THE MUSCULAR SYSTEM. 269 



is to say, in an alteration in the degree of concentration of the 

 plasma with which the muscle is imbued, is perhaps to be 

 sought the principal reason for the readiness with which the 

 colour of the muscles is altered in disease. 



The muscles, although softer and more easily torn than the 

 tendons, possess, nevertheless, considerable tenacity, particularly 

 during life, and they have a certain degree of elasticity. 

 During life, as has been correctly remarked by E. Weber, even 

 when not under the influence of the nerves, they are not for 

 the most part in their natural form, but stretched, or in a state 

 of tension, and like harp strings in the same condition, exert 

 an elastic force. This is satisfactorily shown when the tendons 

 of the extensor muscles in an animal's limb which is strongly 

 flexed, are cut through, the nerves having been previously 

 divided, whereupon the tendons are very considerably retracted 

 (E. Weber). This tension of the muscles varies very much, 

 according to the position of the limbs. It is very slight when 

 the bodv is at rest with the limbs semiflexed, still less or even 

 wholly absent when a muscle falls into a state of repose after it 

 has acted powerfully upon the limb; greater, and manifested 

 in the greatest degree, when the antagonists of a muscle are 

 acting with all their force. According to Weber, the living 

 muscle, when in a state of inactivity, may be compared with 

 caoutchouc, seeing that, like that substance, they possess a very 

 great elastic extensibility; or, in other words, a slight but very 

 perfect elasticity, as may be readily perceived in the muscles 

 even of dead animals, which may be alternately stretched and 

 allowed to retract. Owing to their elasticity, the muscles 

 offer scarcely any hindrance to the movements of the limbs, 

 and in consequence of its perfect nature, they recover their 

 previous form and length even after the greatest possible 

 extension. This is exemplified in the stretching of the 

 abdominal muscles in pregnancy and in certain pathological 

 conditions. When the muscles are in a state of activity, their 

 elasticity alters in a very remarkable manner: 1. During 

 their contraction they become more extensible or less clastic, 

 on which account they exert a much less force by their 

 contraction than would otherwise be the case, had their 

 elasticity remained unchanged, and the same as in the 

 inactive condition. 2. The elasticity of the active muscle, 



