344 THE SKIN. 



Excretion by the Skin. 



The skin, as already stated, is the seat of a twofold excre- 

 tioD ; of that formed by the sebaceous glands and hair-follicles, 

 and of the more watery fluid, the sweat or perspiration, elimi- 

 nated by the sudoriparous glands. 



The secretion of the sebaceous glands and hair-follicles (for 

 their products cannot be separated) consists of cast-off epithe- 

 lium-cells, with nuclei and granules, together with an oily 

 matter, extractive matter, and stearin ; in certain parts, also, it 

 is mixed with a peculiar odorous principle, which is said by 

 Dr. Fischer to contain caproic, butyric, and rutic acids. It is, 

 perhaps, nearly similar in composition to the unctuous coat- 

 ing, or vernix caseosa, which is formed on the body of the 

 foetus while in the uterus, and which contains large quantities 

 both of olein and margariu ( J. Davy). Its purpose seems to 

 be that of keeping the skin moist and supple, and, by its oily 

 nature, of both hindering the evaporation from the surface, 

 and guarding the skin from the effects of the long-continued ac- 

 tion of moisture. But while it thus serves local purposes, its 

 removal from the body entitles it to be reckoned among the 

 excretions of the skin ; though the share it has in the purify- 

 ing of the blood cannot be discerned. 



The fluid secreted by the sudoriparous glands is usually 

 formed so gradually, that the watery portion of it escapes by 

 evaporation as fast as it reaches the surface. But, during 

 strong exercise, exposure to great external warmth, in some 

 diseases, and when evaporation is prevented by the application 

 of oiled silk or plaster, the secretion becomes more sensible 

 and collects on the skin in the form of drops of fluid. A good 

 analysis of the secretion of these glands, unmixed with other 

 fluids secreted from the skin, can scarcely be made ; for the 

 quantity that can be collected pure is very small. Krause in 

 a few drops from the palm of the hand, found an acid reac- 

 tion, oily matter, and margarin, with water. 



The perspiration of the skin, as the term is sometimes em- 

 ployed in physiology, includes all that portion of the secre- 

 tions and exudations from the skin which passes off by evap- 

 oration ; the sweat includes that which may be collected only 

 in drops of fluid on the surface of the skin. The two terms 

 are, however, most often used synonymously ; and for distinc- 

 tion, the former is called insensible perspiration : the latter, 

 sensible perspiration. The fluids are the same, except that the 

 sweat is commonly mingled w T ith various substances lying on 

 the surface of the skin. The contents of the sweat are, in part, 

 matters capable of assuming the form of vapor, such as car- 



