The true skin underneath the epidermis is always red; you know that if you shave off the surface of your skin anywhere, it gets redder and redder the deeper you go down, even though you do not fetch blood. It is red because of the immense number of capillaries, all full of red blood, which are crowded into it. When you look at these capillaries through a great thickness of epidermis, the redness is partly hidden from you, as when you put a sheet of thin white paper over a red cloth, and the skin seems pink or flesh-coloured; and where the epidermis is very thick, as at the heel, the skin is not even pink, but white or yellow, more or less dirty according to circumstances. =46.= But if the moist true skin is thus everywhere covered by a thick coat of epidermis, which keeps the moisture in, how is it that the skin is nevertheless sometimes quite moist, as when we perspire? [Illustration: FIG. 16.--_Coiled end of a Sweat Gland, Epithelium not shown._ _a_, the coil; _b_, the duct; _c_, network of capillaries, inside which the duct gland lies.] If you look at Fig. 15, you will see that the epidermis is at one point pierced by a canal (_h_) running right through it. You will notice that this canal is not closed at the bottom of the epidermis, but runs right into the dermis or true skin, where the canal becomes a tube, with just one layer (_e_) of cells, like the cells of the epidermis, for its walls. There is no room in Fig. 15 to show what becomes of this tube, but it runs some way down under the skin all among the blood-vessels, and then twisting itself up into a knot, ends blindly, as is shown in Fig. 16, where _b_ is a continuation on a smaller scale of the same tube which is seen in Fig. 15. This knot is covered by a close network of capillaries, which at _c_ are supposed to be unravelled and taken away from the knotted tube in order to show them. The capillaries, you will understand, though inside the knot, are always outside the tube. If you were to drop a very diminutive marble in at _h_ (Fig. 15), it would rattle down the corkscrew passage through the thick epidermis, shoot down the straight tube _b_ (Fig. 16), and roll through the knot _a_, until it came to rest at the blind end of the tube. Along its whole course it would touch nothing but cells, like the cells of the epidermis, a single layer of which forms the walls of the tube where it runs below the epidermis. If it got lodged at _h_ (Fig. 15), or got lodged in the knot at _a_ (Fig. 16), it would in both cases be touching epidermic cells. But there would be this great difference. At _h_ it would be ever so far removed from any blood capillary; at _a_ it would only have to make its way through a thin layer of single cells, and it would be touching a capillary directly. At _h_ it might remain dry for some time; at _a_ it would get wet directly, for there is nothing to prevent the fluid parts of the blood oozing out through the thin wall of