346 FOOD INGESTION AND ENERGY TRANSFORMATIONS. 



not sufficient to account for the total excess protein katabolized. 1 The 

 fact should be recognized that this relationship is more apparent than 

 real, for an increment in heat production is likewise found as the result 

 of the ingestion of carbohydrates which is unaccompanied by material 

 changes in the nitrogen excretion; one must therefore be cautious in 

 associating too intimately the increase in the heat production with the 

 increase in the amount of nitrogen excreted in the urine. 



CAUSES OF INCREASE IN METABOLISM SUBSEQUENT TO INGESTION 



OF FOOD. 



In the light of present knowledge, it would appear as a subject for 

 severe criticism that an investigation on the influence of the ingestion 

 of food upon metabolism which continued for a decade should show 

 such relatively slight positive evidence contributing towards an expla- 

 nation of the various phenomena observed. It was hoped that, as the 

 research developed, definite information as to the cause or causes of the 

 increase in the metabolism would be accumulated. Thus, in the earlier 

 part of our research, impressed by the strength of the argument pre- 

 sented by Zuntz and his associates upon the influence of roughage or 

 crude fiber in the diet, we included experiments with popcorn in our 

 study on the influence of pure carbohydrates, on the supposition that 

 the starch of the popcorn and the crude fiber of the hull would give 

 roughage. As the research continued, however, it was found impossible 

 to plan experiments, save under special conditions, for studying the 

 cause of the increased heat production following the ingestion of food. 

 Consequently our data represent for the most part only faithful records 

 of a large number of experiments in which foodstuffs were given, either 

 singly or combined, and the energy transformations subsequently 

 measured. A careful search in our data for conclusive evidence as to 

 the cause of this rise in the metabolism is, however, unsuccessful. 



At the present time three explanations are offered of the increases 

 noted with the ingestion of food. Zuntz and his associates, influenced 

 largely by their extended experience with domestic animals, particu- 

 larly with ruminants which consume considerable roughage and bulky 

 food materials that remain for a long time in the intestine and require 

 considerable digestive activity expressible in forms of muscular activity, 

 maintained that the increase was due to the work of digestion, or 

 Verdauungsarbeit. Rubner, as a result of his critical series of experi- 

 ments on dogs, particularly the experiments with protein, was not 

 inclined to attribute any share of the increase to the work of digestion, 



'Attention should here be called to a recent study on the basal metabolism of dwarfs and 

 legless men (Aub and E. F. Du Bois, Arch. Intern. Mod., 1917, 19, p. 864), in which the authors say 

 that "following the ingestion of large quantities of meat, the excretion of urinary nitrogen during 

 the earlier hours is not an accurate index of the protein metabolism. The sulphur excretion is 

 more rnpid tVnn tho nitro^on 



