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916 METABOLISM.
the diet of a vegetarian when the protein condition was kept almost
but not completely normal for a long time with about 0.6 gram of pro-
tein per kilo. Caspari x
has also made observations upon a vegetarian
for a period of 14 days with an average of 0.1 gram nitrogen (recalculated
as equal to 0.62 gram protein) per kilo, where a nearly complete nitrog-
enous equilibrium was observed as the average result.
According to Voit’s normal figures, which will be spoken of below,
for the nutritive need of man, an average workingman of about 70 kilos
weight, requires on a mixed diet about 40 calories per kilo (true calories
or net calories). In the above experiments with food very poor in pro-
tein the demand for calories was considerably greater; as, for instance,
in certain cases it was 51 (Kumagawa) or even 78.5 calories (Klemperer).
It therefore seems as if the above very low supply of protein was pos-
sible only with great waste of non-nitrogenous food; but in opposition
to this it must be recalled that in Voit and Constantinidi’s experiments
upon the vegetarian, who for years was accustomed to a food poor in
protein and rich in carbohydrate, the calories amounted to only 43.7
per kilo. In the case studied by Caspari a supply of 41 calories per
kilo was entirely sufficient.
Siven has shown by experiments upon himself that the adult human
organism, at least for a short time, can be maintained in nitrogenous
equilibrium with a specially low supply of nitrogen without increasing
the calories in the food above the normal. With a supply of 41-43
calories per kilo he remained in nitrogenous equilibrium for four days
with a supply of nitrogen of 0.08 gram per kilo of body weight. Of the
nitrogen taken, a part was of a non-protein nature and the quantity of
true protein nitrogen was only 0.045 gram, corresponding to about 0.3
gram of protein per kilo of body weight. That this low limit, which
by the way holds only for a short time, has no general validity follows
from other observations. Thus Caspari 2
also, in an experiment on him-
self, could not attain complete nitrogenous equilibrium on a much greater
nitrogen supply. The protein minimum also seems to vary in different
individuals.
The protein minimum can also be different for other reasons. It
varies, as mentioned by Rubner, not only with the kind of foodstuffs,
but also with the nutritive condition of the body. The needs of the
cells for protein varies with the nutritive condition of the body. Where
the protein is eagerly demanded, less supply of protein suffices, and where
the demand is low more protein must be offered (Rubner). The more the
1
Physiologische Studien iiber Vegetarismus, Bonn, 1905.
2
Sivf’n, Skand. Arch. f. Physiol., 10 and 11; Caspari, Arch. f. (Anat. u.) Physiol.,
1901.
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