RESPIRATION AND EXCRETION 355 



warm weather when there is a large amount of blood in the 

 skin, water is collected in large drops upon the skin-surface. 

 As a result of muscular activity, and sometimes during 

 illness, other wastes are eliminated by the sweat glands, 

 particularly when the kidneys fail to function properly. 

 Hence it is that the skin is an important organ of excretion 

 and an important help to the kidneys. 



Regulation of the temperature of the body. — ^The skin 

 has a still more important function to perform for the body, 

 and this is the regulation of its temperature. 



The body must be maintained at a somewhat constant 

 temperature (varying from 97.5° to 99.5° F.) to fulfill its 

 functions normally and healthfully. During cell activity 

 much heat is generated. In a warm climate the body 

 receives heat also from the surrounding atmosphere. But 

 the temperature of the body can remain constant only when 

 the amount of heat produced within the body and received 

 from without is equal to the amount it gives out. Should 

 the amount produced and the amount received increase 

 above that given off, the temperature would rise abnormally. 



The body gives off heat through the aid of the skin in 

 two ways. First, by radiation. The blood as it flows 

 through the organs where metabolism is going on, as the 

 muscles or kidneys, becomes heated. As it flows to other 

 organs less active it transfers part of its heat to surrounding 

 tissues by conduction. Or the heat may be radiated from 

 the surface of the skin, as heat is radiated from a stove. 

 This takes place when the atmosphere is cooler than the 

 body. The greater the difference in the temperature of 

 the atmosphere and that of the body the greater the amount 

 of heat lost and the more rapidly the body cools. 



When, however, the surrounding atmosphere is warmer 

 than the body how is the body to be cooled ? The changing 

 of a substance from a liquid to a gaseous state always requires 

 heat. Place a drop of ether on the finger and notice the 



