92 PHYSIOLOGY OF MUSCLE AND NERVE 



character of rigor mortis are several. First of all we might mention the 

 condition of the muscles at the time of death. Thus, it is a matter of 

 common observation that muscles which have been enfeebled by dis- 

 ease show a rapid onset and dissolution, while strong and vigorous 

 muscles are affected rather slowly. Cold delays and warmth hastens 

 its onset. The same is true of muscular fatigue and certain diseases 

 of the spinal cord and brain. Extensive lesions of these parts greatly 

 favor its development. Young individuals, and especially infants, 

 are affected more rapidly than adults, and red muscles more slowly than 

 pale muscles. 



In analogy with muscular contraction it is believed that rigor 

 mortis is caused by a coagulation of the protein material. It is held 

 that the myosin and myogen are temporarily converted into their 

 insoluble forms, 1 myosinfibrin and myogenfibrin, this change being 

 associated with an increase in the acidity of the muscle. Inasmuch 

 as the latter is dependent upon the production of lactic acid, it has 

 been assumed that this acid is the actual cause of this coagulation, 

 or is at least very closely concerned with it. This inference is entirely 

 justified, because lactic acid is not copiously produced in the presence 

 of an abundant supply of oxygen. Rigor mortis then fails to develop. 

 A deficiency in oxygen, on the other hand, favors the accumulation of 

 lactic acid and hence, also the occurrence of this condition. In accord- 

 ance with this conception, the dissolution is said to be dependent upon 

 the reestablishment of the neutral reaction of the medium or upon 

 intracellular autolyses due to ferments. 2 It has been proved, however, 

 that bacteria are not the primary cause of the dissolution, because the 

 rigor also disappears when their growth is prevented. 3 In analogy 

 with the coagulation of the blood, the attempt has also been made by 

 Danilewsky 4 and others to bring the development of rigor mortis into 

 relation with the calcium content of the muscle plasma. We have prev- 

 iously seen that this relationship is only a general one; moreover, it 

 has been shown that calcium-free solutions of myogen are not exempt 

 from coagulation. 5 



In the third place, a muscle in rigor mortis gives rise to a consider- 

 able amount of carbon dioxid which may have its source either in an 

 increased general catabolism or in those oxidations which are primarily 

 concerned with the reduction of lactic acid. In accordance with the 

 experiments of Fletcher and Brown, 6 this point has been decided in 

 favor of the latter view, the increase in carbon dioxid being the indirect 

 result of the formation and oxidation of the lactic acid. Some ob- 

 servers also claim that the glycogen content of muscle is diminished 

 during rigor mortis. 



1 Saxl, Hofmeister's Beitrage, ix, 1906, 1. 



2 Vogel, Deutsch. Arch, fur klin. Med., 1902, 292. 



3 Bierf reund, Pfliiger's Archiv, xliii, 1888, 195; and Karpa, ibid., cxii, 1906, 199. 



4 Zeitschr. phys. Chemie, vi, 1882, 158. 



6 v. Furth, Hofmeister's Beitrage, iii, 1903, 453. 



Jour, of Physiol., xlviii, 1914, 177. 



