THE TOTAL EXCHANGES OF THE BODY 697 



easy to calculate the amount of heat given off by the animal under 

 investigation. It is generally convenient to maintain a constant 

 difference of temperature between the entering and leaving water by 

 appropriate adjustment of the amount of water passing through the 

 apparatus. The equality of temperature between the inner and 

 outer casing is recorded by electric thermo couples, any difference of 

 temperature being at once compensated by electrically warming 

 the cooler part. The chamber contains a bicycle or other arrange- 

 ment for the performance of mechanical work. It is adequately 

 ventilated by a current of air passing through an apparatus similar 

 to that of Benedict, described on p. 690. It is thus possible to 

 estimate simultaneously the total heat production of an individual 

 as well as the respiratory exchanges, including both carbon dioxide 

 output and oxygen intake. The general principle of the calorimeter 

 is shown in the diagram (Fig. 317). The calorimeter is also supplied 

 with bed, table, chair, &c., and food can be introduced through a 

 double window so that an experiment may be continued over two 

 or three days on one and the same individual 



