66 RIGOR MORTIS. [BOOK i. 



[itself, living muscle contains no myosin, but some substance or 

 (substances which bear somewhat the same relation to myosin that 

 (the fibrin factors do to fibrin, and which give rise to myosin upon 

 (the death of the muscle. 



"We may in fact speak of rigor mortis as characterised by a 

 coagulation of the muscle-plasma, comparable to the coagulation of 

 'blood-plasma, but differing from it inasmuch as the product is not 

 fibrin but myosin. The rigidity, the loss of suppleness, and the 

 diminished translucency appear to be at all events largely, though 

 probably not wholly, due to the change from the fluid plasma to the 

 solid myosin. We might compare a living muscle to a 'number of 

 fine transparent membranous tubes containing blood-plasma. When 

 this blood-plasma entered into the 'jelly' stage of coagulation, the 

 system of tubes would present many of the phenomena of rigor 

 mortis. They would lose much of their suppleness and translucency, 

 and acquire a certain amount of rigidity. 



There is however one very marked and important difference 

 between rigor mortis of muscle and the coagulation of blood : blood 

 during its coagulation undergoes only a slight change in its reaction ; 

 Ibut muscle during the onset of rigor mortis becomes distinctly acid. 



A living muscle at rest is in reaction neutral, or, possibly from 

 some remains of lymph adhering to it, faintly alkaline. If on the 

 other hand the reaction of a thoroughly rigid muscle be tested, it 

 will be found to be most distinctly acid. This development of an 

 acid reaction is witnessed not only in the solid untouched fibre but 

 also in expressed muscle-plasma ; it seems to be associated in some 

 way with the appearance of the myosin. 



The exact causation of this acid reaction has not at present 

 been clearly worked out. Since the coloration of the litmus pro- 

 duced is permanent, carbonic acid, which as we shall immediately 

 state, is set free at the same time, cannot be regarded as the active 

 acid, for the reddening of litmus produced by carbonic acid speedily 

 disappears on exposure. On the other hand it is possible to ex- 

 tract from rigid muscle a certain quantity of lactic acid, or rather 

 of a variety of lactic acid known as sarcolactic acid 1 ; and it has 

 been thought that the appearance of the acid reaction of rigid 

 muscle is due to a new formation or to an increased formation of 

 this sarcolactic acid. But there is considerable doubt whether any 

 such increase of sarcolactic acid does actually take place in rigor 

 mortis. Hence though there can be no doubt that an acid reaction 

 is established, we are not yet in a position to affirm positively the 

 exact manner in which that reaction is produced, the complex 

 nature of the muscular substance suggesting to the chemist several 

 ways in which it might come about. 



Coincident with the appearance of this acid reaction, though 

 as we have said, not the direct cause of it, a large development of 

 carbonic acid takes place when muscle becomes rigid. Irritable 



1 Bee Appendix. 



