16 BULLETIN 507, U. S. DEPARTMENT OF AGRICULTURE. 
Summary of digestion experiments with egg yolk in a simple mixed diet. 
Experi- 
ment No. 
Subject. 
Protein. 
Fat. 
Carbohy- 
drates. 
Ash. 
214 
215 
216 
D. G. G 
K.L.S 
O.E.S 
Per cent. 
83.1 
81.3 
84.1 
85.6 
75.1 
80.1 
Per cent. 
92.0 
91.4 
91.7 
91.0 
90.9 
92.1 
Per cent. 
96.0 
96.1 
96.9 
97.5 
94.5 
95.9 
Per cent. 
64.5 
57.7 
65.4 
217 
302 
303 
R.F.T 
H.F.B 
O.E.S 
Average 
62.2 
42.3 
53.7 
81.6 
91.5 
96.2 
57.6 
It may be noted from the recorded data of these experiments that 
the average amounts of protein, fat, and carbohydrate eaten daily 
were 56, 85, and 326 grams, of which 81.6, 91.5, and 96.2 per cent 
were digested, respectively. The reported digestibility of 91.5 per 
cent for the total fat of the diet is increased to 93.8 per cent for the egg- 
yolk fat by making allowance for metabolic products and any undi- 
gested portion of the small amount of fat the basal ration supplied. 
Inasmuch as the egg-yolk fat comprised 98 per cent of all the fat 
supplied by the diet, this derived value should very closely approxi- 
mate the true digestibility of egg-yolk fat. 
In the course of the analytical work it was observed that the ether 
extracts of both the blancmange and the feces of the experimental 
periods were of a very dark-orange color, somewhat more intense in 
the case of the feces. This discoloration can probably be attributed 
to coloring matter extracted from the egg yolk. 
FISH FAT. 
Though fish fat or oil (for it is liquid at ordinary room temperature) 
is not a culinary or table fat in our temperate regions, nevertheless, 
as it occurs in fish flesh, it forms a not inconsiderable part of the total 
fat of the diet. This is particularly the case in localities where such 
fish as mackerel, butterfish, salmon, shad, etc., are eaten in quantity. 
Except in the case of cod-liver oil, which is a special product used in 
invalid dietetics chiefly because of the medicinal properties attributed 
to it, experimental studies of food uses of fish fat or oil are apparently 
few in number. 
Atwater, 1 in a study of haddock compared with beef, reports that 
the fish fat was 91 per cent digested. Some years later Milner, 2 in 
experiments with four young men, found that the digestibility of the 
fat of a lean fish (cod) was practically the same as that of a fat fish 
(canned salmon), the values being 97.4 per cent and 97 per cent, 
respectively. 
Since fish oil suitable for food purposes was not found on the market 
and it was not practicable to prepare it in the laboratory, fish con- 
taining a fairly high percentage of fat was used instead in the experi- 
i Ztschr. Biol., 24 (1S8S), pp. 16-28. 
2 Connecticut Storrs Sta. Rpt. 1905, pp. 116-142. 
