72 ruvtiioLouv OF MI^CLES AND M:I;\J;S. 



CHAPTER V. 



1. Chemical jiioo -M -s \villiin t lie muscle ; 2. (Jem-nil i"n of warmth 

 daring contraction ; :>. Kxliaiislimi ami HTKWTV ; 4. SMUIVC of 

 musde-i'iin -c : .".. l>r;itli <>f the muscle; C. Death-stiffening 



( /lii/i'l- 



1. Tlie relations just described between the elasticitv 

 and tlie work accomplished Ity the muscle have led us 

 to suppose that a inusdi- has. as it were, two natural 

 I'. TIMS, one convsj>ondin<r to its condition of rest, tin- 

 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 doin^ it contracts. This 

 is, however, rather a description than an explanation 

 of the fact of contraction, AH the muscle on contraction 

 is capable of raising weight, and thus of accomplishing 

 work, it is necessary to inquire how this labour is 

 etl'eeted. According to the law of the con>er\ation 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 proeeed \\itliin 

 the muscle (luring muscular contraction, while others, 

 \\hich pro.-ecd e\eii in the < | uie.-.ceiil muscle, are in- 

 creased in degree during this same contraction. The 

 tin chanical \\..rk must, therefore, be accomplished at 

 the cxpeii-e , ,f these chemical pree>st-s ; and it could 



