statical form, as the organism, it is phenomenally known under its dynamical form as the energy diffusing itself through the organism, and, among other parts, through the nervous system. Given the external stimuli, and the nervous changes with their correlative mental states, * depend partly on the nervous structures and partly on the • amount of this diffused energy: each of which factors is [determined by causes not in consciousness but beneath con- sciousness. The aggregate of feelings and ideas constitut- ing the mental I, have not in themselves the principle of cohesion holding them together as a whole; but the I which continuously survives as the subject.of these chang- ing; states, is that portion of the Unknowable Power which is Statically conditioned in special nervous structures pervaded by a dynamically -conditioned portion, of the JJn- I tnowable Power called energy. (Compare with § 469.)
NOTE TO PABT IV- IN his Principles of Mental Physiology, Dr. Carpenter, referring to the doctrine of mental evolution as caused by the inherited effects of experiences, developed in the foregoing chapters, says: — " But it had been distinctly foreshadowed as regards the Instincts of animals (which are only lower forms of Man's intellectual Intuitions) by Sir John Sebright, Mr. T. A. Knight, and M. lionlin j of \vbose observations a summary has been given by the Writer in the Contemporary Review,, January, 1873H * * * And in the Fourth and Fifth Editions of his * Human Physiology,! published respectively in 1852 and 1S55, the Writer had distinctly expressed; his belief that the Cerebrum of Man grows to the modes of thought in which it is habitually exercised; and that such modifications in its structure are transmissible hereditarily. * * * He here refers to this fact, merely to show that the general doctrine above enunciated * * * is much older than Mr. Herbert Spencer."
Communications to which the above passage led, disclosed the fact that Dr. Carpenter had not read this work; but had, as I understood, purposely refrained from doing so. I pointed out to him the difference between the proposition that transmitted mental modifications produce varieties of mental faculty within the limits of a species; and the proposition that Mind, in all its faculties, is produced by transmissions of such modifications through all the successions of species during the evolution of life upon the Earth. After obtaining from Dr. Carpenter the admission that this latter proposition had not even been entertained (much less elaborated into a system) by those he names, I concluded that he would, in his next edition, alter the above statement. He has not done this, however; and therefore, somewhat reluctantly, I must myself point out the grave misrepresentations it embodies.
Manifestly no one can entertain the belief that the psychical* powers of all creatures have arisen by evolution, without tacitly or avowedly committing himself to the belief that their physical struc- tures have arisen by evolution. Dr. Carpenter is fully aware that* in 1855, when the first edition of this work was published, the " development-hypothesis," as it was then commonly called, was repudiated by men of science, as well as by the world at^Iarge; and further, that any one who held it exposed himself to the ridicule of the scientific. He does not allege that those he names believed it; much less gave a public adhesion to it. Yet now, in the above passage, he asserts that he and others had enunciated in a genera] NOTE TO PART IV.
way, the doctrine elaborated in this work: they avowed a conclu- sion the necessary premises of which they did not admit!
Either Dr. Carpenter is still In the' position of not having read this work, or lie lias read it since the time above referred to. If he has Dot read it. then it is strange that he should undertake to correct the impressions of;i younger readers," concerning the relation between its views and the views previously held (see Contemporary Revieic, for February, 1875). If he has read it, then it is even more strange that he should persist in the above state* rneoc. In the first place, he must have become aware that the facts and inferences named by him, as current before this work was written, are referred to in this work as familiar — are taken • as established (§ ISO, in edition of 1855); not propounded as new. In the second place, he must have seen that these facts and infer- ences are used as part of my data — that my reasonings begin where the reasonings he names leave off. And yet having seen this, he identifies the theory that mental modifications within the limits of a species are producible by inherited effects of experiences, with the theory that the genesis of all mental faculties, down to forms of thought, have been thus produced. He alleges pre- vious currency of the " general doctrine." It seems to me that his ideas of general and special are no less remarkable than his idea of identity. The proposition that such changes of dog-nature as a pointer's habits show, arise by inherited mental modifications, would commonly be thought a special proposition; while the proposition ihat by inherited..modifications., there has been an evol- iiiTon_p^ from reflex action up_to abstract reason aod jii oral sentiment, would commonly be thought a general proposition. But Dr.'~Carpenter thinks the contrary. Doubtless, in*pulrsuance of the same view, he regards the doctrine that pigeons and other domestic animals may have their structures modified by selection, as a "general" one /and the doctrine of Mr. Darwin, that all structures of all animals are caused by natural selection, as a special one. For the two cases are perfectly similar. Between the idea that structural changes are producible within the limits of a species by selection, and the idea that all organization is thus producible, there is a relation exactly parallel to the relation be- tween the idea that the instincts of a species may be changed by inherited effects of experiences, and the idea that all mental or- ganization is producible by the inherited effects of experiences.
Hence, we may expect that when next Dr. Carpenter refers to the hypothesis of " natural selection," he will point out thac it had been distinctly foreshadowed by Sir John Sebright, Mr. Youatt, and others; and after quoting passages from their writings, will remark- that he does so u merely to show that l\& general doctrine " " is macb older than " Mr. Darwin.
PART Y.
PHYSICAL SYNTHESIS.
CHAPTER L A FURTHER INTERPRETATION NEEDED.
§ 221. We are now prepared for dealing with, the remain- ing problem presented by objective Psychology. Though not conspicuous,, the hiatus between the interpretation we have reached and a complete interpretation,, is a deep one; and one which, when first) looked into, appears impassable. For there has still to be answered the inquiry — how is mental evqlution to be affiliated on Evolution at large, regarded as a process of physical transformation? It is not enough that in the preceding General Synthesis the phenomena of psy- chical life have been traced up through their objective manifestations, and, along with the phenomena of physical life, have been found to progress in integration, in hetero- geneity, in definiteness. It is not enough that, in the Special Synthesis just closed, intelligence has been shown to have the same nature and the same law from the lowest reflex action up to the most transcendent triumph of reason; and that, from first to last, its growth is due to the repetition of experiences, the effects of which are accumulated, organ- ized, and inherited. It may yet be asked — By what process; is the organization of experiences achieved? Granting that/ a survey of the facts proves it to take place; still, no an-" swers are given to the questions — Why, does it take pla^e?\ And how does the transformation 'which brings it about*' come^nthin the formula of Evolution in general?
£03 PHYSICAL SYNTHESIS.
Specifically stated, the problem is to interpret mental evolution in terms of the re-distribution of Matter and Motion. Though under its subjective aspect, Mind is known only as an aggregate of states of consciousness, which cannot be conceived as forms of Matter and AJotion, and do not therefore necessarily conform to the same laws of re-distribution; yet under its objective aspect, Mind is known as an aggregate of activities manifested by an or- ganism— is the correlative, therefore, of certain material transformations, which must come within the general pro- cess of material evolution, if that process is truly universal. Though the development of Mind itself, cannot be ex- plained by a series of deductions from the Persistence of Force, yet it remains possible that its obverse, the develop- ment of physical changes in a physical organ, may be so explained; and until it is so explained, the conception of mental evolution as a part of Evolution in general, remains incomplete.
§ 222. Here, then, the structure and functions of tho nervous system, considered as resulting from intercourse between the organism and its environment, form our sub- ject-matter. We have to identify the physical process by which an external relation that habitually affects an or- ganism, produces in the organism an adjusted internal relation.
Of course, it is not to be expected that specific interpre- tations can be given of the particular structures perform- ing particular functions which fit an animal to its particular conditions of existence. All we can hope is to assign a general cause, which, acting under conditions such as are known to exist, is capable of producing effects like those observed. Let us present in its simplest and most definite form the question which alone admits of an answer.
We have seen the law of intelligence to be, that the strength of the tendency which the antecedent of any psy- A FURTHER INTERPRETATION NEEDED. 509 chical change has to be followed by its consequent, is propor- tionate to the persistence of the union between the external things they symbolize. We have seen that the fulfilment of this law is accounted for if, by inheritance through successive organisms, intelligence grows, as it does in the individual or- ganism, in consequence of the fact that, when any two psy- chical states occur in immediate succession, such an effect is produced that when the first recurs, there is a tendency for the second to follow it. And now, to complete the solution, we have to ascertain the universal principle to which this tendency is due. In other words, regarding psychical changes as the subjective faces of what on their ob- jective faces are nervous actions, the inquiry before us is — • from what general law of the re-distribution of Matter and Motion does it result, that when a wave of molecular trans- formation passes through a nervous structure, there is wrought in ibe structure a modification such that, other things equal, a subsequent like wave passes through this structure with greater facility than its predecessor? And — not to evade a still deeper question which immediately follows — is the establishment of nervous communication it- self explicable on this same general principle? Are we enabled by it to understand not only how nerve becomes more permeable, but how nerve is formed?
If to these general questions we discover a satisfactory general answer, we shall do all that is needful. If from a corollary to the Persistence of Force, we can legitimately draw the conclusion that, under certain conditions, lines of nervous communication will arise, and, having arisen, will become lines of more and more easy communication, in pro- portion to the numbers and strengths of the discharges pro- pagated through them; we shall have found a physical interpretation which completes the doctrine of psychical evolution, as set forth in the last two parts. It will be made manifest how the experience of an external relation pro- duces a corresponding internal relation — how, as experiences 510 PHYSICAL SYNTHESIS.
of tlie external relation become more numerous,, the internal relation becomes more coherent — how perpetual repetitions of the one cause indissolubleness of the other — how outer persistences that are almost or quite absolute, establish, in the course of generations., inner cohesions that are automatic or organic; and thus the interpretation of instincts and forms of thought will be assimilated to that of the ordinary phenomena of association.* * The general doctrine elaborated- in the succeeding chapters, was pre- figured in the first edition of this work, in a note on page 544 — the verbal form, however, being such as I should not now use. I made a more definite statement of it in an article published in the Medico-CJururgical Review for January, 1859.
CHAPTER II.
THE GENESIS OF NERVES.
§ 223. In First Principles, Part II., Cliap. IX., we found that in all cases, motion " follows the line of greatest trac- tion, or the line of least resistance, or the resultant of the two." We also saw " that motion once set up along any line "becomes itself a cause of subsequent motion along that line" — equally when the motion is that of matter through space, that of matter through matter, and that of mole- cular undulations through an aggregate of molecules.
In the section dealing with nervous actions (§ 79), it was contended that the mode of motion we distinguish as a nervous discharge, conforms to this law. " Supposing the various forces throughout an organism to "be previously in equilibrium, then any part which becomes the seat of a further force, added or liberated, must be one from which the force, being resisted by smaller forces around, will in- itiate motion towards some other part of the organism. If elsewhere in the organism there is a point at which force is being expended, and which so is becoming minus a force which it before had, instead of plus a force which it before had not, and thus is made a point at which the re-action against surrounding forces is diminished; then, manifestly, a motion taking place between the first and the last of these points is a motion along the line of least resistance. Now a sensation implies a force added to, or evolved in, that part of the organism which is its seat; while a mechanical move- M2 PHYSICAL SYNTHESIS.
ment implies an expenditure or loss of force in that part of the organism which is its seat. * * * When there is anything in the circumstances of an animal's life,, involving that a sensation in one particular place is habitually followed by a contraction in another particular place — when there is thus a frequently-repeated motion through the organism be- tween these places • what must be the result as respects the line along which the motions take place? Eestoration of equilibrium, between the points at which the forces have been increased and decreased, must take place through borne channel. If this channel is affected by the discharge — if the obstructive action of the tissues traversed, involves any reaction upon them, deducting from their obstructive power; then a subsequent motion between these two points will meet with less resistance along this channel than the previous motion met with; and will consequently take this channel still more decidedly."
In the Pr'iYu'lpltjS of Biology, § 302, tnis general proposi- tion was further elaborated. It there became needful to indicate a possible process by which, among other tissues, nerve-tissue arises out of that protoplasm composing the nndifferentiated organism. Here, in an abbreviated form., is the argument which was used: — (C It is to be inferred that a molecular disturbance in any part of a living animal, set up by either an external or internal agency, will almost certainly disturb and change some of the surrounding colloids not originally implicated — will diffuse a wave of change towards other parts of the organism: a wave which will, in the ab- sence of perfect homogeneity, travel further in some direc- tions than in others. Let us ask next what will determine the differences of distance travelled in different directions, Obviously any molecular agitation spreading from a centre, will^ go furthest along routes that offer least resistance. What routes will these be? Those along which there lie most molecules that are easily changed by the diffused molecular motion, and which yet do not take up much THE GENESIS OF NERVES. 6 I'd molecular motion in assuming their new states. * * * Unstable molecules which, in being isornerically trans- formed, do not absorb motion, and still more those which, in being so transformed, give out motion, will readily pro- pagate any molecular agitation; since they will pass on the impulse either undiininished, or increased, to adjacent mole- cules. * * * It may be concluded that any molecular agitation set up by what we call a stimulus, will diffuse itself further along some lines than along others, if " the mingled colloids forming " the protoplasm are not quite homogeneously dispersed, and if some of them are isomeric- ally transformed more easily, or with less expenditure of motion, than others; and it will especially travel along spaces occupied chiefly by those molecules which give out molecular motion during their metamorphoses, if there should be any such. * * * As is shown by those transformations that so rapidly propagate themselves through colloids, molecules that have undergone a certain change of form, are apt to communicate a like change of form to adjacent molecules of the same kind — the impact of each overthrow is passed on and produces another over throw. * * * Is this action limited to strictly isomerio substances? or may it extend to substances that are closely allied? # # # There is reason to suspect that it does. Already when treating of the nutrition of parts, it was pointed out that we are obliged to recognize a power pos- sessed by each tissue to build up, out of the materials brought to it, molecules of the same type as those of which it is formed. * * * If this be a general principle of tissue-growth and repair, we may conclude that it will apply in the case before us. A wave of molecular disturb- ance passing along a tract of mingled colloids closely allied in composition, and isomerically transforming the molecules of one of them, will be apt at the same time to form some new molecules of the same type, at any place where there exist the proxiuiate components, either uncombined or L L 514 PHYSICAL SYNTHESIS.
feebly combined in some not very different way. * * * That is to say, a ware of molecular disturbance diffused from a centre, and travelling furthest along a line where lie most molecules that can be isomerically transformed with facilitv, will be likelv at the same time to further differen- tiate this line, and make it more characterized than before by the easv-transforinability of its molecules/' Referring1 the reader to the Principles of Biology for the details and conclusion of this abridged argument/, it may be well to remind him that in the first part of this work, the interpretations of nerve-structure and nerve-function were grounded on a conception which is a corollary from the conception 'recalled above j and that sundry verifications were there found. We saw that the quantity of effect pro- duced by irritated nerve-fibre, increases with tiie distance between the place of irritation and the place of discharge; and this accumulation of force we found to be just that winch would result from a wave of isomeric transformation through matter of the required kind (§ 19). We saw, too, that the ultimate nitrogenous nerve-threads are severally sheathed in a peculiar substance, which, judging by its un- equalled molecular complexity, is less capable than any other known substance of transferring molecular motion, and therefore best fitted to prevent lateral loss of that growing wave of molecular motion which a nerve-fibre transmits. And we further saw that a close analogy exists between this assumed propagation of isomeric change along a nerve-fibre, and certain observed propagations of like changes along fibres of other substances (§ 34). To which let me here add the fact that protoplasm and its derivatives are distinguished by the great number of their isomeric forms, and the great facility with which these are changed by Very various agents; so that in regarding* a nervous dis- charge as a wave of isomeric transformation, we are re°tard- ing it as one out of the many such transformations which living matter continually undergoes.
THE GENESIS OF NEB FES. 515 . § 224. Another preliminary step remains. We Have to observe the possible modes in which a line of nervous communication may be improved. When, through undif- : ferentiated tissue, there has passed -for the first time a wave ^ of disturbance from some place where molecular motion is f* liberated to some place where it is absorbed, the line of least resistance followed must be an indefinite and irregular one. Fully to understand the genesis of nerve, then, we must understand the physical actions which change this vague course into a definite channel* that becomes ever more permeable as it is more used.
Several actions conduce to this result. The first is that already described, by which, along a line of discharge, there is a genesis of the matter most capable of com- ii lamenting the discharge. Every time an incipient nerve is traversed by another wave of molecular motion, there is apt to be a further formation of the molecules which are isomerically transformed by the wave and pass it on in being transformed. This process acts with continually -increasing power, for two reasons. One is that progressing limitation of the wave to a well-marked line, enables it to produce more decided effects along that line. An illustra- ' tion will here help us. When a body of water flows over a surface offering no distinct course,, it thins out into wide- -; spread shallows near its margin, where it is almost motionless; and it has but little motion even along its central J - deepest parts. But if the inundation is long continued, the j abraiding action of the current along these central deepest t parts where it moves fastest,, tends to deepen its channel ] thei-e more than elsewhere. A secondary result is a retreat ; of the water from the shallows— the current becomes more 1 concentrated. In proportion as it becomes more concentrated the force of its central part becomes greater still, and the deepening more rapid; which entails a further drawing in of the margins and a further addition to the excavating force. So that the growing definiteness of the current 516 PHYSICAL SYNTHESIS.
brings a growing power of making its channel quite definite. Now though, in the case "before us we have not a motion of matter over matter, but} a transfer of molecular motion from molecules to molecules,, the parallel holds. Any greater effect produced by the transfer along one part of its originally-broad course, similarly tends to concentrate the transfer along this part, and thus to intensify the action which makes this part a precisely-marked chan- nel. A further facilitation results from an absolute increase in the amount of the nervous discharge. The more permeable the line of molecules becomes, the greater be- comes the initial quantity of molecular motion it draughts off. As with water, the formation of a definite channel not only makes the transfer easier and adds to the excavatino- power of the current, supposing its volume be constant, but also "(if the reservoir can supply more) augments the volume carried away, which again adds to the excavating power; so the formation of a better line of nervous communication is followed by an increase of the wave that sets out to traverse it, and a consequent increase in the channel-makin en- action. Once more, every addition to the mole- cular motion transmitted, adds to the effectiveness of each discharge in overcoming an obstacle. Suppose the greater part of its channel has become tolerably permeable, but that at some place in it the colloidal matter is less transformed than elsewhere into the fit type. Then the more the rest of its channel increases in permeability, the more powerful must be the wave of molecular motion brought to bear on the un- transforrned part, and the greater must be the tendency to transform it. Hence the channel will progress towards a state of uniform permeability.
There is another possible, and I think probable, way in whiph the passage of a nervous discharge is made easier. The molecules of the peculiar colloid composing a nerve, may be either irregularly arranged or regularly arranged; and if irregularly arranged they will transmit a wave of TEE GENESIS OF SEKVES. 517 molecular motion less readily tlian if regularly arranged. Now when a thread of molecules capable of the required easy isomeric transformation is first formed, the probabilities are infinity to one that adjacent molecules will be unsvmmetrically placed with respect to one another — they will not stand in polar order. Molecules that are highly coiaplex and massive,, either do not crystallize at all or crystallize with great difficulty. Either their colloidal, non-polar arrangement is a permanent one, or it is one out of which they pass into a polar arrangement very slowly, under special conditions. Nevertheless, molecules of every type have a form of distribution in which their polar forces are in equilibrium. Towards this they must ever tend, however feebly j and towards this every slight molecular disturbance enables them to • approach. Hence, if through a line of colloidal molecules wholly out- of polar arrangement, there pass successive waves of molecular motion, each will help adjacent molecules towards polar arrangement, or state of equilibrium. Let us consider the concomitants.