by an object seen within reach; if at b are the roots of fibros which co-operate when this object is grasped; and if be- tween a and b lie the co-ordinating plexuses through which the compound sensory excitements lead to those compound motor excitements that cause prehension of the object, not when in one position only but when in the various positions it may occupy within reach; what will happen if some steps have to be taken before the visual impression is followed by prehension? The recipio-m-otor and diric/o-motor changes gone through during these acts of locomotion, imply sundry compound co-ordinations with their correlative plexuses. "Whatever sets of plexuses are successivelv so excited that the fibres at b are eventually acted on in the way re- quired to cause prehension, it must happen that these sets of plexuses will become a. network of lines of least resistance. For as shown in § 237, muscular co-ordina- tions that fail have, other things equal, less tendency to be THE GENESIS OF DOUBLY-COMPOUND NERVOUS SYSTEMS. 553 repeated when the same conditions recur than those that succeed; because those that succeed open lines of discharge that draw off large amounts of molecular motion. Between a and b, therefore, there will arise intercalated sets of plexuses which co-ordinate the successive locomotions and accompanying visual impressions gone through between the receipt of the original visual impression and the perform- ance of the eventual prehension. These sets of plexuses must be very numerous. Supposing the object to be one step out of reach, it may occupy multitudinous positions, high or low, to the right or left; and the required co-ordinat- ing plexus for each position, while it has much in common with those for adjacent positions, must have something different. But the space between a and b is alreadv occupied by the plexuses which effect the direct co-ordina- tions. Hence the intercalated plexuses which effect these indirect co-ordinations, must be super-posed, as at d; and the co-ordinating discharges must take roundabout courses, as shown by the arrow.
Each such position being reached through visual and muscular co-ordinations which are, within narrow limits, the same for all members of a species, it follows that there will eventually arise in the species an organized set of con- nexions such that the visual impression produced by an object in that position and the muscular actions by which it may be grasped are definitely correlated. Little by little the positions composing wider and wider spheres of space may come to be thus mentally possessed; while there is a concurrent enlargement of the superior co-ordinating centre, by the intercalation of new co-ordinating plexuses at its periphery, as shown at eyfy g.
§ 241. One further elaboration remains. To render the exposition of this doubly-compound co-ordination less difficult to follow,, I have thus far treated of it as though the relational elements involved we^e all of one class. But 554 PHYSICAL SYNTHESIS.
in reality there are two distinct classes of them, requiring distinct centres of co-ordination.
So long as tlie visual, muscular, and tactual impressions to be co-ordinated, refer exclusively to objects within reach, the relations of succession and the relations of co-existence are not definitely parted. It is true that when anything within this range has yielded its visual impressions, a certain series of muscular states has to be gone through before it yields irs tactual impressions. But when these have been gone through, the visual impressions as at first received and the tactual impressions as subsequently gained, co-exist — I can continuously gaze at the thing and continuously grasp it. Moreover, it is to be noted that in all these cases the order of sequence in the consciousness of visual impressions and tactual impressions may be inverted — I can feel the thing first and see it after. But when we pass from these compound co-ordinations to the doubly-compound co- ordinations, the elements of succession become of no less importance than the elements of co-existence. The serial states gone through can no longer be dropped out of the group, and the sequence from visual to tactual cannot by any possibility be inverted. That is to say, the time-relations and the space-relations have become distinctly differentiated. This needs some further explanation. When I walk towards an object, successive clusters of muscular and tactual feelings are implied by the steps I make; there is an accompanying series of gradually- enlarging and otherwise-changing visual impressions from the object as I approach it; and serial changes, more numerous and complicated, are produced through my eyes by adjacent objects. All of these successions, if I keep my eyes open, and certain of them even if I close my eyes, must Jbe gone through before the tactual impressions to be received from the object can be had. The visual impression, which the object made on me before I moved towards it, can be brought into relation with this tactual impression THE GENESIS OF DOUBLY-COiTPOUXD NERVOUS SYSTEilS. 555 only through certain serial states; and tliese not only form an indispensable chain by which the initial and terminal clusters of states are bound together, but they form a chain no one link of which can be taken out of its place — their order is fixed. Here then we have co-ordinations in Space and co-ordinations in Time uniting to achieve the entire co-ordination. Before a step is taken towards the object, the impressions made by it and all things around, stand in a plexus of relations of co-existence. Each step implies muscular and tactual sequences accompanied by numerous visual sequences; and the step ends by bringing about a modified plexus of co-existences. The two orders of relations are therefore correlatives, and serve to interpret one another. Without some means of registering the series of motions to be gone through in reaching the object,, there could be no consciousness of its distance. Without con- sciousness of its distance the muscular feelings jjone through could have no meanings in thought as the equivalents of certain spaces traversed.
But the differentiation of these two great orders of rela- tions implies a differentiation of co-ordinating centres. What form this differentiation takes among inferior types of animals we need not here inquire. In the highest or verte- i >rate type, however, there are, as before pointed out, reasons for concluding that the cerebellum is the organ of doubly- compound co-ordination in Space while the cerebrum is the organ of doubly-compound co-ordination in Time. To the reasons before assigned for this conclusion I may here add some others. One is that these two supreme nervous centres are pedunculated masses^growing out of the enlarged and differentiated extremity of the spinal chord, much as we might expect the centres of doubly-compound co-ordination to grow out of the ^centre of compound co-ordination. Another is that they preserve a general relationship in their development. From fishes "upwards their evolution goes on, if not with equal steps, 556 PHYSICAL SYNTHESIS.
still in something like proportion. This is a trait to be ex- pected; since the greater developments of senses and limbs •which they accompany imply simultaneously-increased ex- periences of time-relations and space-relations. As we approach the highest vertebrate types the cerebrum develops i\t a greater rate than the cerebellum — a fact also to be anticipated. For in the simpler vertebrate animals the only time-relations appreciable are those disclosed along with space-relations by acts of locomotion. But in the more com- plex vertebrate animals, whose organized experiences of time- relations thus acquired yield measures of duration of some length, other orders of sequences become cognizable; and the nervous centre in which time-relations are co-ordinated thus acquires functions peculiar to itself. The compositions of these two great centres harmonizes with the hypothesis. The process described in § 240 implies that a centre of doubly-compound co-ordination will be evolved by the intercalation of plexuses and the superposing of plexuses in successive strata — each new stratum added at the peri- phery of the mass serving to re-coordinate the co-ordinating plexuses below it. The layers of cells and fibres which the cerebellum and cerebrum contain, seem fit to constitute appliances of this kind. Yet again, the minute structure of the cerebellum is more regular tlian that of the cerebrum; and this answers to the comparative homogeneity of its function. Even from the beginning some such difference must tend to arise. The ex- periences disclosing relations of co-existence in space have a great sameness; and though those which bring a consciousness of increasingly -remote space are increasingly complex., yet the complexity increases after a simple sys- tematic manner. If all movements were always made at the same velocities, then the time-relations disclosed in loco- motion would be as uniform as the space-relations; and the nervous centre which co-ordinated the actions to them might be equally homogeneous in structure. But since the movements are very variable in speed, not only as made on different occasions, and as made by different muscles, bat even as made by the same muscle during different parts of its contraction, there is a cause o£ heterogeneity in the co-ordination of time-relations which we may expect to be expressed by some heterogeneity in the nervous plexuses effecting them. Still more must such heterogeneity be looked for when we pass to time-relations of a higher order. The sequences, that become appreciable when intelli- gence becomes high, are sequences of very numerous orders, of very various lengths, and between terms of very various complexities; as instance the contrast between the suc- cession of sounds in speech and the succession of the seasons. After contemplating the multitudes of these time- relations occurring between all kinds of things, differing enormously in their durations, and having countless degrees of heterogeneity, we shall not be surprised to find that the organ of doubly-compound co-ordination in time presents marked unlikenesses of a minute structure in its different regions.
§ 242. I need not attempt further to complicate this synthesis by including those actions in which tastes, odours, sounds, &c., play a part. Already in seeking to build up a general conception of the process of nervous evolution in its higher stages I have elaborated the argument quite far enough — perhaps too far.
Let me, indeed, disclaim the endeavour, which some may suppose I have been making, to explain the process in full. My purpose has been rather to make the possibility of such a process conceivable; and I have taken specific cases and used concrete language because so only could I make myself understood. The actual genesis has bees, much more involved than that which I have described — so in- volved that a true delineation, even could it be made, would be scarcely comprehensible.
558 PHYSICAL SYNTHESIS.
It may be well here to repeat tlie caution against attach- ing literal meanings to some of the terms used. The inter- pretations of such phrases as " nervous connexions " and * ' plexuses of fibres," must not be too strict. We are not warranted by observation in supposing that " connexions " and i( plexuses )} are quite definite; nor does the argument} require us so to suppose them. That which the argument requires is a plexus of channels through which compound stimuli may be united and re-distributed into compound impulses \ and these channels may be formed partly of distinct fibres and partly of unmarked lines of discharge through the imbedding protoplasm. Indeed it is manifest that in the nervous structures which carry on the higher mental actions the connexions must have all degrees of definiteiiess, and that the greater part of them must be very indefinite — the ultimate ramifications of the channels through which the discharges find their ways must be invisible.
CHAPTER VI.
FUNCTIONS AS RELATED TO THESE STRUCTURES.
§ 243. In tracing out the genesis of nervous structures, a good deal has been implied respecting thejgenesis of ac- companying functions. Fully to understand the natures of these functions; however, it is needful to contemplate them, by themselves in their ascending succession.
Throughout the foregoing argument, functions, when re- ferred to, have been expressed in physiological language. It remains^ tojr^nslate this into psychological language.? What have been considered as increasingly- complex nervous actions we have now to consider as increasingly-complex mental states.
§ 244. In reflex action of the earliest kind, a single stimulus at the periphery of an afferent nerve sends a wave of molecular change to a nerve-centre, whence, through ready- made channels, the wave instantly escapes in a more or less augmented form along an efferent nerve and excites some organ or organs — contractile organs being those to which we may here confine our attention. And sucn* fully- fc. established reflex action, not delayed a moment in its course, \ is unconscious.
A compound reflex _ action that is fully established, though" implying the reception of peripheral stimuli by several afferent rerves, the passage of resulting waves 560 PHYSICAL SYNTHESIS.
throngli a ganglionic net-work, and the emission of dis- charges through motor nerves more or less numerous, is also unconscious— the passage through the central plexus not occupying the time which, consciousness implies.
But compound reflex actions in which the co-operating stimuli produce the combined motor impulses only after a pause, caused by incompleteness in the permeability of the central plexus, may be presumed to have some accom- panying consciousness — some feeling that occupies the iuterval between the receipt of the impressions and the escape of the discharges.
Each compound reflex action, accompanied at first by consciousness, but made by perpetual repetition automatic and unconscious, becomes a step towards reflex actions still more compound. These, during their stage of par- tial establishment, imply consciousness that is somewhat more complex and varied than the earlier consciousness which has been lost in automatic action.
Besides the consciousness accompanying those reflex actions which are but partially established, there is im- plied a much larger body of consciousness. For as already shown, the sense-organs that occasionally receive the special combinations of stimuli which cause automatic- ally certain adjusted contractions of muscles, are sense- organs that perpetually receive stimuli not specially com- bined— stimuli which are therefore sending into the central plexuses, waves of disturbance that are not instantly draughted off to particular motor organs. These, dwell- ing in the nervous centres as long as the stimuli continue to be received, imply, as their psychical correlatives, what we call sensations, or something homologous with them.
The great mass of the sensations thus produced by ex- ternai objects on a creature that has reached this stage of evolution, constitute an..imorgg,ni£ed_consciousness — a consciousness of which very few components have~~any spe- cific order or definite meaning. Impressions received FUNCTIONS AS RELATED TO THESE STRUCTURES. 561 through tlie eyes of sucli a creature are mostly mere patches of colour, associated very feebly, if at all, witli the tactual impressions yielded by the same objects. Only in the cases of those environing things to which the com- pound reflex actions or instincts are either adjusted or in course of adjustment, does this raw material of mind rise into nascent intelligence.
This nascent intelligence exists, however, not only where new compound reflex actions are being established, but also where an established compound reflex action is incipiently excited. Suppose such an animal as we have been consider- ing, sees approaching some small creature of the kind on which it preys. Then, while this small creature is coming nearer, but before it has reached the point at which its visual image arouses the reflex action that effects its seizure, a series of visual images, increasing in size and defmiteness, must be yielded by it • and it must yield an accompanying series of stimuli to the eye-muscles. Though the reflex action takes place only when the retinal and muscular im- pressions become combined in a certain way, yet during approach to the required combination the reflex action is tending to arise — there is a gradually-increasing excitement of the nervo-motor apparatus which will presently perform the reflex action. The effect does not stop here. Through the established connexions there is propagated a gradually- increasing excitement of the nervo-motor apparatus which catching the prey will bring into play — there are produced faint revivals of the tactual and gustatory states which capture of such prey has on past occasions yielded. Thus., then, results what we call per oeption; for we havS here a cluster of real feelings carused by the presented object^ joined with a cluster of ideal feelings, representing certain other real feelings which the object has before prdfluced and can again produce.
Perceptions of this order are gradually extended to other surrounding things. The apparatus effecting the percepo o 562 PHYSICAL SYNTHESIS.
tions which are followed by reflex actions/ is capable of effecting perceptions which are not followed by reilex actions. Clustered visual feelings yielded by inanimate bodies, are, like those yielded by animate bodies, apt to be joined in experience with clustered feelings yielded by them to the skin and muscles; and the two clusters so excited, though less frequently forming a sequence, even- tually become correlated in a similar way. Thus the chaotic impressions received from environing objects,, are slowly evolved into a slightly-organized consciousness of environ- ing objects.
§ 245. Between a perception physiologically considered and a perception psychologically considered,, the relation now becomes manifest. We see that a perception can have in a nerve-centre no definite localization, but only a diffused localization. Js"o one excited fibre or cell produces conscious- ness of an external object: the consciousness of such ex- ternal object implies excitement of a plexus of fibres and cells. And not only does this plexus of fibres and cells differ with every different object, but it differs with every different position of the same object. A clear understand- ing of this may be conveyed by an illu^ratipn.
A good piano has, including semi-tones, between eighty and ninety notes — say, for convenience of calculation, a hundred: to which last number, indeed, a pedal piano reaches nearly, if not quite. Such a piano, then, if its keys are struck singly, is capable of yielding but a hundred different tones. If its keys be struck two together, the different combinations that are possible amount to 4,950; if three together, to 161,700; if four together, to 3,921,225; if five together, to 75,287,520. These numbers, increasing thus frith enormous rapidity as the complexity of the chords increases (until we reach chords of fifty notes, after which they begin to diminish), yield, when added up, a total requiring a row of thirty figures to express it — a million, FUNCTIONS A3 BELATED TO THESE STUCCTUfiES. 563 million,, million,, million, millions. Each coinbinatit n is, considered as a set of sonorous vibrations, unlike every other; and though the majority of them are but in- conspicuously different, yet there are millions of mil- lions of them that differ in well-marked ways. So that out of this comparatively-simple structure a prac- tically-unlimited number of functional effects is pro- ducible. If now, instead of the keys of the piano, we suppose a cluster of such sensitive bodies as those which form the retina; if instead of the appliances which convey to the strings the impacts given to the keys, we take the fibres that carry to the optic centres the impres- sions made on these retinal elements; and if instead of strings made to vibrate we put ganglion corpuscles excited by the impulses they receive; we shall see that a percep- tion may be compared to a musical chord. As by striking a certain set of ke}~s there is brought out a par- ticular combination of tones, simple or complex, con- cordant or discordant; so when a special object seen strikes by its image a special cluster of retinal. elements, and through them sends waves to the fibres and cells of a corresponding central plexus, there results the special aggregate of feelings constituting perception of the object.
Without further detail the reader will see how it thus becomes possible for a limited number of fibres and cells to.Jbecome the seat of a relatively- unlimited number of per- ceptions.
While it thus in a general way illustrates perception under one of its aspects, the action of a piano fails wholly to illus- trate it under another of its aspects; as the motions of a dead mechanism must necessarily fail to represent in full the functions of a living one. For, as above pointed out, a perception is formed only when a cluster of real feelings ^excites a correlated cluster of ideal feelings. If our piano were so constituted that after any two chords had been repeatedly sounded in succession, there resulted some struc- 5G4 PHYSICAL SYNTHESIS.
tural change, such that when the first of these chords was again evoked by a performer's hands a faint echo of the second chord followed without aid from the performer's hands, the parallel wonld be nearer. We shonld then have something analogous to what happens when a nervous plexus excited by certain properties of an object,, diffuses its excitement to another plexus that has, on previous occa- sions, been excited by other properties of the object. And here,, indeed,, while we are giving the rein to imagination,, let us take a wider licence — let us suppose that several chords struck in succession, thus aroused faint repetitions of the many following chords forming the rest of the music to which they belonged. We shall then be helped to conceive more nearly how the elements of perceptions become linked together. And on contemplating the infinity of musical effects obtained by combining different compound chords in ever-varying successions, we shall get some idea of the infinity of perceptions that arise by the organizing of clusters of co-existing feelings in endlessly changing ; sequences.
§ 246. We may now pass from perceptions to ideas, properly so- called. Thongh every true perception along with its presentative feelings necessarily contains certain representative feelings, these do not at first become what we usually understand by ideas. They have not the detach - ableness which distinguishes ideas that are fully developed. They can be called into existence only by the sense- impressions with which they are directly connected in experience -y and they can continue to exist only so long as these continue to exist. To return to our illustration — a creature so constructed as to be capable of notBing:"Beyond the compound co-ordinations just described, resembles a piano that is silent until touched by the hands of the per- former. Its nervous system is played upon by external objects, the clustered properties of which draw out answer- FUNCTIONS AS BELATED TO THESE STBCJCTORES. 5G5 ing chords of feelings, followed by faintly-reverberating- chords of f archer feelings; but it is otherwise passive — ii- cannot evolve a consciousness that is independent of the immediate environment.
How does snch independent consciousness become pos- ^sible? When do ideas,, rightly so-called, arise? They arise when compound co-ordination passes into doubly-compound co-ordination. They grow distinct in proportion as the correspondence extends in Space and Time. They acquire a separateness from, direct impressions as fast as there increase those series of clustered sensations which unite the visual sensations received from objects out of reach with the tactual sensations afterwards yielded by such ob- jects. They are the necessary concomitants of that process by which, through intercalated psychical states, there is established a mediate relation between psychical states that cannot be brought into immediate relation. And they have for their seats those intercalated plexuses which co-ordinate the co-ordinating plexuses previously exist- ing. That is to say, ideas form a larger and larger por- tion of consciousness as fast as there develop those two great pedunculated nerve-centres which distinguish the superior animals; ideas become more multitudinous and more separable from direct sense-impressions as these centres increase in size and structure j and eventually., when these centres are highly evolved, ideas admit of combination into trains of thought that are quite independent of present external perceptions.
^!.~rPng a steP former ^e illustration used in the last section, Y£«S2iL£23*S^.S^£%r notion of the parts which; the cerebriim and cerebellum play in mental processes HOP just as, by the actions of* appropriate mechanisms joined to them, musical instruments of certain kinds are made to yield musical combinations without the hands of the performer; so, through the workings of these great appended nerve-centres, there are called out from the 000 PHYSICAL SYNTHESIS.
centres below them, traias of consciousness Independent of, or additional to,, those aroused by impressions on the senses. To make the parallelism understood, let me describe, at some length, one order of these mechanical appli- ances. Every one has watched the revolving barrel of a musical box, as its pins strike, in successive com- binations, the vibrating metal tongues j and every one sees that the set of pins, arranged in a special way, represents, in a sense, the harmonized melody produced. By moving the barrel a small distance longitudinally., another set of pins,, clustered in another way, is brought into position, readv, when the barrel revolves, to brine; out another set of chords and cadences; and so on. The mechanical arrange- ment in this case, restricts very closely the number of musical combinations which the barrel can contain, or rather, which its clustered pins can represent. But it is easy to conceive an arrangement permitting indefinite multiplication of such combinations. If _we suppose the sheet of metal forming the surface of the barrel to be cut lonsntudinallv, and unrolled into a flat surface without disturbing the inserted pins, it- is clear that if this flat surface were moved down vertically in front of the metal tongues, between rollers which kept it properly in place, its pins might- be made to strike the metal tongues just as they now do. And it will at once be seen that any number of such flat plates, all having differently- clustered pins representing different, harmonized melodies, might be made to pass "•through the rollers. A further complication, needed to complete the analogy, will now be readily under-