THE BALANCE OF NUTRITION 



237 



Either, therefore, evaporation must be prevented by keeping 

 the air in the chamber saturated with water, thus introducing 

 more or less abnormal conditions, or the amount of water 

 carried away in the ventilating air current must be determined. 

 If the latter course is followed, it is a relatively simple matter 

 to include also determinations of the carbon dioxid and the 

 combustible gases excreted, and perhaps of the oxygen con- 



FIG. 34. Dulong's water calorimeter (Schaefer, Text Book of Physiology). 



sumed. The apparatus then becomes a combination of res- 

 piration apparatus and animal calorimeter and hence has been 

 called a respiration calorimeter. 



The apparatus used by Dulong in 1822 in his investigation of the 

 source of animal heat, the construction of which is'shown in Fig. 34, 

 may serve to illustrate the form of calorimeter in which a stationary 

 mass of water is used. This type of calorimeter has been used in 

 various modifications, notably in the United States by Wood, 1 Ott 2 



1 Smithsonian Contributions to Knowledge, No. 23 (1880). 

 2 N. Y. Med. Jour., 49 (1889), 342. 



