in medicine, the evacuation of the juices of the body through the pores of the skin. Perpiration is distinguished into sensible and insensible: and here sensible perspiration is the same with sweating, and insensible perspiration that which escapes the notice of the senses; and this last is the idea affixed to the word perspiration when used alone.

The matter of insensible perspiration, is a fine subtle fluid, which exhales from the body in the form of a vapour, and proceeds from the whole surface and from every cavity; it is of an aqueous and saline nature, and seems to have a great analogy with urine; because in a healthy state, the increase of the one diminishes the other. Many experiments prove its existence. Sanctorius found, in Italy, under the circumstances of a moderate diet, middle age, and easy life, that the matter insensibly perspired was five-eighths of that taken in for food; so that there only remained three-eighths for nutrition, and for the decrements of the nose, ears, intestines, bladder, &c. The same author shews, that as much is evacuated by perspiration in one day, as by stool in fourteen days.

But Dr. Bryan Robinson, of Dublin, has found the case very different, both in England and Ireland, and even in South Carolina, in all which places he found that the quantity of urine exceeds that of perspiration; and that if the meat and drink of one day be four pounds and a half, the perspiration of that day will be two pounds, the urine two pounds five ounces, and the stool three ounces.

The matter of sweat is separated from the blood by the milky glands, and is therefore much more gross than that of insensible perspiration; for as there are no glands which serve for the excretion of this last fluid, it is supposed to proceed from the extremities of the capillary arteries.

The use of perspiration is to preserve the suppleness of the papillae of the skin; to carry the saline particles off from the blood, and by this means to render it more pure; to preserve the body from various diseases; and to contribute to the cure of the most dangerous distempers. It may be promoted by exercise, by dry frictions with a coarse linen-cloth or a flesh-brush, by warm baths, and washing the hands, feet, head, &c.