146 



AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



The sooner it conies on, the sooner it goes off. The stiffness can be broken up 

 artificially by forced movements of the parts, and when thus destroyed does 

 not return, provided the rigor was complete at the time. 



The Cause and Nature of the Contraction of Rigor Mortis. The most likely 

 explanation of the contraction of the dying muscle is that it is the result of 

 the coagulation of a part of the semi-fluid muscle-substance within the sarco- 

 lernma. This was suggested by Bruecke, and Kuehne proved that such a 

 coagulation change takes place, by showing that the semi-fluid muscle-sub- 

 stance, " the muscle-plasma," if expressed from the frozen muscle, coagulates on 

 being warmed. The coagulation is a chemical change attributed to the action 

 of a ferment, the myosin ferment, which is thought to be formed at the death 

 of the muscle. 



Another, though less generally accepted view, is that the contraction of the 

 muscle seen in rigor is of the same nature as ordinary muscular contractions. 1 

 Prolonged muscle contractions are observed when a muscle is greatly fatigued 

 or subjected to such a drug as veratria (see p. 128), and there are many points 

 of resemblance between the contraction of normal and dying muscle viz. the 

 change of form, the production of heat, the formation of sarcolactic acid, the 

 using up of oxygen and the production of carbon dioxide, and the fact that 

 the dying and presumably coagulating muscle is, like normal contracting mus- 

 cle, electrically negative as compared with normal resting muscle. To this 

 may be added that, as has been said, the muscle continues to be irritable even 

 when rigor is quite advanced, and that it enters into rigor more quickly if left 

 in connection with the central nervous system. 



On the other hand, one cannot fail to be impressed with the differences 

 between the two forms of contraction. 



Normal Contracting Muscle. 

 Contains uncoagulated myosinogen. 

 Is translucent. 

 Is soft and flexible. 

 Is no less elastic than in repose. 

 Is more extensible than in repose. 

 Contracts rapidly. 

 Fatigues rapidly and relaxes. 



Muscle contracting by Eigor Mortis. 

 Contains coagulated myosin. 

 Is opaque. 

 Is firm and stiff. 

 Is less elastic than before. 

 Is less extensible than before. 

 Contracts very slowly, as a rule. 

 Kemains contracted a long time. 



Furthermore, it may be added that normal contractions only occur when 

 the irritable muscle is stimulated, while a muscle can enter into rigor when its 

 irritability has been taken away by subjecting it to oxalate solutions, 2 also, 

 when it has been curarized and so shut out from all nervous influences. 3 



Kigor is not confined to the voluntary muscles, though it is less easily 

 observed in the case of most involuntary muscles. The heart enters rapidly 

 into rigor, with the formation of sarcolactic acid. The non-striated muscle 

 of the stomach and ureters, too, has been seen to undergo this change. 



Hermann : Handbuch der Physiologic, 1879, Ed. i. p 146. 

 Howell: Journal of Physiology, 1893, vol. xiv. p. 476. 

 3 Nagel : Pfluger's Archiv, vol. Iviii. S. 279. 



