348 FOOD INGESTION AND ENERGY TRANSFORMATIONS. 



Any evidence bearing upon the possibility of intensive peristalsis or 

 digestive action, or any series of experiments in which such stimulating 

 agencies may be present, are of special interest in considering the cause 

 for increased metabolism following food. Thus it is conceivable that 

 the starchy foods would be more slowly acted upon than sugars, and 

 yet an examination of the results of our experiments with such foods 

 shows that they produced nearly as great an increment as the sugars 

 did. (See tables 123, 124, 249, and 250, pages 196, 199, 336, and 338.) 

 This is indeed surprising and might logically be taken as evidence in 

 favor of the Verdauungsarbeit theory. While the dry starch of the 

 popcorn could reasonably be considered as requiring a large amount of 

 digestive work, it is hardly possible that bananas would contain 

 material sufficiently irritating to the intestinal canal to have a great 

 effect upon peristalsis or segmentation. At least two series of experi- 

 ments carried out in this laboratory indicate that intestinal activity, as 

 exemplified by the action of smooth muscle, does not measurably affect 

 the metabolism. In one series the effect of purgatives and agar-agar 

 was studied, 1 and in the second a study was made of the metabolism 

 of dogs with ablated pancreas and consequently deficient digestibility. 2 



In view of the results obtained in these two series of experiments, we 

 find it unconvincing to explain any portion of the increase subsequent 

 to the ingestion of food as being due to Verdauungsarbeit in the sense 

 in which Zuntz uses the term. 



All writers who discuss the cause of the increase in heat production 

 following the ingestion of food are at once confronted by the problem of 

 giving a concrete explanation of the term " specific dynamic action," 

 first used by Rubner. Perhaps no worker has considered this subject 

 more in detail than Lusk, who has written one of the best expositions 

 of Rubner's views that has ever been published. 3 Lusk proposes to 

 compare the increase in heat production with the increased protein 

 katabolized as a measure of the so-called " specific dynamic action," 

 a process which is radically different from that originally employed 

 by Rubner. 4 



Great difficulty is immediately experienced when we attempt to 

 consider our experimental evidence in accordance with the prevailing 

 views as to the cause of the increased heat production following food. 

 Our experience with diabetics and with normal persons with a normally 

 induced acidosis on a carbohydrate-free diet, as well as our experiments 

 with unoxidizable material in the intestinal tract, lead us to favor more 

 strongly the theory of acid-body stimuli, but it would be clearly a misuse 

 of this present series of experiments to attempt to use them as experi- 



'Benedict and Emmes, Am. Journ. Physiol., 1912, 30, p. 197. 

 'Benedict and Pratt, Journ. Biol. Chem., 1913, 15, p. 1. 

 'Lusk, Science of Nutrition, 3d ed., 1917, p. 232, et seq. 

 4 Williams, Riche, and Lusk, Journ. Biol. Chem., 1912, 12, p. 349. 



