ENERGY RELATIONSHIPS. 331 



power plant, and has considerable interest as an index of the possible 

 maximum influence of food. With carbohydrates the basal metabo- 

 lism may be increased to an average maximum of approximately 25 per 

 cent by the ingestion of 100 grams of any one of several sugars. This 

 increment occurs inside of two hours and the metabolism has a tend- 

 ency to return to the base-line somewhat rapidly thereafter. For a 

 detailed discussion of the differences in effect of various forms of sugars, 

 the section on carbohydrates should be consulted. (See page 171.) 

 Of special significance is the fact that the increment with levulose over 

 that with either sucrose or dextrose, which was earlier reported from 

 this laboratory, 1 is not noted when the results of all the experiments 

 are combined, and we find that there is a greater similarity between 

 levulose and dextrose than was at first believed. It will be seen, from 

 table 173, that the levulose has a more pronounced effect upon carbon- 

 dioxide production than the dextrose has, although not so great as that 

 of sucrose. When the comparison is made on the basis of the heat pro- 

 duction, it is found that the difference between dextrose and levulose 

 in large part disappears, although sucrose still shows a higher value. 



Most of the pure sugars were studied with both 75-gram and 100- 

 gram portions. While no uniform variation was noted in the effect 

 upon the metabolism, it was usually found that the increment with the 

 larger amount was greater than with the smaller amount, although the 

 differences were by no means proportional. 



With protein the large increments in metabolism found by all work- 

 ers were also noted in this research. The heat production increased 

 usually to a maximum above the basal level of approximately 25 per 

 cent, with a possible maximum of 45 per cent. (See tables 215 and 

 230.) The increment persisted for a long time, often from 8 to 12 hours. 

 Indeed, our experiments were defective in that the experimental periods 

 were in general not sufficiently extended to obtain the entire effect due 

 to the protein ingestion. This prolonged increment is in striking con- 

 trast to the increments obtained with carbohydrates, which, while fairly 

 high (25 per cent) , nevertheless fell rapidly to a basal value after a rel- 

 atively few hours. 



The experiments with fat are of special interest, though unfortunately 

 the most liable to criticism on the grounds of experimental error and 

 faulty technique. The inherent difficulties in feeding American sub- 

 jects large quantities of pure oil or pure fat made it impossible for us to 

 carry out any experiments with pure oil, as did Gigon, and we were 

 obliged to confine ourselves to experiments with cream and with butter 

 and potato chips. In practically all of the combinations used, a cer- 

 tain amount of other nutrients was inevitably included, which some- 

 what complicated the deductions drawn from the experiments. The 



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



