956 NUTRITION AND HEAT REGULATION. 



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.* The respiration chamber is a small 

 room lighted and furnished so that an individual may remain in 

 it for long periods without discomfort. As shown in Fig. 301, this 

 room is arranged as a calorimeter. It has several walls of metal 

 and wood to prevent loss of heat to the outside or the reverse, and 

 by means of water circulating through a system of pipes within 

 the room the heat given up by the body is carried off. By regulat- 

 ing this flow of water the temperature of the chamber can be kept 

 constant. Knowing the temperature of the water as it enters and 

 leaves the chamber and the volume of the flow, the heat production 

 of the individual may be calculated in terms of calories. For the 

 determination of the carbon dioxid and water air is drawn through 

 the room by means of a rotary pump and a closed circuit is em- 

 ployed, that is to say, the same air is kept circulating through the 

 room, but provision is made for absorbing the CO2 and water as 

 it is formed, and for adding new oxygen from an oxygen tank as it 

 is needed. This arrangement is represented schematically in 

 Fig, 301a. It is possible in this form of calorimeter to determine 

 the amount of oxygen consumed as well as the amount of carbon 

 dioxid eliminated. By this means the observer can ascertain the 

 respiratory coefficient ("q^J, a factor of much value, since it 



throws light on the nature of the material undergoing oxidation 

 in the body. By means of this apparatus many interesting and 

 important experiments have been made upon the nutrition of 

 man under different physiological and pathological conditions, 

 and it seems probable that it will supplant entirely the earlier 

 forms of calorimeter described in the preceding pages. As an 

 indication of its sensitiveness the following result may be quoted 



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

 culture, 1899; and for recent improvements, Atwater and Benedict, "A Respi-> 

 ration Calorimeter," Carnegie Institution, Washington, 1905. 



