§ II.—CHAPTER VII.

SPECIAL ORGANIC PHENOMENA CONTINUED—ANIMAL.

BlCHAT first clearly propounded the distinction between merely vegetable and animal life⁷⁸⁷⁸   Bichat’s own language is organic and relative; but we prefer, for obvious reasons, the less technical, more readily intelligible language. which is now generally accepted. Besides the functions of nutrition and reproduction which the animal shares with the plant, the former is characterised by two special tissues, the muscular and the nervous, issuing in distinctive manifestations of vitality, higher than those to be found in the vegetable kingdom. It is doubtful, indeed, as formerly said, whether the separation thus marked out be clear and decided. We have certainly, among plants, at least the shadow of these higher vital developments which so prominently mark the animal creation, as in the phenomena of irritability in the Venus’ flytrap, the sensitive plant, and some others. In the former plant the leaves are marked by three projecting hairs, which, when touched, have the singular property of causing the leaf to fold upon itself, shutting in the insect which may 152 have caused the movement. The mode in which the leaves of the sensitive plant fold themselves together on the slightest touch is still more familiarly known. Remarkable as these movements are, however, the conclusion of botanical authorities, upon the whole, appears to be against the supposition of their being identical in source with similar movements in animals. “They are not dependent,” says the Professor of Botany in Edinburgh, “on nervous and muscular power, as is the case in animals, but they seem to be caused by the greater or less distension of cells connected with the base of the leaves and of the leaf-stalks.”⁷⁹⁷⁹   BALFOUR’S Sketches, p. 131.

The peculiar property of the muscular tissue is denominated contractility. It is simply the power possessed by the muscles of contracting or shortening themselves. This contractile power is observable in the lowest classes of animals, although they do not present any distinct trace of a fibrous structure. In the inferior zoophytes—such as the Infusoria, Polypi, Medusæ—the whole body seems to exhibit an incessant action upon the surrounding fluid, maintained by means of “very minute and generally microscopic filaments” called cilia, and which apparently serve in the case of these genera not only the purpose of progressive motion, but also of respiration, and of procuring a supply of food.⁸⁰⁸⁰   Dr Roget, Bridg. Treat., vol. i. p. 126. In the Radiata generally, however, no distinct muscles can be said to be traced, and their powers of movement are for the most part very limited.

As we ascend the scale of animal life we begin to observe the formation of fibres, at first irregularly dispersed through 153the soft body, and then, as the organisation becomes more complex, collected into bundles, composing what are properly called muscles.⁸¹⁸¹   Dr Roget, Bridgewater Treatise, vol. i. p. 126. In many of the Articulata the muscular system is highly developed. Lyonet is said to have counted in some species of caterpillar not fewer than four thousand muscular bands; and the extraordinary weights which ants and beetles easily move, prove the muscular energy to be very powerful in these creatures. It is in the Vertebrata, however, and especially as displayed in the human body, that the muscular system has been most carefully studied, and is most familiarly known. And from this comparatively limited, but very adequate sphere, our illustrations will for the most part be drawn.

The bundle-form is one of the most remarkable characteristics of the muscular tissue. The compact bundle is found, on examination, to be composed of a series of lesser and lesser bundles, firmly bound together in sheaths. “The dilatation of the muscular fibres in thickness, which accompanies their contraction in length, would, if these fibres had been loose and unconnected, have occasioned too great a separation and displacement, and have impeded their co-operation in one common effect. Nature has guarded against this evil by collecting a certain number of the elementary fibrils, and tying them together with threads of cellular substances, thus forming them into a larger fibre; and, again, packing a number of these fibres into larger bundles, always surrounding each packet with a web of cellular tissue.”⁸²⁸²   Ibid., p. 130.

As muscular action is wholly the result of the contractile power possessed by the tissue, it is obvious that reciprocal sets of such muscular bundles as we have described are necessary to produce the varied and reciprocal motions of animals. As Paley⁸³⁸³   Natural Theology, vol. i. pp. 104, 105; Knight’s edit. states and illustrates the fact: “It is evident that the reciprocal energetic motion of the limbs, by which we mean motion with force in opposite directions, can only be produced by the instrumentality of opposite or antagonistic muscles—of flexors and extensors answering to each other. For instance, the muscles placed in the front part of the upper arm, by their contraction bend the elbow, and with such degree of force as the case requires or the strength admits of. The relaxation of these muscles after the effort would merely let the fore-arm drop down. For the back stroke, therefore, and that the arm may not only bend at the elbow, but also extend and straighten itself with force, other muscles, placed on the hinder part of the arms, by their contractile twitch, fetch back the fore-arm into a straight line with the cubit, with no less force than that with which it was beat out of it. The same thing obtains in all the limbs, and in every movable part of the body. A finger is not bent and straightened without the contraction of two muscles taking place. It is evident, therefore, that the animal functions require that particular disposition of the muscles which we describe by the name of antagonist muscles. And they are accordingly so disposed. Every muscle is provided with an adversary. They act, like two 155sawyers in a pit, by an opposite pull; and nothing surely can more strongly indicate design and attention to an end than their being thus stationed.” To which Sir C. Bell in a note adds: “The muscles are antagonists certainly, but there is a fine combination and adjustment in their action, which is not illustrated by the two sawyers dividing a log of wood. The muscle having finished what we call its action or contraction, is not in the condition of a loose rope, but, on the contrary, there is always a perfect balance of action preserved between the extent of relaxation of the one class of muscles and the contraction of the other; and there is a tone in both by which the limb may be sustained in any posture that is willed.”

The muscles are attached by tendons or sinews to the parts to be moved; and there is often singular contrivance shown in the mode in which these are made to act. The most obvious and simple mode of producing motion, would of course be to stretch the tendons in a straight line betwixt the parts to be moved. But this would not, in many cases, suit the convenience of the body. The muscles are, in consequence, found in positions whence they can only act on the movable object in an oblique manner, and with a corresponding loss of force, but, at the same time, with an increase of velocity, and a saving of muscular contraction highly advantageous. Muscles acting after this oblique fashion are often used in pairs, in which case the direction of motion is the diagonal line between them,—an arrangement which, in certain movements of the body, is productive 156of a rapid and easy motion particularly desirable. The action of the chest in breathing is of this kind.⁸⁴⁸⁴   Dr ROGET, p. 132.

In certain parts of the body, where mobility is especially requisite, a condensation of muscular fibres would have been especially incommodious. By a skilful provision, the muscles are in such cases placed at a distance, where their presence is subservient to the beauty of the corporeal outline; while they are, at the same time, by a special apparatus of long tendons, stretching like wires from a mechanical centre, brought within range of their appropriate sphere of action. It is in this way that the muscles which move the hands and feet are found respectively in the arm and the calf of the leg, instead of forming, as Paley expresses it, an “unwieldy tumefaction in the hands and feet themselves. The observation,” he adds, “may be repeated of the muscle which draws the nictitating membrane over the eye. Its office is in the front of the eye, but its body is lodged in the back part of the globe, where it lies safe, and where it encumbers nothing.”⁸⁵⁸⁵   Natural Theology, vol. ii. p. 106.

There are many other advantages connected with the use of tendons which have been carefully pointed out.⁸⁶⁸⁶   Dr ROGET, p. 134-135, to whose treatise we are here, and throughout this description, greatly indebted. By their intervention the whole concentrated power of the muscular fibres is conveniently brought to bear upon any particular point where an accumulation of force is necessary. The action is upon the very same principle on which a number of men pull together at a rope, in order to influence by their combined strength a given position. By means of tendons, 157also, a change of direction may be imparted to the moving power, without any alteration of its place. Tendons are thus found, in numerous instances, “to pass round corners of bones, and along grooves or channels expressly formed for their transmission, producing the effect of pulleys.” The trochlear muscle of the eye acts in this manner. It passes round a cartilaginous support and turns back, just like a rope round a pulley. By a similar mode of muscular action the lower jaw is pulled down, the moving power proceeding not from below but from above the jaw—rising, in fact, in the side of the face, and of course descending in the first instance, but, at a certain point, taking a turn and then ascending—which is the direction in which it could alone produce the appropriate effect.⁸⁷⁸⁷   PALET’S Natural Theology, vol. i. p. 116.

The peculiar configuration of certain muscles serves still further to show the design with which they are marked. In many cases “the fibres, instead of running parallel to one another, are made either to converge or to diverge, in order to suit particular kinds of movements; and we frequently find that different portions of the same muscle have the power of contracting independently of the rest, so as to be capable of producing very various effects, according as they act separately or in combination.”⁸⁸⁸⁸   Dr ROGET, vol. i. p. 135. The muscle of the back, called the trapezius, is an example of this. Sometimes they radiate from a common centre, as in the delicate muscle of the ear-drum; and at other times they run in a circular direction, forming what is called an orbicular or sphincter muscle. In the membrane of the eye called the 158iris these two last-mentioned muscles are combined with beautiful effect. On the application of too much light, the circular fibres directly surrounding the pupil instantaneously contract, diminishing its size; while again, when more light is needed, the contraction of the radiating fibres, acting on the circular, serves as instantaneously to enlarge the pupil. The instinctive character of this balanced action (the will having but a slight and occasional control over it) especially evinces foresight; for thus alone does it respond with unerring precision to all the varying necessities and circumstances of the animal. A somewhat corresponding action of circular fibres with longitudinal, distinguishes the muscular coats surrounding canals of various kinds, such as the blood-vessels, and the alimentary tube; the former tending, by their contraction, to extend the canal and propel its contents—the latter, again, by their contraction, having a tendency to shorten it.⁸⁹⁸⁹   Dr ROGET, vol. i. p. 147.

One of the most general and remarkable characteristics of muscular action in the limbs remains to be mentioned. It takes place at what is called a mechanical disadvantage. The axis of motion is much nearer to the exciting force than to the resistance to be overcome. There is, of course, a great sacrifice of power in this way; but while this is compensated, on the one hand, by the special energy of the muscular exertion, on the other hand, velocity and freedom of motion (which are the great requisites in the animal system) are obtained in proportion to the mechanical disadvantage. “Strength is sacrificed,” as Dr Roget observes,⁹⁰⁹⁰   Ibid., vol. i. p. 141. “without 159scruple, to beauty of form or convenience of purpose; and that disposition of the force is always adopted from which, on the whole, the greatest practical benefit results. Everywhere do we find the wisest adaptation of muscular power to the objects proposed, whether it be exerted in laborious efforts of the limbs and trunk; whether employed in balancing the frame or urging it into quick progression; or whether it be applied to direct the delicate evolutions of the fingers, the rapid movements of the organs of speech, or the more exquisite adjustments of the eye, or of the internal ear.”

It were difficult, indeed, to conceive a more impressive display of design than is represented by all the varied and intricate action of the muscular system in any of the higher animals, and in the human frame especially. All is hidden from our view beneath the covering of skin which encases and protects the delicate machinery. But could we see within, and trace the unceasing play of muscular adjustment under any of our most common movements, nothing could be more wonderful than the spectacle exhibited. The movement of the eye in vision, of the ear in hearing, of the tongue and larynx in speaking, all depend upon relations of the nicest and most complicated description, whose operation, unceasing as it is, is at the same time unwearying. How wonderful the muscular endurance of the heart alone, which contracts “with a force equal to sixty pounds eighty times every minute, for eighty years together, without being tired!”⁹¹⁹¹   Animal Physiology, p. 74. Edinburgh: Chambers. When the hand performs any common task—executes 160 a piece of music, for example, or simply writes—how numerous the muscles brought into play, and yet how happily measured, definite, and wholly uninterfering their mutual action! “Not a letter,” as Paley has well described the latter case, “can be turned without more than one, or two, or three tendinous contractions—definite, both as to the choice of the tendon, and as to the space through which the contraction moves; yet how currently does the work proceed! and when we look at it, how faithful have the muscles been to their duty! how true to the order which endeavour or habit hath inculcated!”⁹²⁹²   Natural Theology, vol. ii. p. 113.

The disposition of so many muscles in the human body (anatomists have given names to between four and five hundred), often so closely contiguous to one another, that they are found “in layers, as it were, over one another, crossing one another, sometimes imbedded in one another, sometimes perforating one another,” yet all so perfectly arranged that they never obstruct or interfere with one another—this of itself surely furnishes evidence of design which it is impossible to resist. What, save prescient Wisdom, could have devised an arrangement at once so exquisitely intervolved, and so faultlessly harmonious?

In advancing to a brief consideration of the nervous system, we enter upon a sphere of illustration peculiarly significant for our subject. For the nerves are not, like the muscles, simply examples of organic contrivance; they are the seats of sensation, the media of animal consciousness, 161in whose varied phenomena we find the appropriate evidence, not only of Divine wisdom, but especially of Divine goodness. In this chapter, however, we glance at the nervous system simply in its organic arrangement, as contributing, in the mere complicacy and order of its parts, to the force of our preceding evidence. The mental meaning, which everywhere underlies it, will immediately receive full attention.

The nervous, like the muscular system, is found, in the lower animal races, in a very undeveloped state. In the very lowest, indeed, including the Porifera (sponges); Polypifera (mushroom corals); Polygastrica (infusory animalcules); Acalephae (sea-blubbers); and Entozoa (intestinal worms), no trace of it can be detected by the closest scrutiny. These animals are hence arranged by zoologists into a sub-kingdom by themselves, under the name of Acrita. It must not, however, be supposed that the neurine or nervous matter is really absent in these races. It is no doubt present, although it cannot be traced; not gathered into masses, nor even into threads, but probably diffused in imperceptible atoms through the whole of their very simple structure.*

In the races immediately above the preceding, the nervous matter is distinctly visible in the shape of threads dispersed through the body. They are hence arranged in a sub-kingdom, under the name of Nematoneura, the most interesting and important section of which are the Echinodermata, or star-fishes.

* GOSSE’S Text-Book of Zoology, p. 1.

162 THEISM.

In the Articulata we reach a further and very significant development of the nervous structure. It is no longer merely in the form of threads, but presents the first appearance of a spinal chord, with ganglions or nervous centres collected on it; that is to say, knots or swellings at regular intervals along it, from which the nervous fibres run. From the fact that these ganglions are, in the Articulata, regularly disposed along the main line or chord to which they are attached, it has been proposed to call this general division of the animal kingdom Homogangliata, as being a name more truly distinctive than the older and familiar one of Articulata. The varied and deeply interesting class of insects, as also the Arachnida (spiders, &c.), and Crustacea (crabs, &c.), are representatives of this great division.

In the Mollusca the nervous system does not advance. They are distinguished, Professor Owen has remarked, by the development rather of the vegetal series of organs, or those which are concerned in nutrition and reproduction. The nervous matter is in them also collected into ganglions; but these are no longer symmetrically disposed along a main line, but are unequally scattered throughout the body. “The principal mass of nervous matter takes the form of a thick ring or collar surrounding the gullet, whence threads are sent off in an unsymmetrical manner to other parts of the body; several ganglions being placed around the collar, and others dispersed in other parts, so as best to supply the most important organs.”⁹³⁹³   GOSSE’S Text-Book, p. 193. From this unequal distribution of the nervous centres in the races of this division of the animal creation, it has been proposed to apply to them the more definite and characteristic name of Heterogangliata.

It is only in the Vertebrata that we reach the fully developed form of the nervous system. Here we have a spinal chord, truly so called, not only with ganglionic knots distributed along it, but expanded at the summit into a collection of nervous matter, which gradually becomes of main significance in the system. To this terminal collection of nervous matter the general name of brain is given. In all the classes of the Vertebrata a brain and spinal marrow are present, but the brain especially is extremely diversified in size, and in the relation of its parts. It is composed of two hemispheres, respectively named the cerebrum or proper brain, and the cerebellum or lesser brain. It is by the full development of the former that the nervous system in the human species is distinguished. It extends so far back in man as to cover the whole of the cerebellum, while, in the lower vertebrate orders, the latter becomes always more apparent, till in reptiles and in fishes it is wholly exposed.

With this very summary description of the nervous system in the animal races generally, we will now look, for the sake of special illustration, a little more closely at its structure and operations in man, in whom it assumes its chief interest and importance.

The nervous matter in the human body presents the appearance of an elaborate and intricate trace-work running out to all its parts, from the vertebrate column and encephalon. 164Comparatively dense and unformed in the immediate region of the central line or axis of the body, it branches off into more rare and distinct outline towards the surface extremities. When this matter, as exhibited in the brain, is examined, it is found to be composed of two different substances. The main substance, which is placed internally, is white-looking and of fibrous structure. A coating of grey matter, vesicular in structure, encloses the other, and gathers into large ganglionic masses at the base, where it constitutes, as we shall see, a special centre of nervous force. This twofold material is found also in the spinal marrow, but in an inverted relation, the grey matter here forming the interior, and the white matter the exterior mass. The grey or vesicular matter is supposed to be the generating source of the nervous energy, the white or fibrous matter to form the lines of communication between the different parts of the system.

In the diversified operation of man’s nervous system, we meet, first of all, with centres of nervous action, strictly corresponding to those found in the lower orders, viz., simple ganglions, distributed along the spine, or at least chiefly there. But we also, as might be expected, meet with higher and peculiar centres of such action in what are called the sensory ganglions, collected at the base of the brain, and especially in the cerebrum itself. From these respective centres emanates the whole varied and wonderful activity of human life.

To Sir Charles Bell we are indebted for the great discovery which has opened up the whole field of nervous 165operation. He found that sensation and motion are dependent upon different sets of nervous filaments. The sensiferous filaments, stretching all along the surface of the body, are constantly receiving impulses which they transmit along the line to the different centres of nervous action, whence again proceed the other or motor set of filaments running to all the different parts of the body. These filaments start from distinct roots in the nervous column—the roots of the former being in the posterior, and those of the latter in the anterior, portions of that column. They preserve throughout their distinct character and quality, although in their ramifications they become inextricably intermingled. According to their function, the former set have been called afferent, as conveying impressions towards the centre; the latter efferent, as conveying the respondent movement from the centre.⁹⁴⁹⁴   Also esodic, or ingoing nerves; and exodic, or outgoing nerves. We have thus, in the most simple form of nervous operation, three distinct organs, as it were—the afferent nerve, the gangiionic centre, and the efferent nerve. These together form an apparatus which has often been represented by the analogy of a voltaic battery. The impression communicated at the sensitive surface passes along the line of the afferent nerve to the central station, where it is not expended or thrown away, but, in virtue of its nature, acts upon the vascular structure of the ganglions, developing a motive force which issues along the efferent nerve to the parts originally affected. An act or operation of sense always tends to complete itself in this way. The stimulus passing inwards is reflected to 166the sentient surface whence it started, quickening there a movement of closer contact, or, as it may be, of repulsion towards the object of sensation. When we touch anything, we have thus a tendency either to grasp it more firmly, or to reject it, should there be anything in it disagreeable to the organs of sensation. Without one or other of these results the sensation has not completed its natural round. It has fallen short through its own original weakness, or the weakness of some of the organs; or, as is very commonly the case, in the ceaseless and complex play of the system, it has been interfered with by some opposing influence of greater power bearing on the same centre of nervous force.

The intimate union which is thus seen to exist between the nervous and muscular systems is deserving of notice. The action of the one always tends to pass into that of the other. The two systems are not only combined, but so combined, or rather inwrought, that the one everywhere presupposes and includes the other.

We have been speaking all along of sensation as implied in the nervous process; and so it is. But, in the very lowest forms of this process, that which we peculiarly mean by sensation does not emerge. There are, in other words, appropriate ranges of nervous action which transact themselves beyond the region of consciousness. Among these are the common functions of organic life—the action of the heart, of the lungs, and of the stomach. These, as well as sometimes also special motions of the limbs, are found, in a state of health, to proceed wholly irrespective of any conscious recognition or sensation properly so called. The 167 sense-impulses which have set them agoing do not, as it were, awaken, or realise themselves. And in this we may perceive a special mark of Divine wisdom; for how important is it that those functions upon which our daily health depends, should be thus secured from the distracting influences that would be otherwise constantly bearing upon them! How comparatively imperfect and unhappy would life be, did the respiratory or digestive processes incessantly claim our attention! As it is, these processes, proceeding in a separate round by themselves, minister in the most faithful and efficient manner to our daily maintenance and well-being.

Such simple reflex actions constitute in man, however, only the lowest circle of nervous operation. And even in regard to them there is so intimate a relation between the different parts of the system, that the processes which may be, and in ordinary cases are, transacted beyond the region of consciousness, yet very readily pass into it. For, according to the full law of nervous action, whose exposition we owe only to the most recent physiological labours, every impression is represented as having a tendency to pass along the nerve of transmission upwards through every intermediate position to the cerebrum itself.⁹⁵⁹⁵   MORELL’S Psychology, p. 97. This tendency, we have seen, is not in many cases carried out. The nervous impression is intercepted at a lower ganglionic centre, and reflected there for the performance of various important functions. Yet, even in those cases in which there is no conscious recognition, the relation of the nerves 168 to the higher conscious centre is so intimate that some influence is probably at all times given forth upon it.

The reflections from the sensory ganglions at the base of the brain may be said to form the second range of nervous action in man, which, in its special character, is of the most important kind. These ganglions are the great seat of sensation. The nerves of the senses terminate in them, and hence proceed all our well-known modes of sensation, so various and exquisite. But while this range of nervous action lies so completely within the sphere of feeling and consciousness, it is yet irrespective of the will. The responsive movements flow forth instinctively; they are the simple involuntary play of sensations. Such automatic movements are the winking of the eye, shuddering, balancing of the body to prevent falling, and many others.

The highest and complete range of nervous action proceeds from the cerebrum itself. While, in truth, the lower ganglionic centres are so constituted as to be capable of originating independent ranges of action, they are yet so intimately related to this highest centre as to be constantly within its influence. The effects, for example, of intense thought or of strong emotion upon the processes of organic life are familiarly known. It is deserving of remark, however, that this cerebral influence can only be propagated downwards after a certain manner. The mind can only influence directly the sensory ganglions, the sensations which are the appropriate expression of their action again acting upon the lower ganglionic centres concerned in the processes in question. The idea of a pleasant taste, for 169example, will make the mouth water, and the sensation thus created will stimulate, through the inferior excito-motor centre, the action of the stomach. But the mind cannot operate directly upon the alimentary apparatus.

The cerebrum, it is well known, is the special seat of those varied ideas and emotions which constitute what is peculiarly considered our mental activity. It is the seat, moreover, of that moral activity which in man is the flower of existence. In the will, as the only complete expression of our cerebral energy, the whole complex human life does not certainly take its rise, but here alone it finds its sum and perfection. What grounds there may be for reckoning in the cerebrum two distinct centres of nervous action—an idea-motor, so called and described by Dr Laycock,⁹⁶⁹⁶   In a paper read before the British Association, 1844. and one (the highest of all) specially volitional⁹⁷⁹⁷   See MORELL’S Psychology, p. 100-102.—need not occupy us in so cursory and second-hand a sketch as this.

We have presented more than enough to evince the clear design stamped on every feature of man’s nervous system. On the one hand, its elaborate structure, so nicely and curiously wrought, and on the other hand, its diversified yet never conflicting action, are among the most impressive manifestations of a wisdom which, shining forth everywhere in nature, here shines forth with, perhaps, special significance and beauty. It were a vain effort to exalt any one aspect of creation above another, Divine order being equally conspicuous in all; yet it would seem that here, in the exquisite organisation which we have been contemplating, 170 Reason is eminent with a peculiar lustre. Here, standing at the summit of the physical, on the verge of that self-conscious reason which sees its own forms reflected everywhere, we seem to see the most perfect correspondence between matter and spirit—between the order that merely shows Mind, and the mind that perceives Order. The pious instinct which, on a comparatively inadequate view, lifted the soul of the Psalmist to God, here awakens irrepressibly in every reverent heart, “I will praise Thee; for I am fearfully and wonderfully made.”