50 . THE PHYSIOLOGY OF MUSCLE AND NERVE. 



discussed briefly below. Some of the facts which have been ob- 

 served regarding rigor mortis are as follows: After the death of an 

 individual the muscles enter into rigor mortis at different times. 

 Usually there is a certain sequence, the order given being the jaws, 

 neck, trunk, upper limbs, lower limbs, the rigor taking, therefore, a 

 descending course. The actual time of the appearance of the rigidity 

 varies greatly, however; it may come on within a few minutes or a 

 number of hours may elapse before it can be detected, the chief de- 

 termining factor in this respect being the condition of the muscle 

 itself. Death after great muscular exertion, as in the case of hunted 

 animals or soldiers killed in battle, is usually followed quickly by 

 muscle rigor; indeed, in extreme cases it may develop almost imme- 

 diately. Death after wasting diseases is also followed by an early 



Fig. 24. Curve of normal rigor mortis, gastrocnemius muscle of frog. The curve 

 was obtained upon a kymographion making one revolution in eight days. The marks on 

 the line below the curve indicate intervals of six hours. It will be seen that the shortening 

 required eighteen hours, the relaxation about seventy-two hours. 



rigor, which in this case is of a more feeble character and shorter 

 duration. The development of rigor is very much hastened by many 

 drugs that bring about the rapid death of the muscle substance, such 

 as veratrin, hydrocyanic acid, caffein, and chloroform. A frog's mus- 

 cle exposed to chloroform vapor goes into rigor at once and shortens 

 to a remarkable extent. Rigor is said also to occur more rapidly 

 in a muscle still connected with the central nervous system than 

 in one whose motor nerve has been severed. After a certain 

 interval, which also varies greatly, from one to six days in human 

 beings, the rigidity passes off, the muscles again become soft and 

 flexible; this phenomenon is known as the release from rigor. In 

 the cold-blooded animals the development of rigor is very much 

 slower than in warm-blooded animals. Upon an isolated frog's 

 muscle the most striking fact regarding rigor mortis is the shortening 

 that the muscle undergoes. This shortening or contraction comes 

 on slowly, as is shown in the accompanying figure, but in extent 



