THE CHEMISTRY OF MUSCLE. 69 



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 acid products of metabolism, pass into their insoluble forms, 

 namely, myosin fibrin and myogen fibrin. 



2. There is an increased acidit}^ due to a production of lactic 

 acid. 



3. There is a production of CO 2 . Much importance was 

 attributed formerly to this product on the belief that it indicated 

 the occurrence of a metabolic reaction, a catabolic or oxidative 

 change similar to that taking place in contraction. Fletcher 

 and Brown* give proof, however, so far at least as heat rigor and 

 chloroform rigor are concerned, that the C0 2 formed does not arise 

 from a metabolic breakdown of organic material, but is simply an 

 indirect result of the production of acid. This acid as it accumu- 

 lates acts upon the carbonates in the muscle and thus leads to a 

 liberation of the CO 2 . From this standpoint the CO 2 production 

 in rigor as it usually occurs has no physiological significance. If, 

 however, the muscle during the development of rigor is supplied 

 plentifully with oxygen, then the lactic acid, as it is formed, under- 

 goes oxidation, with the production of CO 2 . According to condi- 

 tions the CO 2 may have two origins. In the absence of oxygen it 

 is derived from the action of the lactic acid on the alkaline car- 

 bonates, while in the presence of oxygen an additional amount is 

 formed by oxidation of the lactic acid itself. 



4. The consumption of glycogen. According to recent ob- 

 servers, carbohydrate disappears during rigor as it does during 

 contraction, and the loss in carbohydrate runs parallel to the 

 increase in lactic acid, f 



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 is thus deprived of its 

 circulation and its proper supply of oxygen, fatigue appears 

 more rapidly and is recovered from less completely. Ranke,t 



* Fletcher and Brown, "Journal of Physiology," 48, 177, 1914. 

 t Parnas and Wagner, "Biochem. Zeit.," 1914, 61, 387. 

 j Ranke, "Tetanus," Leipzig, 1865. 



