66 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



The Formation of Creatin. Great in constitutes the chief nitrog- 

 enous waste product in the muscle, and we should expect that the 

 greater metabolism during activity would result in an increase in 

 the creatin. Some observers state positively that the creatin is 

 increased during contraction. 



Chemical Changes during Rigor Mortis. The chemical 

 changes during rigor have been referred to above, but may be 

 summarized here in brief form : 



1. There is a coagulation of the protein material of the muscle 

 plasma, which at present may be explained by supposing that the 

 contained myosin and myogen, spontaneously, or under the action 

 of an enzyme, pass into their insoluble forms, namely, myosin 

 fibrin and myogen fibrin. 



2. There is an increased acidity, due doubtless to a production 

 of lactic acid. 



3. There is a production of CO 2 . Hermann, in his original ex- 

 periments, asserts that in rigor there is, so to speak, a maximal 

 production of CO 2 , that is, all of the material in the muscle capable 

 of yielding CO 2 is broken down during rigor. The amount of CO 2 

 given off, therefore, by a resting muscle when it goes into rigor 

 is greater than in the case of a worked muscle, since in the 

 latter some of the material capable of yielding CO 2 has been used 

 up during contraction. 



4. The consumption of glycogen. According to some observers, 

 glycogen disappears during rigor as it does during contraction; 

 but others find that the amount is not changed during this process, 

 As the glycogen after death is converted to sugar with some rapidity 

 it is possible that the disappearance noted by the former observers! 

 was not due to the rigor process, but to post-mortem fermentation-.* 



The Relation of the Chemical Changes during Contraction 

 to Fatigue; Chemical Theory of Fatigue. As we have seen, a 

 muscle kept in continuous contraction soon shows fatigue ; it 

 relaxes more and more until, in spite of constant stimulation, it 

 becomes completely unirritable. We may define fatigue, there- 

 fore, as a more or less complete loss of irritability and contractility 

 brought on by functional activity. But even when the fatigue is 

 complete and the muscle fails to respond at all to maximal 

 stimulation, a very short interval of rest is sufficient to bring about 

 some return of irritability. For a complete restoration to its 

 normal condition a long interval of time may be necessary. If 

 the muscle is isolated from the body and thus deprived of its cir- 

 culation, the recovery from fatigue is less rapid and less complete 

 than under normal conditions. In such an isolated muscle, more- 



* Kisch, Hofmeister's "Beitrage zur chem. Physiol. u. Pathol./' viii., 

 210, 1906. 



