240 EXCRETION OP FAT BY THE SKIN. 



by resorting to the expedient of wearing for some days a flannel shirt 

 which had been thoroughly washed in distilled water, ascertained, after 

 it had again been washed in distilled water, that it had become imbued 

 with the chloride of sodium, acetic acid, phosphate of soda, phosphate of 

 lime, oxide of iron, and an animal substance. Berzelius found in the 

 sweat of the forehead chloride of sodium, lactic acid, and muriate of am- 

 monia. Besides these, other chemists have found butyric acid, the car- 

 bonates and sulphates of potash and soda, and the carbonate of lime. 

 That sweat contains sulphur is proved by keeping a portion of it : when 

 putrefaction ensues, the sulphide of ammonium is disengaged. 



Fourcroy first detected urea in perspiration, an observation subse- 

 quently confirmed by Landerer and others. That the skin can, under 

 certain circumstances, excrete urea, is proved by the interesting fact that 

 this substance sometimes occurs as a bluish powdery material on the 

 bodies of those who have died from cholera. 



In the perspiration formic acid also exists, and in certain conditions 

 Occurrence of ^ disease, as > f r instance, intermittent, it occurs in consid- 

 formic acid in erable quantity. Its origin may be from lactic acid, which 

 perspiration. p asses through this combination in gradually proceeding to 

 its.final destruction into carbonic acid and water. It has been asserted 

 that the increased acidity of rheumatic sweats is due to a concentration 

 from evaporation. 



The sudoriparous glands secrete a portion of fat, as is demonstrated by 

 Experiment of the experiment of Krause, who removed from the palm of the 

 Krause. hand, on which there are no sebaceous glands, loose epithe- 



lial scales and fat by means of ether and friction, and then placed upon a 

 square inch of it several thicknesses of filtering .paper, which was kept 

 in contact for one night, and properly protected externally. The paper 

 yielded to the action of ether a fatty substance, which contained marga- 

 rine and oil, in quantity sufficient to make tissue paper translucent. 



But, besides the saline substances thus dissolved in water, the skin, 

 Secretion of fat through the action of its sebaceous glands, secretes oleagin- 

 and oil from ous material. The nature of this fatty substance differs on 

 different regions, or according to the purposes to which it is 

 to be applied. Where the ducts of the sebaceous glands open into the 

 hair follicles, the fat is of a liquid or oily nature. Sometimes stearine 

 and margarine, sometimes cholesterine is set free. Before birth, this last 

 substance is the chief constituent of the vernix caseosa, coating the sur- 

 face of the skin. In this manner, sometimes the saponifiable and some- 

 times the non-saponifiable fats or lipoids are used. 



In the midst of these complex actions a very important principle may 

 Double action be discerned. I have spoken of the double action of the kid- 

 of the skin. nev? i tg mechanism f or removing saline solutions, and also 



