The skin has two kinds of glands, the sebaceous and sweat-glands. The sebaceous glands consist of a gland structure, with a short excretory duct, which opens upon the epidermis or into the hair follicles. These glands secrete an oily substance, which keeps the hair and skin soft and protects them from the sweat. There exists in the sebaceous glands of the skin an infinite number of vulnerable points for infection, and the greater part of the process of cleanliness is directed toward their protection. If in any part of the skin there is an accumulation of bacilli, their toxins, or excretions, and, at the same point, a collection of sebum, the friction of the clothes, caused by the movements of the body, becomes an active agent in effecting their absorption by the skin. Hence, the scientific basis for the necessity of the daily bath. In the _subcutaneous tissue_ we find the fat; it is this part of the skin that contributes to the roundness and beauty of the body. It is increased by abundant fatty food, sedentary habits, and freedom from care. =Functions of the Skin.=—The skin exercises three distinct functions; first, as an organ of sense; second, as an organ of excretion; and third, as an organ of heat regulation. Next to sight, the sense of touch is the most important of all the senses. Through this sense the human organism is made conscious of its contact with the outer world. The cutaneous nerve-endings stand guard, as it were, over most of the functions of the human body. The importance of the action of the skin as an organ of excretion will be better understood from the well-known fact that the skin is one of the most important aids to the kidneys. That the perspiration and the urine are to a certain extent vicarious excretions has been proved. The blood is the circulating medium which not only serves to convey nutritive materials from the stomach to the tissues, and the excrementitious materials from the tissues to the excretory glands, but also to equalize the body temperature. It conveys the surplus heat from the interior of the body to the surface, where it may be dissipated by conduction, radiation, and evaporation. Nearly nine-tenths of the daily heat-loss takes place through the skin; and of this, one-seventh is due to evaporation, which is enormously increased by perspiration. The amount of perspiration produced daily is about two pints, or in the neighborhood of 1/64 the body weight. This is double the amount of water thrown off by the lungs. The watery portions of the perspiration are readily evaporated, and the solid constituents are deposited upon the skin. Urea and uric acid, together with more subtle poisons, are found in the sweat. _Animal Heat._—The heat of the body is wholly derived from foods, which, when completely oxidized within the body, produce practically the same amount of heat and energy that would be generated by their combustion outside the body.