The skin may be regarded as an enormous gland enveloping the body and presenting its excreting surface to the atmosphere. This large glandular surface is covered by a horny protecting plate that is the excreting surface in action, as it is being continually renewed from below, and cast off as the scurf layer of the free surface. The hair and nails are also excrements, and in the old physiologies used to be so called. The chief constituent excreted by this gland is fat; horn fat when it falls off as the scurf layer, and semisolid or liquid fat when excreted by the sebaceous glands. The sudoriferous glands also excrete much fat, as well as water and salts.
Water has a powerful influence on this immense cutaneous surface. For instance, moist heat and warm water are the best means of securing drainage of this huge gland. Moist heat may be applied,