i In the amphibia, in which the skin is thin and moist, the cutaneous respiration is extremely active; and that the respiratory function of the skin in the higher animals is also considerable, is proved not only by measuring the excreted carbonic acid, but by the fact that if the skin is covered with an impermeable varnish, or if the body be inclosed, all but the head, iu a caoutchouc dress, animals soon die, as if asphyxiated, their heart and lungs being gorged with blood, and their temperature before death gradually falling Many degrees. The secretion of the sebaceous glands is a semi-fluid city mass, which often solidifies into a white viscid tallow-like matter on the surface or in the glandular ducts, from which it can be removed by pressure, in a form resembling that of a small whitish worm or maggot. Under the microscope, cells containing fat, free fat mixed with epidermic scales, and sometimes crystals of cholesterin, are observed. Its chemical constituent's, in addition to water, are a peculiar nitrogenous matter resembling casein, fat (consisting of palmitin and olefin, soaps composed of palmitic and oleic acids), choles terin, earthy phosphates, and chlorides and phosphates of the alkalies. Its purpose seems to be that of keeping the skin moist and supple, and by its oily nature, of hinder ing too rapid evaporation. Moreover, considered as an excretion, it must take a share in the purification of the blood.
The skin is, moreover, an organ of absorption: mercurial preparations, when rubbed into the skin, have the same action as when given internally. Potassio-tartrate of anti mony, when rubbed into the skin in the form of ointment or solution, may excite vomiting, or an eruption extending over the whole body, and many other illustrations might be given. The effect of rubbing is probably to force the particles of the mat ter into the orifices of the glands, where they are more easily absorbed than they would be through the epidermis. It has been proved by the experiments of Madden, Berthold, and Mho* that the skin has the power of absorbing water, although to a less extent than occurs in thin-skinned animals, such as frogs and lizards. This fact has a practical application. In severe cases of dysphagia—difficult swallowing—when not even fluids can be taken into the stomach, immersion in a bath of warm water. or of milk and water, may assuage the thirst. Sailors, also, when destitute of•fresh water, find urgent thirst allayed by soaking their clothes in salt water.
The disea•ex of the skin, and their classification into genera and species, have occu pied the attention of many of the most eminent physicians during the last century; but none of the proposed classifications arc very satisfactory. The more important affec tions are noticed in special articles. See ECZEMA, and ECTIIYMA.