OIL-GLANDS. 67 



is poured out: then it is named insensible perspiration. 

 When it is poured out faster than it evaporates, sweat 

 collects in drops on the skin, and especially in regions, as 

 the forehead, where the glands are very abundant. It is 

 then named sensible perspiration. 



15. The Chief Use of the Sweat-Glands is to cool the 

 body when there is danger of its becoming too hot. 

 Whenever a liquid dries up or evaporates, it draws heat 

 from whatever it lies on. Your saliva is warmer than 

 the skin of your finger, but if, after wetting your finger 

 with this warmer liquid, you expose it to the air it feels 

 cool, because as the moisture dries up, it takes heat from 

 the skin. Our bodies only work well when they have a 

 temperature of about 98 degrees of an ordinary or Fah- 

 renheit thermometer. If they get a little hotter than this, 

 fever results, and many organs either cease to work, or 

 work very badly. In health, the sweat-glands pour addi- 

 tional liquid on the skin on a hot day, or when we are 

 heated by exercise; and the heat taken away in the evapo- 

 ration of this extra quantity of water, keeps the body 

 cooled down to its proper temperature. When the body 

 is cold the sweat-glands (except in disease) almost cease 

 to make perspiration, and so loss of heat is checked. 



16. The Sebaceous or Oil Glands of the skin, pour their 

 secretion into the sides of the pits in which the roots of 

 the hairs are contained. The openings of the ducts of a 

 pair of sebaceous glands are seen at k in Fig. 22. The 



15. What is the chief use of the sweat-glands? Explain. What is 

 the proper temperature of the body ? If it become a little hotter what 

 results? When do the sweat-glands secrete freelv ? When little? 

 Why? 



16. Where do the sebaceous glands pour their secretion ? What are 

 its uses? How do the sebaceous glands sometimes cause black spots 

 in the skin ? 



