SWEAT GLANDS 



205 



a knotted mass, the glantf, which is about one-sixtieth of 

 an inch in diameter. 



Secretion. The sweat glands are scattered thickly 

 in the skin, especially in the palms of the hands and 

 the soles of the feet. Their total 

 number is estimated at about 

 2,000,000, and their total secre- 

 tion in twenty-fours hours may be 

 as much as a quart. In warm 

 weather, as a result of vigorous 

 exercise, the secretion may be two 

 or three times as much. It con- 

 sists normally of water containing 

 a small amount of salt. It is 

 ordinarily more or less mixed 

 with the secretions of the seba- 

 ceous glands. When the kidneys 

 are not able adequately to do their 

 work, the sweat becomes much 

 richer in the waste products usually eliminated by them. 



"Pores" of the skin. The mouths of the sweat 

 glands are popularly known as the pores of the skin, 

 and are said to open and close. As a matter of fact, 

 they are always wide open. Occasionally, it is true, a 

 few of them may be clogged with dirt, with resulting 

 pimples or "black heads.' 7 The semi-solid contents of 

 these can be emptied by gentle pressure. The popular 

 term, "opening the pores of the skin," really means 

 increased activity in these glands and visible perspira- 

 tion, or the dilatation of the blood-vessels lying under the 

 skin. 



Inadequacy of the skin's protection. The unbroken 

 skin, even when as delicate as in man, forms ordinarily 

 an adequate protection against the invasion of the body 



FIG. 112. Magnified view 

 of the epidermis, show- 

 ing mouths of the sweat 

 glands. 



