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CALCULATION OF THE CALORIC VALUE. 889
The figures for the oxygen vary less than those for the carbon dioxide,
and this is a reason why the oxygen values are better suited than the
CO2 values for calculating the energy production from the extent of gas
exchange. Other investigators have obtained results which correspond
more or less with the above values for the heat value of oxygen, and E.
Voit and Kummaciiek, 1
who have made calculations in another way,
have obtained still smaller differences for the relative oxygen value.
From what was said above we can calculate the extent of protein
metabolism, the corresponding development of energy and the correspond-
ing absorption of oxygen and carbon dioxide formation, from the quantity
of nitrogen in the urine. If we subtract the oxygen and carbon dioxide
values from the total, directly determined gas exchange, the result repre-
sents the fats and carbohydrates used. According to Zuntz from this
residue we can calculate the heat value of the oxygen used as well as the
division of the decomposition of the fat and carbohydrate by consider-
ing the respiratory quotient. For this purpose Zuntz and Schumburg
have constructed a table, an abstract of which we give below, taken
from the work of Magnus-Levy.2
Division in per cent.
Carbohydrate. Fat.
100
83 17
66 34
49 51
32 68
15 85
100
As the calorific oxygen values in the combustion of protein, fat
and carbohydrate show no great differences among themselves, in those
cases where, as in starvation, the part taken by the proteins in the total
metabolism is relatively small, one can calculate the total energy exchange,
without any striking error, from the respiratory quotient and the oxygen
used. This is especially important in experiments of short duration
where the protein metabolism cannot be directly determined, but is
calculated from the nitrogen elimination occurring during a longer time.
The method of Zuntz and Geppert, mentioned on page 869, has shown
itself especially useful in the study of the material and force exchange
in these experiments of short duration, while the respiration apparatus
constructed on Pettenkofer’s or the Regnault-Reiset principle are
only useful in experiments over a longer period.
Kaufmann ’ incloses the individual to be experimented upon in a capacious
sheet-iron room, which serves both as a respiration-chamber and a calorimeter,
1
Voit, Zeitschr. f. Biol., 44; Kummacher, ibid.
A. Magnus-Levy in v. Noorden’s Handb. d. Pathol, des Stoffwechsels, Bd. 1. (1906).
1
Arch. d. Physiologie (5), 8.
R. Q.
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