MUSCLE IN RIGOR MORTIS 527 



portion to the lateness of its accession. Heat is developed during the passage 

 of a muscular fiber into the condition of rigor mortis. 



Since rigidity does not ensue until muscles have lost the capacity of being 

 excited by external stimuli, it follows that all circumstances which cause a 

 speedy exhaustion of muscular irritability induce an early occurrence of the 

 rigidity, while conditions by which the disappearance of the irritability is 

 delayed are succeeded by a tardy onset of the rigidity of rigor. This is the 

 explanation of its speedy occurrence, and equally speedy departure, in the 

 bodies of persons exhausted by chronic diseases; and its tardy onset and long 

 continuance after sudden death from acute diseases. In some cases of 

 sudden death from lightning, violent injuries, or paroxysms of passion, rigor 

 mortis has been said not to occur at all; but this is not always the case. It 



FIG. 332. Curve of Shortening of the Gastrocnemius Muscle of the Frog, During Heat 

 Rigor. The numbers indicate degrees centigrade. 



may, indeed, be doubted whether there is really a complete absence of the 

 postmortem rigidity in any such cases; for the experiments of Brown- 

 Sequard make it probable that the rigidity may supervene immediately 

 after death, and then pass away with such rapidity as to be scarcely 

 observable. 



The occurrence of rigor mortis is not prevented by the previous existence 

 of paralysis in a part, provided the paralysis has not been attended with very 

 imperfect nutrition of the muscular tissue. 



The rigidity affects the involuntary as well as the voluntary muscles, 

 whether they be constructed of striped or unstriped fibers. The rigidity 

 of involuntary muscles with striped fibers is shown in the contraction of 

 the heart after death. The contraction of the muscles with unstriped fibers 

 is shown by an experiment of Valentin, who found that if a graduated tube 

 be connected with a portion of intestine taken from a recently killed animal, 



