72 rilYSlOLOGY OF MUSCLES AND 2sEllVES. 



CHAPTER . V. 



1. Chemical procesaes within the muscle ; 2. Generation of warmth 

 during contraction ; 3. Exhaustion and recovery; 4. Source of 

 muscle-force ; 5. Death of the muscle ; G. Death-stiffening 

 {Rigor mortis). 



1. The relations just described between the ekisticity 

 and the work accomplished by the muscle have led xis 

 to suppose that a muscle has, as it were, two natural 

 forms, one corresponding to its condition of rest, the 

 other — a shorter form —corresponding to. its active con- 

 dition. Irritation induces the muscle to pass from one 

 form into the other, and in so doing it contracts. This 

 is, however, rather a description than an explanation 

 of the fact of contraction. As the muscle on contraction 

 is capable of raising weight, and thus of accomplishing 

 work, it is necessary to inquire how this labour is 

 effected. According to the law of the conservation of 

 energy, the labour so accomplished can only come into 

 existence at the expense of some other energy. Now, 

 it can be proved that chemical processes proceed within 

 the muscle during muscular contraction, while others, 

 which proceed even in the quiescent muscle, are in- 

 creased in degree during this same contraction. The 

 mechanical work must, therefore, be accomplished at 

 the expense of these chemical processes ; and it could 



