The dermal excretion under controlled environmental conditions of nitrogen and minerals in human subjects, with particular reference to calcium and iron.

Under non-sweating conditions there is a loss of nitrogen and minerals from the skin in the so called “insensible perspiration.” Since “insensible perspiration” occurs in all animals, regardless of the presence or absence of sweat glands, the term is not a good one. In man, insensible perspiration is evident to a normal extent in the rare condition known as congenital ectodermal defect (l), in which the sweat glands are totally absent, and in normal persons it persists without diminution when the sweat glands are inactivated by repeated anodal cataphoresis of formaldehyde into the skin (2). Probably insensible perspiration is the result of a passive diffusion of water from the subdermal tissues to the surface of the skin, dependent on a vapor tension gradient. McCance (3) has shown that this diffused fluid, on evaporation at the surface of the skin, deposits there appreciable amounts of nitrogen, potassium, sodium, and chloride. Freyberg and Grant (4) confirmed the presence of these elements in insensible perspiration, together with sulfate sulfur, and in amounts that may be of considerable importance to the accurate determination of mineral balances. Calcium and phosphorus were not found in this excretion. On the initiation of sweating, the loss of water and solutes in the insensible perspiration presumably stops wherever the surface of the skin is covered with a film of water. The sensible sweat that supersedes this insensible water (and solute) loss apparently contains all of the minerals found in the blood. Besides sodium, potassium, calcium, magnesium, chlorine, sulfur, and phosphorus, iodine (see (5) and earlier workers) and fluorine (6) have been identified, and concentrations and, in some cases, losses per hour under controlled environmental conditions have been determined. The presence of considerable amounts of bromine in sweat was observed, but not measured, by Spector in the routine of his determinations of iodine in sweat.