CH. XII.] 



PROTEINS OF MUSCLE 



139 



the clotted condition ; but myosinogcn, called myogen by v. Fiirth, first passes into 

 a soluble condition (coagulable by heat at the remarkably low temperature of 

 40 C.) before it clots : the soluble stage he calls soluble mi/ oy en- fibrin ; a better name 

 is soluble my ox in. 



We may put this in a diagrammatic way as follows : 



Proteins of the living muscle. 



Paramyosinogen 



Myosinogen. 



Soluble myosin. 



Myosin 

 (the protein of the Muscle-clot). 



V. Fiirth also calls attention to some characters of myosinogen which separate 

 it from the typical globulins ; e.g., it is not precipitable by dialysingthe salts away 

 from its solutions. It may be therefore called an atypical globulin. 



In mammalian muscle, soluble myosin is only found as a stage in the process 

 of rigor mortis, but in the muscles of the frog and other amphibia it is present 

 as such in the living muscle. 



The muscle-plasma from fishes' muscle contains another protein termed myo~ 

 protein by v. Fiirth. It is precipitable by dialysis, but not coagulable by heat. 



Brodie, and later, Vernon, did some interesting experiments on heat rigor. 

 When a muscle is heated above a certain temperature it becomes contracted and 

 stiff, losing its irritability completely. This is due to the coagulation of the muscle 

 proteins. If a tracing is taken of the contraction, it is found to occur in a series of 



muscle is used, there are three steps, namely, at 40 (coagulation temperature of 

 soluble myosin), 47, and 56. This work of Brodie's is especially valuable because 

 it teaches us that the proteins in muscle-plasma, or in saline extracts of muscle, 

 are present also in the actual muscle-substance. He also made clear another 

 important point, namely, that the irritability of the muscle is lost after the first 

 step in the shortening has occurred. In other words, in order to destroy the 

 vitality of muscular tissue, it is not necessary to raise the temperature sufficiently 

 high to coagulate all its proteins, but that when one of the muscular proteins has 

 been coagulated, the living substance as such is destroyed ; the proteins of muscle 

 cannot therefore be regarded as independent units; the unit is protoplasm, and if 

 one of its essential constituents is destroyed, protoplasm as such ceases to live. 



Hans Przibram has attempted to classify the Animal kingdom on the basis of 

 the muscle-proteins ; his conclusions are based on the examination of only thirty 

 species of animals, ana may require revision in the future, but such as they are, they 

 are as follows : 



Invertebrates : paramyosinogen present ; myosinogen absent. 



Vertebrates : paramyosinogen and myosinogen both present. 



Fishes : in addition to these two principal proteids, soluble myosin and myo- 

 protein (in large quantities) occur. 



Amphibians : like fishes, except that myoprotein is only present in traces. 



Reptiles, birds, mammals : myoprotein is absent, and soluble myosin is only 

 present when rigor mortis commences. 



