DIGESTIBILITY AND AVAILABILITY OF FOOD. 24 1 



It has been commonly supposed that if the quantity of any 

 ingredient of the diet is very large the body will avail itself of 

 a smaller proportion than if the total quantity consumed is 

 smaller. In a number of the metabolism experiments (those 

 designated by "fat diet" and "carbohydrate diet" in Table 

 134) the purpose was to study the value of different nutrients 

 as sources of energy to the body, and especially to compare fat 

 and sugar in this respect. To do this, the diet was arranged 

 so that the amount of one of these would be relatively large 

 and that of the other relatively small. In the earlier experi- 

 ments this was accomplished by taking out of the diet in some 

 cases a certain quantity of fat, and substituting for it enough 

 of sugar to supply the energy removed, or, in other cases, re- 

 moving sugar or other carbohydrates from the diet and substi- 

 tuting fat. In later experiments, more particularly those with 

 J. C. W., a definite basal ration, with a moderate quantity of 

 both fat and carbohydrates, was used, and to this was added a 

 decidedly large quantity of sugar in some cases and a corre- 

 sponding amount of fat in others. In other words, in order 

 to make the comparative tests of fat and sugar effective, the 

 quantities of either were in the earlier experiments somewhat 

 larger, and in the later experiments very much larger than in 

 the ordinary diet. In all cases where sugar and fat were thus 

 compared the attempt was made to have the two diets as nearly 

 equivalent in available energy as practicable. 



In the experiments with J. F. S. on a fat diet, the lowest co- 

 efficient of availability of fat was 94.1, and the highest 98.3; 

 in the average of seven experiments it was 96.7. In similar 

 experiments with J. C. W., the lowest coefficient was 95.3, 

 and the highest 98.0, the average of ten experiments being 

 also 96.7. 



In the experiments with J. F. S. on a carbohydrate diet, the 

 lowest coefficient of availability of carbohydrates was 98.4, and 

 the highest 98.7; in the average of four experiments it was 

 98.6. In similar experiments with J. C. W., the lowest co- 

 efficient was 93.7, but this was the only case in which it was 

 below 98.0; the highest was 98.8, and the average of nine ex- 

 periments it was 98.0. The averages of all the experiments 

 with " fat diet " and all those with " carbohydrate diet " with 

 both subjects are summarized below, in comparison with the 



