750 THE PHYSIOLOGY OF THE CONTRACTILE TISSUES 



Certain analogies between rigor and muscular contraction were 

 early pointed out. In both there is (i) shortening; (2) heat-pro- 

 duction; (3) formation of lactic acid; (4) discharge of carbon 

 dioxide ; (5) electrical changes. As regards the production of lactic 

 acid, there is reason to believe that the process is fundamentally 

 the same as in contraction, and the study of rigor, especially of 

 certain of the artificially induced forms e.g., heat rigor in relation 

 to the liberation of lactic acid, carbon dioxide, and heat, has thrown 

 light upon the changes normally occurring in muscle. Another 

 analogy might be forced into the list by anyone who was deter- 

 mined to see only rigor in contraction: the rigor passes off as the 

 contraction passes off, although the ' resolution ' of a rigid muscle 

 takes days, the relaxation of an active muscle a fraction of a second. 

 The disappearance of rigor is not dependent on putrefaction; it 

 takes place when growth of bacteria is prevented (Hermann). 

 Possibly it is connected with autolytic processes due to intracellular 

 ferments (p. 588). 



Why does coagulation of myosin occur at the death of the muscle ? 

 To this question no clear answer can be given. Some have looked 

 on the process as analogous to the clotting of blood when it is shed, 

 and it has even been suggested that just as a fibrin ferment is 

 developed when the leucocytes and blood-plates begin to die, a 

 myosin ferment, which aids coagulation, is developed in dead or 

 dying muscle. But no proof has been given of the existence of such 

 a ferment. And it is easy to make too much of the apparent 

 analogy between the clotting of muscle and the clotting of blood, 

 for there are differences as well as resemblances. For instance, the 

 addition of potassium oxalate does not prevent coagulation of 

 muscle extracts, as it does of blood and blood-plasma. If the 

 development of lactic acid in the muscle is not the primary cause 

 of the coagulation which constitutes the essential feature of rigor 

 mortis, it seems to be closely related to it. For when excised 

 muscles are abundantly supplied with oxygen, no lactic acid 

 accumulates in them, and the final loss of excitability of the muscle 

 is not followed by rigor. In any case, direct precipitation of 

 hitherto unclotted muscle proteins may be induced by the acid, or 

 the acid salts formed in its presence. Deficiency of oxygen is 

 associated with the occurrence of rigor mortis, as it is with the 

 accumulation of lactic acid, and a developing rigor can be abolished 

 by oxygen, and its onset long or indefinitely delayed. When strict 

 aseptic technique is observed an excised sartorius muscle of the 

 frog may remain irritable in sterile Ringer's solution, even without 

 oxygenation, for as long as three weeks (Mines). 



Various influences affect the onset of rigor. Fatigue hastens 

 it; heat has a similar effect; the contact of caffeine, chloroform, 

 and other drugs causes most pronounced and immediate rigor. 



