582 Journal of Agricultural Research vol. vi.no. 16 



but it is hardly possible that they were definitely aware of the source 

 of the meat. If this was the case, it is reasonable to believe that the 

 appetite of the subjects and the digestibility of the food were not af- 

 fected by any psychic factor. 



The three-day or nine-meal experimental period, which is very often 

 used in investigations of this kind, was again adjudged to be most sat- 

 isfactory. In order that the subjects should experience no monotony 

 while eating the ration, each test period of three days per week was 

 followed by a rest period of four days; and, furthermore, the digestion 

 experiments were conducted only on alternate weeks. During- the in- 

 tervening weeks tests were made 'of the digestibility of other food 

 materials. 



SUBJECTS 



Five subjects assisted in making this investigation. They were 

 active young men of good physique and, as dental students, all were 

 sufficiently interested in physiological questions to appreciate the im- 

 portance of carrying out carefully such directions as were given them. 

 They were urged to observe accuracy especially in the collection of 

 feces, since in considering the digestibility of any food material it is 

 more essential to know the amount of food retained and assimilated 

 by the body than only the total amount of food consumed. To assist 

 in identifying the feces of the test period, charcoal, which imparts a 

 dark color to the feces, was given with the first meal of the test period 

 and with the first meal following the period. The feces showing a 

 dark color and all excreted until the dark color imparted by the char- 

 coal was again noticed were retained for analytical purposes. The sub- 

 jects were asked to bring notes describing their physical condition 

 before, during, and after each test period. They all reported that with 

 the exception of one or two colds they were in normal physical con- 

 dition during the entire time that the investigation was in progress. 

 Consequently, it has not been considered necessary to give in detail any 

 of the individual reports which were received. 



EXPERIMENTS WITH VERY YOUNG VEAE 



Inasmuch as lean meat like very young veal consists almost wholly of 

 water and protein, these experiments are concerned only with the 

 digestibility of protein. One method of determining the digestibility of 

 a single food of a mixed diet is to determine by digestion experiments 

 with the basal ration alone the amount of undigested residue occurring 

 from the accessory foods, and for which a corresponding correction may 

 be applied to the digestibility of the total ration. A second method con- 

 sists in estimating the digestibility of the basal ration. Since the digesti- 

 bility of the protein of wheat flour, fruit, and butter have been accurately 

 determined by previous investigators, satisfactory factors are available 



