CHAPTER XIV. 



THE MUSCULAR SYSTEM. 



The actual motive-power in the body, whether it be in the 

 moving of the skeleton, the contraction of the heart, or 

 the transport of the ingesta, is performed by the muscular 

 system. It is one of the largest systems in the body, 

 representing no less than 45 per cent, of the body weight. 

 The movement produced by the muscles of the skeleton, 

 heart, and intestinal canal is very different in nature ; the 

 skeletal muscles soon tire, the heart and visceral muscles 

 never tire. We find that muscles exist in two well-marked 

 classes — the striated or striped or voluntary variety, and 

 the unstriated or involuntary ; the red muscles represent 

 the voluntary or skeletal muscles, whilst the white repre- 

 sent the involuntary or visceral. There is, however, a 

 remarkable exception to this rule : the muscular fibres of 

 the heart, though quite involuntary, are both red and 

 striped. 



Composition. — Muscle when examined chemically is found 

 to consist principally of proteids and salts, in addition to 

 which may be found a small quantity of acid, glycogen, t races 

 of urea, and carbonic acid gas. J5y suitable precautions a 

 fluid can be obtained from perfectly fresh muscle termed 

 muscle plasma: this undergoes coagulation like blood, and 

 yields a clot termed myosin and a serum termed muscle 

 serum. Muscle plasma is a yellowish neutral or alkaline 

 fluid; after clotting and the formation of the muscle serum, 

 the latter is found to be acid. Myosin is a substance obtained 

 after the death of the muscle ; there is every reason to 



