156 COMPOSITION OF SWEAT. 



the amount of blood supply. In exercising, the skin is usually 

 redder from the greater blood supply, and at the same time 

 the glands are more active, as they should be; for, during 

 exercise, and immediately after it, there is more waste matter 

 to be thrown out. But the activity of the gland is not a 

 mere filtering process, due to the greater blood pressure. 

 There may be a cold sweat ; i.e., when the skin is pale. Here 

 is evidence that the activity of the glands is primarily due 

 to nerve impulses from some nerve center to the gland cells. 



The sweat glands rid the body of certain waste matters 

 that can no longer be used. They are Excretory glands. In 

 structure they are Simple glands. 



The sweat glands are thickly distributed over the whole 

 surface of the body, but are especially numerous and large on 

 the palm of the hand and the sole of the foot. In the arm- 

 pit the glands are very large. 



The Oil glands of the skin are distributed over all the sur- 

 face except the palms of the hand and soles of the feet. The 

 oily matter is usually poured out around the hairs as they 

 emerge from the skin. It serves to oil the hair and the skin, 

 and keep them from becoming too dry. 



Composition and Amount of Sweat. Sweat is mostly 

 water ; about one per cent is solid matter, including salt and 

 certain matters which, like the organic waste matter from the 

 lungs, easily putrefy, and some oily matter from the oil glands 

 of the skin. 



Thrust the hand into a glass jar, preferably a jar that has 

 been in a cool place. Note the moisture that soon gathers on 

 the inside of the jar from the insensible sweat of the hand. 

 A common fruit-jar will do for a small hand ; but a candy-jar 

 is better, having a larger mouth and clear glass. 



Ordinarily the sweat is evaporated as fast as it is poured 

 out j in distinction from this insensible perspiration it is 



