2 BULLETIN 613, U. S. DEPARTMENT OF AGRICULTURE. 
stearin, ox-marrow, and ox-tail fats were obtained already rendered 
from commercial concerns. In order to insure uniform composition 
a sufficient quantity of each of the f ats for the purpose of the study 
was thoroughly mixed before it was incorporated in the blancmange, 
which served as a medium for supplying the fat to the diet. 
METHODS OF PROCEDURE. 
The regimen followed was the same as that in previous experi- 
ments, foods containing a minimum amount of fat being chosen as a 
basal diet, i. e., wheat biscuits, oranges, and sugar. The fat to be 
studied was incorporated in a cornstarch pudding, a caramel solution 
being added to conceal any pronounced flavor. A sufficient amount of 
this pudding was prepared for the entire experiment. It was de- 
sired that such quantities as were necessary to provide about 100 
grams of fat should be eaten by each subject daily, this amount be- 
ing approximately one-third the total energy of the diet which is the 
average proportion furnished by fat. Coffee and tea, without cream, 
were permitted according to individual preference. The experimen- 
tal diet was eaten for three days or nine meals in each case. This 
period has been found satisfactory in the previous tests as it is 
sufficient to give satisfactory results and not so long as to introduce 
any undesirable physiological effect due to monotony. A 4-days 
period of normal diet was always followed before beginning a 
new test. 
For separation of the feces from this diet, charcoal was adminis- 
tered in gelatin capsules with the first meal on the fat-containing 
diet, and with the first meal on resuming the customary diet. The 
feces were collected in weighed-glass containers, weighed, and then 
dried in an electric oven at 95° C., pulverized and analyzed. No urine 
analyses were made and no effort to maintain a nitrogen equilibrium, 
the digestibility of the fats being the special object of investigation. 
The coefficients of digestibility of the protein, fat, and carbohydrate 
supplied by the diet as a whole were determined directly. From 
these data the digestibility of the fat under consideration was esti- 
mated by the method commonly followed and outlined in detail in 
a previous bulletin. 1 In computing the figure for digestibility of the 
fat alone, in each experiment correction was made for metabolic 
products and the small amount of undigested basal ration fat which 
occurs in the ether extract of the feces. 
In general it has been the practice during the study of the digesti- 
bility of the edible fats to conduct not less than five tests of three 
days' duration each. Since the available supply of fat in the case of 
a number of fats here studied was small, as few as three experi- 
ments were made in some instances. 
X U. S. Dept. Agr. Bui. 310 (1915), pp. 22. 
