4 BULLETIN 64:9, U. S. DEPARTMENT OF AGRICULTURE. 



were allowed to follow their customary dietary routine preceding and 

 following the experimental period. For the purpose of identifying 

 the feces of the experimental period, three or four gelatin capsules 

 containing about 0.3 gram of pulverized charcoal were taken with 

 the first meal of the experimental period and with the first meal fol- 

 lowing it; the separation of the feces due to the diet under investiga- 

 tion was easily made at the lines of demarcation made by the por- 

 tions dully colored by the charcoal. 



Inasmuch as this study is concerned principally with the coefficient 

 of digestibility of the protein and fat of the fish, no attempt was made 

 to maintain a nitrogen equilibrium or uniform body weight of the sub- 

 jects. The urine resulting from the experimental periods was not 

 collected, for it was considered that any constituents of the foods 

 which had been sufficiently broken down to appear in the urine 

 had undergone the process of digestion: furthermore, the results ob- 

 tained by collecting and analyzing the urine of a short test period 

 are not entirely conclusive since the urine can not be separated as 

 satisfactorily as the feces. 



PREPARATION OF FISH. 



In this study of the digestibility of different types of fish, fresh 

 butterfish and Boston mackerel were used, and canned grayfish and 

 canned salmon. A fish loaf seemed to be the best form in which to 

 prepare the fish for eating, since sufficient quantities for the entire 

 experimental period could be prepared at one time. Furthermore, 

 it was easy to prepare a fish loaf having a uniform composition and 

 one which would not change materially on standing by the settling 

 out of fat or evaporation of water. 



The butterfish and mackerel received a preliminary cooking before 

 being incorporated in the fish loaf. The fish, after being cleaned, were 

 thoroughly washed and placed as close as possible to each other in a 

 covered cooker, water was added, and they were cooked for one-half 

 hour. They were not boiled, but steamed in a very small quantity 

 of water which prevented browning or sticking to the pan. To 

 prevent any loss due to extracted fat and protein, the water in 

 which the fish were steamed was retained and mixed with the fish 

 meat, Beythien x having reported that the water in which fish 

 were boiled contained 8.8 to 11.3 per cent of the total fish protein. 

 After this preliminary cooking of the butterfish and mackerel, the 

 bones, any pieces of fins, etc., were removed and the fish meat was 

 cut in an ordinary household meat cutter. The bones and bits of 

 skin were removed from the canned grayfish and salmon, and the 

 solid meat was minced in a meat cutter. From this point the prepa- 



i Pharm. Centralhalle, 47 (1906), p. 140. 



