CH. XIII.] CHEMICAL COMPOSITION OF MUSCLE 155 



precipitates, as the insoluble oxalate of calcium, the lime salts 

 essential for the coagulation process. In both cases the clotting is 

 produced by the action of a ferment developed after death. In both 

 cases the precursor of the solid clot is a proteid of the globulin class 

 which previously existed in solution. 



Fibrin in the blood-clot is formed from the previously soluble 

 fibrinogen of the blood-plasma. Myosin in the muscle-clot is formed 

 from the previously soluble myosinogen * of the muscle-plasma. When 

 the blood-clot contracts it squeezes out blood-serum ; when the 

 muscle-clot contracts it squeezes out muscle-serum. The muscle- 

 serum contains small quantities of albuminous material, together with 

 the extractives and salts of the muscle. The origin of the sarco- 

 lactic acid is a controversial question : some believe it originates from 

 the carbohydrate (glycogen and sugar) ; others think it comes from 

 the proteid molecules in the muscle. 



The general composition of muscular tissue is the following : 



Water . 

 Solids 

 Proteids . 

 Gelatin . 

 Fat 



Extractives 

 Inorganic salts 



75 per cent. 



25 



18 



\2 to 5 



0-5 

 1 to 2 



The proteids, as already stated, chiefly pass into the clot : very 

 little is found in the muscle-serum. 



The extractives comprise a large number of organic substances, 

 all present in small quantities, some of which are nitrogenous, like 

 creatine, creatinine, xanthine, and hypoxanthine : the rest are non- 

 nitrogenous namely, fats, glycogen, sugar, inosite, and the variety 

 of lactic acid known as sarco-lactic acid. The inorganic salts are 

 chiefly salts of potassium, especially potassium phosphate. 



The condition of dead muscle reminds one somewhat of contracted 

 muscle. Indeed, the similarity is so striking that Hermann has 

 propounded the idea that contracted muscle is muscle on the road to 

 death, the differences between the two being of degree only. He 

 considers that, on contraction, inogen (see p. 149) is broken up into 

 carbonic acid, sarco-lactic acid, and myosin; on death the same 

 change occurs, only to a much more marked extent. 



This idea is a far-fetched one, but it is a useful reminder of the 

 similarities of the two cases. In chemical condition, contracted and 

 dead muscle are alike, so far as the formation of acid products is 

 concerned ; there is, however, no evidence of any formation of a 

 muscle-clot (myosin) during the contraction of living muscle, as 

 there is in dead muscle. Then heat is produced in both cases, 



* For further details see small text at the end of this chapter. 



