20 



the fat of the bread was digestible. The results thus found would 

 probably be below rather than above what was actually the case. 



As in the preceding experiments, the balance of income and outgo 

 of nitrogen was learned b}^ determining the daily amounts ingested 

 in the food and excreted in the urine and feces. In the experi- 

 ments with soft winter wheat in 1901-2 determinations were also made 

 of the phosphoric acid in the samples of food, feces, and urine. Such 

 data, however, are reserved for further study. 



The particular difference between the digestion experiments given 

 here and those formerly reported is in the length of the experimental 

 period, this being four days long here and only two in the earlier 

 experiments. The longer experimental period is believed to be pref- 

 erable, because it is generally considered that there is less danger 

 of error due to uncontrollable factors that may vitiate the results in 

 a short digestion period. 



As is well known, the results obtained from a digestion experiment 

 are not absolute, bvit only relative. But inasnuich as in the diges- 

 tion (Experiments reported in this bulletin the object is to deter- 

 mine the relative rather than the absolute digestibility^ of three 

 different kinds of bread, it is believed that the results obtained are 

 satisfactory for this purpose, because whatever error may be intro- 

 duced in one experiment is introduced alike in all of any given series, 

 since the conditions were kept uniform throughout the series. While 

 the results of a single digestion experiment are open to criticism, the 

 results obtained from a series of experiments are much less so and are 

 of value in determining whether one food is more digestible than 

 another under similar experimental conditions. Hence in discussing 

 the results ol)tained from these digestion experiments they are c>»n- 

 sidered in relation to one another rather than alone. 



DETAILS OF THE DIGESTION EXPERIMENTS WITH BREAD FROM 

 DIFFERENT GRADES OF HARD SPRING WHEAT FLOUR. 



The details of the digestion experiments with hard wheat products 

 are given in the following pages. ISine digestion experiments, each of 

 four days' (or twelve meals') duration were made with three different 

 subjects. In every case the diet consisted of bread and milk, and all of 

 the experiments were conducted in the same manner, except that bread 

 made from a different kind of flour was used in each series. In making 

 the bread no shortening or milk was used, but simply yeast, flour, salt, 

 and water. 



The subjects were universit}?^ students who spent from three to four 

 hours each day at light muscular work out of doors. All had served 

 as subjects in former digestion experiments and were thoroughly 

 familiar with the requirements of such work. 



The experiments were practically made in triplicate — that is, the 

 same kind of an experiment was made with each of three subjects at 



