856 



NUTRITION AND HEAT REGULATION. 



small calories. In physiology calorimeters have been used for two 

 main purposes: to determine the heat equivalent of foods, that is, 

 the amount of heat given off when the various foodstuffs are burned, 

 and, secondly, to determine the heat produced and the heat dissi- 

 pated by living animals during a given period. For the first pur- 

 pose the apparatus that is most frequently employed at present is 

 the bomb calorimeter devised by Berthelot. The bomb consists 

 of a strong steel cylinder in which the food to be burned is placed 



Fig. 275. Reichert's water calorimeter. 



and which is filled with oxygen. The combustion of the foodstuff 

 is initiated by means of a spiral of platinum wire heated by an 

 electrical current. The bomb is immersed in water and the heat 

 given off raises the water to a measured extent of temperature. 

 The weight of water being known, the amount of heat is easily 

 expressed in calories. For the purpose of measuring the heat 

 given off by living animals two principal forms of calorimeter are 

 used, each form having a number of modifications. These two 

 forms are the water calorimeter and the air calorimeter. The 

 water calorimeter was the form used in the first experiments on rec- 

 ord (Crawford, 1779). In principle it consists of a double-walled 

 box with a known weight of water between the walls. The animal 

 is placed in the inner box and the heat given off is absorbed by the 



