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. FICK 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., 1866, 309. 



2 Pfliiger's Arch., 50. 



