Various experiments show, that not less than a pound and four ounces of waste matter is thrown off by the skin every twenty-four hours. This is according to the lowest calculation. Most of those, who have made experiments to ascertain the quantity, represent it as much greater; and all agree, that the skin throws off more redundant matter from the body, than the whole of the other organs together. In the ordinary state of the skin, even when there is no apparent perspiration, it is constantly exhaling waste matter, in a form which is called _insensible perspiration_, because it cannot be perceived by the senses. A very cool mirror, brought suddenly near to the skin, will be covered, in that part, with a moisture, which is this effluvium thus made visible. When heat or exercise excites the skin, this perspiration is increased, so as to be apparent to the senses. This shows the reason why it is so important frequently to wash the entire surface of the body. If this be neglected, the pores of the skin are closed by the waste matter thrown from the body, and by small particles of the thin scarfskin, so that it cannot properly perform its duties. In this way, the other organs are made to work harder, in order to perform the labor the skin would otherwise accomplish, and thus the lungs and bowels are often essentially weakened. Another office of the skin, is, to regulate the heat of the body. The action of the internal organs is constantly generating heat; and the faster the blood circulates, the greater is the heat evolved. The perspiration of the skin serves to reduce and regulate this heat. For, whenever any liquid changes to a vapor, it absorbs heat from whatever is nearest to it. The faster the blood flows, the more perspiration is evolved. This bedews the skin with a liquid, which the heat of the body turns to a vapor; and in this change, that heat is absorbed. When a fever takes place, this perspiration ceases, and the body is afflicted with heat. Insensible perspiration is most abundant during sleep, after eating, and when friction is applied to the skin. Perspiration is performed by the terminations of minute arteries in every part of the skin, which exude the perspiration from the blood.