344 FOOD INGESTION AND ENERGY TRANSFORMATIONS. 



calories). The remainder of the energy is then apportioned between 

 fat and carbohydrate on the basis of the non-protein respiratory quo- 

 tient. As previously stated (see page 203) , this was not done in our com- 

 putations of the energy from the gaseous exchange, as the non-protein 

 quotient has relatively little significance, save in those experiments in 

 which an excessive amount of protein was ingested. 



By using the nitrogen excretion as an index of the protein katabolized, 

 computing the total energy derived from protein and comparing it with 

 the increment in the energy due to the ingestion of a protein food, cer- 

 tain relationships are made possible. This method of computation 

 may be illustrated by using the results of the experiment with A. H. M. 

 on April 5, 1907, in which 777 grams of beefsteak were taken by the 

 subject. (See table 198, page 267.) The basal nitrogen excretion used 

 was 1.06 grams per 2 hours (see table 28, page 80). The nitrogen 

 excretion in the first 2-hour period following the ingestion of the food 

 was 4 grams. The increment in the nitrogen excretion due to the in- 

 gestion of this large amount of a protein food was therefore 2.94 grams. 

 As each gram of nitrogen in the urine represents a heat production 

 from protein katabolized of 26.51 calories, the increment of 2.94 

 grams of nitrogen represents 78 calories of energy due to the increase in 

 the amount of protein katabolized during this 2-hour period. Inas- 

 much as the total increment in heat production for the first period 

 was but 31 calories, it is evident that at least 47 calories from the 

 protein combustion took the place of energy originally derived from 

 carbohydrate-fat combustion in a 2-hour period of the basal experi- 

 ment. The total nitrogen excretion in the 8 hours of the experiment 

 was 11.49 grams; the excess nitrogen excretion was therefore 7.25 

 grams, with an energy production of 192 calories due to the increase 

 in the protein katabolized. The total increment in the heat pro- 

 duction was but 136 calories; we may assume, therefore, that the re- 

 placement of basal energy derived from material other than protein 

 was at least 56 calories. 



The direct measurement of the protein disintegration from the nitrogen 

 in the urine leads to the possibilities of further computation to determine 

 the cause of the increase in the energy output following the ingestion of 

 food. For example, when a protein food, such as beefsteak, is given in 

 an experiment, we may compare the subsequent total increase in the 

 metabolism (1) with the total energy of the food intake; (2) with the 

 fuel value of the intake, thus obtaining the "cost of digestion"; (3) 

 with that portion of the total energy or fuel value of the diet which is 

 derived from protein alone; (4) with the total energy of the katabolized 

 protein; or (5) with the increment in the heat production due to the 

 increase in the amount of protein katabolized. 



In the experiment with A. H. M. on April 5, 1907, the total effect of 

 the ingestion of beefsteak wasnot obtained, as there was still a consider- 



