ENERGY RELATIONSHIPS. 347 



but explained the increase upon the theory that each foodstuff exhibited 

 a specific dynamic action, believing that the elaboration of food 

 materials preparatory to absorption and oxidation, particularly the 

 cleavage and elaboration of the protein molecule, accounted for the 

 excess heat production. More recently the hypothesis of Friedrich 

 Mueller 1 has been revived, 2 in that it has been maintained that the 

 increase in the heat production is due to a stimulus to the cells as the 

 result of products obtained from the food materials ingested or elabo- 

 rated from them. That these products are in all probability of an 

 acid nature is evidenced by experiments from this laboratory; the influ- 

 ence of amino-acids has been definitely proved by Lusk. 3 



Although practically none of our experiments were ideally planned to 

 determine definitely the cause of this increase, certain phases of the 

 work should be considered as an attempt to find if the phenomena agree 

 with any of these explanations. Our experimental plan included, first, 

 the establishment of a base-line, and second, a post-absorptive condi- 

 tion for the subject in each experiment, i. e., that the subject should 

 have been without food for at least 12 hours. It was assumed that 

 comparison with such a base-line would give a true measure of the 

 increase in metabolism due to food. The various factors affecting 

 the basal metabolism have been considered in detail elsewhere 4 and 

 likewise in our chapter on basal metabolism. (See page 47.) It is 

 of interest to point out here, however, that even after the active 

 digestion of food has ceased, Gigon concludes that there is consid- 

 erable internal work which is characterized by Zuntz as Verdau- 

 ungsarbeit. Indeed, Gigon ingeniously ascribes a depression found 

 by him in the metabolism following the ingestion of 50 grams of olive 

 oil as being due to the fact that the presence of the oil caused an 

 abatement of the Verdauungsarbeit which had persisted during the 

 experimental period. Furthermore, X-ray studies have definitely 

 proved 5 that even during relatively prolonged fasting the motility 

 of the stomach and the intestines does not entirely cease ; this was like- 

 wise found by Boldireff. 6 In discussing the influence of the ingestion 

 of food, it is especially necessary to bear in mind this activity of the 

 digestive organs during the absence of food, including the movements 

 of the alimentary tract, the secretion of the various digestive juices, 

 and similar movements, for the ingestion of food may be supposed to 

 increase the activity of all these factors. 



r, Volkraann's Sammlung klin. Vortrage, May, 1900 (N. F. No. 272), p. 17. 



'Benedict, Trans. 15th Int. Cong. Hygiene and Demography, 1913, 2 (2), p. 394. 



'Lusk, Journ. Biol. Chem., 1915, 20, p. 555. 



4 Benedict, Emmes, Roth, and Smith, Journ. Biol. Chem., 1914, 18, p. 139; Benedict and Roth, 

 Journ. Biol. Chem., 1915, 20, p. 231; Benedict and Smith, Journ. Biol. Chem., 1915, 20, p. 243; 

 Benedict and Emmes, Journ. Biol. Chem., 1915, 20, p. 253; Benedict, Journ. Biol. Chem., 1915, 

 20, p. 263. 



'Cannon, The mechanical factors of digestion, 1911. 



6 Boldireff, Arch. d. Sci. Biol., 1905, 11, p. 1. 



