54 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



a death rigor that is rapidly developed by the high temperature, 

 this latter condition accelerating the chemical changes leading to 

 rigor, as is the case, for instance, in the action of chloroform. This 

 view is supported by a study of the chemical changes that take place 

 under the two conditions, as will be described later, and by the fact 

 that some of the conditions that influence one phenomenon have a 

 parallel effect upon the other. For instance, death rigor is accel- 

 erated by previous use of the muscle, and the same is true for heat 

 rigor. While a resting frog's muscle begins to go into heat rigor, 

 as judged by the shortening, at 37 to 40 C.; a muscle that has 

 been greatly fatigued shows the same phenomenon at 25 to 

 27 C.* According to other observers, heat rigor is due to an 

 ordinary heat coagulation of the proteins present in the muscle 

 fiber, and it has been claimed that a separate contraction may 

 be obtained on heating for each of the proteins said to exist in 

 the muscle fiber, f More recent observations! seem to show 

 that when a frog's muscle is gradually heated, only two really 

 distinct contractions are obtained, one at 39 C. (38 to 40) 

 or slightly lower, and one at 50 C. (49 to 51). Mammalian 

 muscle gives also two contractions when heated, one at 47 C. 

 (46 to 50) and one at 62 C. (61 to 64). In each of these 

 cases the second contraction is due to the action of heat on the 

 connective-tissue elements of the muscle. The first contraction is, 

 therefore, the one that is characteristic of the muscular substance 

 proper and the one that marks the occurrence of heat rigor. 

 At the tempertures stated, 39 C. for frog's muscle and 47 C. 

 for mammalian muscle, the viscous material within the sarco- 

 lemma coagulates. It does not follow necessarily that this coagula- 

 tion is the direct cause of the shortening. Meigs states that 

 plain muscle heated to 50 C. lengthens instead of shortening, 

 although at that temperature much of its contained protein is 

 coagulated. In striated muscle, on the other hand, coagulation 

 may be produced by alcohol without any noticeable shortening. 

 It may be, therefore, that coagulation and shortening are separate 

 results following upon the chemical changes preceding the death 

 of the muscle substance. The coagulation produced in heat rigor 

 is apparently more complete and resistant than that of death rigor, 

 for ordinary death rigor passes off after a certain interval, even if 

 putrefactive processes are excluded; the rigor from heat or from 

 chloroform, on the contrary, shows no release. With regard to the 



* Latimer, "American Journal of Physiology," 2, 29, 1899. 

 f Brodie and Richardson, " Philosophical Trans., Roy. Soc.," London, 

 1899, 191, p. 127; also Inagaki, "Zeitschrift f. Biol.," 1906, 48, 313. 

 t Vrooman, " Bio-chemical Journal," 1907. 2, 363. 

 \ Meigs, "American Journal of Physiology," 24, 1 and 178, 1909. 



