SECTION V 

 CHEMICAL CHANGES IN MUSCLE 



CHEMICAL COMPOSITION OF VOLUNTARY MUSCLE 



VOLUNTARY muscle consists of elongated cells, the muscle fibres being 

 embedded in a connective tissue framework, and, as in all cellular tissues, 

 proteins form its chief chemical constituents. The contents of the fibres 

 are semi-fluid and can be expressed from the finely divided muscle as a 

 viscous fluid known as muscle plasma. 



Muscle plasma is obtained in the following way. The living muscle of frogs is 

 frozen, minced with ice-cold knives and pounded in a mortar with four times its weight 

 of sand containing -6 of common salt. The mixture is then thrown on to a filter kept 

 at C. when an opalescent fluid filters through. The filters scon become clogged 

 and therefore must be frequently changed, and their temperature must not be allowed 

 to rise above 2 to 3 C. 



If the temperature of the muscle plasma be allowed to rise, clotting 

 takes place, the clot later on contracting and squeezing out a serum, as is 

 the case with blood plasma. 



The muscle-plasma is neutral or slightly alkaline. When coagulation 

 takes place, however, it becomes distinctly acid, and this acidity is due to 

 the formation of sarcolactic acid in the process. Arguing chiefly from 

 analogy with the blood-plasma, the muscle-plasma has been said to contain 

 a body, myosinogen, which is converted when clotting takes place into 

 myosin. 



The exact nature of the proteins in muscle-plasma, as well as of the protein con- 

 stituent of the clot, which we have called myosin, is still a subject of debate. Kuhne, 

 to whom we owe our first acquaintance with muscle -plasma, described the clot as 

 consisting of myosin, a globulin, soluble in 5 per cent, solutions of neutral salts, such 

 as NaCl or MgSO 4 , precipitated by complete saturation with MgSO 4 , and coagulated 

 on heating to 56 C. In the muscle-serum, obtained after separation of the clot, he 

 found three proteins, one coagulating at 45 C., one he called an albumate (i.e. a derived 

 albumen or metaprotein), and the third coagulating about 75 C., and apparently 

 identical with serum albumen. Halliburton extended these researches to the muscles 

 of warm-blooded animals. He described four proteins as existing in muscle-plasma, 

 of which two, paramyosinogen and myosinogen, gave rise to the clot of myosin. 



In no case, however, is it possible entirely to dissolve up the clot when once formed, 

 and it seems that the so-called solution in dilute salt solutions was merely an extraction 

 of still soluble protein in the meshes of the clot. Von Fiirth has shown that if the 

 muscles of a mammal are washed free of adherent lymph and blood, the plasma obtained 

 by extraction with normal salt solution contains only two proteins. These proteins 

 are extremely unstable, and are gradually transformed on standing into insoluble 



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