2 BULLETIN 751, U. S. DEPARTMENT OF AGRICULTURE. 
and the effect of a modification in milling upon the nutritive value 
of the resulting flours assumed unusual importance to those con- 
cerned with the feeding of large numbers of people. 
In the modern milling processes the germ, together with, a large 
portion of the outer layers of the wheat kernel, is removed. The 
removal of the germ, which contains practically all of the wheat fat 
or oil, lowers the energy value somewhat but improves the keeping 
quality of the flour. Chemical analysis shows that the outer layers 
of the wheat kernel, also removed in the preparation of patent flour, 
contain protein, carbohydrate, and mineral matter, constituents which 
are necessary for the proper nutrition of the body. Very recently 
it has been demonstrated by McCollum and coworkers 1 that the 
wheat germ contains Fat-soluble A, and this and the outer layers of 
the wheat kernel some Water-soluble B, 2 both of which are essential 
in the dietary to prevent nutritional diseases. These substances are 
present, it is true, in limited amounts, insufficient for the needs of the 
body during its entire lifetime and yet in amounts not wholly negli- 
gible. With these facts in mind the question very naturally arises 
whether it is not desirable to include the entire kernel in wheat flour 
rather than to utilize only the interior portions of the kernel. In 
order to arrive at an intelligent solution of this question it appears 
necessary to consider the large number of factors influenced by a 
modification* of milling conditions. Of special interest to the student 
of nutrition is the effect on the digestibility of wheat flour of includ- 
ing a part or the whole of the wheat germ and the outer layers of the 
wheat kernel in the flour. 
Since wheat flours contain very little fat, interest has been cen- 
tered on the digestibility of the protein and carbohydrate supplied 
by the different types of wheat flours ; and in general the digestibility 
of wheat protein has received the most attention. 
The earlier work of the Department of Agriculture included a large 
number of studies of the digestibility of wheat flours, prepared from 
both spring and winter wheats, and from wheat grown in different 
localities. In the tests referred to below, the wheat was milled so as 
to produce from the same lot of wheat, white (patent) flour represent- 
ing 72 per cent of the wheat kernel, entire or whole-wheat flour 
representing 85 per cent of the wheat kernel, and graham flour repre- 
senting 100 per cent of the wheat kernel. 
TToods and Merrill 3 conducted 13 digestion experiments with 
white-flour bread in which the protein was 86.1 per cent and the 
carbohydrate 98.3 per cent digested, five experiments with entire- 
ijour. Biol. Chem., 25 (1916), Xo. 1, pp. 105-131. figs. 19: 28 (1916), No. 2, pp. 
211-229, figs. 17. 
2 Jour. Biol. Chem., 24 (1916), Xo. 4. p. 493. 
3 U. S. Dept. Agr., Ofiice Expt. Stas. Bui. So (1900), pp. 32, 33. 
