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928 METABOLISM.
Katzenstein by the statement that during work two kinds of chemical
processes act side by side. The one depends upon the work which is
connected with the production of carbon dioxide, also in the absence
of free oxygen, while the other brings about the regeneration which takes
place by the taking up of oxygen. When these two chief kinds of chemical
processes make the same progress the respiratory quotient remains
unchanged during work; if by hard work the decomposition is increased
as compared with the regeneration, then a raising of the respiratory
quotient takes place. If, on the contrary, moderate work is continued
and performed in a way so that irregularities and occasional changes
in the circulation and respiration are excluded or are without importance,
then the respiratory quotient may correspondingly remain the same
during work as in rest. Its extent is thus determined in the first place
by the nutritive material at its disposal (Zuntz and his pupils).
The theory of Loewy and Zuntz, that the raising of the respiratory quotient
during work is to be explained by an insufficient supply of oxygen, is opposed
by Laulanie. 1
He has observed the reverse, namely, a diminution in the
respiratory quotient during continuous excessive work, and this is not reconcilable
with the above statements. He considers that sugar is the source of muscular
energy, and that the rise in the respiratory quotient is due to an increased combus-
tion of sugar. Its diminution, he explains, is caused by a re-formation of sugar
from fat which takes place at the same time and is accompanied by an increased
consumption of oxygen.
In sleep metabolism decreases as compared with that during waking
hours, and the most essential reason for this is the muscular inactivity
during sleep. The investigations of Rubner upon a dog, and of Johans-
son 2
upon human beings, teach us that if the muscular work is elim-
inated the metabolism during waking hours is not greater than in sleep.
The action of light also stands in close connection with the question
of the action of muscular work. It seems positively proven that metabo-
lism is increased under the influence of light. Most investigators, such as
Speck, Loeb, and Ewald,3
consider that this increase is due to the move-
ments caused by the light or an increased muscle tonus, and in man an
increase in metabolism under the influence of light with complete rest
has not been observed. Divergent results have been obtained in animals,
and our knowledge of the truth is not yet complete.4
Menial activity docs not seem to have any influence on metabolism
according to the means at hand for studying this influence.
1
Arch, de Physiol. (5), 8, 572.
1 Rubner, Ludwig-Festechr., 1887; Loewy, Berl. klin. Wochenschr., 1891, 434;,
Johansson, Skand. Arch. f. Physiol., 8.
1
Speck, 1. c; Loeb, Pfluger’s Arch., 42; Ewald, Journ. of Physiol., 13.
4
See larger handbooks for the literature on this question.
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