58 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



terminology employed has not been uniform, and the facts so far 

 as they are known to us seem to be obviously incomplete. Ac- 

 cording to von Fiirth, two proteids may be obtained from mam- 

 malian muscle by extracting it with dilute saline solutions, namely, 

 myosin and myogen, the latter existing to three or four times the 

 amount of the former. Myosin belongs to the globulin group of 

 proteids (see appendix); it is coagulated by heat at 44 to 50 C, 

 it is precipitated by dialysis or by weak acids, it is easily precipi- 

 tated from its solutions by adding an excess of neutral salts, such 

 as sodium chlorid, magnesium or ammonium sulphate. With 

 the last salt it is completely precipitated when the salt is added 

 to one-half saturation or less. Its most interesting property, how- 

 ever, is that on standing at ordinary temperatures it passes over 

 into an insoluble modification which separates out as a sort of 

 clot. Following the terminology used for the blood, this insoluble 

 modification is called myosin fibrin. Myogen, the other proteid, 

 seems to fall into the group of albumins rather than globulins. 

 It is not precipitated by dialysis and requires more than half 

 saturation with ammonium sulphate for its complete precipitation. 

 It is coagulated by heat at a temperature of 55 to 65 C. Solutions 

 of myogen on standing also undergo a species of clotting, the in- 

 soluble proteid that is formed in this case being called myogen fibrin. 

 It appears, however, that in changing to myogen fibrin the myogen 

 passes through an intermediate stage, designated as soluble myogen 

 fibrin, in which its temperature of heat coagulation is as low as 

 30 to 40 C, the lowest temperature recorded for any proteid. 

 As was stated in the paragraph on muscle rigor, it is known that 

 frog's muscle goes into heat rigor at about 37 to 40 C, and in 

 accordance with this fact it is stated that this proteid, soluble 

 myogen fibrin, which is not present in mammalian muscle, occurs 

 normally in the muscle of the frog and also of the fishes. On the 

 basis of these facts the rigidity of death rigor is explained by as- 

 suming that both of these proteids exist in the living muscle, and 

 that after death they undergo a partial or complete coagulation 

 according to the following scheme : 



Mvosin. Mvogen. 



I I 



Myosin fibrin. Soluble mvogen fibrin. 



Myogen fibrin. 



In the dead muscle we should find, therefore, the insoluble 

 myosin fibrin and myogen fibrin, together with more or less of the 

 original myosin and myogen. Myogen is said not to occur in the 



