DIGESTIBILITY OF SOME ANIMAL FATS. 3 
were simple, the fat-containing food, which was the principal item, 
being supplemented in each case by carbohydrate foods (such as 
biscuits or crackers, and mashed potato), fruit (oranges or apples), 
and tea or coffee with sugar, if a beverage besides water was desired. 
The subjects were not required to eat like quantities of the food 
supplying the fat, or of the other foods, but in every case they were 
expected to eat an amount of fat which would supply about 30 
per cent of the total energy value of the ration, this being the quan- 
tity which fat contributes to the average American and European 
diet, as shown by a compilation of data made for this study. With 
the experimental diets chosen this would mean about 100 grams of 
fat. Special pains were always taken to use fat which was not 
rancid, since Adler, 1 on the basis of experimental data, has attributed 
a hemolytic action to the presence of free fatty acids in foods. 
In making up the diets for the experiments a stiff cornstarch pud- 
ding or blancmange (heavily flavored with caramel to mask any 
distinctive fat flavor) was used as a vehicle for the separated fats. 
The same sort of blancmange was also used in the experiments with 
cream and egg yolk. For the study of fish oil a typical fat fish was 
used as the source of the fat. 
In these, as in the earlier digestion experiments reported, the three- 
day or nine-meal test period proved entirely satisfactory. The test 
periods were followed by rest periods of four days, in which the sub- 
jects were permitted to eat whatever they desired. Obviously, the 
diet during the experimental periods was limited to the prescribed 
ration. In every case weighed portions of the different foods were 
prepared in advance for each meal for each subject and the subjects 
were instructed to reserve any uneaten portions of the diet for weigh- 
ing, in order that the exact amount eaten might be ascertained. 
They were also instructed to observe due care in the collection and 
separation of the feces pertaining to an experimental period. 
The records of the experiments include data for the amounts of 
food eaten and for the feces. Samples of both food and feces were 
analyzed to determine what percentages of protein and carbohydrate 
as well as fat were available to the body. 
The percentage of fat in the feces was determined by ether extrac- 
tion of the air-dried sample for 18 to 20 hours by the Soxhlet method, 
as described by the Association of Official Agricultural Chemists. 2 
It is recognized that by this method some fat in the form of soaps 
may not be extracted. However, comparative tests by the Folin- 
Wentworth 3 method and the Soxhlet method, made as a part of the 
digestion work of this office, have given results that are not uniform 
and are not significant from the standpoint of dietetics. 
The ether extract obtained by the method followed is assumed to 
represent the fat of undigested food, and this quantity less the pro- 
i Jour. Med. Research, 28 (1913), No. 1, pp. 199-226. 2 U. S. Dept. Agr., Bur. Chem. Bui. 107 (1912). 
s Jour. Biol. Chem., 7 (1910), No. 6, pp. 424, 425. 
