DIGESTIBILITY OF SOY-BEAN AND PEANUT FLOURS. 15 



In order that the major portion of the protein supplied by the 

 experimental diet should be derived from the soy-bean and peanut 

 flours, the accessory foods w ere chosen to supply only a minimum of 

 protein, and included oranges, butter, and tea or coffee with sugar if 

 desired. Since the subjects ate very generous amounts of the bis- 

 cuits but had a very limited diet in other respects it was thought that 

 they would use large quantities of butter. It was found, however, 

 that though they could have all they wanted they ate on an average 

 only about 56 grams daily. 



DETAILS OF THE EXPERIMENTS. 



In this study of the digestibility of the proteins supplied by soy- 

 bean and peanut flours the methods which were employed were very 

 similar to those foUowed in the study of the grain sorghums.^ The 

 usual 3-day or 9-meal experimental period was considered satis- 

 factory for this study. No attempt was made to maintain a uniform 

 body weight of the subjects or to maintain nitrogen equihbrium 

 during the period. As is usual in such cases, sufficient food material 

 was prepared at one time to supply aU the subjects for the entire 

 experimental period, representative samples of all the foods being 

 retained for analysis. These samples and those of the air-dried 

 feces of each subject resulting from the experimental diet were ana- 

 lyzed in the usual way. The differences between the amounts of pro- 

 tein, fat, and carbohydrates present in the foods and in the feces were 

 taken to represent the amounts of these constituents digested. This 

 method of procedure gives data regarding the digestibility of protein, 

 fat, and carbohydrate supplied by the entire diet. Since in thia 

 study the coefficients of digestibility of the soy-bean and peanut pr0'» 

 teins are of special interest they have been estimated by making 

 allowance for the undigested protein material occurring in the diet, 

 The method followed in estimating the digestibility of the proteins 

 supplied by the soy beans and peanuts is indicated by the following 

 equations : 



[Weight of protein in accessory food materials] X [Percentage of 

 undigested protein in each] = [Protein in feces from food other than 

 bread]. 



[Total protein in feces] — [Protein in feces from food other than 

 bread] = [Weight of undigested bread protein.] 



[Weight of protein in bread] — [Weight of undigested bread pro- 

 tein] -T- [Weight of protein in bread] = [Estimated percentage of avail- 

 ability of bread protein.] 



In determining the amount of undigested protein present in the 

 accessory food materials in the experimental diet it was assumed that 



1 IT. S. Dept. Agr. Bui. 470 (1916), pp. 30. 



