce #ce ,it must be understood that some of the things dealt with in these appendices are very hard to understand by the reader acquainted only with the results of biological science4 ,we urge1 however1 that they are all relevant if biological results are to be employed speculatively4 ,,infinity ,what is really meant when the mathematician uses the concept of infinity in his operations8 ,suppose that we take a line of finite length and divide it into halves1 and then divide each half into halves1 and so on ad infinitum4 ,we make cuts in the line1 and these cuts have no magnitude1 so that the sum of the lengths into which we divide the line is equal to the length of the undivided line4 ,we can divide the line into as many parts as we choose1 that is1 into an 8infinite0 number of parts4 ,suppose that we are making a thing which is to match another thing1 and suppose that we can make the thing as great as we choose4 ,if1 then1 no matter how great we make the thing1 it is still too small1 the thing that we are trying to match is infinitely great4 ,substitute 8small0 for 8great10 and this is also a definition of the infinitely small4 ,clearly the idea of infinity does not reside in the results of an operation1 but in its tendency4 ,it inheres in our intuition of striving towards something1 but not in the results of our striving4 ,,functionality ,if we pour some mercury into a ,u-tube closed at one end1 the air in this end will be contained in a closed vessel under pressure4 ,we can increase the pressure by pouring more mercury into the open end of the tube4 ,we can measure the volume of the air by measuring the length of the tube which it occupies4 ,we can measure the pressure on this air by measuring the difference of length of the mercury in the two limbs of the tube4 ,by taking all necessary precautions we shall find that for each value which the pressure attains there is a corresponding value of the volume of the air4 ,we thus find the pressure values1 p#a1 p#b1 p#c1 p#d1 p#e1 etc41 and the corresponding volumes1 v#a1 v#b1 v#c1 v#d1 v#e1 etc41 and we may then plot these values so as to make a graph4 ,illustration3 ,,fig4 #bg4 ,in this figure the values represented along the horizontal axis are pressure-values1 and those represented along the vertical axis are volume-values4 ,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 argument4 ,for each value of the pressure1 or argument1 there is a corresponding value of the volume1 which depends on the pressure--let us call these values of the volume values of the dependent variable or function4 ,we can make arbitrary values of the pressure1 but whenever we do this the corresponding values of the volume are fixed4 ,we say1 then1 that the volume is a function of the pressure4 ,in general1 when we choose one value of an independent variable1 or argument1 there can be only one1 or a small number1 of values of the dependent variable1 or function4 ,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 argument4 ,there is a strict functionality between the two series of variables4 ,in the experiment we have chosen this functionality is expressed by the equation pv k7#a at71 where p is the pressure1 v the volume1 k and a constants1 and t is the temperature at which the experiment is carried out4 ,in a number of experiments like that which we have mentioned1 k1 a1 and t are the same throughout1 and this is why we call them constants4 ,we give p any value we like1 and then v can be calculated from the equation4 ,,rate ,,of ,,variation ,if we know the equation pv k7#a at71 we can find how much the volume changes when the pressure changes1 that is1 the rate of variation of v with respect to p4 ,but even if we don't know that this equation applies1 we can still find the rate of variation from our experiments4 ,we see from the graph that1 when the pressure increases from p#a to p#b1 the volume decreases from v#a to v#b but that if the pressure is again increased to p#c1 that is1 by a similar amount to the increase of pressure from p#a to p#b1 the volume decreases from v#b to v#c4 ,now we find1 by measurements made on the graph1 that the decrease v#a to v#b is greater than the decrease v#b to v#c1 and the latter decrease is greater again than the decrease from v#c to v#d4 ,evidently the rate of variation of volume is not like the rate of variation of pressure1 that is1 the same throughout1 and when we look at the graph we see that the rate of variation is greatest where the slope of the curve is steepest4 ,the latter is steepest near the point a1 less steep near the point b1 and still less steep near the point c4 ,now any small part of the curve is indistinguishable from a straight line4 ,let us draw a straight line ee#a1 which appears to coincide with a small part of the curve near a1 and similar straight lines ff#a1 and gg#a1 which also appear to coincide with small parts of the curve near b and c4 ,then the steepness of the curve will be proportional to the angles which these straight lines make with the axis op1 and these angles are measured by their tangents1 that is1 by the ratio oe#a_/oe1 which is the tangent that e#a;e makes with op1 the ratio of#a_/of1 and the ratio og#a_/og4 ,illustration3 ,,fig4 #bh4 ,the point a on the curve corresponds with a pressure a#a and a volume a#aa4 ,the point b corresponds with a pressure b#a and a volume b#aa1 and c with a pressure c#a and a volume c#aa4 ,the average rate of variation of the volume of the gas1 as the pressure changes from a to c1 is therefore proportional to the sum of the tangents oe#a_/oe and og#a_/og1 divided by #b4 ,,the ,,notion ,,of ,,the ,,limit ,suppose that we wish to find the rate of variation of volume for a pressure change in the immediate vicinity of the value b#a1 that is1 the rate of variation as the pressure changes from a little less than b#a to a little more than b#a4 ,if we find the point b on the curve corresponding to b#a1 and if we then draw a line ff#a1 touching the curve at the point b1 we shall obtain the angle off#a4 ,it might appear now that the tangent of this angle1 that is1 the ratio of#a_/of1 would give us a measure of the rate of variation of volume4 ,but the reasoning would be faulty4 ,the line ff#a only touches the curve1 it does not coincide with an element of the curve4 ,also at the point b#a the pressure has a certain definite value1 and there is no change4 ,at the corresponding point b#aa the volume also has a certain definite value1 and there is no change4 ,there can therefore be no rate of variation4 ,the value of the tangent does not give us a measure of the rate of variation3 it gives us the limit to the rate of variation1 when the pressure is changing in the immediate vicinity of b#a4 ,we must stick to the notion of a pressure change in the immediate vicinity of b#a4 ,what do we mean by 8immediate vicinity08 ,we mean that we are thinking of a range of pressure-values in which the particular pressure-value b#a is contained1 but not as an end-point4 ,we mean also that we choose a definite standard of approximation to the value b#a1 so that any pressure-value within our interval differs from b#a by less than this standard of approximation4 ,it means further that1 no matter how small is the number representing this standard of approximation1 any pressure-value within the interval will differ from b#a by less than this number4 ,this is what we really mean when we say that the interval we are thinking about is an 8infinitely small one40 ,now corresponding to this interval of pressure-values in the immediate vicinity of b#a1 there will be an interval of volume-values in the immediate vicinity of b#aa1 and1 as before1 any one of these volume-values will differ from b#aa by less than any number representing a standard of approximation to b#aa4 ,we then find the point on the curve corresponding to both b#a and b#aa1 that is b1 and we draw the line ff#a1 and find the tangent of the angle which this line makes with op4 ,the value of this tangent is the limit of the rate of variation of the volume of the gas when the pressure undergoes a change in the immediate vicinity of b#a4 8,rate of variation0 is a function of the argument 8pressure40 ,this function has the limit l for a value of its argument b#a1 when1 as the argument varies in the immediate vicinity of b#a1 the value of the function approximates to l within any standard whatever of approximation4#cf #cf ,if the reader does not understand this1 he should read ,whitehead's 8,introduction to ,mathematics40 ,he should read this book in any case4 ,we should not1 of course1 find the rate of variation of volume of the gas by this means4 ,we should calculate the value of the differential co-efficient dv_/dp from the equation pv k7#a at73 this would be k 7#a at7_/p#b4 ,but the reasoning involved in the methods of the calculus are those which we have attempted to outline4 ,we try to avoid the terms 8infinitely small10 8infinitely near10 8infinitely small quantities10 and so on1 by the device of standards of approximation4 ,it may appear to the non-mathematical reader that all this is rather to be regarded as 8quibbling10 but the success of the methods of mathematical physics should convince him that such is not the case4 ,he should also reflect that clear and definite ideas on the fundamental concepts of the science are just as necessary in speculative biology as they are in mathematics4 7,another example47 ,let us consider the case of a stone failing from a state of rest4 ,observations will show that when the stone has fallen for one second it has traversed a space of #af feet2 at the end of two seconds it has fallen through #fd feet2 and at the end of three seconds the space traversed is #add feet4 ,from these and similar data we can deduce the velocity of motion of the stone as it passes any point in its path4 ,the velocity is the space traversed in a certain time s_/t4 ,if we take any easily observable space 7say five feet7 on either side of the point chosen1 and then determine the times when the stone was at the extremities of this interval1 and divide the interval of space by the interval of time1 we shall obtain the average velocity of motion of the stone over this fraction of the whole path chosen4 ,but the velocity did not vary in a constant manner during this interval 7as we see by considering the spaces traversed during the first three seconds of the fall74 ,therefore our average velocity does not accurately represent the velocity of the stone as it passes the point at the middle of the path chosen4 ,we therefore reduce the length of the path more and more so as to make the average velocity approximate closer and closer to the velocity near the middle portion of the path4 ,in this way we find the ratio s_/t1 where s is a very small interval of path containing the point chosen1 but not as an end-point1 and t is a very small interval of time4 ,perhaps this average velocity may be near enough for our purposes1 but perhaps it may not4 ,the interval of path s is still a finite interval1 and t is still a finite time1 and so long as these values are finite ones the velocity deduced from them remains a mean one4 ,all that we can say is that it approximates to the velocity1 as the arbitrary point was passed1 within a certain standard of approximation4 ,obviously the smaller the interval s1 the closer will be this approximation4 ,suppose1 then1 that we diminish s till it 8becomes zero40 ,it might appear now that when s coincides with the point chosen we shall obtain the velocity of the stone at this point4 ,but if there is no interval of path1 and no interval of time1 there can be no velocity1 which is an interval of path divided by an interval of time2 and if the stone is 8at the point10 it does not move at all4 ,we must stick to the idea of intervals of space and time1 and yet we must think of these intervals as being so small that no error whatever is involved in regarding the mean velocity deduced from them as the 8true velocity40 ,we therefore think of the point as being placed in an interval of path1 but not at an end-point of this interval4 ,we think of the velocity as a mean one1 but we must have a standard of approximation1 so that we may be able to say that the mean velocity approximates to the 8actual0 or limiting velocity of the stone as it passes the point1 within this standard of approximation4 ,the smaller we make the interval1 the closer will the mean velocity approximate to the limiting velocity4 ,we therefore think of the stone as moving in the immediate vicinity of the point in the sense already discussed4 ,we say that the 8immediate vicinity0 is an interval such that any point in it1 p#a1 approximates to the arbitrary point p which we are considering within any standard of approximation3 that is1 no point in the interval is further away from p than a certain number expressing the standard of approximation1 and this can be any number1 however small4 ,we say the same thing about the interval of time4 ,that is to say1 we make the intervals as small as we like3 they can be smaller than any interval which will cause an error in our deduced velocity1 no matter how small this error may be4 ,the limit of the velocity of a stone falling past a point in its path is1 therefore1 that velocity towards which the mean velocities approximate within any standard of approximation1 when we regard the interval of space as being the immediate vicinity of the point1 and the interval of time as being the time in the immediate vicinity of the moment when the stone passes the point4 ,the limit of the velocity is not s_/t but ds_/dt1 dt and ds being1 not finite intervals of time and space1 but 8differentials40 ,we determine this limit by the methods of the differential calculus4 ,,frequency ,,distributions ,,and ,,probability ,let the reader keep a note of the number of trumps held by himself and partner in a large number of games of whist 7the cards being cut for trump74 ,in #bjj hands he may get such results as the following3 ,no4 of trumps in his own and partner's hands--#j1 #a1 #b1 #c1 #d1 #e1 #f1 #g1 #h1 #i1 #aj1 #aa1 #ab1 #ac4 ,no4 of times this hand was held--#j1 #j1 #j1 #a1 #i1 #bi1 #ec1 #eb1 #ce1 #ad1 #f1 #a1 #j1 #j4 ,he should note also the number of times that trumps were spades1 clubs1 diamonds1 and hearts3 he will get some such results as the following3 spades1 #df2 clubs1 #ec2 diamonds1 #ea2 hearts1 #ej4 ,the numbers in the lower line of the first series form a 8frequency distribution10 for they tell us the frequency of occurrence of the hands indicated in the numbers above them4 8,no4 of trumps0 is the independent variable1 and 8no4 of times these nos4 of trumps were held0 is the dependent variable4 ,a frequency distribution represents the way in which the results of a series of experiments differ from the mean result4 ,a particular result is expected from the operation of one1 or a few1 main causes4 ,but a number of other relatively unimportant causes lead to the deviation of a number of results from this mean or characteristic one4 ,yet since one1 or a few1 main causes are predominant1 the majority of the results of the experiment will approximate closely to the mean2 and a relatively small proportion will deviate to variable distances on either side of the mean4 ,if a pack of cards were shuffled so that all the suits were thoroughly mixed among each other1 then we should expect the trumps to be as equally divided as possible between the four players4 ,but a number of causes lead to irregularities in this desired uniform distribution1 and so the results of a large number of deals deviate from the mean result4 ,it is possible1 by an application of the theory of probability1 to calculate ideal1 or theoretical frequency distributions1 basing our reasoning on the considerations suggested above4 ,we then find that the observed and calculated frequency distributions may be very much alike4 ,in biological investigation1 far more than in physical investigation1 we deal with mean results4 ,it is1 however1 just as important that the mean should be considered as the individual divergences from the mean4 ,we want to know the mean results1 and the way and the extent in which the individual results diverge from the mean4 ,there is a mean or 8ideal0 result1 but we must think of a great number of small independent causes which cause the actually obtained results to diverge from this mean4 ,if these small un-co-ordinated causes are just as likely to cause the results to be less than the mean1 as greater than the mean1 we shall obtain a frequency distribution resembling the one given above1 in that the variations from the mean are equal on both sides of the mean4 ,but if the general tendency of the small un-co-ordinated causes is to cause the results1 on the whole1 to tend to be greater than the mean1 then the frequency distribution will be 8one-sided10 that is1 if we represent it by a curve the latter will be an asymmetrical one4 ,curves which are asymmetrical are those most frequently obtained in biological1 statistical investigations4 ,,matter ,our generalised notion of matter is that it is the physical substance underlying phenomena4 ,immediately1 or intuitively1 we attain the notion of matter because of our perceptions of touch1 and our perception of muscular exertion4 ,the distance sense-receptors1 visual1 auditory1 and olfactory1 would not give us this intuition of matter4 ,material things are extended1 that is1 they have form1 and they exclude each other1 so that they cannot occupy the same place4 ,they appear to us to be aggregates of different nature3 they may be solid and homogeneous1 like a piece of metal2 or solid and porous1 like a piece of pumice-stone2 or loose and granular1 like sand2 or viscous or liquid1 like pitch or water4 ,they may have colour4 ,they are opaque1 or transparent in various degrees4 ,they may have odour4 ,material things1 as they are perceived by the distance sense-receptors1 appear to have qualities4 ,material things are aggregates of molecules4 ,the aggregates may possess essential form1 like that of a crystal1 or an organism4 ,the form of the aggregate may be essential and homogeneous1 so that it consists of molecules1 all of which are of the same kind1 like a crystal4 ,it may be heterogeneous and essential1 like the body of the organism1 when it consists of molecules which are not all of the same kind4 ,the aggregates may have accidental form1 like that of a river valley1 or a delta1 or a mountain1 and the form in these1 and similar cases1 is not a part of the essential nature of the aggregate4 ,the molecules are selections 7in the mathematical sense7 of some of about eighty different kinds of atoms4 ,a molecule is a small number of atoms arranged together in a definite way1 and its nature depends1 not only on the kinds of atoms of which it is composed1 but also on the arrangement of these atoms4 ,two or more different arrangements of the same atoms are1 in general1 different molecules4 ,,mass ,when matter is perceived by the tactile and muscular sense organs1 we have the intuition of mass4 ,it is heavy1 and the degree of heaviness is proportional to the quantity of matter in the body which we feel1 that is1 to its mass4 ,heaviness is synonymous with weight1 but weight does not depend alone on the quantity of matter in the body4 ,if the latter were removed to an infinite distance from the earth or other cosmic bodies1 its weight would disappear1 but its mass would remain4 ,we could still touch and move it1 and we should still find that different degrees of muscular exertion would be necessary when bodies of different masses had to be moved4 ,,inertia ,if the body were in motion1 we should find that muscular exertion is necessary in order that it might be brought to rest2 and if it were at rest1 we should find that muscular exertion was necessary in order that it might be moved4 ,the body1 matter in general1 possesses inertia1 and this is its most fundamental attribute4 ,mass we can only conceive in terms of inertia4 ,if two bodies were at rest1 and if the same degree of muscular exertion conferred on each the same initial velocity of motion1 their masses would be equal4 ,if the same degree of muscular exertion conferred different velocities on different bodies1 their masses would be different1 and would vary directly with the initial velocities conferred4 ,,force ,the feeling which we experience when we move a body from a state of rest1 or stop a body which is moving1 is what we call force4 ,if on climbing a stair in the dark we think there is one step more than there is1 and so have the queer1 familiar1 feeling of treading on nothing1 we have the intuition of energy2 but when we tread on the steps1 and so raise our body1 we have the intuition of force4 ,force is that which accelerates the velocity of a mass4 ,if the latter is at rest1 we consider it to have zero velocity4 ,if it is moving1 and we stop it1 there is still acceleration1 but this is negative4 ,matter1 that is1 the substantia physica1 is clearly to be conceived only in terms of energy4 ,it is1 to our direct intuitions1 resistance1 or inertia1 that which requires energy in order that it may be made to undergo change4 ,our static idea of physical solidity1 or massiveness1 disappears on ultimate analysis4 ,molecules are made up of atoms1 and the atoms are assumed to have all the characters of matter3 we could not see them1 of course1 even if we possessed all the magnifying power that we wished1 for they would be too small to reflect light4 ,modern physical theory is compelled to regard atoms as complex1 and imagines them as being composed of moving electrons4 ,the electron is immaterial--it is the unit-charge of electricity4 ,it is said to possess mass1 but mass is now understood to mean inertia4 ,so long as the electron is moving1 it sets up a field of energy round it1 and this field--the electro-magnetic one--extends in all directions4 ,periodic disturbances in it constitute radiation1 and this radiation travels with the velocity of light4 ,it is because of the existence of this field that we are obliged to postulate the existence of an ether of space4 ,unfamiliar to us until the discovery of ,hertzian waves and 8wireless0 telegraphy1 this electro-magnetic radiation in space is now accessible to our direct intuitions4 ,we can initiate it by setting electrons in motion1 that is1 by expending energy 7producing the sparking in the transmitters of the wireless telegraphy apparatus72 and we can stop it1 if it is in existence1 by absorbing the energy 7in the receivers of the wireless telegraphy apparatus74 ,this is essentially what we understand by the inertia of gross matter4 ,we set a body in motion by expending energy on it 7the explosion of the powder in a cartridge1 which converts potential chemical energy into the kinetic energy of the moving projectile72 and we can stop a body which is in motion by absorbing this energy of motion 7by causing the projectile to strike against a target1 when the kinetic energy of its motion becomes the kinetic energy of the heat of the arrested body74 ,inertia is therefore the same thing whether it be the inertia of visible1 material bodies1 or the inertia of invisible1 material molecules1 or the inertia of the immaterial1 non-tangible ether4 ,it is the condition that energy-changes must occur if anything accessible to our observation is to change its state of rest or motion4 ,,energy ,energy is therefore indefinable4 ,it is an elemental aspect of our experience4 ,nature to us is an aggregate of particles in motion4 ,we have to speak of massive particles1 whether we call these visible material bodies1 or molecules1 or atoms1 or electrons1 in order that we may describe nature4 ,we must employ the fiction of a substantia physica4 ,we only know the substance or matter in terms of energy2 it is really the latter that is known to us4 ,it is the poverty of our language1 or rather it is the legacy of a materialistic age1 that compels us to speak of particles that move1 rather than of motions as entities in themselves4 ,considering1 then1 the idea of particles in motion as a fiction necessary for clear description1 we can study energy4 ,there is only one kind1 or form1 of energy which presents itself to our aided or unaided intuitions1 that is kinetic energy4 ,bodies that move possess this energy represented by their motion3 they can be made to do work1 that is1 their energy can be transformed into other forms of energy4 ,all things are in motion4 ,a gas consists of molecules incessantly moving with high velocity1 and colliding and rebounding from each other4 ,the energy of a gas is the sum of one-half of the masses of all the molecules1 multiplied by the squares of the velocities of all the molecules1 that is1 #a_/bmv#b4 ,this is also the kinetic energy of a projectile1 or of a planet revolving round the sun4 ,kinetic energy is that of the uniform1 unchanging motion of some entity possessing mass1 but we must extend our notion of mass so as to include immaterial1 imponderable entities such as electrons4 ,this energy cannot be destroyed or created--the law of conservation of energy4 ,this is a principle or mode of our thought4 ,we are unable scientifically or philosophically to think of an entity ceasing to be4 ,dreams and phantoms show us entities which are real while they last1 but which cease to exist4 ,if we do attempt to think of entities that appear from1 or disappear into1 nothing1 we surrender the notion of reality4 ,the more we think of it the more clearly we shall see that the things which we call real are the things which are conserved4 ,yet energy1 to our immediate intuitions1 seems to disappear4 ,a flying bullet strikes against a target and becomes flattened out into a motionless piece of lead4 ,a red-hot piece of iron cools down to the temperature of its surroundings4 ,a golf-ball driven up the side of a hill comes to rest in the grass4 ,a current of electricity passing through water is used up1 that is1 electricity of a higher potential is required to force the current through water than to force it through thick copper wire4 ,in all these cases we might think that energy is lost1 but we cannot believe this4 ,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 composed2 for the latter becomes greatly heated when its flight is arrested and this increased heat ought to be equal to the kinetic energy of the bullet in flight4 ,the red-hot piece of iron cools1 and the kinetic energy of its molecules becomes less and less1 but this does not cease to exist1 for the energy is simply transferred by radiation and conduction to the surrounding bodies1 the temperature of which it raises4 ,the golf-ball driven up the hill comes to rest and loses its kinetic energy4 ,some of this has been transferred to the air through which it passes1 the latter being heated very slightly2 some of it is expended by friction with the grass over which the ball rolls before coming to rest1 and this energy is traceable in heat-effects1 or in mechanical effects1 but the rest of it apparently ceases to exist4 ,but this would be contradictory to the principle of conservation1 and so we say that the lost kinetic energy has become potential4 ,the current of electricity may heat the water through which it passes1 and some of the energy which seems to disappear is so to be traced1 but the greater fraction is apparently lost4 ,a quantity of free hydrogen and oxygen is1 however1 generated1 and we say that the kinetic energy of the moving electrons has become transformed into the potential chemical energy of the gaseous mixture4 ,,potential ,,energy ,therefore1 if energy disappears or appears1 we do not say that it is destroyed or is created3 we invent potential energies1 into which we suppose that the energies in question have become transformed1 in order that we may still think of them as being subject to an a priori principle of conservation4 ,although a particle of radium continually generates heat1 we do not therefore think of the first principle of energetics as being invalidated1 for we suppose that the energy which thus appears was really potential in the atoms of radium4 ,but it was contrary to all our former experience of atoms that they should contain any other energy than that of their own motion1 and so the further assumption was made that the atom1 at least the atom of the radio-active substance1 is really complex1 and not simple1 as chemical theory demands4 ,it is made up of smaller particles1 and possesses a definite structure4 ,in certain circumstances the atom may disintegrate1 and the energy which held together its particles1 whether these were simpler corpuscles or electrons1 is given off as the heat which the radio-active substance apparently generates4 ,the potential energy of the chemical atom is therefore a hypothesis which has been devised in order to preserve the validity of the law of conservation1 and the reality of this hypothesis is being tested by investigation4 ,if we accept it as true1 are the deductions made from it justified in our experience8 ,that is the test which must be satisfied in all the hypotheses where potential energies are invented1 and the potentials are only real if the test is satisfactory4 ,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 hill3 it is capable of developing energy1 for a touch may cause it to roll down the hill1 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 ball4 ,the atoms of hydrogen and oxygen which 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 molecules of water4 ,their state when the gases are in the elementary condition1 or are 8free10 is that of molecules moving rapidly and incessantly1 rebounding from each other after colliding with each other3 they possess energy of position--potential energy--because they are separate from each other4 ,if they 8combine10 as when a minute electric spark explodes the mixture of gases1 they tractate together1 and remain in proximity to each other1 becoming molecules of water4 ,the energy which became potential in the gaseous mixture1 when the electric energy of the current seemed to disappear1 now appears as the heat generated by the combustion1 that is1 as the greatly increased kinetic energy of the molecules of the gas 7steam7 which takes the place of the mixture of hydrogen and oxygen4 ,previous to the explosion this gas was a mixture of molecules of hydrogen and oxygen 7#b;,h#b #b,o7 at the ordinary temperature1 but after the explosion it consists of a smaller number of molecules at a very much higher temperature4 ,what is 8energy of position08 ,the golf ball at the bottom of the hill was at a distance of ,r feet from the centre of the earth1 but at the top of the hill it is at a distance of ,r #ajj feet from the centre of the earth4 ,in the first case it was free to fall ,r feet1 but in the second case it is free to fall ,r #ajj feet4 ,the atoms of the constituent molecules of water occupy the position ,h - ,o - ,h1 the bonds 7-7 indicating that the atoms are very close together2 but when the water is decomposed by an electric current1 the atoms occupy the positions ,o - ,o ,h - ,h ,h - ,h1 the 77 indicating that the atoms are relatively far apart from each other4 ,now the golf ball and the earth1 or the atoms of hydrogen and oxygen1 are physically the same material entities1 whether they are close together or far apart1 yet when the earth and the ball1 or the atoms of oxygen and hydrogen1 are separated from each other1 their 8properties0 are different from what they are when they are close together4 ,what is it that makes the difference8 ,it is that which is between them4 ,is it1 in the last case1 8the potential energy of chemical affinity08 ,this dreadful phrase is actually used in a recent book on biology3 8,in the elements carbon and oxygen1 so long as they remain separate1 a certain amount of energy remains latent4 ,when the carbon and oxygen atoms are allowed to come together and unite1 this potential energy of chemical affinity is liberated as kinetic energy40 ,what is changed by the tractation and pellation 7the terms suggested by ,soddy in place of the anthropomorphic ones1 8attraction0 and 8repulsion078 ,it is the ether which has become changed in some way4 ,potential energy resides therefore in the ether of space4 ,,isothermal ,,and ,,adiabatic ,,changes ,let us consider the changes which occur in a gas under the influence of changes in temperature and pressure1 premising that the remarks which we have to make can be applied to bodies in the liquid and solid conditions1 with some necessary modifications4 ,a gas1 then1 consists of a very great number of particles1 or molecules1 in motion4 ,these molecules move in straight lines at very high velocities1 and if the envelope in which the gas is contained is a restricted one1 the molecules collide with each other1 and with the walls of the envelope2 and1 being assumed perfectly elastic1 they rebound from each other1 and from the walls of the vessel1 with the same velocity which they had when they collided4 ,the pressure of the gas 7say that of steam at a temperature of #aaj ,c41 and a pressure of #abj lbs4 to the square inch in a steam boiler7 is the sum of the impacts of the molecules on the walls of the containing vessel4 ,when the temperature is high the molecules are moving at a higher mean velocity than when the temperature is lower1 and their mean free path tends to become greater4 ,the volume of a certain mass of gas1 that is1 the volume occupied by a certain very great number of molecules1 is greater the higher is the temperature1 provided the envelope is one capable of yielding4 ,if we reduce the capacity of the envelope in which the gas is contained1 the pressure will rise1 for the intrinsic energy of the gas is still the same2 but we have done work on it1 and by the law of conservation this work1 or at least the energy represented by it1 must still exist4 ,it is represented by the decreased length of free path of the molecules1 and this means that the impacts on the walls of the vessel will be greater than they were4 ,there is1 therefore1 a certain relation between the volume of a gas and its pressure1 and this relation can be represented by an equation involving the temperature1 the pressure1 and the volume4 ,illustration3 ,,fig4 #bi4 ,the diagram represents the pressure and the volume of a gas when these things change4 ,there are two conditions1 7#a7 when the heat developed by the compression is allowed to escape through the walls of the vessel to the outside1 or when the heat lost in the expansion of the gas is compensated by the conduction of heat through the walls of the vessel from outside2 and 7#b7 when the heat developed is retained in the gas1 as when the latter is contained in a vessel the walls of which do not conduct heat4 ,the pressure of the gas is measured along the horizontal axis1 and the volume is measured along the vertical axis1 and a curve is drawn so that for any value of the pressure there is a corresponding value of the volume4 ,thus the values of the pressures p and p#a in the diagram correspond to the value of the volume v4 ,the curve relating the change of pressure with a corresponding change of volume is1 in general1 that called a rectangular hyperbola4 ,but there are two kinds of such curves3 7#a7 that which we obtain by plotting the corresponding values of pressure and volume1 when the temperature of the gas remains constant throughout the series of changes1 that is1 when the 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 gas4 ,such a series of changes of pressure and volume is called an isothermal one4 7#b7 ,when the heat developed by the compression of the gas is retained in the gas1 as when the walls of the vessel in which these changes are effected are such as do not conduct heat3 such a series of changes is called an adiabatic one4 ,adiabatic curves are steeper than are isothermal ones4 ,,the ,,carnot ,,engine ,this is an imaginary mechanism which performs a certain cycle of operations4 ,it does not really exist1 but the conception of its operation is of the greatest value in the consideration of energy-transformations1 and it is for this reason that we discuss it here4 ,consider a gas1 or some other substance capable of expanding or contracting4 ,it contains intrinsic energy1 and it is capable of doing work4 ,thus1 since a gas can expand indefinitely it can be made to do mechanical work4 ,a mass of gas at a pressure p#a1 and having a volume v#a1 and at a temperature ,t1 can do work by expanding till its pressure is reduced to p1 and its volume increased to v4 ,if it expands adiabatically its temperature will fall to t4 ,let us suppose that t is the temperature of the surrounding medium3 the gas cannot therefore cool further1 and we can obtain no more work from it4 ,if the gas is the substance which we wish to employ as the working substance in the ,carnot engine1 we must therefore bring it back to the condition represented by ,a4 ,that is1 we must raise its temperature to ,t1 we must reduce its volume to v#a1 and we must increase its pressure to p#a4 ,illustration3 ,,fig4 #cj4 ,thus the steam of an engine is 7say7 at a temperature of #aaj ,c41 and a pressure of #abj lbs4 to the square inch4 ,when it has passed through the cylinder and condenser it is water at a temperature of1 say1 #ae ,c41 and it is at atmospheric pressure4 ,we must1 therefore1 bring it back to its former condition by heating this water in the boiler till it is steam under the former conditions of temperature and pressure4 ,therefore we must1 in order to obtain a self-acting engine1 cause the working substance1 and the mechanism of the engine1 to perform a series of cyclical operations4 ,the ,carnot engine is a cylinder containing a gas called the working substance ,s1 and this gas can be brought into thermal contact with a source of heat1 or a refrigerator1 that is1 the gas can be heated or cooled by a mechanism outside itself4 ,the walls of the cylinder are made of some substance which is a perfect non-conductor of heat1 but the bottom of the cylinder is made of a substance which conducts heat perfectly4 ,there is a piston in the cylinder which fits it closely1 but which moves up and down without friction4 ,at the bottom of the latter is a valve which can be turned so as to place the bottom of the cylinder1 and therefore the gas1 in thermal contact with a reservoir of heat 771 or a refrigerator 7-74 ,but when the valve is turned so that the non-conducting part ,o fills the bottom1 the gas is perfectly insulated1 and heat can neither enter nor leave it4 ,illustration3 ,,fig4 #ca4 ,such an engine is1 of course1 an imaginary one1 since there can be no mechanism in which there is not a certain amount of friction between moving parts1 and there are no substances which conduct or insulate heat perfectly4 ,the engine is1 in fact1 the limit to a series of engines each of which is supposed to be more perfect than the last one4 ,it is a fiction which is of considerable use in theoretical work4 ,,the ,,carnot ,,positive ,,cycle ,we have therefore a substance which can be heated by contact with a hot body1 and which can then expand1 doing mechanical work by raising a piston1 and perhaps turning a flywheel1 and on which work is then done so that it returns to its original condition4 ,this is a cycle of operations4 ,if we consider only the changes which occur in the working substance we can represent these changes by a diagram4 ,illustration3 ,,fig4 #cb4 ,first operation1 7#ab74 ,we suppose that the valve is turned so that the non-conducting plug closes the cylinder4 ,the piston is in the position ,,ii 7,fig4 #ca74 ,heat cannot then enter or leave the gas4 ,but the latter already contains heat3 it is at a temperature of ,t#b1 so that it can expand doing work4 ,let it expand1 forcing up the piston4 ,during this operation the pressure of the gas will fall from a point on the vertical axis opposite #a to a point opposite #b1 and its volume will increase from a point on the horizontal axis beneath #a to a point beneath #b4 ,it will cool because it has expanded1 and no heat is allowed to enter it during this act of expansion4 ,the expansion is therefore adiabatic2 the temperature falls from ,t#b to ,t#a2 and work is done by the gas4 ,second operation1 7#bc74 ,the piston is now at the position ,i1 that is1 at the upper end of its stroke1 and we must bring it back again to the lower end of the cylinder4 ,the valve is turned so that the bottom of the cylinder is placed in thermal communication with the refrigerator 7-71 and the piston is pushed in to the position ,,ii4 ,the gas is therefore compressed until its volume decreases from a point beneath #b to a point beneath #c4 ,as it is being compressed1 heat is generated and its temperature would rise1 but as this heat is generated it flows into the refrigerator1 so that the temperature of the gas remains the same during the operation4 ,the contraction is therefore an isothermal one2 the temperature remains at ,t#a2 and work is done on the gas from outside4 ,third operation1 7#cd74 ,but the piston is not at the lower end of its stroke yet4 ,we turn the valve so that the bottom of the cylinder is closed by the non-conducting plug ,o1 and then push in the piston until it reaches the position ,,iii4 ,the gas is still further compressed1 and this compression generates heat4 ,but the heat cannot escape1 so that the temperature of the gas rises until it reaches ,t#b4 ,the contraction is therefore an adiabatic one4 ,work is done on the gas4 ,fourth operation1 7#da74 ,the piston is now at the lower end of its stroke4 ,we turn the valve so that the bottom of the cylinder is placed in communication with the source of heat 774 ,the gas expands from the point beneath #d to the point beneath #a1 raising the piston to the position ,,ii4 ,this expansion of the gas would lower its temperature1 but it is in communication with the source of heat1 and so it does not cool1 but draws heat from the source and remains at a constant temperature1 ,t#b4 ,the expansion is therefore an isothermal one4 ,work is done by the gas4 ,this completes the cycle4 ,but the gas is heated1 and when the piston is at position ,,ii1 the valve is turned so as to close the cylinder by the non-conducting plug ,o4 ,the heat already contained in the gas continues to expand1 the latter doing more work1 but this expansion causes the temperature to fall from ,t#b to ,t#a4 ,this is the operation with which the cycle commenced4 ,summarising the positive ,carnot cycle1 we see that the engine takes heat from a source 77 and gives up part of this to a refrigerator 7-71 7in an actual steam-engine heat is taken from the boiler and given up to the condenser water74 ,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 water4 ,what becomes of the balance8 ,it is converted into the mechanical work of the engine4 ,the ,carnot engine therefore takes a quantity of heat1 ,q#b1 from the source and gives up another quantity of heat1 ,q#a1 to the refrigerator4 ,we find that ,q#b is greater than ,q#a and the balance1 ,q#b - ,q#a1 is represented by the work done by the engine4 ,heat-energy falls from a state of high1 to a state of low potential1 and is partly transformed into mechanical work4 ,,the ,,carnot ,,negative ,,cycle ,this is simply the positive cycle reversed4 ,the reader should puzzle it out for himself if he is not already familiar with it4 ,it consists of an adiabatic contraction #ba1 an isothermal contraction #ad1 an adiabatic expansion #dc1 and an isothermal expansion #cb4 ,a quantity of heat1 ,q#a1 is taken from the refrigerator at a temperature ,t#a1 and another quantity1 ,q#b1 is given up to the source at a temperature ,t#b4 ,but ,q#b is greater than ,q#a1 and the engine therefore gives up more heat than it receives1 while1 further1 heat flows from a body at a low temperature to another body at a higher temperature4 ,where does the engine get this energy from8 ,it gets it because work is done upon it by means of an outside agency1 and all of this work is converted into heat4 ,,reversibility ,the ,carnot engine and cycle are therefore perfectly reversible4 ,not only can the engine turn heat into work1 but it can turn work into heat4 ,this perfect1 quantitative reversibility is1 however1 a property of the imaginary mechanism only1 and it does not exist in any actual engine4 ,,entropy ,let us consider the cycle more closely4 ,in the operation #da1 which is an isothermal expansion1 there is a flow of heat-energy from the source and a transformation of energy into work4 ,the gas in the condition represented by the point #d had a certain pressure and a certain volume4 ,in the condition represented by the point #a1 its pressure has decreased1 its volume has increased1 and its temperature is the same4 ,its physical condition has been changed1 and to bring it back into its former condition something must be done to it4 ,let1 then1 the gas continue to expand without receiving any more heat1 or parting with any3 that is1 let it undergo the adiabatic expansion #ab until its temperature falls to that of the refrigerator1 ,t#a4 ,we now compress the gas while keeping it at this temperature1 that is1 we cause it to undergo the isothermal contraction #bc1 during which operation it is giving up heat to the refrigerator1 so that there is again a flow of heat-energy4 ,we then compress it still further without allowing heat to escape from it1 that is1 we cause it to undergo the adiabatic contraction #cd4 ,during this operation the gas rises in temperature to ,t#b4 ,it is now in the condition that it was when the cycle commenced4 ,in this cycle of operations heat first entered1 and then left the gas1 and with this entrance or rejection of heat1 the condition of the gas with respect to its power of doing work changed4 ,we investigate this flow of heat1 and the concomitant change of properties of the substance1 with regard to which the flow took place1 by forming the concept called entropy4 ,we make the convention that when heat enters a substance the entropy of the latter increases1 and when heat leaves it its entropy decreases4 ,we call the quantity of heat entering or leaving a substance ,q1 and the temperature of the substance ,t4 ,then ,q_/,t is proportional to the change of entropy of the substance when the quantity of heat1 ,q1 enters or leaves it4 ,now it is a fact of our experience that heat can only flow1 of itself1 from a hotter to a colder body4 ,consider two such bodies forming an isolated system1 the temperature of the hotter one being ,t#b1 and that of the colder one ,t#a4 ,let ,q units of heat flow from the body at ,t#b to that at ,t#a no work being done4 ,then the loss of entropy of the hotter body is ,q_/,t#b1 and the gain of entropy of the colder body is ,q_/,t#a4 ,the nett change of entropy of the system is ,q_/,t#a - ,q_/,t#b4 ,since ,t#b is greater than ,t#a1 ,q_/,t#b is less than ,q_/,t#a4 ,therefore the expression ,q_/,t#a - ,q_/,t#b is positive1 that is1 the entropy of the system1 as a whole1 has increased4 ,when heat flows from a hotter to a colder body the nett entropy of the two bodies1 therefore1 increases4 ,but we can also cause heat to flow from a colder to a hotter body by effecting a compensatory energy-transformation4 ,such a compensation would not occur by itself in any system capable of effecting an energy-transformation1 if it is to be effected some external agency must act on the transforming system4 ,we can suppose it to happen in a perfectly reversible imaginary mechanism4 ,suppose a ,carnot engine works in the positive direction1 taking heat from a reservoir at temperature ,t#b1 and giving up part of this heat to a refrigerator at ,t#a1 and doing a certain amount of work ,w4 ,suppose that this work is stored up1 so to speak1 say by raising a heavy weight1 which can then fall and actuate the same ,carnot engine in the opposite 7negative7 direction4 ,the engine then exactly reverses its former series of operations4 ,the work it did is reconverted into heat1 and as much of this heat flows from the refrigerator into the source1 that is1 from a colder to a hotter body1 in the negative operations1 as flowed from the source to the refrigerator in the positive operations4 ,in this primary energy-transformation1 combined with a compensatory energy-transformation1 there is no change of entropy4 ,the mechanism is an ideal one--the limit to an irreversible mechanism4 ,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 friction1 in which some parts will conduct heat imperfectly1 and other parts will insulate heat imperfectly4 ,let the friction generate q units of heat1 and let the quantity of heat which is 8wasted0 by imperfect conduction and insulation be q#a4 ,this heat will flow into the refrigerator1 or will be radiated or conducted to the surrounding medium1 which we suppose to be at the same temperature as the refrigerator4 ,if1 then1 we divide this total quantity of heat by the temperature ,t#a1 we get 7q q#a7_/,t#a ,s#a as the quantity of entropy which is generated as the result of the imperfections of the engine1 in addition to the quantity of entropy1 ,s1 which would be generated if the engine were a perfect one4 ,both ,s and ,s#a are positive4 ,also in the working of the engine in the negative direction a certain quantity of entropy1 ,s#a1 is generated for reasons similar to those mentioned above4 ,the entropy generated when the engine works in the positive direction is therefore ,s ,s#a1 and when it works negatively the quantity generated is also ,s#a4 ,the entropy destroyed when the engine works negatively is ,s4 ,the total change of entropy is therefore #b,s#a ,s - ,s1 that is1 #b,s#a4 ,in an actual energy-transformation combined with a compensatory energy-transformation there is therefore an increase of entropy4 ,we can generalise these statements so that they will apply not only to a heat-engine but to all mechanisms which effect energy-transformations4 ,in all such transformations entropy is generated4 ,therefore the ,entropy of the ,universe tends to a maximum4 ,,available ,,and ,,unavailable ,,energy ,consider the ,carnot engine as a perfect mechanism4 ,it takes heat-energy from a source at a temperature ,t#b1 and it gives up heat to a refrigerator at a temperature ,t#a1 ,t#b being greater than ,t#a4 ,in the adiabatic expansion #ab the gas continues to expand until its temperature becomes equal to that of the refrigerator4 ,it cannot1 then1 expand and do work any longer1 and thus the proportion of the heat1 ,q#b1 received from the source1 which can be converted into work1 depends on the difference of temperature ,t#b - ,t#a4 ,the greater is this difference the greater will be the proportion of the heat-energy received which can be converted into work4 ,if the engine were a perfect one1 and if the gas were also a perfect one 7that is a gas which would continue to expand according to the equation for the adiabatic expansion of gases71 and if the refrigerator were absolutely cold1 then all the heat energy received from the source could be converted into work4 ,we cannot produce a refrigerator of absolute temperature #j1 and therefore only a certain proportion of the heat which is received by the engine can be transformed into mechanical work4 ,but this work can be used to reverse the action of the engine1 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 source4 ,the perfect engine is therefore reversible without loss of available energy4 ,now consider still the engine as a mechanism which takes heat from a source and gives it to a refrigerator1 but let it be an actual engine4 ,instead of giving up a certain fraction of the heat received to the refrigerator--a fraction equal to ,q#a 7,t#a_/,t#b71 it gives up rather more1 because it is not a perfect mechanism1 that is1 it generates friction1 etc4 ,some of the heat received thus ceases to be available for the performance of work2 and passes into the refrigerator4 ,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 worked1 or was imagined to work1 but in the actual engine this fraction is increased4 ,if we divide the increase of unavailable energy by the temperature of the refrigerator1 the product is the increase of entropy generated in the actual engine over that generated in the ideal engine4 ,because of this reduction of available energy the actual engine is an irreversible mechanism4 ,this is the connection between unavailable energy and entropy4 ,in all transformations some fraction of the transforming energy becomes heat1 and this heat flows by conduction and radiation into the surrounding bodies4 ,in general this heat simply raises the temperature of the medium into which it flows1 and becomes unavailable for further transformations4 ,with every transformation that occurs some part of the energy involved becomes unavailable4 ,therefore although the sum of the available and unavailable energy of the ,universe remains constant1 the fraction of unavailable energy tends continually to a maximum4 ,,inert ,,matter ,we can see now what is indicated by ,bergson's 8inert matter40 ,it is not matter deprived of energy--such an expression has no meaning--it is energy which is unavailable for further transformations4 ,the matter in which we choose to say that this energy is inherent has become inert4 ,let us substitute for the ,carnot engine the actual steam-engine of a ship1 the condenser of which is cooled by the sea water which is taken in1 and which is then heated and flows out again into the sea4 ,the heat derived from the source1 that is1 from the furnace of the boiler where coal is burned to raise steam1 thus passes out into the sea4 ,now the heat capacity of the sea is so great that the temperature of the water is not appreciably raised by this heat1 which drains into it from the engine3 even if it were appreciably raised1 the heat would be conducted into the earth1 or would be radiated out into space1 and would then raise the temperature of the material bodies of the universe4 ,but let all this heat remain in the sea4 ,it then simply raises the temperature of the water by an exceedingly small amount1 and the motions of the molecules become infinitesimally increased4 ,but the heat becomes equally distributed by conduction and convection throughout the mass of the water in the sea1 and as there are no differences in adjacent parts there are no means whereby the energy which thus passes into the sea can be again transformed4 ,a new order of things is the result of the processes we have indicated4 ,the segregated1 available heat-energy of material bodies has become transferred to the un-co-ordinated1 diffuse1 unavailable energies of the molecules which compose these bodies4 ,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 condition1 as regards this energy1 from adjacent aggregates4 ,but when this energy becomes equally distributed among the molecules of all the aggregates1 the matter in which it inheres becomes inert4 ,if we could1 by a sorting process like that of ,maxwell's hypothetical demons1 a process which does not expend the energy with which it deals1 separate the molecules which were moving slowly from those which were moving more quickly1 we could make this energy again available4 ,but it must clearly be understood that our physics is the physics not of individual molecules1 but of aggregates of molecules4 ,,index ,absolute1 ,driesch's theory of1 #dg4 ,acceleration 7in physics71 #cee4 ,acquired characters induced by the environment1 #baf2 a means of transformism1 #bbj2 evidence of transmission scanty1 #bbe2 transmission not inconceivable1 #bbf4 ,actions1 categories of1 and consciousness1 #bhb2 deliberative1 #bhc2 mechanistic hypothesis of1 #aeg2 stereotyped1 #bhc2 at a distance1 #cjd4 ,activation of the ovum1 #agf4 ,adaptability1 indicative of dominance1 #beh4 ,adaptation1 #bag2 and acquired characters1 #bai2 and changes of morphology and function1 #bai2 not inherited1 #bbj2 causes of1 #bci4 ,adaptive response1 #bai4 ,adiabatic changes1 #cfa4 ,aggregates1 molecular1 #cec4 ,alg1 distribution of1 #bfj4 ,allelomorphs1 ,mendelian1 #bca4 ,alternation of generations1 #age4 ,amido-substances1 #hh4 ,anabolism1 #hh4 ,anatomical parts1 homologies of1 #bea4 ,animal action1 considered objectively1 #bgh4 ,animal and plant contrasted1 #bfi4 ,animality1 #bfi4 ,annectant forms of life1 #bec4 ,annelids1 morphology of1 #bdh4 ,anthropomorphism in theories of action1 #adh4 ,anti-enzymes1 #id4 ,antitoxins1 #cf4 ,ants1 a dominant group1 #bfj4 ,appendix vermiformis1 #bej4 ,approximation1 standards of1 #cdg4 ,armoured animals1 #bfc4 ,arthropods1 morphology of1 #bdi2 a dominant group1 #bei2 distribution1 #bfj2 musculature of1 #bge2 adaptations for mobility1 #bge2 limits to size of1 #bge4 ,assimilation1 #fg4 ,atoms1 constitution of1 #cee2 arrangements of1 #cec4 ,automatism of animals deduced from mechanistic theories1 #bhj4 ,autonomy in development1 #cbb4 ,available energy1 #fb2 and entropy1 #cgd4 ,bacteria1 a dominant group1 #bei2 distribution1 #bei2 geological history1 #bei1 #bfa2 morphology1 #bfh2 metabolism1 #bff2 specialisation1 #bfc2 parasitism1 #bei2 nitrogen1 #gc2 prototrophic1 #aai1 #bff2 paratrophic1 #bff2 putrefactive1 #bff2 fermentation1 #bff2 and ,brownian movements1 #aai2 compensatory to plants1 #bfg4 ,bergson1 #bh2 creative evolution1 #bdd2 duration1 #aed2 animals and plants1 #gh2 eye of ,pecten1 #bcd2 inert matter1 #cge2 infinitesimal analysis of the organism1 #aaa2 kinematographic analysis1 #aaj2 theory of intellectualism1 #ea2 memory1 #aef2 morphological themes1 #bej2 theory of pain1 #bha2 theory of perception1 #g1 #aj2 the vital impetus1 #cah4 ,biology1 systematic1 #bja1 #bjc4 ,biophors1 #acb2 size of1 #ahc2 growth of1 #ahe4 ,biotic energy1 #cbe4 ,borelli and animal mechanism1 #abe4 ,brownian movement1 #aah2 significance of1 #aai4 ,bryan and thermodynamics1 #fb4 ,bud-formation1 #afe4 ,calculus1 infinitesimal1 #be1 #aae1 #cej4 ,calorimetric experiments1 #fe1 #fh4 ,capacity-energy factors1 #fa4 ,carnot's cycle1 #fi1 #gh1 #aac2 negative1 #cfh2 description of1 #cfc1 #cff2 compared with plant metabolism1 #ge2 compared with the organism1 #gc4 ,catalysis1 #ij2 universality of1 #ia4 ,catalysts1 characters of1 #ia4 ,categories of organisms1 #bji4 ,central nervous system1 specialisation of1 #bgc2 a switchboard1 #bgc2 evolution of1 parallel with evolution of muscular system1 #bha4 ,chance in evolution1 #bcg4 ,chemical affinity1 #cfa4 ,chemical energy1 degradation of1 #ge4 ,chemical reactions1 direction of1 #gh2 exothermic1 #hf2 explosive1 #hf2 similar in organic and inorganic systems1 #gh4 ,chemical synthesis1 involve vital activity1 #cah4 ,chemistry1 medieval1 #abe4 ,chlorophyll1 #fi4 ,chlorophyllian organisms1 #hh2 metabolism of1 #bfe2 a dominant group1 #bei2 essential morphology of1 #bfh2 distribution of1 #bfj4 ,chromatin of the nucleus1 #acj2 the material basis of inheritance1 #ahb4 ,chromosomes1 #acj1 #ahb1 #ahc4 ,classification of organisms1 #bji4 ,classificatory systems1 are artificial arrangements1 #bhi2 suggest evolutionary process1 #baj4 ,clausius1 #ed2 and ,carnot's ,law1 #aac4 ,clenterates1 morphology of1 #bdh4 ,clomate animals1 #bef4 ,colloidal platinum1 #ia4 ,colloids1 #ajg4 ,colonial organisms1 #afd4 ,comparative anatomy1 task of1 #bea4 ,compensatory energy-transformations effected by life1 #cji4 ,conjugation1 #agc2 and heredity1 #agf2 a stimulus to growth1 #age4 ,consciousness involves analysis of the environment1 #aa2 analysis of1 is an arbitrary process1 #ab2 a feeling of normality1 #f2 a part of crude sensation1 #dj2 simplified by reasoning1 #da2 an intensive multiplicity1 #cjc2 degree of1 is parallel to development of sensori-motor system1 #bhj2 not existent outside ourselves1 #bgh2 not a function of chemico-physical mechanism1 #afj2 intense in difficultly performed operations1 #bha2 and activity of cerebral cortex1 #bha2 absent in parasites1 #bia4 ,conservation a test of reality1 #ceg4 ,conservation of energy1 #eb2 in organisms1 #hc4 ,conservation of structure1 #bec1 #bef4 ,constants1 mathematical1 #cdd4 ,continuity of cells in embryo1 #aga4 ,contractility1 #ajj2 muscular1 #ajc4 ,co-ordinates1 systems of1 #bc4 ,corals1 #afd4 ,cosmic evolution1 #cad2 is a tendency towards degradation of energy1 #caf4 ,creation1 special1 #bad4 ,curvature1 #bg4 ,curves1 isothermal and adiabatic1 #cfb4 ,cuttle-fishes1 #bej4 ,cytoplasm1 #acj4 ,darwin1 and natural selection1 #bba2 acquired characters are inherited1 #bbj2 hypothesis of pangenesis1 #aha4 ,death1 is catastrophic katabolism1 #cdj4 ,degradation of energy1 #ha4 ,deliberation and consciousness1 #bha4 ,demons1 ,maxwell's1 #aaf4 ,descartes and mechanism1 #aba2 the rational soul1 #abc1 #cah2 his physiology1 #abb2 his spiritualism1 #abd2 and animal automatism1 #abe4 ,descent1 collateral1 #beg4 ,determinants in embryology1 #acb1 #ahc2 arrangement of1 #ahd2 latent in regenerative processes1 #adb4 ,development1 organisation in1 #abh2 parthenogenetic1 #agf2 reverses inorganic tendencies1 #cbd2 impossibility of chemical hypotheses1 #ada2 is the assumption of a mosaic structure1 #cja2 blastula stage in1 #abi2 gastrula stage in1 #acj2 pluteus stage in1 #adj2 individual1 #cjj4 ,developmental systems prospective value of1 #ach2 prospective potency of1 #ach4 ,diatoms1 #afc2 distribution of1 #bfj4 ,differential elements1 #aae4 ,differentiation in development1 #agj4 ,diffusion in the animal body1 #ie4 ,digestion1 #fg2 chemistry of1 #gb4 ,dinosaurs1 an unsuccessful line of evolution1 #bge4 ,dissipation of energy1 #aad2 in physical mechanisms1 #ei2 by the organism1 #fh1 #gi4 ,distribution of organisms1 #bfb2 limits to1 #bei2 indicative of dominance1 #beh4 ,diversity1 physical1 #ed2 effective and ineffective1 #aae4 ,dominance in geological time1 #beh2 implies long geological history1 #bfa2 ,mendelian1 #aif4 ,dominant organisms1 #beh1 #bei1 #bfd4 ,driesch natural selection1 #bbi2 analytical definition of the organism1 #cca2 entelechy1 #cah2 experimental embryology1 #acd2 historical basis of reacting1 #aed2 logical proof of vitalism1 #acf2 proof of vitalism from behaviour1 #aec2 theory of the absolute1 #dg4 ,duration1 #bh2 duration and time illustrated1 #cj2 illustrated by immunity1 #ce2 more than memory1 #aee2 a factor in responding1 #aee4 ,ecdysis1 #bgf4 ,echinoderms1 morphology of1 #bdh4 ,ectoderm1 #agg4 ,effector organs1 #aeh1 #bga4 lan vital1 #afa4 ,electromagnetism1 #cee4 ,electrons1 #cjd1 #cee4 ,elimination1 natural1 #bbi4 ,embryological stages compared with physical phases1 #cjh4 ,embryology1 #abg2 hypotheses of1 #abh2 physical hypotheses fail1 #abh2 experimental1 #abh2 suggests phylogenetic history1 #bac4 ,emulsoids1 #ajh4 ,endoskeleton1 #agg1 #bgf4 ,energetics1 first law of1 #ea2 second law of1 #aac4 ,energy1 #cef2 available and unavailable1 #ee2 biotic1 #cbe2 chemical1 #fa2 and causation1 #ed2 degradation of1 #fc2 dissipation of1 #ec2 electrical1 #fa2 forms of1 #cbe2 kinetic1 #eb1 #ceg2 mechanical1 #fj1 #fa2 potential1 #ec1 #ceh2 of position1 #cfj4 ,energy-transformations1 #ed1 #cga2 anabolic1 #hi2 in the animal1 #gj2 compensatory1 #hh2 compensatory organic1 #bfh2 irreversible1 #ei2 in physical mechanisms1 #eh2 in the plant1 #ga4 ,engelmann1 and the artificial muscle1 #aje4 ,entelechy1 #afa1 #cah2 not energy1 #cbi2 is power of direction1 #cbi2 not spatial but acts into space1 #ccj2 an intensive manifoldness1 #ccj2 is arrangement1 #cbc2 involves regulations1 #cbc2 arrests inorganic happening1 #cbg2 initiates chemical happening1 #cbg2 compared with enzyme action1 #cbg2 illustrated by analogy1 #cbb4 ,entropy1 #ed2 augmentation of1 #ge2 and ,carnot engine1 #cfi4 ,environment1 does not select variations1 #bce2 made by the organism1 #bcf4 ,enzymes1 #ij2 nature of1 #ib2 pancreatic1 #ic2 reversible1 #ic2 activation of1 #ib4 ,enzyme activity1 #ic4 ,epigenesis in development1 #abi4 ,equilibrium1 chemical1 #ajb4 false1 #hf1 #aea4 ,ether of space1 #df1 #cjd1 #cfa2 potential energy resides in1 #cfa4 ,evolution tendencies of1 #beb1 #bfd1 #bgf1 #bie2 separation of tendencies1 #bif2 a transformation of intensive into extensive manifoldness1 #cji2 a dissociation of tendencies originally coalescent1 #cje2 increases diversity1 #caj2 segregates energy1 #caa2 compared with permutations and combinations1 #cja2 a series of phases in a transforming system1 #bih2 a logical hypothesis1 #bad2 parallel processes in1 #bcd2 geological time inadequate for1 #bcg2 side paths in1 #bfb2 mechanistic hypotheses inadequate1 #bcg2 cosmic1 #bad1 #big1 #cad2 of the crust of the earth1 #bfd4 ,excretory products1 #bfi4 ,exoskeleton1 #bgf4 ,exothermic reactions1 #hf4 ,experience and duration1 #aef4 ,experimental biology proves evolution1 #bdf4 ,explosive reactions1 #aja4 ,extension in space1 #ah4 ,extinct groups1 #bfc4 ,fats1 digestion of1 #ic4 ,fecundity of animals1 #agi1 #bci4 ,ferments1 #ib4 ,fertilisation 7in reproduction71 #agf4 ,finalism1 #baf4 ,fishes1 distribution of1 #bfa4 ,fluctuating variations1 #bjj4 ,food-stuffs1 absorption of1 #hi4 ,force1 #ced4 ,form1 accidental and essential1 #afg1 #cec2 geological1 #afh2 crystalline1 #afh4 ,frequency distributions1 #bb1 #ahg1 #cej4 ,frog1 development of egg of1 #aca4 ,functionality1 #cdc2 in physical systems1 #cjg4 ,galvanotropism1 #ade4 ,gases1 compression of1 #cfb2 kinetic theory of1 #aag1 #cfa4 ,gastrea-theory1 #agg2 illustrated1 #bee2 limitations of1 #bef4 ,genera1 stability of1 #ahf4 ,geometry1 ,cartesian1 #be2 ,euclidean1 #ai1 #be2 perceptual and conceptual limits1 #ba4 ,geotropism1 #add4 ,germ-cells1 #age2 and soma1 #agi4 ,germinal selection1 #bda4 ,germ-layers1 #agg2 theory of1 #bef4 ,germ-plasm1 a mixture1 #bdj2 stability of1 #bdj4 ,givenness1 #dg4 ,gonads1 #agi4 ,growth law of1 in the organism1 #agb2 by accretion1 #afi2 by ecdysis1 #bgf2 geometrical1 #afi2 physical1 #afg2 of crystals1 #afg2 and differentiation1 #agj2 variability of1 #agb4 ,haeckel1 the ,gastrea-,theorie1 #agg1 #bed4 ,harmonic analysis1 #aa4 ,harvey1 and the circulation of the blood1 #aba4 ,heat1 flow of1 #aag2 production of1 in physical changes1 #aad4 ,heliotropism1 #add4 ,heredity1 #aha4 ,hertzian waves1 #cee4 ,homoiothermic animals1 #fg4 ,hormones1 #bbe4 ,human activity1 tends to arrest dissipation of energy1 #cab4 ,huxley1 #hd2 and mechanistic biology1 #abg2 and the physical basis of life1 #aac2 and mechanism1 #ajf2 and universal mathematics1 #bae4 ,hybrids1 ,mendelian1 #aif2 infertility of1 #aie2 between ,linnean species1 #aid4 ,hydra1 regeneration of1 #afb4 ,idants1 #ahc4 ,idealism founded on pure reasoning1 #de2 of ,berkeley1 #de4 ,ids1 #ahc4 ,immunity1 #ce4 ,individual1 #afb2 definition of1 #afg4 ,individuality1 orders of1 #afc2 physical concept of1 #afe2 morphologically an artificial concept1 #aff2 in societies1 #aga4 ,inertia1 #ced4 ,infinity1 a definition of1 #cdb4 ,inorganic happening abolishes diversity1 #caj4 ,instinct1 a problem for naturalists1 #bhc2 an inheritable adaptation of behaviour1 #bhg4 ,instinct and intelligence1 #bhc2 distinction not absolute1 #bid2 may coexist1 #cjf4 ,instinct and functioning1 #bhf4 ,instinctive actions not necessarily unconscious1 #bhc2 not learned1 #bhf2 not necessarily perfect1 #bhd2 effective from the first1 #bhe2 capable of improvement1 #bhe4 ,intelligent actions1 non-inheritable adaptations of behaviour1 #bhg2 involve deliberation1 #ej1 #bhg2 involve conscious relations with the environment1 #bhh2 involve use of tools1 #bhd4 ,intensity-factors1 #fa4 ,intensive multiplicity1 #cjc4 ,irreversibility1 #fb4 ,irritability1 #ajj4 ,isothermal changes1 #cfa4 ,james1 ,william 7and academic philosophies71 #hj4 ,jennings1 and physiological states1 #aed2 behaviour of ,protozoa1 #bic2 animal movements1 #adi2 the avoiding reaction1 #adi4 ,katabolism1 #ij4 ,kinases1 #ib4 ,kinematographic analysis1 #caf4 ,lamarck1 hypotheses of evolution1 #bbj4 ,lamarckian inheritance1 an inadequate cause of transformism1 #bbg4 ,lankester1 acquired characters not inherited1 #bba4 ,laplace1 and universal mathematics1 #bae4 ,laplacian mind1 #bii4 ,larval stages1 #agj4 ,latency 7of characters71 #aie4 ,lavoisier1 and chemistry of the organism1 #abg4 ,life and adaptation to physical conditions1 #cch2 and reversibility1 #cci2 a direction of energies1 #cda2 defined energetically1 #ccg2 cosmic origin of1 #cch2 physical conditions for1 #cch2 limited in power1 #cjf2 sparsity of1 on the earth1 #cjf2 tends to arrest dissipation of energy1 #cad2 its origin a pseudo-problem1 #ccg4 ,life-substance1 the primitive1 #cja4 ,locomotion1 #beh4 ,loeb and the associative memory1 #aee2 and artificial parthenogenesis1 #agf2 mechanism and life1 #abg2 stereotropism1 #ai2 theory of tropisms1 #add2 tropistic movements1 #adf2 theories of heredity1 #aha4 ,limit1 the mathematical1 #cdf4 ,limits to perceptual activity1 #bc4 ,links1 missing1 #beb4 ,linnean species1 #bja4 ,manifoldness1 intensive1 #cjb4 ,mass1 #cec4 ,mass action1 #adj4 ,materialism1 #he4 ,mathematics1 evades consideration of time1 #ce4 ,matter1 #cec2 inert1 #cge2 notion of is an intuitive one1 #ceb4 ,maxwell1 and sorting demons1 #aaf1 #cgg4 ,mayow1 and chemical physiology1 #abf4 ,mechanical work1 done by the animal1 #fg2 not done by the plant1 #ga4 ,mechanism1 organic and inorganic1 #gh2 the thermodynamic1 #ff2 radical1 #bae2 in life1 #aba4 ,membranes1 semi-permeable1 #ie4 ,memory1 #ci2 a possible cerebral mechanism of1 #aeh2 mechanistic hypotheses impossible1 #aeg4 ,mendelism1 #aif2 a logical hypothesis1 #aii2 terminology is a symbolism1 #aih2 analogy of unit characters with chemical radicles1 #aig2 transmission of characters of1 #bcj4 ,mesoderm1 #agg2 origin of1 #bee4 ,metabolism1 #cg1 #hh1 #bji2 analytic1 #bfi2 of animals1 #fe1 #fg2 constructive1 #bfi2 destructive1 #bfi2 direction of1 #fi2 in green plant1 #gj1 #ge2 intra-cellular1 #ii2 integration of its activities1 #aaa2 rle of oxygen in1 #aje2 specialisation of during evolution1 #cje2 synthetic1 #bfi4 ,metaphysics of science1 #de4 ,metazoan animals1 #afb4 ,mitosis1 #ahb4 ,mobility1 organic1 #bfi2 structural adaptations tending to1 #bge4 ,modifications of structure adaptive and non-adaptive1 #bea4 ,molecules1 #cec2 size of1 #aaf2 in a gas1 #aae2 aggregations of1 #ajh4 ,molluscs1 morphology of1 #bdi4 ,morgan1 and physico-chemical mechanisms1 #abh1 #adc4 ,morphogenesis1 #beg4 ,morphological evolution1 tendencies of1 #bie4 ,morphological structures degeneration of1 #bea2 suppression of1 #bej2 coalescence of1 #bej2 replacement of1 #bej2 specialisation of1 #bej2 change of function of1 #bea4 ,morphology1 #bji2 a basis of classification1 #baj2 relates groups of organisms1 #baa2 distinctions of1 not absolute1 #bhe1 #bij2 generalised1 #bej2 suggests blood relationships1 #bac2 schemata of1 #bdi1 #bia2 cannot be considered apart from physiology1 #bhe4 ,mosaic-theory of development1 #aca4 ,motion not an intellectual concept1 #bg2 not considered in ,euclidean or ,cartesian geometry1 #bf2 bodily motion is absolute1 #bd2 outside ourselves is relative1 #bd4 ,motor-habits1 #ch1 #aee4 ,multicellular organisms1 evolution of1 #bbc4 ,muscular contraction1 #ajd2 metabolism in1 #ajd2 heat production in1 #ajd4 ,muscular and nervous organs1 #bge4 ,musculature and weight of body1 #bge4 ,mutations1 #ahi2 essential nature of1 #aic2 causes of1 #bjj2 must be co-ordinated1 #bca2 physical model of1 #aib2 the material for selection1 #bcj4 ,ngeli1 and autonomy in development1 #afj4 ,natural selection1 #bbh2 generality of1 #bbi2 a slow process1 #bcj4 ,nebul1 #cae4 ,nebular hypothesis1 #bif4 ,nerve impulses1 #ajj2 velocity of1 #aja2 integration of1 #bgc4 ,nervous system1 #bgb2 in co-ordination of activities1 #aga2 paths in1 #aeg4 ,nervous activity1 #ajg2 metabolism in1 #ajg2 electric changes in1 #ajg2 influence of metabolism on1 #ig4 ,nothing1 a pseudo-idea1 #ah4 ,nucleus1 evolution of1 #bbb2 division of1 #acj1 #ahb4 ,ontogenetic stages1 #bee4 ,orders of individuality1 #aga4 ,organism1 definition of1 #cca2 analysis of its activities1 #aji2 animal and plant1 #gf2 considered energetically1 #gg2 the dominant1 #beh2 a function of the environment1 #baf2 a mechanism1 #ea2 the primitive1 #bbb2 a physico-chemical system1 #fe2 a thermodynamic mechanism1 #ajd4 ,organic chemical syntheses1 #cag4 ,organisation in development1 #acg4 ,organ-rudiments1 #beg4 ,osmosis1 #ie1 #ii4 ,ostracoderms1 #bia4 ,ostwald on catalysis1 #ia4 ,ovum1 development of1 #abi2 maturation of1 #aih1 #bci2 an intensive manifoldness1 #cjb4 ,oxidases1 #aje4 ,oxygen in metabolism1 #fi4 ,pain1 ,bergson on1 #bha4 ,palontology1 #baj2 relates groups of organisms1 #baa4 ,pangenesis1 #aha4 ,paramcium1 division of1 #agc1 #age2 responses of1 #d4 ,parasitism1 #bei2 tends to immobility1 #bij4 ,parthenogenesis1 #agf2 artificial1 #agf4 ,particles1 #cef4 ,pecten1 eye of1 #bcc4 ,perception not merely physical stimulation1 #g2 involves effector activity1 #g2 involves deliberative action1 #i2 arises from acting1 #ej2 and choice of response1 #aee2 is unfamiliar cerebral activity1 #h2 skeletonises consciousness1 #dj4 ,peridinians1 #gg1 #afc2 distribution of1 #bfj4 ,personal equation1 #de4 ,personality1 #afg2 an intuition1 #afg2 division of1 #agc2 is absolute1 #dh4 ,pflger1 and experimental embryology1 #aca4 ,phases in physical systems and organic systems1 #cba2 in transforming systems1 #cjh4 ,phenomenalism1 #df4 ,photosynthesis1 #gj1 #gf1 #hf4 ,phototaxis1 #add4 ,phyla animal1 #bdg2 morphology of1 #bdg2 relations between1 #beb2 ancestries of1 #beb4 ,phylogenies1 #bec2 are summaries of morphological results1 #bed2 indicative of directions of evolution1 #bed2 criteria of1 #bec4 ,phylogeny1 #bdf4 ,phylum1 #baj4 ,physical basis of life1 #hd4 ,physico-chemical reactions1 #hj2 are directed1 #aah2 the means of development and behaviour in the organism1 #afj4 ,physico-psychical parallelism1 #afj4 ,physics1 a statistical science1 #aaf1 #cgg4 ,physiology ,galenic1 #abb2 an analysis of organic activity1 #abj1 #cbh4 ,plants1 geological history of1 #bfa2 characterised by immobility1 #bgg2 contrasted with animals1 #bgg4 ,platonic ideas1 #bjd4 ,platyhelminths1 morphology of1 #bdh4 ,poikilothermic animals1 #fh4 ,poincar1 and ,brownian movement1 #aai4 ,polar bodies1 #aih4 ,polyzoa1 #afd4 ,porifera1 #bdh4 ,potential1 #fa4 ,potential energy1 #eh1 #aad4 ,preformation an embryological hypothesis1 #abh4 ,probability1 #cej4 ,proteids1 digestion of1 #ij4 ,proto-forms1 #bed4 ,protoplasm1 nature of1 #ajf2 artificial1 #ajf2 disintegration of1 #ajg2 activities of1 #ajg2 similar in plant and animal1 #bid4 ,protozoa1 #bdg2 behaviour of1 #bic4 ,pterodactyls1 #bgd4 ,races 7in specific groups71 #aid4 ,radiation1 #cee2 of sun1 #ea2 transformation of energy of1 #eg4 ,radio-activity1 #ef1 #cei4 ,reality1 objective1 #dc4 ,reception1 #c2 organs of1 #bga2 by specialised sense-organs1 #aa4 ,recessiveness1 ,mendelian1 #aif4 ,reflex action1 #d1 #bgb2 concatenated1 #aej2 a complex series of actions1 #f2 not necessarily accompanied by perception1 #aee2 the basis of instincts1 #aej2 a schematic description1 #e2 in decapitated frog1 #f2 frictionless cerebral activity1 #h2 involves a limited part of the environment1 #ej4 ,reflex arcs1 #bgb4 ,regeneration1 #adb2 in ,hydra1 #afd2 in sea-urchin embryo1 #afd2 in ,planaria1 #afd4 ,regression1 #ahi4 ,reinke1 and structure of protoplasm1 #ajf4 ,reintegration in development1 #aga4 ,rejuvenescence1 #age4 ,releasing agencies1 #aeg4 ,reproduction1 #afg2 asexual1 #age2 by brood-formation1 #agc2 by conjugation1 #agc2 sexual1 #agd2 by division1 #agb2 compared with minting machine1 #bdb2 of the tissues1 #ahj4 ,responses of organisms1 #bag2 directed1 #bfi2 of magnet1 #bgi2 of green plant1 #bgi4 ,reversibility1 physical1 #cfi4 ,rodewald1 chemical nature of protoplasm1 #ajf4 ,roux1 experimental embryology1 #aca2 development the production of a visible manifoldness1 #cjg4 ,saliva1 secretion of1 #if4 ,salivary glands1 metabolism of1 #if4 ,salivary secretion1 not a purely mechanistic process1 #aab4 ,sea1 not really rich in life1 #cjf4 ,sea-urchin gastrula1 #agj4 ,secretion described mechanistically1 #ih4 ,secretion1 psychical1 #ii4 ,segmentation of the ovum1 #abi4 ,selection1 natural1 #bbh2 from fluctuating variations1 #ahi2 from mutations1 #aij4 ,semon1 mnemic hypothesis of heredity1 #aha4 ,senescence1 #age4 ,sensation1 #b2 analysis of1 #ac4 ,sense-receptors and the idea of matter1 #ceb4 ,sensori-motor system1 #bgj2 dominant in animals1 #bga1 #bgc2 specialisation of1 #bga1 #bgc2 essentially the same in all animals1 #bid2 absent in plants1 #bfi2 vestigial in some parasites1 #bij4 ,sexuality1 #agd4 ,siphonophores1 regeneration in1 #afc4 ,size of animals1 #bgd4 ,skeleton of vertebrates1 #bgf2 of arthropods1 #bgf2 and mobility1 #bgf4 ,soddy1 and chemical energy1 #cfa4 ,soma1 #agi2 evolution of1 #bbc4 ,space1 form of1 #ah2 #c-;dimensional1 #ah2 #c-;dimensional space an intuition1 #ai2 #b-;dimensional1 #ai2 the form of1 depends on modes of activity1 #ba1 #be4 ,species1 are categories of structure1 #bja2 comparison with ,platonic ideas1 #bjd2 criteria of1 #bjb2 elementary1 #aic2 are intellectual constructions1 #bjc2 individuality of1 #bjc2 ,linnean1 #bja1 #bhi2 are phases in an evolutionary flux1 #bjf2 are families in the human sense1 #bjh2 systematic1 #bja4 ,specific organisation1 stability of1 #ahf4 ,stahl1 and the phlogistic hypothesis1 #abf2 and vitalism1 #abf4 ,stimuli1 elemental1 #aea2 physico-chemical1 #aea2 formative1 #agf2 complex auditory1 #aeb2 integration of1 #aeb2 individualised1 #aeb1 #bgj2 contractile1 #ajc4 ,stimulus and response1 functionality of1 #aeb4 ,substantia physica1 #df1 #cee4 ,surface tension1 #aje1 #ajf4 ,suspensoids1 #ajh4 ,sylvius1 the organism a chemical mechanism1 #abe4 ,symbiosis1 #gg4 ,symbiotic organisms1 #hh4 ,synapses1 in central nervous system1 #aeh1 #bgb4 ,synthetic chemistry1 #bcf1 #cag4 ,system1 isolated1 #fc4 ,systems in development equipotential1 #aci2 harmonious equipotential1 #aci2 complex equipotential1 #adj4 ,taxis1 #add2 no perception in1 #aee4 ,telegraphy1 wireless1 #cee4 ,temperature of sun1 #ef2 of space1 #eg4 ,thermodynamics1 #ea2 #ast law of1 #ea2 #bnd law of1 #ed1 #fc1 #cji1 #caf2 and ,maxwell's demons1 #aah2 laws of subject to limitations1 #aae4 ,thermodynamical mechanism1 the organism not a1 #fi4 ,thomson1 ,w41 dissipation of energy1 #aac4 ,time a series of standard events1 #bh2 astronomical1 #cd2 time differentials1 #cd4 ,tissues1 evolution of1 #bbc4 ,tools1 nature of1 #bhe2 use of must be learned1 #bhe2 bodily1 #bhe4 ,toxins1 #cf4 ,transformism1 #bac4 ,trematodes1 larval stages of1 #afe4 ,trial and error1 #bic2 in reasoning1 #bic2 a hypothesis of animal movements1 #aej4 ,trigger reactions1 #hg4 ,trilobites1 an ancient group1 #bfa4 ,tropisms1 #add2 in plants1 #bfi1 #bgi2 in moths1 #bhj2 and natural selection1 #adg2 and movements of caterpillars1 #adf2 an inadequate basis for a theory of animal movements1 #adg4 ,tunicates1 suppressed notochord of1 #bej4 ,unavailable energy and entropy1 #cge2 tendency to increase of1 #cge4 ,unicellular organisms1 energy-transformations in1 #agg4 ,unit-characters1 #bcj4 ,van't ,hoff's law1 #bah4 ,variability1 #agb1 #ahf2 continuous1 #ahh2 discontinuous1 #ahh2 examples of1 #ahg2 and the environment1 #ahi2 independent of the environment1 #bci2 and growth1 #ahh2 tendencies of1 #bce4 ,variation1 rate of 7mathematical71 #cdd2 in biology1 #ahf2 atavistic1 #aie2 direction of1 #bcc2 fluctuating1 #ahi2 must be co-ordinated1 #bca2 mathematical probability of co-ordination of #bcc2 the material for selection1 #bbi2 origin of1 #bcj2 selected by the organism1 #bcg2 cause of1 a pseudo-problem1 #bdb2 arise de novo1 #bdd4 ,variables 7mathematical71 #cdc4 ,varieties1 specific1 #aid4 ,vegetable life1 #bfe4 ,vertebrates1 #bdi2 adaptations securing mobility1 #bge2 ancestry of1 #bec2 morphology of1 #bdi2 a dominant group1 #bei2 distribution of1 #bfj4 ,verworn1 and mechanism in life1 #abg4 ,vesalius1 anatomical school of1 #aba4 ,vital activities1 integration of1 #abh2 co-ordination of1 #aga4 de ,vries and mutations1 #aia2 fluctuating variations inherited1 #bbj4 ,vital force1 #cah4 ,van der ,waal's equation1 #cjh4 ,weber's law1 #af2 a quasi-mathematical relation1 #ag4 ,weismann1 hypothesis of heredity1 #ahb2 hypothesis of germinal selection1 #bda2 hypothesis of development1 #acb2 mosaic-theory1 #aca2 preformation hypothesis1 #acc2 hypothesis of the germ-plasm1 continuity of the germ-plasm1 #aha2 germinal changes inconceivable1 #bbd2 size of biophors1 #ahc2 origin of life1 #cci2 spontaneous generation a logical necessity1 #cci4 ,weismannism1 a series of logical hypotheses1 #cbj2 physico-chemical analogies1 and subsidiary hypotheses1 #bbc4 ,whales1 an unsuccessful line of evolution1 #bgd4 ,whitehead1 and mathematical reasoning1 #cdg4 ,wilson1 mosaic-theory of development1 #aci4 ,yerkes1 and behaviour of crustacea1 #bic4 ,zymogens1 #ib4 ,zymoids1 #id4 ,,printed ,,by ,,turnbull ,,and ,,spears1 ,,edinburgh ,spelling corrections3 animo-acids amino-acids animo-substances amino-substances differen tkinds different kinds algae alg organsim organism 7x#b7 diffusbility diffusibility marjoity majority hythothesis hypothesis execretory excretory conconsidered considered