i GENERAL PHYSIOLOGY OF MUSCLE 37 



coagulation is accelerated by agitation and by rise of temperature. 

 Cold checks coagulation ; above C. it proceeds very slowly ; at 

 higher temperatures it becomes faster, and at 40 very rapid. 

 Addition of distilled water or acids causes instantaneous co- 

 agulation. 



It is obvious that the coagulation of muscle plasma corresponds 

 to the rigor that develops after the death of the muscle. Muscle 

 plasma indeed contains the whole of the soluble proteins of living 

 muscle, and as on cooling muscle to - 7 C. its excitability is not 

 abolished, but merely becomes latent, it may reasonably be 

 concluded that extraction of muscle plasma at a low temperature 

 destroys its structure, but produces no chemical alteration in the 

 substance of living muscle. 



Kiihne's discoveries on frog's muscle were extended to the 

 muscles of warm-blooded animals by Halliburton (1887), who nob 

 only employed cooling to check the coagulation of muscle plasma, 

 but also added neutral salts (sodium chloride, sodium and 

 magnesium sulphate), as in the preparation of salted blood 

 plasma (Vol. I. Chap. V.) The addition of water to salted muscle 

 plasma causes it to coagulate like blood plasma when the fluid 

 is at body temperature, while it does not clot at C. When 

 coagulation sets in the reaction of the plasma becomes acid. In 

 blood plasma fibrin is formed from fibrinogen by the action of an 

 enzyme, and similarly in muscle plasma myosin is formed by the 

 action of an analogous enzyme from a mother-substance, which 

 Kiihne and Halliburton termed myosinogen. As in blood, 

 fibrinogen, not fibrin, is pre-existent, so in muscle myosinogen pre- 

 exists, not myosin. 0. v. Fiirth (1902-3), however, denies this 

 analogy between the coagulation of blood and of muscle, as he 

 failed to obtain experimental proof that the rigor mortis of muscle 

 depends on the action of any ferment. 



Myosin has the same chemical composition as globulin ; it is 

 insoluble in distilled water, soluble in solutions of neutral salts 

 (sodium chloride, sodium and magnesium sulphate), and it coagu- 

 lates at a temperature of 55-60 C. Myosin when dissolved in 

 neutral salts has all the properties of myosinogen, and can easily 

 be reconverted into myosin on simple dilution (Halliburton). 



The fact that myosin dissolved in a weak salt solution at a low 

 temperature is doubly refracting in polarised light, justifies the 

 assumption that the anisotropous discs that are actively concerned 

 in muscular contraction are principally composed of myosinogen 

 (C. Schipiloff and A. Danilewsky). 



Halliburton succeeded by means of fractional heat coagulation, 

 and by salt solutions of different concentrations, in separating five 

 different proteins from the muscle plasma, four of which are 

 coagulable at different degrees of temperature, and one is un- 

 coagulable. This last is a proteose, and is apparently identical 



