THE PROTEIN SUBSTANCES. 85 



of what is known will be given in the chapter on the blood. 



As a chemical substance fibrinogen is not known in per- 

 fectly pure condition, since to hold it in soluble form various 

 agents must be added to the blood. But the fibrin formed, 

 doubtless through ferment action, is easily obtained and its 

 properties are well established. As usually prepared it is a 

 white, elastic, stringy mass, insoluble in water, but somewhat 

 soluble in salt solutions. Like other proteins it undergoes 

 true coagulation through elevation of temperature or action 

 of various reagents. Fibrinogen, as prepared by salting out 

 from plasma at a low temperature, coagulates when warmed 

 to 56. Its specific rotation has been found only in presence 

 of salt or alkali and varies from []z = 36 to 53 

 according to the nature of the admixture or method of prepara- 

 tion. It undergoes digestion with the body ferments very 

 readily and has therefore often been used as a starting point 

 in digestion experiments. 



MYOSIN AND MYOGEN. The living muscle plasma contains 

 a number of protein substances, one of which, at least, possesses 

 the property of spontaneous coagulation as observed in the 

 solidification of the muscle after death. At one time the term 

 myosin was applied to this body and it was supposed to be very 

 simple in nature. Numerous investigations, however, have 

 shown that the chemistry of the muscle proteins is compara- 

 tively complex and that the results of experiments do not well 

 agree. In the older sense this myosin was assumed to be 

 derived from a preexisting body, myosinogen, in the living 

 muscle, much as fibrin is considered as derived from fibrinogen. 

 The solidified myosin behaves as a globulin, which may be 

 illustrated by the following experiment : 



Ex. Free muscle (round steak) as far as possible from traces of fat 

 and sinews, and then thoroughly disintegrate it by passing through a 

 sausage mill. Then wash it repeatedly with cold water until the latter 

 is no longer reddened, and the residue appears white. This is placed 

 in a ten per cent solution of ammonium chloride and allowed to remain 

 about a day, with occasional shaking. Myosin dissolves in the ammonium 

 chloride and is found in the nitrate when the mixture is filtered. Pour 



