366 THE MUSCLE-TISSUE. 



While this procedure is applicable in the case of mammalian 

 muscle-tissue in general, special precautions are necessary if the 

 muscles of the lower animals are to be studied. In the frog, for 

 example, the tissue, after removal of the blood, must be frozen in 

 a gradual manner, after which the entire process is continued at 

 a temperature below 3 C. A snow-like mass is finally obtained, 

 which melts at 3 C. 



The color of the muscle-plasma varies with the color of the 

 muscles from which it has been obtained. In the case of the dog it 

 is of a brownish color, in rabbits it is yellowish red, and in frogs 

 a light yellow. The particular shade of color, as will be seen later, 

 is a direct expression of the degree of functional activity of the 

 individual muscles, and is in part due to haemoglobin and in part to 

 certain lipochromes. 



The reaction of the plasma is neutral or slightly alkaline. 



On standing for a length of time mammalian muscle-plasma 

 gradually undergoes a process of coagulation, but it is to be noted 

 that the coagulum which separates out is slight in amount. In 

 the case of the frog, on the other hand, the entire bulk of the 

 plasma becomes gelatinous, and, in contradistinction to the mam- 

 malian plasma, this process begins at a temperature of C. As in 

 the case of the blood-plasma, the coagulum gradually contracts, and 

 the liquid which remains is spoken of as muscle-serum. The reac- 

 tion is then acid. The substance which composes the clot is termed 

 my og en-fibrin. The behavior of muscle-plasma is thus quite simi- 

 lar to that of blood-plasma, and here, as there, the resulting fibrin 

 is derived from an albuminous substance which was previously pres- 

 ent in solution. This substance is termed myogen. In addition 

 the muscle-plasma contains another albuminous body, myosin ; and 

 it appears from the researches of v. Fiirth that these two substances 

 are the only soluble albumins which are contained in muscle-tissue, 

 if we disregard a variable amount of a soluble myogen-fibrin, which 

 is itself a derivative of myogen. 



Myogen. Isolation. Myogen is most conveniently obtained 

 from muscle-plasma after the myosin has been removed by the 

 previous addition of ammonium sulphate to the extent of 28 per 

 cent. The resulting precipitate is filtered off and the filtrate saturated 

 with the same salt in substance. The myogen is thus thrown down 

 together with the soluble myogen-fibrin. It is washed with a satu- 

 rated solution of ammonium sulphate, dissolved in water, and freed 

 from the soluble myogen-fibrin by heating to 40 C., when this is 

 transformed into the insoluble form and is filtered off. The remain- 

 ing solution contains the myogen in pure form. 



In its general properties it resembles the albumins proper, in con- 

 tradistinction to the globulins. It is soluble in water, and can be 

 precipitated by alcohol, by salting with ammonium sulphate, sodium 

 chloride, and magnesium sulphate. The two latter salts, however, 

 do not cause a complete precipitation. Alcohol (92 per cent.) 



