The osmotic passage of water and gases through the human skin

Abstract

It has been known for long that part at least of the “insensible” passage of water which is constantly passing through the skin is not due to the activity of sweat-glands, since in the rare cases of congenital absence of sweat-glands some water is nevertheless given off through the skin. Two cases of this kind were investigated by Loewy and Wechselmann (1911), who inferred that at an ordinary air-temperature as much as 18 grams of water might pass through the skin in an hour. The cases were those of two brothers, whose father had apparently suffered from the same defect. A further, more complete, study of a similar case was recently made by Richardson (1926). In our previous paper (1929) we brought forward evidence to show that in ordinary insensible perspiration through the skin, salts do not penetrate the skin in anything like either the same concentration or the same composition as would be the case if they had been excreted in sweat, and several similar results were given by Moss (1927). Hence since sweat contains salt, and in fairly constant concentration, little or none of this insensible perspiration is due to sweating, and the passage of water is presumably due to an osmotic process. The present paper contains further evidence in this direction, together with data as to variations in the osmotic transference and their relation to regulation of body-temperature. Variations in the rate of transference of gases through the skin have also been studied. We may define osmosis as the passage, molecule by molecule, of a substance, such as water, through a membrane or surface which is permeable to it, though it may not be to another substance present in the same state on one side of the membrane or surface. The consequence of the presence of the other substance is that the substance which can pass through the membrane can do so against adverse pressure on the side on which the other substance is present; and the maximum amount of this pressure is known as the osmotic pressure. As was pointed out recently by one of us (Haldane, 1928), this passage is due simply to diffusion, the diffusion-pressure of the substance which passes through being necessarily greater on the side from which it passes, so that for this reason the substance can pass through against mechanical pressure. It is thus simply with a diffusion process that we are dealing in the case of osmotic transfer of water through the skin, and what is usually called the osmotic “pressure” existing in a solution is more correctly called osmotic depression. It is with this depression that depression of the vapour-pressure of the solution runs parallel.