CALORIMETRY. 



953 



and the methods of calorimetry before attempting to explain the 

 mechanism of heat regulation. 



Calorimetry. — ^A calorimeter is an instrument for measuring 

 the quantity of heat given off from a body. The unit employed in 

 these determinations is the calorie, — that is, the amount of heat 

 necessary to raise 1 gm. of water 1° C.,or more accurately the amount 

 of heat required to raise 1 gm. of water from 15° to 16° G. This 

 unit is sometimes designated as a small calorie to distinguish it 

 from the large calorie (C), — that is, the quantity of heat necessary 

 to raise 1 kgm. of water 1° C. The large calorie is equal to 1000 



Fig. 300 — Reichert's water calorimeter. 



small calories. In physiology calorimeters have been used for two 

 main purposes : to determine the heat ecj[uivalent 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. The combustion of the foodstuff 

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



