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MUSCLE WORK. 597
question as to the material basis of muscular activity so far as it has
its origin in chemical processes. In the past the generally accepted
opinion was that of Liebig, that the source of muscular action con-
sisted of a catabolism of the protein bodies; to-day another generally
accepted view prevails. FlCK and Wislicenus 1
climbed the Faulhorn
and calculated the amount of mechanical force expended in the attempt.
With this they compared the mechanical equivalent transformed in the
same time from the proteins, calculated from the nitrogen eliminated in
the urine, and found that the work really performed was not by any
means compensated by the consumption of protein. It was, therefore,
proved by this that proteins alone cannot be the source of muscular
activity and that this depends in great measure on the metabolism of
non-nitrogenous substances. Many other observations have led to the
same result, especially the experiments of Voit, of Pettenkofer and Voit,
and of other investigators, whose observations show that while the
elimination of nitrogen remains unchanged, the elimination of carbon
dioxide during work is very considerably increased. It is also gen-
erally considered as positively proved that muscular work is produced,
at least in greatest part, by the catabolism of non-nitrogenous substances.
Nevertheless there is no warrant for the statement that muscular activity
is produced entirely at the cost of the non-nitrogenous substances,
and that the protein bodies are without importance as a source of
energy.
The investigations of Pfluger 2
are of great interest in this connec-
tion. He fed a bulldog for more than seven months with meat which
alone did not contain sufficient fat and carbohydrates even for the pro-
duction of heart activity, and then let him work very hard for periods
of 14, 35, and 41 days. The positive result obtained by these series
of experiments was that " complete muscular activity may be effected
to the greatest extent in the absence of fat and carbohydrates," and the
ability of proteins to serve as a source of muscular energy cannot be
denied.
The nitrogenous as well as the non-nitrogenous nutriments may serve
as a source of energy; but the views are divided in regard to the relative
value of these. Pfluger claims that no muscular work takes place
without a decomposition of protein, and the living cell-substance prefers
always the protein and rejects the fat and sugar, contenting itself with
these only when proteins are absent. Other investigators, on the con-
trary, believe that the muscles first draw on the supply of non-nitrogenous
1
Vierteljahrsschr. d. Zurich, naturf. Gesellsch., 10, cited from Centralbl. f. d. med.
Wiss., 18G6, 309.
2
Pfliiger’s Arch., 50.
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