CALORIMETRY. 859 



The Respiration Calorimeter. When a calorimeter is so arranged 

 that the composition of the air drawn through the apparatus for 

 ventilation can be determined as well as the amount of heat pro- 

 duced, the apparatus becomes a respiration calorimeter. In such 

 an apparatus, if proper provision is made for analyzing the urine, 

 the feces, and the food, the total carbon and nitrogen excretion may 

 be obtained simultaneously with the heat loss. Since we may 

 calculate from the carbon and nitrogen excretion how much pro- 

 tein, fat, and carbohydrate, have been burnt in the body, and since 

 the heat values of these constituents are known, it is evident that 

 we may reckon indirectly how much heat ought to be produced 

 from the combustion of so much material. This method of arriv- 

 ing at the heat production is designated indirect calorimetry. With 

 an adequate respiration calorimeter it is possible to ascertain 

 whether the results calculated by the method of indirect calorim- 

 etry really correspond with the heat obtained by direct measure- 

 ment. In the hands of good observers the correspondence is 

 very close, and gives substantial proof of the scientific belief 

 that in the living body the energy liberated as heat or as heat 

 and work is all contained in potential form in the foodstuffs 

 eaten. By means of the respiration calorimeter we can obtain a 

 balance between the energy income and outgo of the body as well 

 as between the material income and outgo, that is, the carbon and 

 nitrogen equilibrium. The most complete and elaborate form of 

 respiration calorimeter used is that devised by Atwater and Rosa for 

 experiments upon man.* Considered as a calorimeter the appara- 

 tus used by these investigators belongs to the type of water cal- 

 orimeters. Instead, however, of having a stationary stratum of 

 water to be warmed by the heat given off from the body, the appara- 

 tus is arranged so that a stream of water may be circulated between 

 the walls, and this stream is so regulated, as to quantity and 

 temperature, as to keep the temperature of the calorimeter as a 

 constant point. In other words, the heat given off from the body 

 is carried away by the circulating water, and the quantity of the 

 heat may be calculated when the temperature and amount of the 

 water are known. By means of this apparatus many interesting 

 and important experiments have been made upon the nutrition 

 of man under special conditions. Such results as the following 

 have been obtained (Atwater and Benedict) in the case of a man 

 who, while in the apparatus, did much muscular work on a bicycle 

 ergometer: 



* See Atwater and Rosa, Bulletin 63, United States Department of Agri- 

 culture, 1899; and for recent improvements, Atwater and Benedict, ''A Respira- 

 tion Calorimeter," Carnegie Institution, Washington, 1905. 



