VOLUNTARY MUSCLE. 39 



RIGOR MORTIS. 



Within a few hours after an animal dies, its muscles undergo a 

 pronounced irreversible change. They contract and lose their 

 extensibility. The contraction is not vigorous as can be shown by 

 resisting it with slight tension. 



The chemical changes which seem to underlie the process, are 

 the production of carbon dioxide and lactic acid, which by causing 

 coagulation of the muscle proteins, myosinogen and paramyosingen, 

 bring about the contraction. Incomplete oxidation seems to favour 

 the development of rigor, for if plenty of oxygen is supplied neither 

 rigor mortis nor lactic acid is present. 



Heat is also produced as rigidity comes on, which accounts for 

 the warmth which may be noticed sometimes hours after death. 



Rigor mortis being due to chemical changes, anything which 

 hastens these causes an earlier development of the condition. 

 Thus the onset is much earlier at high temperatures; low tempera- 

 tures, conversely, postpone. Fatigue, by speeding up the produc- 

 tion of lactic acid and other substances, causes an earlier appear- 

 ance of rigor. 



This coagulation of the muscle in rigor mortis may last for two 

 or three days, when it is terminated by autoly 



Coagulation of muscle proteins may be caused by heat. If a 

 muscle is gradually heated two stages are found to be present in 

 the development of rigor, the first at 39 C. in the frog and 47 C. 

 in the mammal, the second at 50 C. in the frog and 62 C. in the 

 mammal. The first is due to the muscle proteins proper and the 

 second to the connective tissue substances. 



Heat rigor is more complete and does not disappear when auto- 

 lysis supervenes. 



Similarly, clotting of the muscle proteins may be produced by 

 alcohol, chloroform or other substances. 



ELECTRICAL CHANGES IN MUSCLE. 



Electrical changes accompany the contraction of muscle. This 

 can be shown by connecting a sensitive galvanometer to a muscle 

 which is caused to contract voluntarily or through artificial stimu- 

 lation. A wave of negative variation travels from the point 



