456 MANUAL OF PHYSIOLOGY. 



is constantly present in muscle after prolonged contraction, and 

 varies in amount in proportion to the degree of activity the 

 muscle has undergone. It therefore varies directly with the CO 2 , 

 which would seem to suggest a relationship between the origin of 

 the two acids. 



The amount of glycogen and grape sugar is said to diminish 

 in muscle during its activity, and it is stated that sarcolactic acid 

 can be produced from these carbohydrates by the action of certain 

 ferments. - 



Active muscle contains more substances than can be extracted 

 by alcohol, and less that are soluble in water than passive 

 muscle. 



The chemical changes which take place during muscle contrac- 

 tion are probably the result of a decomposition of some carbo- 

 hydrates, in which the albuminous substances do not take any 

 part that requires their own destruction. This seems supported 

 by the fact that the increased gas exchange in muscle during 

 active exercise can be recognized in a corresponding change in 

 the gas exchange in pulmonary respiration ; and, moreover, there 

 seems no relation between muscular labor and the amount of 

 nitrogenous waste, as estimated by the urea elimination, which 

 one would expect if muscular activities were the outcome of a 

 decomposition of the nitrogenous (albuminous) parts of the 

 muscle substance. 



The chemical changes which are commonly said to take place 

 in muscle during its contraction are : 



1. The contractile substance, which is normally neutral or 

 faintly alkaline, becomes acid in reaction, owing to the formation 

 of sarcolactic acid. 



2. More oxygen is taken up from the blood than in the muscle 

 at rest. This using up of oxygen occurs also in the isolated 

 musle, and its amount appears to be independent of the blood 

 supply. 



3. The extractives soluble in water decrease, those soluble in 

 alcohol increase. 



4. A greater amount of CO 2 is given off, both in the isolated 

 muscle as well as in the muscles in the body, and the change in 



