2 BULLETIN 1033, U. S. DEPARTMENT OF AGRICULTURE. 
disease were common and physiologists generally believe that this 
was due, to some extent at least, to a lack of vitamin A. It should 
also be remembered that fats and oils represent the most concen- 
trated source of body fuel, a fact that has an important bearing on 
the food transportation problem and on the cost of food to the con- 
sumer. An adequate national food policy therefore requires that an 
abundant fat supply be maintained during peace times as well as 
during war, and there is justification for the efforts made to find 
new sources of food fats and to make better use of those we now 
have. 
For such reasons the Department of Agriculture has outlined a 
broad program for the study of edible fats, which includes investiga- 
tion of the source of supply, methods of production and rectification, 
the relation of feed to fat production in farm animals, including 
the cost at which fat is produced at different ages, and the relation 
of this to the production of meat and dairy products. It also in- 
cludes studies of the economical use of fat in cookery and its rela- 
tion to the quality of the cooked product and of the thoroughness 
of digestion of fats and oils and the tolerance of the body to dif- 
ferent kinds. These latter aspects of the problem have been for some 
years under investigation in the Office of Home Economics of the 
States Relations Service, cooperation with other bureaus being se- 
cured whenever this has seemed desirable. 
The digestibility of 60 or more different fats and oils, some of 
animal and some of vegetable origin, has been tested in the Office of 
Home Economics. In a few cases, fish oil and avocado fat for in- 
stance, the fat was not extracted but was eaten as it occurs in these 
foods as ordinarily served. In most cases, however, the fat was 
rendered or otherwise freed from the tissue in which it occurs, and 
if necessary, further purified. These studies have been reported 
from time to time in publications of this department and in pro- 
fessional journals. 3 This bulletin reports two groups of studies, one 
with a variety of fats and oils regarding which information was 
needed for special reasons, and one with blended hydrogenated fats 
such as are now in common use. 
EXPERIMENTAL METHOD. 
The method followed in these experiments was the same as that 
developed in the previous digestion experiments of this office. Xo 
method has yet been devised by which the proportion of nutrients 
actually digested from any one food material in a mixed diet can be 
directly measured, and all the methods now in use admit of at least 
3 U. S. Dept. Agr. Buls. 310 (1915). 505 (1917),, 507 (1917). 630 (1918), 6S7 (1918), 
613 (1919), 781 (1919); Jour. Biol. Chem., 41 (920), No. 2, pp. 227-235; Au.er. Jour. 
Physiol., 54 (1921), No. 3, pp 479-488 
