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METABOLISM WITH FOOD RICH IN PROTEINS. 907
In the first case (1) the metabolism of meat before the beginning of
the actual experiment on feeding with 500 grams of meat was 447 grams,
and it increased considerably on the first day of the experiment, after
feeding with 1500 grams of meat. In the second case (2), in which the
animal was previously in nitrogenous equilibrium with 1500 grams of
meat, the metabolism of flesh on the first day of the experiment, with
only 1000 grams meat, decreased considerably, and on the fifth day an
almost nitrogenous equilibrium was obtained. During this time the
animal gave up daily some of its own proteins. Between that point below
which the animal loses from its own weight and the maximum, which
seems to be dependent upon the digestive and assimilative capacity of
the intestinal canal, a carnivore may be kept in nitrogenous equilibrium
with varying quantities of proteins in the food.
The supply of proteins, as well as the protein condition of the body,
affects the extent of the protein metabolism. A body which has become
rich in proteins by a previous abundant meat diet must, to prevent a loss
of proteins, take up more protein with the food than a body poor in pro-
teins.
In regard to the rapidity with which the protein catabolism takes
place Falta x
found in man but not, or at least not to the same extent,
in dogs, that quite great differences exist between the different proteins.
Thus on feeding pure proteins the chief amount of the nitrogen is more
quickly eliminated after feeding casein than after genuine ovalbumin.
This latter is more easily demolished after a previous modification by
coagulation than in the native state, which indicates that an unequal
resistance of the different proteins toward the digestive juices plays a
part. Hamalainen and Helme 2
have also obtained similar results.
Even on feeding with easily decomposable proteins it always takes several
days before the total nitrogen corresponding thereto is eliminated, which
depends, according to Falta, upon a progressive demolition of the pro-
tein. From the unequal rate at which the different proteins are decom-
posed it follows that in the passage from a diet poor in protein to one
rich in protein the time within which nitrogenous equilibrium occurs
depends chiefly upon the kind of protein contained in the food.
Pettenkofer and Voit have made investigations on the ?netabolism
of fat with an exclusively protein diet. These investigations have shown
that by increasing the quantity of proteins in the food the daily metab-
olism of fat decreases, and they have drawn the conclusion from these
experiments, that there may even take place a formation of fat under
these circumstances. The objections presented by Pfluger to these
1
Deutsch. Arch. f. klin. Med., 86.
1
Skand. Arch. f. Physiol., 19.
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