CHAPTER XIV. 



MUSCLE-NERVE PHYSIOLOGY. 

 Chemical Composition of Muscle. 



THE muscles make up about one-half of the total body weight. The 

 principal substance which can be extracted from muscle, when examined 

 after death, is the proteid body, Myosin^ some of the reactions of which 

 have been already discussed, p. 116. This body appears to bear some- 

 what the same relation to the living muscle as fibrin does to the living 

 blood, since the coagulation of muscle after death is due to the formation 

 of myosin. Thus, if coagulation be delayed in muscles removed imme- 

 diately from recently killed animals, by subjecting them to a temperature 

 below 0Co, it is possible to obtain from them by expression a viscid 

 fluid of slightly alkaline reaction, called muscle-plasma (Kiihne, Halli- 

 'burton). And muscle plasma, if exposed to the ordinary temperature of 

 the air (and more quickly at 37-40 C.), undergoes coagulation much 

 in the same way as, under similar circumstances, does blood plasma, 

 separated from the blood corpuscles by the action of a low temperature. 

 The appearances presented by the fluid during the process are also very 

 similar to the phenomena of blood-clotting, viz., that first of all an in- 

 creased viscidity appears on the surface of the fluid, and at the sides of 

 the containing vessel, which gradually extends throughout the entire 

 mass, until a fine transparent clot is obtained. In the course of some 

 hours the clot begins to contract, and to squeeze out of its meshes a fluid 

 corresponding to blood-serum. In the course of coagulation, therefore, 

 muscle plasma separates into muscle-clot and muscle-serum. The muscle 

 clot is the substance myosin. It differs from fibrin in being easily soluble 

 in a 2 per cent solution of hydrochloric acid, and in a 10 per cent solu- 

 tion of sodium chloride. It is insoluble in distilled water, and its solu- 

 tions coagulate on application of heat. It is in short & globulin. During 

 the process the reaction of the fluid becomes distinctly acid. 



The coagulation of muscle plasma cannot only be prevented by cold, 

 but also, as Halliburton has shown, by the presence of neutral salts in 

 certain proportions; for example, of sodium chloride, of magnesium 

 sulphate, or of sodium sulphate. It will be remembered that this is 

 also the case with blood plasma. Dilution of the salted muscle plasma 

 will produce its slow coagulation, which is prevented by the presence of 

 the neutral salts in strong solution. 



It is highly probable that the formation of muscle-clot is due to the 



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