4 BULLETIN 525, U. S. DEPAETMENT OF AGRICULTURE. 



judged, had no digestive abnormalities. During the experimental 

 period they were requested to observe their usual routine as regards 

 amount of exercise taken, hours of eating, etc. Because of their in- 

 terest in the study of physiology and their previous experience in this 

 type of work they were sufficiently informed of the nature of theii 

 duties to appreciate the importance of carefully following the direc- 

 tions given them. 



For the purpose of identifying the feces of the experimental 

 period, three or four gelatin capsules containing about 0.3 gram each 

 of pulverized charcoal were taken with the first meal of the ex- 

 perimental period and with the first meal following the test period. 

 The separation of the feces due to the diet under investigation was 

 easily made at the line of demarcation between the portion colored 

 by the charcoal and the lighter portion due to the ordinary food. 



The subjects were allowed to follow their customary dietary 

 routine before and after the experimental periods. Since this 

 study of millet is concerned with the coefficients of digestibility 

 only, no attempt was made to maintain a nitrogen equilibrium or 

 to maintain uniform body weight of the subjects. The urine result- 

 ing from the experimental periods was not collected, for it was con- 

 sidered that any constituents of the food which had been sufficiently 

 broken down to appear in the urine had undergone the process of 

 digestion. 



In this study a determination has been made of the digestibility 

 of protein, fat, carbohydrates, and ash of the entire ration, and the 

 digestibility of the protein and carbohydrates of the bread alone has 

 been estimated by a method commonly employed in investigations 

 of this character, which consists of making proper allowance for 

 the amount of undigested residue occurring from the various con- 

 stituents of the diet other than bread. The following equations will 

 serve to indicate the method by which this allowance has been made : 



[Weight of protein in potato, butter, and fruit] X [Per cent of 

 undigested protein occurring in each] = [Weight of undigested pro- 

 tein present in feces derived from basal ration]. 



[Total undigested protein in feces] — [Undigested protein in feces 

 from basal ration] = [Undigested protein occurring from bread] . 



[ (Total protein of bread) — (Undigested protein from bread)] -f- 

 [Total protein of bread] = [Estimated percentage digestibility of 

 protein in bread alone]. 



The factors used in the above equations for estimating the co- 

 efficients of digestibility of the protein and carbohydrates of bread 

 alone have been determined in previous investigations as being for 

 the protein of potatoes, 83 per cent ; ^ of butter, 97 per cent ; ^ and 

 of fruit, 85 per cent;^ while the digestibility of carbohydrates in 



1 Connecticut Storrs Sta. Rpt. 1899, p. 104. 



