ENERGY RELATIONSHIPS. 345 



able increment in the metabolism even in the last period. We can not 

 use the results, therefore, for an illustration of computing the specific 

 dynamic action. 1 An experiment better adapted for this purpose is 

 that with the same subject on May 24, 1907, in which the basal metab- 

 olism was obtained in the last period of the experiment and the total 

 increment due to the ingestion of the beefsteak was therefore secured. 

 ( See table 200 , page 269 . ) Following the usage of Rubner , the fuel value 

 rather than the total energy of the diet may be used in the computa- 

 tion. The fuel value of the beefsteak eaten in this experiment was 644 

 calories, of which 70 per cent was derived from protein, or approxi- 

 mately 450 calories. The total increase in the heat production subse- 

 quent to the ingestion of the food was 70 calories. The total nitrogen 

 excretion in the 8 hours of the experiment was 8.26 grams; as the basal 

 nitrogen excretion which may be used for the same period is 4.24 

 grams, the excess nitrogen excretion due to the ingestion of the food 

 was therefore 4.02 grams. This corresponds to an excess in the amount 

 of protein katabolized (4.02 by 26.51) of approximately 107 calories as 

 the result of an intake of 450 calories from protein. 



A part of this increment of 70 calories may be properly ascribed to the 

 influence of fat ingestion, since there was a considerable proportion of 

 fat present in the beefsteak, but our evidence, as well as that of other 

 investigators, indicates that the ingestion of fat has but a slight effect 

 upon the metabolism and may probably be neglected in computations 

 of this kind. Indeed, this was done in computing the values given in 

 tables 249 and 250. The possibilities of differentiating between fat and 

 protein in determining the influence upon the metabolism of the inges- 

 tion of a protein-fat diet should not, however, be lost sight of. It may 

 be noted in this connection that Rubner carefully made such corrections 

 in considering the influence of the protein-fat diets used in his experi- 

 ments. 



The experiments in our research with a predominatingly protein diet 

 were not sufficiently extended or carried out with a sufficient degree of 

 accuracy to justify a computation from their results of the so-called 

 ''specific dynamic action" of protein in the case of man. There is no 

 question but that such a relationship exists between the increment in 

 the protein katabolism and the increment in the heat production, but it 

 may or may not be causal. Our experiments show that subsequent to 

 the ingestion of a diet containing an excessive amount of protein there is 

 prolonged and excessive heat production which continues for several 

 hours. The nitrogen in the urine is likewise increased, although, as is 

 seen from the foregoing discussion, the increase in heat production is 



'Williams, Riche, and Lusk (Journ. Biol. Chem., 1912, 12, p. 352) have pointed out in an in- 

 teresting manner the methods of computing the specific dynamic action, so called, from an increase 

 in the protein katabolism. 



