SECTION V 

 THE CHEMICAL CHANGES IN MUSCLE 



CHEMICAL COMPOSITION OF VOLUNTARY MUSCLE 



IT is impossible to speak with certainty about the chemical com- 

 position of any living tissue, since in the act of analysis we destroy 

 the life of the tissue ; all we can do in most cases is to find the proxi- 

 mate principles present in the dead tissue. But, by using certain 

 precautions, we may learn some interesting facts about the chemistry 

 of living muscle. Muscle of cold-blooded animals may be cooled 

 below C. without losing its irritability on re- warming, and therefore 

 we may say without its life being destroyed. If the living muscle of 

 frogs be frozen, then minced with ice-cold knives as finely as possible 

 and pounded in a mortar with four times its weight of snow containing 

 0-6 per cent, of common salt, and the mixture thrown on to a filter and 

 kept at a little over C., an opalescent fluid filters through. The 

 filters soon get clogged and therefore must be frequently changed. 

 Their temperature must not be allowed to rise over 2 or 3 C. This 

 fluid is called muscle-plasma. If its temperature be allowed to rise 

 to that of the room, it clots, and the clot soon contracts, squeezing 

 out a serum, just as in the case of blood- plasma. 



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

 tion takes place, however, it becomes distinctly acid, and this acidity 

 has been shown to be 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 con- 

 verted when clotting takes place into myosin. 



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

 tein constituent of the clot, which we have called myosin, is still a subject of 

 debate. Kiihne, 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), 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, 



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