6 BULLETIN 751, U. S. DEPARTMENT OF AGRICULTURE. 
(88.2 per cent, 84.4 per cent, and 90 per cent) and for carbohydrates 
93.4 per cent (93 per cent, 92.8 per cent, and 94.3 per cent) and the 
digestibility of bread from the same flour without the bran was for 
protein 90.9 per cent (90.2 per cent, 91.9 per cent, and 90.6 per cent), 
and for carbohydrates 97.7 per cent (96.7 per cent, 98.2 per cent, 
and 98.1 per cent). As noted by Snyder, “Subject No. 3 digested 
practically the same proportion of the protein from the flour with 
the bran as from that without it,” and considering these data alone 
one could conclude that the digestibility of bran protein was 90 per 
cent. If, on the other hand, the figures reported for subject No. 2 
for the digestibility of protein of flour with bran, 84.4 per cent, and 
without bran, 91.9 per cent, are considered alone, the calculated 
digestibility of bran protein would be approximately 39 per cent. 
In general, however, the average values obtained in these tests for 
the digestibility of the mixture of white and bran flours, 85.9 per cent 
for the protein and 93.4 per cent for the carbohydrate, as compared 
with the digestibility of white flour alone, 90.9 per cent for protein 
and 97.7 per cent for carbohydrate, are in agreement with those ob- 
tained in the earlier studies of the digestibility of white and 
graham flours and indicate that the addition of bran, even if finely 
ground, to flour lowers the digestibility of the flour. 
It is very generally believed that the difference in the digestibility 
of the protein and carbohydrate contained in graham flour and white 
flour is due to relative insolubility of bran cellulose in the human in- 
testinal juices. That there is experimental evidence to substantiate 
such a theory is indicated by results of digestion experiments in 
which the crude fiber present in the foods and feces was studied. 
Prausnitz? reports that the crude fiber of wheat bread is 53 per 
cent (52.6 per cent and 53.4 per cent) digested. This value, 53 per 
cent, is somewhat lower than the figures obtained by other investi- 
gators for the digestibility of the crude fiber of fruits and vegetables. 
In 30 digestion experiments conducted by Jaffa* to determine the 
digestibility of common fruits and nuts he found that on an average 
the crude fiber was 78.54 per cent digested. Constantinidi* states 
that the crude fiber of potatoes is 79 per cent digested. As the result 
of two experiments Weiske * concludes that the crude fiber of a diet 
of celery, cabbage, and carrots is 55 per cent (63 per cent and 47 per 
cent) digested. Bryant and Milner® report that the crude fiber of 
green corn is 60 per cent digested, that of potatoes 74 per cent, that 
of cabbage 77 per cent, that of beets 88 per cent, and that of apple 
1Ztschr. Biol., 30 (1894), p. 350. 
2U. S. Dept. Agr., Office Expt. Stas. Bul. 1382 (1901-2), p. 69. 
3 Ztschr. Biol., 23 (1887), p. 452. 
4 Ztschr. Biol., 6 (1870), pp. 456-466. 
6 Amer, Jour. Physiol., 10 (1903), No. 2, p. 97. 
