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918 METABOLISM.
and a non-nitrogenous part. The potential energy set free immediately
as heat in the combustion of the nitrogenous part, which is quantitatively
used within the region of the chemical heat regulation but is otherwise
lost, has been called the specific dynamic action by Rubner.1
The
remainder of the energy which is represented by the non-nitrogenous
part of the proteins, serves, like all other foodstuffs, in satisfying the
energy requirement of the cells. According to Rubner only non-nitrog-
enous groups (of the proteins, fats and carbohydrates) come almost
entirely, if not completely, in consideration for purposes of energy.
In close relation to the second purpose, the betterment of the condi-
tion of the cells, stands the question as to the conditions favoring the deposi-
tion of flesh in the body, which is closely associated with the question as
to the conditions of fattening the body. In this connection it must be
remembered in the first place that all fattening presupposes an overfeed-
ing, i.e., a supply of foodstuffs which is greater than that catabolized in
the same time.
In carnivora a flesh deposition may take place on the exclusive feeding
with meat. This is not generally large in proportion to the quantity of
protein catabolized. In man and herbivora, who cannot cover their
calorific needs by protein alone, this is not possible, and the question as
to the conditions of fattening with a mixed diet is of importance.
These conditions have also been studied in carnivora, and here, as
Voit has shown, the relation between protein and fat (and carbo-
hydrates) is of great importance. If much fat is given in proportion
to the protein of the food, as with average quantities of meat with con-
siderable addition of fat, then nitrogenous equilibrium is but slowly
attained and the daily deposit of flesh, though not large, is quite constant,
and may become greater in the course of time. If, on the contrary,
much meat besides proportionately little fat is given, then the deposit
of protein with increased catabolism is smaller day by day, and nitrog-
enous equilibrium is attained in a few days. In spite of the somewhat
larger deposit per diem, the total flesh deposit is not considerable in
these cases. The following experiment of Voit may serve as example:
Number of
Days of Ex-
perimentation.
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