The skin is the covering of the body, and has very important functions to perform. It is more abundantly supplied with nerves and blood-vessels than any other part; and there is no spot of the skin where the point of the finest needle would not pierce a nerve and blood-vessel. Indeed, it may be considered as composed chiefly of an interlacing of minute nerves and blood-vessels, so that it is supposed there is more nervous matter in the skin, than in all the rest of the body united, and that the greater portion of the blood flows through the skin.
The whole animal system is in a state of continual change and renovation. Food is constantly taken into the stomach, only a portion of which is fitted for the supply of the blood. All the rest has to be thrown out of the system, by various organs designed for this purpose. These organs are,--the lungs, which throw off a portion of useless matter when the blood is purified; the kidneys, which secrete liquids that pass into the bladder, and are thrown out from the body by that organ; and the intestines, which carry off the useless and more solid parts of the food, after the lacteals have drawn off the chyle. In addition to these organs, the skin has a similar duty to perform; and as it has so much larger a supply of blood, it is the chief organ in relieving the body of the useless and noxious parts of the materials which are taken for food.
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.