THE TOTAL EXCHANGES OF THE BODY 



669 



the animal or individual in the chamber being communicated to the water 

 passing through the chamber. The temperatures of the entering and leav- 

 ing water are taken by accurate thermometers reading to a hundredth or a 

 thousandth of a degree Centigrade. Knowing the amount of water that has 

 passed through in a given time and the difference in temperature during the 

 same time, it is 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 appro- 

 priate adjustment of the amount of water passing through the apparatus. 

 The equality of temperature between the inner and outer casing is recorded 



Water 



Water 



Air 4 Watir + CO,; deficient in Oxy 



Air minus C0 2 and Water; deficient in Oxygen 



Oxygen enters. 



FIG. 331. Diagram to show the principle of the Atwater-Benedict calorimeter. 



(After HALLIBURTON.) 



by electric thermo couples, any difference of temperature being at once 

 compensated by electrically warming the cooler part. The chamber con- 

 tains a bicycle or other arrangement 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. 663. It is thus 

 possible to estimate simultaneously the total heat production of an individual 

 as well as the respiratory changes, including both carbon dioxide output 

 and oxygen intake. The general principle of the calorimeter is shown in 

 the diagram (Fig. 331). The calorimeter is also supplied with bed, table, 

 chair, etc., 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. 



