NORMAL PROCESSES OF ENERGY METABOLISM 585 



of tlie law of the conservation of energy to the animal body was thus 

 demonstrated. 



Atwater and his colleagues, Rosa, Woods, Benedict, Smith and Bryant 

 studied this balance of energy in a series of rest and work experiments by 

 means of the Atwater-Rosa calorimeter (Atwater and Benedict(a, 6) ). On 

 four different human subjects the agreement between the direct and indi- 

 rect methods were almost as close as those reported by Rubner. The re- 

 sults may be summarized briefly as follows: 



TABLE 12 



HEAT PRODUCTION OF HUMAN SUBJECTS BY DIRECT AND INDIRECT CALORIMETRY 



(Atwater et al.) 



The results are perfectly clear-cut. The heat-production as calculated 

 from the heat value of the food and from the heat value of the excreta 

 (for method of calculation see page 552) agrees exactly with the amount 

 of heat eliminated. The food in these experiments consisted of the three 

 classes of foodstuffs and on certain days included alcohol in small amounts. 

 The assumption was made (see page 554) that carbohydrate absorbed 

 enters into combustion before the fat. The close agreement between direct 

 and indirect measurement seems to justify the assumption. 



All of the experiments thus far cited in support of the principle of the 

 conservation of energy continued for 24 hours. We now know, however, 

 that the principle holds for short periods as well. Thus Howland(o.) work- 

 ing with the Cornell calorimeter found that with young children the heat 

 production, expressed in calories per hour, as measured by the calorimeter 

 differed from the heat production as calculated from the respiratory ex- 

 change and the nitrogen output, on six different days, by only 2.1 per cent. 



With the same calorimeter Murlin and Lusk found in a series of twenty- 

 two experiments in hourly periods on a dog, which was being fed large 

 amounts of fat alternating with fasting periods, 2244 calories 5 by indirect 

 calorimetry as against 2230 calories by direct calorimetry, a difference of 

 0.6 per cent. A large part of the energy was derived from the emulsified 

 fat given for the most part without other food. These peculiar circum- 

 stances did not interfere in any way with the fundamental dynamic prin- 

 ciple. 



'Throughout this chapter the large calorie is not capitalized unless abbreviated 

 as in Table 12. In human metabolism the large calorie is always understood unless 

 otherwise designated. 



