4 BULLETIN 525, U. S. DEPARTMENT 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 ; 1 of butter, 97 per cent ; l and 
of fruit, 85 per cent; 1 while the digestibility of carbohydrates in 
1 Connecticut Storrs Sta. Rpt. 1899, p. 104. 
