RIGOR MORTIS. 471 



of the nutrition and loss of irritability. Thus when the nerves 

 supplying the voluntary muscles are injured, there is considerable 

 danger of atrophy and tissue degeneration of the muscles; the 

 contractile substance becomes replaced by fat granules. This de- 

 generation also occurs in the stump when a limb is amputated, 

 the distal attachments of the muscles having been cut, they atro- 

 phy ; for, although their nervous supply is uninjured, they cannot 

 act, and after some time muscle tissue can hardly be recognized 



in them. 



DEATH RIGOR. 



The death of muscle tissue is preceded by, and associated with, 

 a set of changes which are a kind of exaggeration of those observed 

 in its active state. The most obvious phenomenon is an unyielding 

 contraction, which causes the stiffening of the body after systemic 

 death. Hence it is called rigor mortis. The muscles harden ; 

 lose their elasticity, and the tissue is torn if forcibly stretched. 

 When isolated, the muscle is seen to be opaque, and its reaction 

 is found to be distinctly acid. A considerable quantity of heat is 

 developed during the progress of the rigor. The electric currents 

 alter in direction and finally disappear. 



The period at which rigor comes on, as well as the time it lasts, 

 depend on (a) the state of the muscles themselves, and (6) the 

 circumstances under which they are placed at the time of death. 

 All influences which tend to facilitate the approach of tissue-death 

 also tend to induce early and rapidly-terminating rigor, viz., (1.) 

 Prolonged activity as may be shown in a muscle artificially 

 tetanized, or may be seen in an animal whose death was preceded 

 by intense muscular exertion causes rigor to appear almost im- 

 mediately, and to terminate rapidly. (2.) Within certain limits, 

 a high temperature facilitates the production of rigor in dying 

 muscles, and indeed a temperature not much exceeding that nor- 

 mal to the tissue induces rigor immediately. This form of con- 

 traction, which is called heat-rigor, is brought about in mammalian 

 muscles by a temperature of about 50 C., and in frogs' muscles 

 below 40 C. If, however, the temperature of a muscle be sud- 

 denly raised to the boiling point, it is killed, and the chief phe- 

 nomena of rigor are prevented from occurring. (3.) Freezing 



