EXCRETION. 135 



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 the nerve impulses from some 

 nerve center to the gland cells. 



Sweat Glands are Simple and Excretory. 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. 



Distribution of Sweat Glands. The sweat glands are 

 thickly distributed over the whole surface of the body, 

 but are especially numerous and large on the palms of the 

 hands and the soles of the feet. In the armpits the glands 

 are very large. 



The Oil Glands. The oil glands of the skin are dis- 

 tributed over all the surface except the palms of the hands 

 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 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. 



Experiment to show Insensible Perspiration. 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 insen- 

 sible 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. 



Kinds of Perspiration. Ordinarily the sweat is evapo- 

 rated as fast as it is poured out ; in distinction from this 

 insensible^ perspiration, there is the so-called sensible per- 



