METABOLISM IN NEUROMUSCULAR DISEASES 709 



The Source of Energy for Muscular Contraction 



When a muscle contracts and does work, the energy expended is de- 

 rived largely from the oxidation of glucose to carbon dioxid and water. 



This is one of the most important chemical reactions taking place in 

 the body more important in some respects than 'the hydrolytic cleavages 

 involved in protein metabolism, for the latter do not involve energy changes 

 and it has been much studied in health and disease. 



We do not know the cause of this reaction. It -cannot be carried out 

 artificially that is, without the aid of living cells or products of living 

 cells at body temperature. It has been attributed to enzymes, but such 

 enzymes must be different from the ordinary amylolytic, peptolytic, and 

 lipolytic enzymes, for the hydrolytic cleavages caused by the latter do 

 not involve energy changes. Though they do not know the cause of this re- 

 action, physiologists are now in accord with regard to one important 

 fact concerning it: The reaction is determined by intrinsic factors 

 factors within the cell itself and not by extrinsic factors. 



Three factors are involved in this reaction: (a) the oxygen supply; 

 (b) the glucose supply; (c) the living cell itself. 



THE OXYGEN SUPPLY 



During the years 1866 to 1878 one of the fiercest polemics in the his- 

 tory of physiology raged over the question of the significance of the oxygen 

 supply, most of the great physiologists of that time Voit, Pfliiger, Lud- 

 wig, Liebig, and others taking part in it. The facts are now stressed 

 in books on physiology and metabolism. Lusk (/) , for example, in the very 

 first part of his introductory chapter states, "... the respiration does 

 not cause or regulate the metabolism. On the contrary, the metabolism 

 regulates the respiration. The metabolism, of the tissues, through its oxy- 

 gen requirement and its carbon dioxid production, changes the condition 

 of the blood and thereby regulates the respiration. These distinctions are 

 of fundamental importance." l And Krehl(d) devotes the very first para- 

 graph of the first chapter, in his well known book, to pointing out that it is 

 not true, as formerly believed, that the function of the organs depends upon 

 the amount of material they receive from the blood, but upon the con- 

 dition of the cells themselves. Von Noorden's(^) book on metabolism is 

 equally explicit. "All foundations for the view that the O 2 consumption 

 and CO 2 output, are dependent upon the number and functional capabil- 

 ity of the erythrocytes, or upon the quantity and functional utility of the 

 hemoglobin, has been entirely removed by the investigations just described, 

 and the theory of Voit and Pfliiger, according to which the cells of the 



1 The italics are Lusk's. 



