102 
BULLETIN OF THE BUREAU OF FISHERIES. 
It will be seen that under the conditions of these experiments there was no very 
great difference in the digestibility of the egg and the mussels, while the beef was con- 
siderably more digestible than either. It must, however, be pointed out that beef has 
more nitrogenous extractives than egg and that the greater digestibility of the beef 
may be accounted for in part by the fact that under the conditions of these experiments 
the nitrogenous extractives are calculated as protein. How much nonprotein nitroge- 
nous extractives mussels contain is not known. It must be noted, however, that, judged 
by sight, the greater part of the mussels went into solution. The undissolved portions 
consisted mainly of the tough portions, such as the foot and posterior adductor muscle. 
Finally, it should be pointed out that experiments such as these must be inter- 
preted cautiously. Digestion in vitro is surely not so effective as digestion in the intes- 
tinal canal. It is even probable that in the intestinal canal all these three foodstuffs 
may be equally perfectly utilized. This can be determined by careful metabolism 
experiments. 
METABOLISM EXPERIMENTS. 
The metabolism experiments were made a special subject of research by Dr. Donald 
D. Van Slyke, assisted by Messrs. W. M. Clark and C. B. Bennett. In Doctor Van 
Slyke’s report, which follows, the rate of digestion and proportion of nutriment absorbed 
from cooked mussels and squid is compared with that of beef as a standard: 
The work outlined was undertaken to determine the comparative rapidity and completeness with 
which various sea foods are digested, absorbed, and utilized in the animal organism and the effects of 
different modes of preparation and preservation upon the food value. The substances were compared 
with beef as a standard. The experimental animal was a fox terrier bitch of 1 2 1 /, pounds weight. While 
more valuable results, from a practical standpoint, might be obtained from experiments on men, the 
latter could not tolerate for a long time the simple diet used, nor be subject to regular catheterization. 
The experiments, furthermore, were for comparison of the behavior of different protein foods under the 
same conditions, and it is probable that the foods would rank in the same order when tested in dogs or 
in men, although the absolute completeness and rapidity of utilization varies with different species 
and individuals. 
PRINCIPLES OF METHODS. 
The daily rations were so proportioned, from analyzed foods, that the dog obtained just the amount 
of protein required to maintain nitrogenous equilibrium. Fats and carbohydrates were also kept 
constant. The amount of protein digested was calculated from analysis of the food and feces, the 
nitrogen in the latter being ascribed to undigested protein. The rate at which the protein is digested, 
absorbed, and utilized is measured by the rate at which its nitrogen is excreted in the urine. 
methods in detail. 
The dog was brought to nitrogenous equilibrium by feeding on a constant diet of cracker dust, 
lard, lean beef, and salt. In the experiments with fish flesh, the beef was replaced by an amount of 
steamed fish meat. The fish was cleaned and the flesh steamed immediately after the fish was caught, 
in order to prevent autolytic or bacterical changes. The remainder of the ration was the same as 
in the beef diet, except the amount of lard was reduced in proportion to the fat content of the fish flesh, 
so that the fat content of the ration was kept the same as in the standard beef diet. All foods were 
analyzed for nitrogen and fat. On alternate days animal charcoal was mixed with the ration, in order 
that the feces from food consumed on successive days might be separated by their colors. In case 
the entire daily ration was not consumed, the remainder was fed through a tube. 
