598 MUSCLES. 



nutriments, and according to SEEGEN, CHAUVEAU, and LAULANIE 1 

 the sugar is the only direct source of muscular force. The last-men- 

 tioned investigator holds that the fat is not 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 S the CC>2 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* 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. 



2 Loeb, Arch. f. (Anat. u.) Physiol., 1894; Heinemann, Pfluger's Arch., 83; Frentzel 

 and Reach, ibid.-, Atwater and Benedict, U. S. Dept. of Agric., Bull. 136, and Ergeb- 

 nisse der Physiologie, 3. 



3 Skand. Arch. f. Physiol., 13. 



4 Zeitschr. f. physiol. Chem., 22. 



