14 BULLETIN 649, TJ. S. DEPARTMENT OF AGRICULTURE. 
SUMMARY. 
In the study of the digestibility of the protein and fat supplied 
by some common varieties, fish in the form of "fish loaf" was served 
as the major part of a simple mixed diet, which also included pota- 
toes, crackers, fruit, sugar, and tea or coffee. The principal results 
are summarized in the following table: 
Summary of results of all digestion experiments. 
Number of 
experiments. 
Kind of fish. 
Average 
amount of 
i fish eaten 
per man 
per day. 
Digestibility 
offish 
protein. 
Digestibility 
of fish fat. 
Grams. 
3 Mackerel 448 
3 ; Butterfish 471 
8 j Gravnsh 440 
4 Salmon 355 
Per cent. 
93.1 
91.9 
92.8 
93.2 
Per cent. 
95.2 
86.4 
94.3 
93.7 
On an average, the subjects ate 448 grams of Boston mackerel, 
471 grams of butterfish, 440 grams of grayfish, and 355 grams of 
salmon daily, which would indicate that in every case the fish was 
eaten with relish. 
Considering the experiments as a whole, the total diet supplied on 
an average 99 grams of protein, 60 grams of fat, and 160 grams of 
carbohydrates daily, the fuel value being 1,576 calories. The low 
amount of fat and of carbohydrates was due to the fact that butter 
and similar fat were omitted and the foods other than fish loaf which 
supplied both protein and carbohydrates, were limited in order that 
both the fat and the protein in the diet might be contributed in as 
large proportion as possible by the fish. 
The average coefficients of digestibility ' for fish proteins were: 
Boston mackerel, 93.1 per cent; butterfish, 91.9 per cent; grayfish, 
92.8 per cent; and salmon, 93.2 per cent. In view of the close 
agreement, it would seem, from a dietetic standpoint, that the differ- 
ent fishes studied would supply protein in equally available form. 
The average coefficients of digestibility of the fish fats were found to 
be as follows: Boston mackerel, 95.2 per cent; butterfish, 86.4 per 
cent; grayfish, 94.3 per cent; and salmon, 93.7 per cent. As these 
figures show, the fats were well assimilated in the case of the mack- 
erel, grayfish, and salmon, which, according to the usual custom, are 
to be regarded as u fat fishes." Considering the experiments as a 
whole, the very complete utilization of the protein and fat supplied 
by the fishes studied offer additional experimental evidence that 
fish is a very valuable food and that its extensive use in the dietary 
is especially desirable. 
