CHEMICAL CHANGES DURING CONTRACTION. 453 



venous blood of a limb, when the muscles are contracted, con- 

 tains more CO 2 than when they are relaxed. The increase of CO, 

 can also be detected in a muscle removed from the body and kept 

 in a state of contraction. Moreover, this increase in the forma- 

 tion of C0 2 in a muscle takes place whether there is a new sup- 

 ply of oxygen given to it or not, and the quantity of CO., given 

 off always greatly exceeds the quantity of oxygen that is used 

 up. So that it is not exclusively, if at all, from the newly-sup- 

 plied oxygen that the CO, is produced. 



Muscle tissue, when passive, is neutral or faintly alkaline; 

 during contraction, however, it becomes distinctly acid. The lit- 

 mus which it changes from blue to red is permanently altered, 

 and we can, therefore, conclude that CO 2 is not the only acid that 

 makes its appearance. The other acid is sarcolactie acid, which 

 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 sarcolactie acid 

 can be produced from these carbohydrates by the action of cer- 

 tain 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 ex- 

 ercise 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 nitro- 

 genous waste, as estimated by the urea elimination, which one 

 would expect if muscular activities were the outcome of a de- 

 composition of the nitrogenous (albuminous) parts of the muscle 

 substance. 



