In the same phenomena we may trace a nascent sense of; taste. The ability to discriminate between organic and1 inorganic matter, appears to. be. possessed. in some degree 308 GENERAL SYNTHESIS.
even by the.simplest animals. lUnzopods do nob absorb indiscriminately all fragments of available sizo; nor do tlio tentacles of polypes commonly bohavo in the same wny when touched by inorganic bodies as \vheu touched by organic bodies. And bearing in mind that to creatures living in water, the inorganic or mnutritivo matters are, generally speaking, the insoluble, while the organic or nutritive are the soluble; it may be inferred that the selective power which they possess is due,, as above implied, to the setting up of an assimilative process when assimilable, matter is brought in contact/ with them, and to tlio abseueo of that process when the matter presented is not assimilable. So that this selective power, which is an. incipient sense of taste, is, primarily, one aspect of that integrating action which mainly constitutes the life. For thus interpreting the facts we have the warrant that, even in. its highest developments, tasting forms one link in the chain of assimi- lative actions. The mouth is part of the alimentary canal, which secretes digestive fluids and takes up dissolved sub- stances. The mouth does both these: its saliva, is a diges- tive fluid, and in the act of tasting, some of tlio dissolved substances are absorbed through the mucous membrane of the tongue and palate.
Smell has the same root with taste, and remains through- out closely associated with it. In aquatic creatures the two senses can be but degrees of the same: the 0110 responding •to a more dilute solution of nutritive substance, and tho other to a more concentrated solution. As tlio solublo matters which surround a fragment of animal tissue arc not confined to its actual surface, but are diil'used in tlio sur- rounding water with an abundance that decreases as tho distance increases, it is obvious that a greater susceptibility will render the fragment perceptible before there is absolute contact; and that so, taste must pass gradually into smell. The mtimate connection of taste with smell, and of both with touch, "is displayed even in man. Tho nerves of both THE CORRESPONDENCE AS EXTENDING IN SPACE. 809 are spread out under a membrane that is continuous with, and but a slight modification of, the skin; they lie under adjacent parts of this membrane, near its junction with the skin; the sensations they give are so closely allied that, knowing the smell of a substance, we can frequently form, an approximately true judgment of its taste; and to both, the substances to be perceived must be presented in solu- tion— the sapid must be either already dissolved, or dis- solvable by the saliva, and the odorous must be condensed by the film of moisture covering the membrane which lines the olfactory chambers. Thus, the difference is less between the modes in which the sensations are ulti- mately produced,, than between the forms under which the substances producing them originally exist — liquid or solid in the one case; gaseous or vaporous in the other. Further, the relationship of the sense of smell to the fundamental organic actions, is directly traceable even in ourselves. The nostrils and the olfactory chambers which open out of them, are simply divergent branches of the alimentary canal_, from which, in the embryo, they are not separate,* and absorbing into the system, as they do, some of the floating particles given off by the food that is being eaten, or is about to be eaten, their action, too, is but an evanescent form of nutri- tion. Add to which, that in so far as the olfactory action is not nutritive it is respiratory; and thus, in a sense, lies between the two primary vital processes.
Again, in its initial stages even the faculty of sigh/ is implicated with the functions of organic life. The organ- isms which occupy the border land between the animal and vegetal kingdoms, share with plants the ability to decom- pose carbonic acid under the influence of light. Water containing Protozoa gives off oxygen on exposure to the sun;s rays. The link between the two great divisions of living forms, which these lowest creatures present in struc- ture, development, and chemical character, they appear to present in their nutritive action also* Naturally, then, we 310 GENERAL SYNTHESIS.
may expect that on passing from them to vegetal and animal organisms respectively,, we shall on the one hand find the ability to decompose carbonic acid by the agency of light more and more developed, and on the other hand more and more wanting. Recently disclosed facts answer to the ex- pectation. In the first place, the researches of Sdmlfczc go to establish an identity between the chlorophyll of plants,, and the colouring matter of sundry low types of animals,, as for instance the Hydra. In the second place, the ][ydr<t habitually shuns the light — habitually chooses the dark side of the vessel in which it is placed. May we not infer that the sensitiveness to light which the Hydra exhibits, results from, the action of light on its contained chlorophyll; that as in plants, this action is one through which the components of chlorophyll are assimilated; and that thus, the power which the primordial tissue possesses to distinguish light, from dark- ness— a power which forms the germ of the visual faculty — is due to a modification produced by light OH the general vital processes? Any doubt that may be felt respecting this hypothesis, will, I think, disappear on remembering jthat even in ourselves the general surface of the body I resins a physiological sensitiveness to light. The darken- ing of the skin caused by long exposure to sunshine, imnlies a modified assimilation in the tissue penetrated by light- — a change in the absorption of materials supplied by the blood, In transparent and semi-transparent creatures, any such photogenic effect must pervade the whole body; and if so it is easy to understand how light may produce marked changes in such creatures.
That hearing has, like the other senses, a root in the primitive vital functions, there is little if any direct evidence. But for suspecting that it, too, is differentiated from thorn, we have the reason that to sound, as to light, tho whole animal organism in its simplest forms possesses a feeble susceptibility. A slight tap, causing a vibration to pass through the vessel containing them, is responded to by THE CORRESPONDENCE AS EXTENDING IN SPACE. 311 creatures in whom no sign of an auditory organ exists. And if we call to mind the facts that congenitally deafi persons are acutely affected by sonorous vibrations in iJie5' bodies they touch, and can perceive such vibrations even in the air when produced by loud concussions, as the firing of ] cannon — if we infer, as we must, that even in man tlv,r whole body is in some degree sensitive to sound, and that' the extreme sensitiveness of one part is simply a specializa- tion of this general sensitiveness; we shall have no difficulty in understanding how the humblest zoophytes and mollus- coid animals feel the jar of those rapid undulations which constitute objective sound. Of lax tissue, and of like specific gravity with its medium, one of these creatures must be permeated by such undulations throughout its entire mass, almost as though it were so much water; and can scarcely fail to have the substance of its tissues so dis- turbed as to produce a marked change in their general state, and some consequent change in the external mani- festations. Still it may be asked — How do these facts and inferences affiliate the faculty of hearing on the primary vital processes? I reply — They tend to do this by suggesting that the contraction produced by any sonorous vibration permeating a zoophyte's body, results from some modifica- tion of these vital processes. The life of one of these creatures is little else than the cumulative result of the lives of its component cells or nucleated portions of protoplasm, which severally absorb the nutrient juices percolating among them, are severally bathed by the oxygenating medium, and severally carry on the integrating and disintegrating actions by and for themselves. Now anything which causes a sudden agitation of the aerating liquid diffused through this almost homogeneous tissue, will produce a sudden increase of vital activity in all the components of the tissue. A rapid succession of undulations propagated through it must do this. And we have but to suppose that the in- creased vital activity of each component is accompanied by '312 GENERAL SYNTHESIS.
some change, probably isomeric, which alters its form, to understand how a contraction of the entire creature may result.
Thus, there is not a little reason to think that all forms of sensibility to external stimuli, are, in their nascent shapes, nothing but the modifications which those stimuli produce in that duplex process of integration and disintegration winch constitutes the primordial life, physiologically con- sidered. A zoophyte cannot be touched without the fluids diffused throughout the disturbed tissues being put hi motion, and so made to supply oxygon and nutriment with greater rapidity. Nutritive matter brought in cout.act with the surface, which is everywhere absorbent, must oxcito the vital actions still more; and so must cause the touch of nutritive matter to be specially responded to. A diffusion of such matter in the form of an odour, will tend in a slight degree to produce analogous effects. Tho tissue having the requisite chemical nature, light, also, must modify the assimilative actions. And, as just shown, sonorous vibrations probably do the like. If we make tho reasonable assumption that the protoplasm of these almost unorganized creatures is isornerically changed by changes in Iheir vital activity, we have an adequate explanation of the effects which outer agencies produce. fcSo. far as they go, facts harmonize with the deduction from the law of organic "development — the deduction that as the primitive tissue out of which are evolved, the organs of vegetative life, possesses, to some extent, the functional powers of those organs; so must it, to some extent, possess the functional powers of the organs of animal life, and among thorn of the senses, which similarly arise out of it by a continuous differ- entiation, and integration.
Closing here these speculations respecting the genesis of the several faculties through which the animal organism holds communication with the external world, let us now go on to our immediate subject — that extension of the corro- 7RE CORRESPONDENCE AS EXTENDING IN SPACE. 313 spondence in Space,, which accompanies the evolution of those faculties.
§ 141. Differentiated gradually, as, in aquatic creatures, smell is from touch and taste, its nascent form is not likely to be detected without careful experiments; and I have not- met with accounts of such. " How far any sense of smell exists in the lower invertebrata, cannot be satisfactorily deter- mined/' says Dr. Carpenter: " but it would seem not im- probable that even where no special organ is apparent, some part of the general surface may be endowed with olfactive sensibility." But however the sense of smell originates, we . may conclude that only when in some degree localized, does it become a means whereby internal relations can be brought into something like definite correspondence with external relations which do not occur in contact with the body. Supposing, for argument's sake, that along with its other diffused faculties the whole mass of the primitive animal possesses a feeble susceptibility to odours; the only corre- spondence which may be established through this, must be seen in some state of readiness to seize the prey, or avoid the enemy, whose proximity an odour implies. Though, by means of such endowment, an inner relation can be adjusted to an outer relation a little removed from the surface; yet, there can be no adjustment to relations either of direction in space or of distance in space. But as soon as there exists a susceptibility that is somewhat localized, the organism /• must be differently affected by an odoriferous body, according as it is situated in this or that position. And when, as an accompaniment of specialization, there is increased effi- ciency, a feebly-scented object near to the more highly sensitive tract, may produce a response as great as a strongly-scented object somewhere in its neighbourhood produces in an organism possessed of a diffused but inferior susceptibility.
Passing from these vague beginnings, it will be obvious 314 GENERAL SYNTHESIS.
that as fast as there is developed at the entrance of the respiratory passages a definite apparatus capable of being excited by floating particles, there must be an extension of the space through which co-existences and sequences in the environment can establish corresponding co-existences and sequences in the organism. When we trace up the evolu- tion of the faculty to that perfection in which it is possessed by dogs and by deer, we see that one of the aspects under which the advance presents itself, is the increasing distance at which certain inner and outer relations can be brought into adjustment; and that, other things equal, there is a simultaneous advance in the degree of life.
§ 142. Though that ability to distinguish light from dark- ness which characterizes the entire body in sundry of tho humblest types, foreshadows the visual faculty, nothing like what we call sight results until this ability is concentrated in a particular spot. The rudimentary eye consisting; as in a Planar ia, of some pigment grains, may be considered as simply a part of the surface more irritable by light than the rest. Some idea of the impression it is fitted to receive raay be formed by turning our closed eyes towards the light, and passing the hand backwards and forwards before them. Bat as soon as even this slight specialization of function is reached, it becomes possible for the organism to respond to the motions of opaque bodies that pass near. While only a general sensitiveness to light exists, the intercepting of the sun's rays by something which throws the whole or a greater part of the creature into shade, is required to produce an internal change; but when there comes to be a specially sensitive spot, anything which casts a shadow on that spot alone, produces an internal change. And as that which obscures only a small part of the organism is usually a comparatively small object, this advance from diffused sensitiveness to concentrated sensitiveness enables the onranism o to respond, not only to marked general changes in luminous- THE CORRESPONDENCE AS EXTENDING IN SPACE. 315 ness which its environment undergoes, but also to marked special changes in luminousness caused by the motions of adjacent bodies.
The contrast between light and darkness., or rather "be- tween widely different degrees of light, being all that the most rudimentary vision recognizes; and distinct obscura- tion being producible by an adjacent small object only when it is very close; we may infer that nascent vision extends to those objects alone which are just about to touch the organism, either in consequence of their motion or of its motion. We may infer that it amounts at first to little more than anticipatory touch; and that so there is estab- lished in the organism a general relation between visual and tactual impressions, corresponding to the general relation between opacity and solidity in the environment. Be this as it may, however, it is clear that an incipient faculty of sight, though the vaguest imaginable in the sensations it gives, and the most limited that can be conceived in range, I implies not only some extension of the correspondence in space, but a new order of correspondence.
As we ascend to creatures haying more developed eyesj we find an increase in the sphere of surrounding space! throughout which external relations can establish correspond-* ing internal relations. A slight convexity of the epidermic layer lying over the sensitive tract, first serves, by concen- trating the rays, to render appreciable less marked varia- tions in the quantity of light; and thus brings into view the same bodies at a greater distance, and smaller or less opaque bodies ^ the same distance. From this point up- wards, through the various types of aquatic creatures to the higher air-breathing creatures, we trace, under various forms and modifications, a complicating visual apparatus and a widening space througfi which the correspondence extends. It is needless to go into details. Hypotheses and! illustrations aside, it is obvious that from the polype which! does not stir till touched, up to the telescopic-eyed vulture!
gi6 GENERAL SYNTHESIS.
lor the far-sighted Bushman, one aspect of progressing life ]is the greater and greater remoteness at which visible rela- :tions in the environment produce adapted relations in the § 143. Similarly with the auditory faculty. So long as the susceptibility to sonorous vibrations is slight, and pos- sessed by the body at large, there is nothing like what we call hearing. Only when the susceptibility conies to be in- tensified in one place, can a sound proceeding from a par- ticular point in the environment, be distinguished from a tremor of the environment as a whole. After there has arisen a rudimentary ear, consisting of a dermal sac con- taining otolithes, which multiply the vibrations striking the skin that covers them as the primitive cornea concentrates the rays passing through it; then, a moderate sound at some distance or a slight sound close to it, may produce on the creature as great an effect as the violent shock of its entire medium produces on a creature not thus endowed. And along with this new sense there comes into existence a new set of correspondences — those between certain audi- tory impressions and consequent motions in the organism, and certain sound-causing powers and co-existent properties in adjacent bodies.
Successive improvements of this faculty, as of those already dealt with, expand the surrounding sphere through- out which certain relations in the environment cause adapted relations in the organism. It cannot be denied that though the minor irregularities involved by their special habits are considerable, yet, viewed in the mass, animals of higher .and higher types show us greater and greater ranges in their auditory correspondences.
§ 144. The extension of the correspondence in space does not end "with the perfecting of the senses. In crea- tures of comparatively-advanced organization, there arise THE CORRESPONDENCE AS EXTENDING IN SPACE. 317 powers of adjusting inner relations to outer relations that are far too remote for direct perception. The motions by which a carrier-pigeon finds its way home though taken a hundred miles away, cannot be guided by sight, smell, or hearing, in their direct and simple forms. Chased animals that make their way across the country to places of refuge out of view, are obviously led by combinations of past and present impressions which enable them to transcend the sphere of the senses. And thus also it must be with creatures that annually migrate to other lands.
Ill jm^, this secondary process of extension is carried j still further. Though the correspondences he effects by <! immediate perception have a narrower range in space than those of some inferior creatures; and though in that species of indirect adjustment just exemplified, he is behind sundry wild and domestic animals; yet, by still more indirect means, he adjusts internal relations to external relations that are immensely beyond the appreciation of lower beings. By combining his own perceptions with the perceptions of j others as registered in maps, he can reach special places | lying thousands of miles away over the Earth's surface. A **• ship, guided by compass, and stars, and chronometer, brings* him from the antipodes information by which his purchases I here are adapted to prices there. From, the characters j of exposed strata he infers the presence of coal below; and thereupon adjusts the sequences of his actions to co- existences a thousand feet underneath. Nor is the environ-1;- ment through which his correspondences reach, limited to) the surface and the substance of the Earth. It stretches into the surrounding sphere of infinity. It was extended to the nib OIL when the Chaldeans "discovered how to predict eclipses; to the sun and nearer planets when the Coperni- can system was established; to the remoter planets when an improved telescope disclosed one, and calculation fixed the position of the other; to the stars when, their parallax: \ and proper motion were measured; and, in a vague way, ] 318 GENERAL SYNTHESIS.
even to tlie nebulae, when their composition and forms of structure were ascertained.
§ 145. Before leaving this general proposition, that tho progress of life and intelligence is, under one of its aspects, an extension of the space through which the correspondence between the organism and its environment reaches, it may be well to remark that its truth is independent of all con- clusions as to the modes in which the correspondence is developed. In the earlier part of the chapter I have filled up some of the gaps in our knowledge by reasonings that are partially hypothetical; and have thus opened the door to possible criticisms, which may at first sight be supposed to tell against the doctrine at large. But a moment's con- sideration will show that by whatever steps the senses of smell, sight, and hearing, arise, the result remains the same. Unquestionable facts form the substance of the argument. It is a fact that where the sense of touch is the only one definitely manifested, the correspondence between tho organism and its environment extends only to that part of the environment by which the organism is bathed. It is a fact that the appearance of the higher senses, even in their most rudimentary forms, is accompanied by some extension of the space throughout which correspondences can be effected. It is a fact that the successive stages in tho development of each sense imply successive enlargements of this sphere of space. And it is a fact that the advent of rationality is, among other ways, shown in the carrying of tEese enlargements still further.