350 FOOD INGESTION AND ENERGY TRANSFORMATIONS. 



the basal value after food has been found in any case. As our work 

 was with man, it was obviously impracticable for us to use pure nutri- 

 ents save in the case of sugars, and our experiments are thus open to 

 this criticism. Hence, if we attempt to establish mathematical rela- 

 tionships for the effects of carbohydrates, fat, and protein, we at once 

 meet the criticism that while the carbohydrates selected were, for the 

 most part, pure nutrients, the fat and protein food materials were 

 mixed nutrients, as, for instance, beefsteak, in which the protein was 

 combined with fat, which also supplied a certain amount of energy. 



Notwithstanding this defect in our experimental plan, the evidence 

 obtained with diets in large part protein agrees with that secured by 

 other observers with a protein diet, as an effect was found which was 

 more pronounced and extended than that of any other nutrient. It 

 appeared to make no difference whether the protein used was an ani- 

 mal or a vegetable protein, for the experiments with glidine on the 

 one hand and with beefsteak and plasmon on the other are usually 

 comparable. 



Unfortunately the evidence obtained regarding fat is not so convinc- 

 ing, for our experiments are admittedly too few in number to give con- 

 clusive results and in the diets used the fat was combined with other 

 substances; still the available energy derived from fat in the food 

 intake was so large in most instances that the increment in the metabo- 

 lism must necessarily have been due to this factor. Although the 

 effect obtained was by no means so great as that found with protein, 

 it can not be considered as negligible. 



The most sharply defined results were those secured in the series of 

 experiments with carbohydrate diets. It was possible to make a care- 

 ful analysis of these data, compare the results obtained with the indi- 

 vidual carbohydrates, and determine not only the total effect upon the 

 metabolism measured, but likewise the time relations and the rapidity 

 of the action of the food material. These results show in a striking 

 manner that all of the carbohydrates influence the total metabolism 

 and differ but little in this respect, although levulose and sucrose appear 

 to exert a somewhat more powerful influence than the other sugars. 



The experiments with mixed diets, especially those with excessive 

 amounts of food, showed that it was possible by the ingestion of a large 

 meal to stimulate the metabolism to 40 per cent above the basal value 

 for a number of hours, and to 20 per cent for at least 8 hours; indeed, 

 there was every reason to believe that the stimulus to the metabolism 

 would have been found to continue considerably longer than the ex- 

 perimental period of 8 hours if the observations had been prolonged. 

 This fact has a special practical significance in its relation to the daily 

 life of human individuals. While it is possible for a human being to 

 live with greatly reduced activity when sound asleep, without food in 

 the stomach, and without extraneous muscular activity, his efficiency 



