DIGESTION EXPERIMENTS. 295 



digestion experiment, or an experimental verification of the earlier con- 

 tention that under these conditions the digestibiUty of nitrogen, to use 

 the older term, is the same with practically all healthy men. 



The comparison of the digestibiUty in the later series after the men 

 had been for some time upon the low diet is somewhat difficult, owing 

 to the decidedly wide variations in the food ingestion. In fact, the 

 nitrogen in food per day varied so widely with the different men after 

 the middle of October that no considerable number of days can be 

 selected to study the uniformity of the relationship between food 

 nitrogen and fecal nitrogen. This will be implied from the per- 

 centage values for the utilization of nitrogen. But none of the figures 

 show an abnormal nitrogen utilization. The low values, which fall 

 to 82 and 85 per cent, are comparable with other observations, 

 especially when it is remembered that the amount of animal protein 

 was somewhat decreased in these observations. 



The largest excretions of total nitrogen in the feces are those for 

 Gar and Mon on December 10 to 15. These values correspond to their 

 highest nitrogen intake other than in the first digestion period, that is, 

 13.20 grams with Gar, and 13.92 grams with Mon. That the presence 

 of bran in the diet does not affect the nitrogen in feces is strikingly 

 shown by the fact that Gar had no bran during the period of December 

 10 to 15 while Mon consumed 168 grams. Thus, one must be somewhat 

 conservative in putting emphasis upon the presence of bran in the 

 diet in considering the utilization of nitrogen. The conclusion can, 

 however, be fairly drawn that the reduction in diet did not materially 

 alter the digestibility of nitrogen. 



The lowest utilization of nitrogen occurred with 7 of the 12 men in 

 the digestion experiment of December 10 to 15, but an examination 

 of the intake of nitrogen shows that this usually represented a period 

 of high rather than low nitrogen intake, so that the low utilization of 

 nitrogen is not coincidental with low nitrogen in the intake, as perhaps 

 might be expected. In 5 cases, Vea, October 31 to November 4, Spe, 

 November 12 to 18, Tom, December 10 to 15, Gul and Pec, January 

 14 to 30, we find the lowest utilization of nitrogen coincidental with 

 the lowest nitrogen in food. 



The available energy was, in all instances, highest during the first 

 digestion period, that is, when the men were on normal diet. During 

 the first digestion period the available energy averaged for the squad 

 measurably above 92 per cent. Thereafter there was a distinct tend- 

 ency for it to fall, values as low as 85 or 86 per cent being occasionally 

 found. The absolute minimum was 84 with Moy and Kon on No- 

 vember 12 to 18. Seven of the men show the lowest available energy 

 in the experiment of November 12 to 18. With all of the men the 

 tendency is for the lowest available energy to occur with the minimum 

 calories in the diet, this being in rather striking contrast to the 

 evidence for the utilization of nitrogen. 



