PERSPIRATORY GLANDS. 



415 



presence of fatty acids resulting from the decomposition of the 

 sebum. In uremia the amount of urea may be so great as to 

 crystallize on the skin ; in diabetes sugar may be found in the 

 sweat ; and in cases of gout uric acid has been detected. 

 The following table shows the composition of sweat : 



Water. 99.00 per cent. 



Urea 0.15 " 



Neutral fats, fatty acids, cholesterin, sodium and 



potassium chlorids, and other salts . . . 0.85 " 



100.00 



Office of Perspiration. One of the important means of regulat- 

 ing the temperature of the body is the perspiration. Without it, 



FIG. 232. c, Corneous (horny) layer ; g, granular layer; m, mucous layer (rete 

 Malpighii). The stratum lucidum is the layer just above the granular layer. 

 .Nerve-terminations : n, afferent nerve ; b, terminal nerve-bulbs ; I, cell of Lang- 

 erhans (after Ranvier). 



exposure to high temperatures would be injurious, and in some 

 cases would even be fatal. An external temperature of 52 C. is 

 not infrequently met with in the southern part of the United States ; 

 to this heat human beings are exposed without suffering from its 

 effects. The evaporation of the perspiration abstracts heat from 

 the body. Of the heat given off from the body, 88 per cent, 

 passes off by the skin ; of this amount, 73 per cent, is by radia- 

 tion and conduction, and 14.5 per cent, by evaporation. 



