CH. XIH.] HEAT RIGOR 157 



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

 it from the typical globulins ; e.ff., it is not precipitable by dialysing the salts away 

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



In mammalian muscle, soluble myogen-fibrin 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 proteid termed myo- 

 proteid 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 

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

 steps : the first step in the shortening occurs at the coagulation temperature of the 

 paramyosinogen (47-50 C.), and if the heating is continued, a second shortening 

 occurs at 56 C., the coagulation temperature of myosinogen. If, however, a frog's 

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

 soluble myogen-fibrin), 47, and 56. This work of Brodie's is especially valuable 

 because it teaches us that the proteids 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 proteids, but that when one of the muscular proteids has 

 been coagulated, the living substance as such is destroyed ; the proteids 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-proteids ; his conclusions are based on the examination of only thirty 

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

 are as follows : 



Invertebrates : para-myosinogen present ; myosinogen absent. 



Vertebrates : para-myosinogen and myosinogen both present. 



Fishes : in addition to these two principal proteids, soluble myogen-fibrin and 

 myoproteid (in large quantities) occur. 



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



Reptiles, birds, mammals : myoproteid is absent, and soluble myogen-fibrin is 

 only present when rigor mortis commences. 



Steyrer has recently stated that on prolonged tetanisation (in rabbits' muscle) 

 the amount of paramyosinogen diminishes, but when degeneration occurs after the 

 motor nerves are cut, the amount of this proteid increases. Such results must, 

 however, be accepted with caution until more satisfactory methods than those at 

 present in use are adopted for the estimation of the muscle-proteids. 



