From the foregoing it is evident that the skin has many varied and important duties to perform.  As we might expect, moreover, an organ with such functions is of complicated structure.  Its component parts, therefore, deserve to have some little attention paid to them, since the importance of the skin from a health point of view will then be all the more appreciated.  The skin is most conveniently considered under three divisions—­the skin itself; the glands, producing perspiration, oil, and hair, which are found within it; and the appendages belonging to it, the hair and the nails.  The skin itself may be described as the soft and elastic tissue which invests the whole of the surface of the body, and consists of two layers, the outer or scarf skin, and the deeper or true skin.  The interior of the body is likewise lined with a covering, which is termed mucous membrane, from the fact that from its surface, or from certain special glands within it, or from both, there is constantly being secreted a thin semi-transparent fluid called mucus.  At the various openings of the body, as the mouth, the nostrils, and other parts, the external and internal skins are continuous with one another.  Indeed, at these apertures the mucous membrane, or internal skin, takes leave of absence from the world to line the cavities within the body.  So that, as Professor Huxley expresses it, “every part of the body might be said to be contained within the walls of a double bag, formed by the skin which invests the outside of the body, and the mucous membrane, its continuation, which lines the internal cavities.”

The use of the scarf skin is manifestly to protect the more delicate true skin, while at the same time it allows the waste products and used-up material to escape from the body.  In the substance of the true skin are thousands of minute little bodies called papillae, which are specially concerned in the sense of touch, for the vast majority of these papillae contain the end of a small nerve.  The numberless fine ridges seen on the palmar surface of the hands and fingers, and on the soles of the feet, are really rows of these papillae, covered of course by the layers of the outer skin.  The supply of blood to the skin is also very plenteous, each of its innumerable papillae being abundantly supplied in this respect.  As a proof of the amount of blood circulating within the skin, and of its extensive nerve supply, it is only necessary to mention the fact that the finest needle cannot be passed into it without drawing blood and inflicting-pain.  In addition to the foregoing the skin also contains a countless number of very fine tubes, which penetrate through its layers and open on its surfaces by minute openings called pores.  There are altogether three different varieties of these tubes distributed throughout the skin, namely, those intended for perspiration; secondly, those which lead from the oil glands; and lastly, those which enclose each hair of the body.  The first of these,