EFFECT OF MUSCULAR WORK ON METABOLISM 717 



CO 

 9 Material Respiratory quotient -j-p 



Starch 1-0 



Cane sugar . . . . .1-0 



Glucose . . . . !() 



Animal fat . . . . . 0-711 



Protein ..... 0-809 



The respiratory quotient in an animal at any given time is there- 

 fore determined by the nature of the substances which are under- 

 going oxidation in its body. If- the performance of muscular work 

 involved special chemical processes, a metabolism of one of the 

 main constituents of the body in preference to either of the others, 

 this sudden change in the quality of the metabolism should show 

 itself in the respiratory quotient. It has been proved, however, 

 by Speck and Lowy that moderate muscular work, i.e. work which 

 is not associated with dyspnoea and deficient oxygenation of the 

 muscles, although attended by a large increase both in the carbon 

 dioxide output and the oxygen intake of the body, does not disturb 

 in any degree the relation between these two substances, i.e. the 

 respiratory quotient. This result indicates that the metabolism 

 of the body which furnishes the energy of muscular activity is qualita- 

 tively of the same nature as that which occurs during rest, i.e. that 

 the energy for muscular contraction can be derived from any or 

 all of the three classes of food-stuffs or proximate constituents 

 of the body. 



