434 THE SKIX. 



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 run from the forehead in drops, Berzelius found 

 lactic acid, chloride of sodium, and chloride of ammonium. 

 Anselmino placed his arm 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 exhala- 

 tion 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 phos- 

 phate 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, therefore, 

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

 fat, acetic, butyric and formic acid, urea, and salts. The 

 principal salts are the chlorides of sodium and potassium, 

 together with, in small quantity, alkaline, and earthy phos- 

 phates 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, 



