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Besides being the completing portion of sensational circles, and the tool, as it were, of the senses, the muscular system sets agoing actions solely on its own account, or for its own gratification. These movements will be guided and chosen by the agreeableness of the feelings that result from them. There is a pleasure in mere exercise; but the pleasure is still further enhanced by the manner of it; and animals deeply sensible of the satisfaction of regulated, harmonious, or rythmical motions will be ready to fall into such motions of themselves, or to catch them up by imitation. Every creature has its own favourite mode of disporting itself.
The muscular system appears to have the special function of connecting one nervous circle with another; that is, the muscular response of a circle of sense, for example, yields the sensation that acts upon a second active circle, and this tells upon a third in the same way; and so on. This will have to be more particularly dwelt on in our next section.
Compound Instincts. The mechanism of the senses has been treated of above as a system of individual and isolated nervous circles, having each their sensitive surface, ingoing-nerve, ganglion, outgoing-nerve, and muscular apparatus respectively. We have had occasion to allude to cases where the responsive muscular tension that terminates a sensation is not final, but leads to the wakening up of a train of other activities. This carries us to the higher organisation of the nervous system, or to the means adopted in nature for connecting the separate sensibilities and activities into harmonious wholes.
In this obscure and interesting subject, our insight is derived partly from the anatomy of the nervous system, and partly from what we can observe of the way that stimuli and movements succeed one another in the living body. The following laws of intercommunication of nervous circles seem to be borne out by both these sources of evidence:
1. When any moving organ reaches its extreme position, it sets agoing a stimulus to the opposing muscles to retrace the motion. Every moving member must have two classes of muscles to counteract each other, and a distinct ganglionic centre must exist for each. Thus the arm has its flexors and extensors, and a similar adaptation exists everywhere over the system. Now it would seem to be a rule of organisation, that when one set of muscles have been contracted to the extreme, the sensibility of the contraction should be transmitted by a particular nerve to stimulate the ganglion of the counter set, and to cause an opposite or returning movement; while the muscles of this last movement yield in like manner & stimulus to the first. In short, a connection is established such as to keep up a movement of see-saw among the active members of the system. This kind of movement is not uniformly sustained, unless among what are called the involuntary muscles; as, for example, the muscles of respiration and the heart: among the voluntary muscles it is apt to be overborne by other
. tendencies, and it is proved to exist only by the natural facility there is to fall into and sustain a swinging motion. It is indispensable in locomotion, and is a great help in every kind of mechanical operation, there being always a necessity, after every exertion of the muscles, to bring back the parts moved from their extreme situation. The principle stated in the last section with reference to the intermediate position of the muscular system is evidently borne out in this instance; for we cannot conceive of any other stimulus to the counter movement, except the muscular tension of the first movement. The muscular sensation of the contracted flexors of the arm passes by a distinct nerve to the ganglion of the extensors, and unless some other power interfere, it stimulates a movement of extension by means of that ganglion.
2. The principle of alternation thus announced is still farther extended, so as to include the two halves of the body, or the corresponding members of the right and left sides. There is evidently a communication established between the circles that move the two sides, such that a motion in one, having reached its extreme, sets agoing the same motion in the other. Hence arises the alternate swing of the two arms or legs, a movement inherent in the primitive constitution of the animal system, and seen in the earliest movements of infancy. This alternation coincides with rather than contradicts the other. The alternate swing of the arms or legs of a human being combines both.
3. The communication of the successive circles of the body through the spinal cord and brain serves to operate the fact of vermicular movement, or of the movements propagated from one end of the trunk to the other. In this case the muscular contraction in one circle yields a sensation or stimulus which is carried by a nerve to the next circle, and it is contracted in consequence, and yields a stimulus to a third; and so on through the whole line of the body. The movements of crawling reptiles exhibit this in its most marked form; but it also applies to the locomotive quadrupeds and to the human subject. There is along with the alternate swing of the legs a movement of the entire trunk, propagated from one vertebral circle to another, on this principle. It is also exemplified in the action of the intestines, which convey the food along by successive contractions, propagated from one muscular ring to another.
The act of walking on all-fours, which is true instinct or inborn capacity, involves all the three kinds of nervous connection above enumerated. The swing backwards and forwards of each separate limb exemplifies the first kind, the alternation of the individuals of each pair proceeds on the second, and the alternate movements of the fore and hind legs is a case of the third, or of the vermicular tendency. The order of alternation of the four legs varies in different animals as well as in the same animal under different impulses; whence arises the varieties of trot, canter, gallop, &c. These do not affect the general principles above described : they merely indicate differences in the adjustment of the details.
4. Many of the instinctive actions are referable to the tendency there is in the system at large to accord or fall in with the state of any one part. Whatever excitement has seized any one of the active circles seems to spread itself over all the rest. The cerebro-spinal axis which maintains the communications above described between the various isolated ganglia, and which contains the ganglia themselves, allows of a transmission of excitement from one circle to another, as if by contagion, and the whole system becomes fired with one common impulse. Thus it is that rapid movements in the limbs produce a like rapidity in the exclamations, looks, features, gestures, and even in the thinking processes; and in the same way the quick motions of the eye caused by an exciting and bustling spectacle
, or the excitement of the ear by quick music, induce activity and quickness of execution over every part of the frame. The entire muscular system of the body being linked together by nervous connections joining all the separate circles, there arises this tendency to unity and harmony of action and state, and it becomes possible to influence any portion by acting on almost any other portion. The consequences of this comprehensive linking of the activities of the frame are far-reaching and numerous.
Proceeding upon these four general laws of the nervous organisation, we can, in addition to the instincts already traced as flowing from them, undertake the discussion of a still more complicated class of instinctive operations.
There is no fact of animal existence more deeply rooted or more constant in its recurrence than what we denominate by the term pursuit, taken, in its widest acceptation, as meaning every instance of the exertion of the active faculties towards some object or end. The senses or the intelligence descry something in the distance desirable to be attained, and, by the activity of the frame, this something is gradually approached and finally possessed. Now, we wish to shew that this tendency belongs to the inherent and inborn peculiarities of the animal organisation, and that it is in a great measure derived from the sensibilities and the laws of nervous communication above described. Take the case of a creature that seeks its prey by scent. The odour of the victim, by the responsive stimulus, excites the respiratory muscles into increased activity; their intensified alternation induces, by the laws of nervous communication, the similar state of alternation on the locomotive organs, just as the activity of the locomotive apparatus always increases the energy of the respiration. There is thus furnished a direct stimulus to pursuit, through the diffusion of like states from one part of the system to another. In the same way it could be shewn that the tension of the muscles of the eye, when fixed on a distant object, imparts, through this same tendency to a common attitude or state, a stimulus to the erecting muscles of the body; and these being stretched to the full, readily bring on the counter movement of energetic flexion, and no more is needed to set agoing a motion towards the object in question. Were there no other organisation than the arrangements above assumed, we believe that pursuit, the taking of an aim, the following of a lead, would happen in all cases as a matter of course, it being understood that every animal takes a certain length of time and exercise to acquire the use of its most familiar organs. It is also to be kept in view that any impulse of the system may at any time be suppressed by the presence of a stronger.
The instinct of preserving a basis of firm support, and maintaining & steady balance, with the dread of falling, is a remarkable example of the class of inborn propensities. Its explanation does not appear to be difficult on the principles above laid down. In the first place, it is to be remarked that there is not a more horrible feeling of the muscular system than the sudden giving way of one of the fixed supports of the body. It happens not merely in the support of the feet but in the case of any muscle whatever that happens to be in a state of energetic tension. It is the state well known as sea-sickness, and also the state of giddiness from looking down precipices. Now an animal being made painfully conscious of the loss of its footing by
this sensation coming over it, is urged by an instantaneous reflex process to exert its muscles somehow to gain a new posture. But this is not all. The
eye has a strong sympathy with the body in general on the point of firm support. It becomes accustomed to rest on the ground as it were, or it acquires a fixed habitual glance towards the earth; and this reposing glance becomes associated with the feeling of support, and a sudden sinking of the ground away from the eye has the very same sickening effect that the actual loss of the solid rest of the body has to the general frame.
The instinct of vocal utterance springs partly out of the mere possession of active organs of voice, and partly out of the law of the propagation of similar states over the system. The respiratory organs, as has been already remarked, are in full connection with the locomotive and other active members; and the voice requires that their action should accompany the action of the muscles of the larynx, or those that tighten up and control the vocal chords. That these laryngeal muscles are associated by nervous connections with the general system is evident from observation, if it cannot be positively shewn by anatomy. An animal in the heat of pursuit has all its activities fired by contagion, and the vocal organs among the rest. Hence the sounds partake, in their expression, of the character of the animal's entire movement. Fierce, vehement, rapid movements of the body kindle up similar movements in the respiration and larynx, and sharp, hard, vehement sounds are the result. We may therefore state, in regard to vocal utterance, that it is inspired, first, by the mere tendency of every active organ to put forth its activity; and secondly, by communication or contagion from the other parts of the frame. To these we may add a third stimulus, derived from what may be called emotional states-grief, joy, terror, affection and the like; and fourthly, a still more refined stimulus from the pleasures of the effect on the ear.
What we have thus briefly noted - respecting vocal utterance applies to expression in general, to the play of feature and member that accompanies and indicates the excitement that possesses the system at any one time. The law of homogeneous movement points out the necessary sympathy of the eye,
the countenance, and the gesture, with whatever movements have been impressed on the other active organs. The inferior animals being unsophisticated in their expression, and incapable of putting forth the power of concealment and hypocrisy, are the best examples of this tendency to unity and identity of state, and consequent truthfulness in all their demonstrations.
The instinct of Imitation, which it would be a self-contradiction to call an acquired faculty, must also be pronounced an mple of the same law of homogeneous movement. In imitating sounds the muscles of the ear are first sympathetically affected with the character of the original, and these aural muscles inspire a corresponding class of movements in the muscles of the larynx. The nervous connection between the ear and larynx may be very special and powerful, or it may be but slender; in the one case the imitation is easy and prompt, in the other it is difficult
. In imitating actions and movements, the eye catches the original, and is itself similarly affected in following the course of the movement. The hand, foot, or body, fall in with the course thus impressed upon the eye; that is, they go through a corresponding course of motions up and down, to and fro, slow
or quick; and here the same remark holds true, that imitation will be easy in proportion to the goodness of the nervous communications between the circles of sight and the circles of movement of the other members. It may be observed in the human subject, that it is easier to imitate actions by the upper extremities than by the lower; the nervous connections between the eyes and the lower members apparently being much feebler than between the eyes and the upper members. But the goodness of these bonds of intercommunication among the nervous circles is subject to an infinity of variation among the various animal species.
These examples will serve to illustrate the application of the laws of nervous organisation which we have ventured to lay down as a basis of explanation of the commoner animal instincts. Before proceeding to a still higher class of instinctive and mental activities, some notice should be taken of the appetites and emotions that seem to pervade the animal kingdom, serving as the stimulants of those higher powers, and being in fact, along with the sensations, the end of existence to the brute nature in general.
Animal Appetites. The term Appetite, or craving, points to certain states of irritated consciousness, requiring something to be done to supply a want or remedy a disorder. It is a kind of bodily feeling or sensation that may arise in any part of the system, in consequence of something being deficient or deranged in that part. There are certain special cravings that make up the ordinary class of appetites; such as thirst, hunger, exercise, repose, sleep, &c.
These allude to the periodical wants, necessities, or cravings of the healthy system; and means have to be adopted for their regular and stated gratification. Their occurrence is at once a spur to the activity and an element in the happiness of life. They are of that imperious nature, that they leave the creature no alternative between the gnawings of their unsatisfied condition and the luxuriousness of their being fully gratified.
The appetites, therefore, are a species of our sensations arising not from outward objects, but from states of the bodily organs themselves, and directing attention upon those organs through the sense of locality or direction that we have in reference to all local feelings. The cravings for exercise, rest, or sleep, bring on their own gratification; but in the cases of hunger and thirst, and in the still more perplexing instances of pain and disease, there is not in the nervous circle of the appetite itself any provision for supplying the want or remedy. The only effect of the craving is to produce an irritation of feeling that spreads over the whole mental system, and leads to efforts being made by some of the many active capacities to allay the distress. Before all experience of the proper course of proceeding, there is nothing to be done but grope about, trying this thing or that thing till a hit is made that proves successful. The plan of acquiring knowledge and practical ability by groping, or trial and error, has to be practised to an unspeakable extent by all orders of created beings, and must be reckoned as a main source of the acquired capacities of man and beast. In the attempt to lull the inexplicable cravings of the animal system everything is tried that is within reach; sometimes a com