l6o CHANGES IN MUSCLE. [CH. xin. 



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 . . . . -75 P er cent. 



Solids . . . . . 25 



Proteids . . . .18 



Gelatin . . . ) 



Fat | 2t 5 



Extractives . . . . 0^5 ,, 



Inorganic salts . . i 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 con- 

 tracted muscle. Indeed, the similarity is so striking that Her- 

 mann 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. 155) is broken up into carbonic acid, sarco-lactic acid, and 

 myosih ; 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, 

 and in both cases also the muscle is negatively electrical to un- 

 contracted muscle. 



Here, however, the analogy must end : for living contracted 

 muscle is irritable, dead muscle is not. Living contracted muscle 

 is more extensible than uncontracted muscle ; muscle in rigor 

 mortis is not so (see fig. 156, p. 134). 



