436 THE SKIN. 



for distinction, the former is called insensible perspiration : 

 the latter, sensible perspiration. The fluids are the same, 

 except that the sweat is commonly mingled with various 

 substances lying on the surface of the skin. The contents 

 of the sweat are, in part, matters capable of assuming the 

 form of vapour, such as carbonic acid and water, and in 

 part, other matters which are deposited on the skin, and 

 mixed with the sebaceous secretion. Thenard collected 

 the perspiration in a flannel shirt which had been washed 

 in distilled water, and found in it chloride of sodium, 

 acetic acid, some phosphate of soda, traces of phosphate of 

 lime, and oxide of iron, together with an animal substance. 

 In sweat which had ru^i from the forehead in drops, Berze- 

 lius found lactic acid, chloride of sodium, and chloride of 

 ammonium. Anselmino placed his aj?m in a glass cylinder, 

 and closed the opening around it with oiled silk, taking 

 care that the arm touched the glass at no point. The 

 cutaneous exhalation collected on the interior of the glass, 

 and ran down as a fluid : on analysing this, he found 

 water, acetate of ammonia, and carbonic acid ; and in the 

 ashes of the dried residue of sweat he found carbonate, 

 sulphate, and phpsphate of soda, and some potash, with 

 chloride of sodium, phosphate and carbonate of lime, and 

 traces of oxide of iron. Urea has also been shown to be 

 an ordinary constituent of the fluid of perspiration. 



The ordinary constituents of perspiration, may, there- 

 fore, according to Gorup-Besanez, be thus summed up : 

 water, fat, acetic, butyric and formic acids, urea, and salts. 

 The principal salts are the chlorides of sodium and potas- 

 sium, together with, in small quantity, alkaline and earthy 

 phosphates and sulphates ; and, lastly, some oxide of iron. 

 Of these several substances, none, however, need particular 

 consideration, except the carbonic acid and water. 



The quantity of watery vapour excreted from the skin, 

 was estimated very carefully by Lavoisier and Sequin. 

 The latter chemist enclosed his body in an air-tight bag, 



