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598 MUSCLES.
nutriments, and according to Seegen, Chauveau, and Laulani6 1
the sugar is the only direct source of muscular force. The last-men-
tioned investigator holds that the fat is net directly utilized for work,
but only after a previous conversion into sugar. Zuntz and his collabora-
tors have made strong objections to the correctness of such a view. If
according to Zuntz, the fat must be first transformed into sugar before
it can serve as the source of muscular work, a definite expenditure of
force must require about 30 per cent more energy with fatty food than
it does with carbohydrates; but this is not the case. The investiga-
tions of Zuntz (together with), Loeb, Heinemann, Frentzel and Reach
show that all foodstuffs have nearly the same power of serving as the
material for the work of the muscles. The extensive metabolism investi-
gations of Atwater and Benedict 2
have also led to similar results
as to the fats being a source of muscular energy. The law of the sub-
stitution of the foodstuffs, according to their combustion equivalents,
is also true for muscular work, and fat correspondingly acts with its full
amount of energy without previously being transformed into sugar.
The question which of the foodstuffs the muscle prefers is dependent upon
the relative quantities of the same at the disposal of the muscle. A
direct substitution of the body material by the bodies supplied as food
does not take place in the muscular activity in the ordinary nutritive
condition. According to Johansson and Koraen 3
the CO2 excretion
produced by certain work is not influenced by the supply of foodstuffs
(protein or sugar).
Siegfried considers, as above stated, the phosphocarnic acid as a source of
energy. According to his and Kruger’s 4
researches, phosphocarnic acid, which
yields on cleavage, among other bodies, carbon dioxide, occurs in part preformed
in the muscle, and in part as a hypothetical aldehyde compound of the same
—
a compound which forms phosphocarnic acid on oxidation. Siegfried therefore
makes the suggestion that in the resting muscle, which requires more oxygen
than exists in the carbon dioxide eliminated, this reducing aldehyde substance is
gradually oxidized to phosphocarnic acid, which is used in the activity of the
muscle with the splitting off of carbon dioxide.
Quantitative Composition of the Muscle. A large number of analyses
have been made of the flesh of various animals for purely practical
purposes, in order to determine the nutritive value of different varieties
1
See Seegen, footnote 4, page 592. The works of Chauveau and his collaborators
are found in Compt. Rend., 121, 122, and 123; Laulanie, Arch, de Physiol. (5), 8.
- Loeb, Arch. f. (Anat. u.) Physiol., 1894; Heinemann, Pfliiger’s Arch., 83; Frentzel
and Reach, ibid.; Atwater and Benedict, U. S. Dept. of Agric, Bull. 136, and Ergeb-
nisse der Physiologic, 3.
• Skand. Arch. f. Physiol., 13.
* Zeitschr. f. physiol. Chera., 22.
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