idermis 



Fat 

 glands 



Capillaries 



Dermis 



SECTION OF THE SKIN 



The sweat gland consists of a fine tubule opening to the surface of the skin at one 

 end and coiled up in a knot at the other. The coiled portion is surrounded by blood 

 vessels from which water, salts, and traces of urea are withdrawn into the gland 

 tube. Around the base of each hair ore fat glands. Sensitive nerve endings come 

 close to the surface 



directly through the lining cells, in part carried by the white corpuscles (see 

 page 188), and in part through the secretions of the liver. From the intes- 

 tine these substances are removed, together v^^ith the refuse from the food, 

 in the feces. 



Sweat is excreted by special glands which open on the surface of the 

 skin (see illustration above). The water part of the perspiration usually 

 evaporates as fast as it comes out of the glands, leaving a solid deposit of the 

 wastes. When perspiration is more rapid, we can see the drops of sweat on 

 the skin. When this dries, the solids are left on the outside of the skin, in- 

 stead of in the mouths of the tubules. Ordinarily we perspire from 400 to 

 750 cubic centimeters daily. The sweat contains about 2 per cent of solids. 

 Thus miners and other laborers who sweat excessively lose some of the 

 essential materials of the body. They need to perspire freely to keep the 

 body cool. But they need also to increase intake of water and salt to com- 

 pensate for the materials lost through the sweat glands (see page 195). 



217 



