708 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



the same way as myosin can be converted into myosinogen, which will 

 again coagulate with the formation of myosin. The ease with which 

 myosin can thus be made to clot and unclot outside the body might 

 seem to be a confirmation of Hermann's view that a similar clotting and 

 re-solution of myosin accompanies the contraction and relaxation of 

 muscle during life ; in other words, that each contraction is the partial 

 death of a muscle. We must remember that the most important simi- 

 larity between rigor mortis and contraction is the formation of sareolactic 

 acid, and not the development of a clot of mj'osin ; in fact, as a muscle 

 becomes more extensible during contraction, it becomes in a sense more 

 liquid, not more solid, as it does when myosin is formed post-mortem. 



Dr. Halliburton further suggests that the passing off of rigor mortis 

 is due to the reconversion of myosin into myosinogen, brought about by 

 the pepsin present in muscle. For when muscle becomes acid in rigor 

 mortis the pepsin which it contains is enabled to act, and at the suitable 

 temperature (35°-40° C.) albumoses and peptones are formed by a 

 process of self-digestion. This is a more satisfactory explanation of the 

 disappearance of rigor mortis than putrefaction, for rigor mortis occa- 

 sionally persists after putrefaction has set in, and at other times disap- 

 pears within an hour after death. 



The chemical processes continually occurring in living muscle also 

 undergo change on the death of the muscle. It has been found that liv- 

 ing muscle is continually appropriating oxygen from the arterial blood 

 and setting free carbon dioxide. In the death of the muscle the absorp- 

 tion of oxygen ceases, while the exhalation of carbonic acid may continue 

 for a certain time, even if the dead muscle be placed in an atmosphere 

 free from oxygen ; it is, therefore, evident that in the act of death or in 

 the production of rigor mortis some complex compound is split up and 

 carbon dioxide set free. 



Living muscle is, then, alkaline and contains in solution in the sub- 

 stance of its fibres a coagulable proteid in the muscle-plasma. 



Dead muscle, on the other hand, is acid in reaction from the devel- 

 opment of sareolactic acid, and the coagulable plasma has become con- 

 verted into a solid myosin in muscle-serum. When muscles are sub- 

 jected to the vacuum of a mercurial air-pump, a certain amount of gas, 

 which is almost solely C0 2 , is extracted, which has been in part dissolved 

 in the muscle-plasma and in part combined with its salts. In muscles in 

 which rigor mortis has not taken place, 2.74 volumes per cent, of CO, 

 represent the free gas, 1.95 per cent, the fixed gas. If, however, rigor 

 mortis be produced, then 15 volumes per cent, of CO s may be obtained. 

 Therefore, in rigor mortis a large amount of CO a becomes free, but this 

 is not due to the decomposition of carbonates by the acid formed in the 

 same process. So also in muscular contractions there is an increase in 



