198 I^SENTJALS OF CHEMICAL PHYSIOLOGY 



and myosinogen (v. Fiirth's myogen), the two precursors of the muscle-clot 

 or myosin (v. Fiirth's muscle -fibrin). Small quantities of other proteins also 

 present are mainly due to unavoidable mixture with small amounts of blood 

 and lymph. 



These two proteins differ in temperature of heat coagulation. Take the 

 extract and heat it in a test-tube within a water-bath ; at 47 D C. para- 

 myosinogen is coagulated ; filter this off and heat the filtrate ; at 56 C. 

 flocculi of the coagulated myosinogen separate out. 



6. Paramyosinogen is precipitable by dialysis and is a true globulin. 

 Myosinogen is what is called an atypical globulin, and corresponds to the 

 pseudo-globulin of blood serum and egg-white. Though readily salted out of 

 solution like paramyosinogen it is not precipitable by dialysis. 



7. In the process of clotting, such as occurs in rigor mortis, paramyosino- 

 gen is directly converted into myosin ; whereas myosinogen first passes into 

 a soluble modification (coagulable by heat at the remarkably low temperature 

 of 40 C.) before myosin is formed. This is shown in a diagrammatic way 

 in the following scheme : 



Proteins of the living muscle 



Paramyosinogen Myosinogen 



Soluble myosin 



Myosin 

 (the protein of the muscle-clot). 



8. When a muscle is gradually heated, at a certain temperature it con- 

 tracts permanently and loses its irritability. This phenomenon is known as 

 heat-rigor, and is due to the coagulation of the proteins in the muscle. If a 

 tracing is taken of the shortening, it is found that the first shortening occurs 

 at the coagulation temperature of paramyosinogen (47-50 C.), and if the 

 heating is continued a second shortening occurs at 56 C., the coagulation 

 temperature of myosinogen. If frog's muscles are used there are three 

 shortenings namely, at 40, 47, and 56 ' C. ; frog's muscle thus contains 

 an additional protein which coagulates at 40 C. This additional protein is 

 the soluble myosin alluded to above, some of which, in the muscle of cold- 

 blooded animals, is present before rigor mortis occurs. 



In addition to the proteins mentioned, there is a small quantity of micleo- 

 protein. 



9. Involuntary Muscle. The main facts just described for voluntary are 

 true also for involuntary muscle. The chief distinction lies in the quantity 

 of nucleo-protein, which is more abundant in those forms of muscle the 

 fibres of which are least different from the mesoblastic cells from which all 

 ultimately originate. This may be readily shown by the following simple 

 experiment. 



