1090 



ANIMAL HEAT 



ascertain the latter factor, it becomes necessary to employ an instru- 

 ment which is known as the calorimeter,^ and presents itself in the form 

 of two modifications, designated as the water-calorimeter and air- 

 calorimeter. In either case, this apparatus consists of a central 

 compartment in which the animal is kept, and a narrow outer com- 

 partment which is filled either with water or with air. Externally its 

 walls are covered with a heavy layer of some non-conductile material 

 to prevent all losses of heat. The heat liberated by the animal is then 



Fig. 627. — Water Calorimeter. (Reichert.) 

 A, Inner compartment for animal; SH, space filled with non-conductile material; 

 ENT and EXT, tubes for the respiratory air; CT, thermometer in jacket filled with 

 water; S, stirrer to equalize the temperature of the water. 



transmitted to the water, the temperature of which is read off by 

 means of a stationary thermometer. 2 In the case of the air calorime- 

 ter, the heat evolved by the animal gives rise to an expansion of the 

 air contained in the outer compartment, which is then transferred by 

 calculation into degrees of heat. Consequently, since the total amount 

 of the animal's heat is derived under this condition from the chemical 

 energy of its food, the former must constitute a direct index of the 

 oxidative processes. 



The unit generally employed in measuring the amount of heat 



1 The first calorimeter experiments upon animals were made by Lavisier and 

 Laplace in 1780 (Mem; de I'Acad. d. Sciences). 



2 Equally large masses of different bodies require different amounts of heat, 

 that of water being nine times greater than that of iron. 



