824 



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 

 and which is filled with oxygen under high pressure.' The combus- 

 tion of the foodstuff is initiated by means of a spiral of platinum 



CT 



Fig. 266. Reichert's water calorimeter. 



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 calorim- 

 eter 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 



