318 



THE SKIN 



as it passes away from it. It is only because of its location on the body- 

 surface that the skin rather than some internal organ excretes the sweat, 

 for it passes off largely by evaporation, for the purpose just considered 

 above. 



The purely excretory aspects of the sweat have been briefly treated of 

 especially in the chapter on Nutrition (see page 252). We have now to 

 describe its composition, mode of production, and relations to the skin 

 and to thermotaxis rather than to the removal of waste from the body. 

 First, a few words as to its physical and chemical nature. 



Human sweat is a somewhat opalescent colorless liquid with a specific 

 gravity varying between 1003 and 1010 according to the conditions under 

 which it is produced, but averaging perhaps 1005; it is, then, one of the 

 most watery of the body-liquids. Three samples analyzed by Camerer 

 had an average of 98.5 per cent, of water and 1.5 per cent, of "solids :" 



FIG. 176 



A human sweat-gland: a, the knot of the gland surrounded by veinlets; 6, excretory duct; 

 c, basket-like capillary network about the gland. (Todd-Bowman.) 



three-quarters of the ash was sodium chloride. In reaction sweat 

 appears to be either alkaline or (later) acid, depending on the time it 

 has been in contact with the epidermis. Camerer found the sweat 

 poured out in a hot-air bath to be acid, that in the more sudorific vapor- 

 bath, alkaline. There is some evidence that what one might call mus- 

 cular-katabolic sweat tends to be more acid than that excreted by the 

 glands during bodily rest, the more profuse the sweat the greater its 

 liability to be neutral or alkaline. There are present small proportions 

 of neutral fats, urea, uric acid, aromatic oxy-acids, sulphates of phenol, 

 skatol, etc., kreatinin, formic and acetic acids, and traces of proteid 

 (especially in alkaline sweat). Altogether about 0.15 per cent, of nitrogen 

 are present, most of which are in the urea and uric acid. The universally 

 excreted cholesterin does not fail to be present. There are contained 



