Absorption through the surface of the integument has always been a matter of dispute. At one time a system of administration of medicine was in fashion, under the name of the endermic system, and was certainly based on a decided belief in the absorbing powers of the skin, but the system itself implied the use of considerable friction with mercurial preparations mixed with fatty materials in the form of ointment, the fatty matter being the more readily absorbed if it were rancid. It is stated that De Collin produced absorption in an experiment to which he had recourse, which consisted in causing water impregnated with cyanide of potassium to fall in drops on a horse's back for several hours; the horse died from poisoning resulting from the passage of the salt, through the skin, into the system.

The power to absorb water through the skin was maintained in former times, but modern physiology rejects this idea entirely; in fact, the circumstance of patients affected with skin diseases remaining immersed in water for long periods, and still being subject to thirst, and requiring to drink as much liquid as if they were not in the water at all, proves that no appreciable quantity of that fluid is taken in through the skin. On the whole, the power of the skin to absorb fluid is generally accepted as an extremely limited one. It appears, however, that the skin can be permeated by gas. Bichat's experiment proves that the skin of a limb, if immersed in putrid gases, absorbs them, and it is alleged that all kinds of miasma may penetrate into the organism in this way with ease. Common observation suggests that the absorbing powers of the skin may have been underrated; it is admitted that it acts to a certain extent as an organ of respiration, absorbing oxygen and exhaling carbonic acid. It is recorded that Gairlach collected 1/2 oz. carbonic acid in half an hour from the skin of horses at rest, and 3 ozs. at work. The poisonous action of certain fluids when applied to the skin in the ordinary processes of sheep-dipping, and dressing the skin for mange and other diseases, has come under the writer's own notice repeatedly. On one occasion liquid carbolic acid was painted over the skin of two dogs suffering from mange, under a mistaken impression as to the proper mode of using the agent, which should have been mixed with fifty parts of water. The immediate effect was the occurrence of a species of epileptic fit; the animals fell over on to the ground, frothing at the mouth and showing a spasmodic twitching of the muscles. The prompt application of warm water with plenty of soap, by the aid of which the greater part of the lotion was removed, relieved the urgent symptoms, and the dogs ultimately recovered, but they continued to suffer from depression, loss of appetite, and difficulty of movement for several days.

On another occasion the dipping of sheep in a mixture of carbolic acid soap and a small quantity of turpentine, with the addition of 40 parts of water to 1 part of the mixture, was followed by the sudden death of five sheep in succession, after they had been kept in the dipping-tub for the usual two minutes. Directly the fleece had been wrung by the attendant for the purpose of removing excess of fluid, the animals rolled over on to the ground in violent convulsions, and were dead in the course of a few seconds. On looking at the mixture, which was the same that had been used repeatedly with perfect success, a quantity of brown scum was discovered on the surface, proving that the carbolic acid had not become emulsified as it should have been, for the reason, as it was afterwards ascertained, that the water was extremely hard. The addition of some washing-soda to the water had the effect of producing a perfect emulsion, and the process of dipping the flock was continued without any further disaster.

It had previously been known that the poisonous action of carbolic acid was especially marked when the agent was applied to the skin, and the explanation ordinarily given was, that it acted as a powerful depressor of nerve function. It must, however, be allowed that it could not possibly act upon the nerves without being absorbed in the first place through the cuticle, beneath which the nerves terminate on the surface of the true skin.

The absorption of fatty material by the skin probably largely depends on the affinity which it has with the sebaceous secretion, enabling it to pass into the follicles, and there certainly appears to be good reason to suppose that some of the nutritive constituents of milk are thus taken into the system, especially the fatty matters, as young children when incapable of taking nourishment by the mouth have been sustained for some time by being kept for considerable periods in baths of warm milk.