MUSCLE-XERVE PHYSIOLOGY. 521 



Muscle in Rigor Mortis. 



After the muscles of the dead body have lost their irritability or capa 

 bility of being excited to contraction by the application of a stimulus, 

 they spontaneously pass into a state of contraction, apparently identical 

 with that which ensues during life. It affects all the muscles of the 

 body; and, when external circumstances do not prevent it, commonly 

 fixes the limbs in that which is their natural posture of equilibrium or 

 rest. Hence, and from the simultaneous contraction of all the muscles 

 of the trunk, is produced a general stiffening of the body, constituting 

 the rigor mortis or post-mortem rigidity. 



When this condition has set in, the muscle (a) becomes acid in reaction 

 (due to development of sarcolactic acid), (b) gives off carbonic acid in 

 great excess, (c) diminishes in volume slightly* (d) becomes shortened and 

 opaque, its substance setting firm. Eigor comes on much more rapidly 

 after muscular activity, and is hastened by warmth. It may be brought 

 on, in muscles exposed for experiment, by the action of distilled water 

 and many acids, also by freezing and thawing. 



Cause. The immediate cause of rigor seems to be a chemical one, 

 namely, the coagulation of the muscle plasma. We may distinguish 

 three main stages (1.) Gradual coagulation. (2.) Contraction of coag- 

 ulated muscle-clot (myosin), and squeezing out of muscle-serum. (3.) 

 Putrefaction. After the first stage, restoration is possible through the 

 circulation of arterial blood through the muscles, and even when the 

 second stage has set in, vitality may te restored by dissolving the coag- 

 ulum of the muscle in salt solution, and passing arterial blood through 

 the vessels. In the third stage recovery is impossible. 



It has been noticed that the relaxation in muscles after rigor some- 

 times occurs too quickly to be caused by putrefaction, and the suggestion 

 that in such cases at any rate such relaxation is due to a ferment-action 

 is very plausible. It is known that pepsin is present in muscles, and 

 that this ferment will act in an acid medium. The conditions for the 

 solution of the coagulated myosin are therefore present as the reaction 

 of rigored muscle is acid. 



Order of Occurrence. The muscles are not affected simultaneously oy 

 rigor mortis. It affects the neck and Lower jaw first; next, the upper 

 extremities, extending from above downward; and lastly, reaches the 

 lower limbs; in some rare instances only, it affects the lower extremities 

 before, or simultaneously with, the upper extremities. It usually ceases 

 in the order in which it begins: first at the head, then in the upper 

 extremities, and lastly in the lower extremities. It never commences 

 earlier than ten minutes, and never later than seven hours after death; 

 and its duration is greater in proportion to the lateness of its accession. 



