40 THE HUMAN BODY 



and doubtless many others of which we know nothing. The study 

 of these cell activities is comprehended under the head of Me- 

 tabolism. 



The chemical activities which go on in the cells of the body give 

 rise to much heat. Some cells generate more heat than others. 

 One of the functions of the circulating medium is to distribute this 

 heat uniformly over the body. There is constant loss of heat from 

 the surface of the body. In warm-blooded animals, which have 

 a nearly constant body temperature, the maintenance of balance 

 between heat production and heat loss in the face of constantly 

 varying outside temperatures is a function of great importance. 

 It is studied under the head of Heat Production and Heat Regula- 

 tion. 



Not immediately concerned with the well-being of the body it- 

 self, but devoted to the well-being of the race as a whole through 

 perpetuating the species is the Reproductive System. 



