into the hoof, receive the vibrations of that body and by that means the horse is sensible to the motion and pressure of its foot, or to its percussion against the ground; without which provision, there would be a certain imperfection in the limb.

In a former part of this treatise,. I have shown by what a curious mechanism the horse's foot is rendered yielding and elastic, to enable it to bear the shocks to which it is liable. But owing to the hardness of our made roads, and the defects of shoeing, the pressure and concussion are too severe and too incessant not to be attended with injury of the foot: accordingly, inflammation follows; and then the protecting sensibility is converted into a source of pain; the horse is "foundered." There is a remedy for this condition, by dividing the nerve across before it reaches the foot; the consequence of which operation is, that the horse, instead of moving with timid steps, puts out his feet freely, and the lameness is cured. But were we to leave the statement thus barely, the fact would be opposed to the conclusion, that for the perfection of the instrument, the mechanical provision and sensibility are equally necessary, and require to be associated. It may relieve us from the difficulty, if we consider that pressure against the sole and crust is essential to the play of the foot, and to its perfection: when the foot is inflamed, and the animal does not put it freely down, it does not bear its weight upon the hoof so as to bring all the parts into action; hence contraction is produced, the most common defect, as we before said, of the horse's hoof. But when the animal is relieved from its pain by the division of the nerve, it then uses the foot freely, and use restores all the natural actions of this fine piece of mechanism.

It is obvious, however, that when the nerve is cut across, there must be a certain defect; the horse will have lost his natural protection, and must now be indebted to the care of his rider. He will not only have lost the sense of pain to guard against over-exertion, but the feeling of the contact of the ground, necessary to his being a safe roadster.

The teeth are endowed with sensation, and in the same manner as the hoof of the horse. Although neither the substance nor the enamel of the tooth is itself sensible, yet a branch of the sensitive nerve (the fifth) enters into the cavity of each tooth; a vibration can thus be communicated through

the tooth to the nerve; and the smallest grain between the teeth is easily felt.

To return to the human hand. If a man use the fore-hammer, the cuticle of his fingers and palm will become thickened in a remarkable manner; but the grooves on the inner surface become also deeper, and the papillæ, projecting into them, longer; the consequence of which is, that owing to the cuticle retaining its aptitude to convey impressions to the included nerves, he continues to possess the sense of touch in a very useful degree.

In the foot of the ostrich,* we may behold a magnified view of the cuticle, with processes disposed like the thickset hairs of a brush, each process enclosing a papilla, into which the lengthened nerves are prolonged. The outer skin of the foot, in this "runner," almost equals in thickness the hoof of the horse. In separating it from the skin, the papillæ, containing within them the nerves, are withdrawn from each of the processes of cuticle, and leave corresponding foramina or pores. If the object had been merely to protect the foot by an insensible covering, it would have sufficed to invest the sole with a succession of dead layers of cuticle; and that would have been the case had the scarf skin been simply thickened by pressure; but the structure is adapted in all respects to the habits of the bird: besides having adequate callosity, it is endowed with sensation proportioned to its wants.

Such, then, is the structure of the organ of touch: obvious in the extremities of the fingers; magnified in the foot of the horse, or of the ostrich; and existing even in the delicate skin of the lips.

I have casually noticed that increased vascularity, as being necessary to sensibility, always accompanies the distribution of nerves to a part. In the museum of the College of Surgeons, we see that Mr. Hunter had taken pains to demonstrate this, by injecting the blood-vessels of a slug; although the coloured size was injected from the heart, the blush of the vermilion extends principally over its "foot ;" the foot, in these gasteropoda, being the whole lower flat surface or belly on which the animal creeps. This vascular surface is also the organ of touch, by

* See engravings, pp. 66, 87.

which the slug feels and directs its motions. It is the same principle, if we may compare such things, that explains the rosy-tipped fingers and ruby lips; the colour implies that high vascularity is combined with the fine sensibility of these parts.

Having described the relation of the cuticle to the nerves in the organ of touch, we may notice the advantages which accrue from the roughness of its surface. We must be sensible that on touching a finely polished object, the sense is but imperfectly exercised, compared with touching or grasping a rough and irregular body. Had the cuticle been perfectly smooth, it would have been ill suited to touch; but being, on the contrary, slightly rough, its quality is more adapted to convey sensation.

A provision for increasing friction is especially necessary, in some parts of the skin. Thus, the roughness of the cuticle in the palm of the hand, and in the sole of the foot, gives us a firmer grasp and a steadier footing: nothing is so little apt to slip, as the thickened scarf-skin, either of the hand or foot. In the hoofs of animals, as might be expected, roughness and tenacity in the structure are further developed. It is owing to this quality that the chamois, ibex, or goat, steps securely at great heights on the narrow ledges of rocks, where it would seem impossible to cling. So in the pads or cushions of the cat, the cuticle is rough and granular; and in the foot of the squirrel, indeed of all animals which climb, we find the pads covered with the cuticle, similarly roughened, allowing them to descend the bole of the tree securely, while their claws enable them to grasp and cling to the branches.

In concluding this section, we perceive that the organ of touch consists of nerves, appropriated to receive impressions of contact from bodies capable of offering resistance. Fine filaments of sensitive nerves, wrapped up in delicate membrane, with their accompanying arteries and veins, project from the true skin into papillæ on the surface, and these again are lodged in corresponding grooves or foramina of the cuticle. The filaments are not absolutely in contact with the cuticle, but are surrounded with a semi-fluid matter; by which and the cuticle the nerves are protected, at the same time that they are sensible

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to pressure, cutting, pricking, and heat. But this capacity, we repeat, is not owing, strictly speaking, to anything in the struc ture of the organ; it is to the appropriation of the nerve to this class of sensations.

CHAPTER IX.

OF THE MUSCULAR SENSE.

A NOTION prevails that although the young of the lower animals are directed by instinct, there is an exception in regard to the human offspring. It is believed that in the child we may trace the gradual dawn and progressive improvement of reason, independently of instinct. That is not true. We doubt whether the actions of the body, if not first instinctive, or directed by sensibilities which are innate, would ever be exercised under the influence of reason alone.

The sensibilities and motions of the lips and tongue are perfect in the young infant from the beginning. The dread of falling is shewn by the infant long before it could have experience of violence of any kind.

The hand, destined to become the instrument for perfecting the other senses, and for developing the endowments of the mind itself, is, in the infant, absolutely powerless. Pain is poetically figured as the power into whose "iron grasp" we are consigned when introduced to a material world. Now, although the infant is capable of expressing pain in a manner not to be misunderstood, yet it is unconscious of the part of the body which is injured. There occur certain congenital imperfections which require surgical assistance in early childhood; but the infant will make no direct effort with its hand to repel the instrument, or disturb the dressing, as it will do at a period somewhat later. The lips and tongue are the parts first exercised by the child; the next motion is to put its hand to the mouth, to suck it: and, as soon as the fingers are capable of grasping, whatever they hold is carried to the mouth. Hence the sensibility to touch and power of action in the lips and tongue, are the first inlets to knowledge. The use of the hand is a later acquirement. The knowledge of external objects cannot be acquired, until the organ of touch has become familiar with our own body. We cannot be supposed capable of judging of the form or tan