Why do we shake hands? It is a very old-fashioned way of indicating friendship. Jehu said to Jehonadab, “Is thine heart right as my heart is with thine heart? If it be, give me thine hand.” It is not merely an old-fashioned custom; it is a strictly _natural_ one, and, as usual in such cases, we may find a physiological reason, if we will only take the pains to search for it. The Animals cultivate friendship by the sense of touch, as well as by the senses of smell, hearing, and sight; and for this purpose they employ the most sensitive parts of their bodies. They rub their noses together, or they lick one another with their tongues. Now, the hand is a part of the human body in which the sense of touch is highly developed; and, after the manner of the animals, we not only like to see and hear our friend (we do not usually smell him, though Isaac, when his eyes were dim, resorted to this sense as a means of recognition), we, also, touch him, and promote the kindly feelings by the contact and reciprocal pressure of the sensitive hands. Observe, too, how this principle is illustrated by another of our modes of greeting. When we wish to determine whether a substance be perfectly smooth and are not quite satisfied with the information conveyed by the fingers, we apply it to the LIPS and rub it gently upon them. We do so, because we know by experience that the sense of touch is more acutely developed in the lips than in the hands. Accordingly, when we wish to reciprocate the warmer feelings we are not content with the contact of the hands, and we bring the lips into the service. A SHAKE-OF-HANDS suffices for friendship, in undemonstrative England at least; but a KISS is the token of a more tender affection. Possibly it occurs to you that the TONGUE is more sensitive than either the hands or the lips. You have observed that it will detect an inequality of surface that escapes them both, and that minute, indeed, is the flaw in a tooth which eludes its searching touch. You are right. The sense of touch is more exquisite in the tongue than in any other part of the body; and to carry out my theory, it may be suggested that the tongue should be used for the purposes of which we are speaking. It is so by some of the lower animals. But, in man, this organ has work enough to do in the cultivation and expression of friendship in its own peculiar way; and there are obvious objections to the employment of it in a more direct manner for this purpose. _The Skin of the Hand._ By the aid of the accompanying drawings you will be able to form some idea of the structure of the SKIN of the hand. [Illustration: Fig. 70. Skin.] One of them (fig. 70) represents a section of the skin, made perpendicular to the surface, as seen under the microscope. It is from the end of the thumb, and includes three of those delicate lines, or ridges that are found there.