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inhalation and promoting expiratory movements. It thus happens that the sensitiveness to smell may be the means of sensibly exalting or depressing the function that more than any other connects itself with the vital energy of the system—namely, the purification of the blood by the lungs. The circle of the sense of smell, acting by itself, has no other effect beyond this of modifying the breathing. But this circle is brought into connection with other circles, and originates through these a wider range of activity. It is impossible to get rid of unpleasant smells by merely retarding the process of inhalation, and employing strong expiratory efforts; the effect still continues to irritate the system, and must at last rouse up the movement of flight or some other activity at the command of the creature of a kind to rid it of the evil.

The sensations of smell appear in various ways to be instrumental in setting on general activity. Animals that pursue their prey have in many cases the power of detecting it through their scent; and the far-darting odour of the creatures preyed on seems to have the power both of stimulating the lungs, and through them the vital energy or animal spirits, and also of inflaming the entire nervous system with an uncontrollable energy of pursuit. The carnivorous creature has all its bloodthirstiness fired by the smell of its accustomed victims, and with this are wakened up the whole destructive energies of its nature. Hunger and the flavour of meat are sufficient to spread an irritation over the active system of this class of animals. Nature has thus based extensive endowments on the sense of smell. The detection of prey and of the means of subsistence is given by this sense acting within its own circle; and when once a victim comes within the scent, there is produced by it a stimulus proceeding to other circles, and causing the other movements that bring the prey within reach, and end in its being finally devoured. Smell, therefore, like taste, is of itself a knowledge-conferring faculty, and is a commencing link in some of the more complicated instinctive operations.

5. Sensations of Touch.-The sense of Touch is situated all over the surface of the animal body, and is conceived as residing in the skin. The true sense of touch, as distinguished from the sensibility to shocks or pressure, consists in discerning a substance in contact with the body, as made of separate parts, and having extension in space. None of the foregoing senses can give any feeling of the solidity or dimensions of bodies; indeed they can hardly be said to recognise of themselves the external existence of matter.

The ganglion of the sense of touch requires to be much more complicated than the ganglion of taste or smell. The power of discriminating different points in a surface implies a series of independent nerve-fibres distributed in the skin, and having each a distinct connection with the muscles of the part; the general ganglion must, in fact, be a mass of smaller ganglia, with outgoing threads connecting all of them with the corresponding muscular apparatus. This constitutes a higher order of nervous organisation than would appear to belong to the four first senses, and it may be expected to yield a more complex kind of instinctive action.

It is actually found that the movements responsive to the sense of touch are more various and remarkable than the responses of the above-named senses. In the human hand, for example, an object laid on the palm, and

touching the five fingers, stimulates all the muscles necessary for clenching the fist; and even the paw of an inferior animal is led into a variety of movements by the touch of any solid body.

Touch is highly developed in the tongue, and enters into the sense of taste, acting as a guide to mastication and deglutition.

The muscular feelings of force and resistance are inevitably mixed up with the sense of touch, but are nevertheless perfectly distinct. Touch is also the medium of many indescribable electric or magnetic stimuli, especially in the contact of living beings; every individual creature being a huge machine for generating this species of influence.

The whole of the action of animals upon the outer world is through the sense of touch and the moving organs. The material things coming in contact with the body stimulate a constant activity and an enterprising turn; whence arises a great development of the mechanical capacities, and a variety of durable impressions of outward things, a sort of germ of natural knowledge in its lowest form. An animal comes to feel in the first grapple with solid masses that the sensation changes with every movement and turn that it takes, and a renewed stimulus is thus given to groping and manipulation.

6. Sensations of Hearing.-The sense of Hearing is lodged in a very refined and delicate organ of touch. Sounds being a series of mechanical blows or pressures, they require for their reception a surface affected by pressure. The nerves of hearing are spread out on a membraneous surface in the inner ear, which surface floats in the liquid contents of the chamber. The vibrations of sound strike first a tight membrane, next a series of little bones, and lastly the liquid of the inner ear. This liquid, when compressed itself, compresses the nerve, and gives the sensation of sound. The responsive action that completes the auditory nervous circle is directed to the small muscles of the ear, whose connection leads them to tighten or relax the membrane of the tympanum, according as the sound is agreeable or the contrary. Such is the delicacy of the hearing organ in the higher animals that sounds differing in the smallest peculiarity may be perfectly discriminated. This discrimination is at the basis of much knowledge of the world, and of great variety of action, particularly in the vocal organs, these being more especially connected with the organ of hearing. The communication established between the ear and the voice is one of the higher arrangements of the nervous system, and from it proceeds the whole development of the vocal powers of the animal.

Hearing, like touch, is a sense giving a feeling of expansion and volume, and also of direction, but not in a very accurate way. This sense is also remarkable for the pleasures that may be imparted through its instrumentality.

7. Sensations of Sight.-Sight is in many respects the highest and most commanding of the senses. It reveals the outspread creation with a degree of fidelity that closer examination can but rarely impugn. The impressions that it leaves behind it are largely involved in the operations of intellect as well as in the highest class of emotions.

The organ of sense is an optical lense formed so as to project a picture of outward things upon the back of the eyeball, where lie outspread the filaments of the nerve of vision. The pictorial impression thus pro

duced is conveyed inwards in fragments, each along a distinct fibre of the optic nerve, which are thus kept asunder on their way to the optic ganglion. Each fibre must be conceived, as in the case of touch, to have an independent connection with the muscles of the eyeball in the responsive action, and to stimulate a position appropriate to its own place in the retina. The attempt of the muscles to adjust the eyeball to the picture is the returning action of the circle. It is impossible to fix the eye upon all the points thus conveying a stimulus to the optic ganglion; what is done in actual vision is to fix the eye upon one point at a time, and to run it backwards and forwards across the field of view.

The muscles of the eyeballs are themselves very sensitive, and their feelings mix with the sensation of light in the various processes of vision. The feeling of distance from the eye is muscular; likewise the feelings of lateral dimensions and superficial area; and the feeling of solidity from all combined.

The recognition of the forms and appearances of the outer world, and the guidance of the movements of the individual, are the great practical endowments conferred immediately by the organ of sight. As the higher senses never exist without possessing the power of fixing and retaining their impressions to some degree-a power which, surprising as it is, seems to be a constant attribute of the nervous system-every animal gifted with eyes has the power of recognising and identifying the place of its own habitation and all its familiar haunts. Hence vision is in all cases the means of making the creature at home somewhere in the wide world.

The nervous circle of vision is, even by itself apart, a complicated and versatile mechanism: moreover, its connections with the nervous system at large, and with all the other energies of the framework, are wide and deep. In those connections we have to search for a great number of the instinctive and other capacities of animal life. The intimate alliance above noticed between the ear and the voice is paralleled in a grand scale in the present case; the eye and its sensations are deeply associated with the action of the body as a whole, and with all those exertions and manipulations that engross the entire system. Locomotion and pursuit are closely controlled by sight; the same is true of every kind of mechanical process operated by the moving organs at large. In our subsequent expositions we shall have to revert to the visual mechanism, and its alliances with the active circles generally.

Muscular System.

In this preparatory survey of the elementary mechanism of sense and activity, a few words require to be said on the muscular system in addition to the notice taken of it as a part of every circle of sensation. We do not assert too much when we denominate it the essential instrument of action, emotion, and thought, throughout the entire animal system.

The muscles are subject to a great variety of states, and yield as many varieties of feelings to the general consciousness. They may be tense or relaxed; they may move rapidly or slowly, continuously or interruptedly, irregularly or rythmically. Some of their movements are luxurious in the extreme, others are painful or disagreeable; and this distinction determines a preference in the turn of activity.

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 a 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

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