194 THE HUMAN MECHANISM 



body. This fact is strikingly illustrated in the case of a "chill," 

 when the internal temperature is almost always really above, 

 and not below, the normal, and the feeling of warmth pro- 

 duced by muscular activity or by warming one's self at a fire 

 merely indicates a higher temperature of the skin, not a higher 

 temperature of internal organs. 



Having now learned the more obvious facts about the 

 constant temperature of the body, we have next to inquire 

 by what means this constant temperature is maintained. 



9. The production and the loss of heat. We must first 

 remember that the body produces or liberates heat. The 

 chemical changes, largely oxidative in character, which are 

 at the basis of the work of its muscles, glands, nerve cells, 

 etc., liberate heat just as truly as the burning of coal in the 

 furnace of an engine liberates heat. Heat production is there- 

 fore an indispensable result of cellular and organic activity, 

 and it is greatest in those organs, like the muscles and liver, 

 which carry out the most active chemical processes. The 

 body is warm for the same reason that a stove is warm; 

 that is, because heat-producing chemical changes, largely of 

 an oxidative character, are going on within it. In the second 

 place, the body is always losing heat, and this in two ways: 

 (1) by the transfer of heat by conduction, convection, and 

 radiation * to colder objects or to the colder air with which 

 the body is surrounded, and (2) by the evaporation of water 

 from the surfaces of the body especially by the evaporation 

 of water of perspiration. 



Everyone knows in a general way that when a warm 

 body is brought near a colder one, the former becomes colder 

 and the latter warmer; heat is transferred from the warmer 

 body to the colder. In this way the clothing is warmed by 



1 Those not familiar with the meaning of the terms "conduction," "con- 

 vection," and "radiation" will find them explained in section 26 of this 

 chapter (p. 211). In the following discussion we have arbitrarily adopted 

 the term "heat transfer" to include these three means of heat loss, in order 

 to distinguish them from the loss of heat by evaporation. 



