244 PHYSIOLOGY 



body, we shall see that it is impossible to draw any qualitative distinc- 

 tion between the metabolism which results in muscular work, and the 

 metabolism of the resting animal. Thus the relative proportion of 



the C0 2 produced to the oxygen taken in, the ' respiratory quotient ' 







will vary according to the food that is being consumed, being unity 



with carbohydrates, less than unity with proteins, and still less with 

 fats. It is found that muscular work does not alter the respiratory 

 quotient, i.e. during work the qualitative metabolism of the whole 

 body is the same as during rest. We must conclude therefore that 

 the muscle derives its energy from the combustion of all three classes 

 of food-stuffs, although in the absence of food it will perform its work 

 at the expense of stored-up fat or carbohydrate, proteins not under- 

 going any storage in the body. 



The absence of change in the respiratory quotient during exercise 

 shows moreover that, in a muscle under normal conditions, the two 

 processes, viz. the taking in of oxygen and the giving out of C0 2 , keep 

 pace one with the other. In warm-blooded animals the shutting off 

 of the oxygen supply rapidly induces paralysis and loss of irritability 

 of the muscles. This result, coupled with the fact that, as mentioned 

 above, the final results of muscular activity differ according as the 

 muscle is or is not supplied with oxygen, suggests that the oxygen 

 takes part in the process of activity only after the disintegration of the 

 complex living molecule has already begun. 



Such a conclusion is, however, opposed to the generally accepted 

 views on the nature of the oxidation processes in the cell. According 

 to Hermann, Pfliiger, Verworn, and others, there is during rest a 

 building up both of oxygen and food material into the living molecule. 

 Activity consists in a rearrangement of the molecule (spoken of 

 by Hermann as the inogen molecule), with the assumption of more 

 stable positions by the oxygen and carbon atoms, and a consequent 

 production of C0 2 . (Compare the explosion of gun-cotton or nitro- 

 glycerin.) The presence of this intramolecular oxygen in an unstable 

 position would be a necessary condition both for the irritability as 

 well as for the activity of all forms of living tissue, especially muscle 

 and nerve. 



If the muscle can use all classes of food-stuffs in its metabolism, 

 one would expect to find some change in the nitrogenous constituents 

 as the result of activity. Physiologists have searched in vain, however, 

 for any evidence of the formation of creatin or urea in excised muscle 

 during contraction. Cathcart and Brown have found an insignificant 

 increase of creatin in excised frog's muscle during contraction and a 

 more significant decrease if the circulation has been maintained intact 



