168 The Feeding of Animals 



lent exercise by the animal greatly increases the produc- 

 tion of heat. We know this is so because under these 

 conditions an increased amount of blood is thrown to 

 the surface of the body, thereby greatly increasing the 

 loss of heat by radiation; perspiration sets in and with 

 it the consequent evaporation of much more moisture, 

 thus disposing of much heat. The dog, and sometimes 

 other animals, pants and thereby causes a large loss of 

 heat from the expanded surface of the moist tongue. 

 All this occurs without reducing the body temperature 

 below the normal. In fact, nature adopts these various 

 devices, such as increased circulation of the blood and 

 perspiration, in order to regulate the body temperature 

 and prevent its rising above the proper point. The 

 explanation of this greater heat during labor is that the 

 mechanical energy manifested by the muscles is con- 

 verted to heat, which under circumstances of severe 

 exercise is more than enough to keep the body at its 

 usual temperature and maintain the usual radiation. 

 When it is severely cold, on the other hand, vigorous 

 exercise is sometimes necessary in order to keep suffi- 

 ciently warm. 



The view is held by some that all body heat is a 

 secondary product, that combustion first supports mus- 

 cular activity which changes to heat, in fact, that no 

 food is burned primarily to keep the animal warm. 

 Convincing proof of this position is still lacking, how- 

 ever. There appears to be no good reason why we 

 should deny the possibility of combustion of food for 

 the specific purpose of warming the body. Certainly 

 an Arctic climate causes a consumption of food which 



