ELASTICITY OF MUSCLE. 447 



stretch to the full extent the weight is capable of effecting, but a 

 certain time, which varies with circumstances, is allowed for its 

 complete extension. The rate of extension is at first rapid, then 

 slower, until it ceases. As a muscle loses its powers of contrac- 

 tion from fatigue, it becomes more easily extended. Dead muscle 

 has a greater but less perfect elasticity than living, i. e., it requires 

 greater force to stretch it, but does not return so perfectly to its 

 former shape. The importance of the elastic property of muscle 

 in the movements of the body is noteworthy. The muscles are 

 always in some degree on the stretch (as can be seen in a frac- 



FIG. 180. 





1. Shows graphically the amount of extension caused by equal weight increments 

 applied to a steel spring. 2. Shows graphically the amount of extension caused by equal 

 weight increments applied to an India-rubber band. 3. The same applied to a frog's 

 muscle. Showing the decreasing increments of extension, the gradual continuing 

 stretching, and the failure to return to the abscissa when the weigh't is removed. 



tured patella, the fragments of which remain far apart and cause 

 the surgeon much anxiety), and brace the bones together like a 

 series of springs, the various skeletal muscles being so arranged 

 as to stretch others by their contraction. When one muscle 

 for example, the biceps contracts, it finds an elastic antagonist 

 already tense ; this it has to stretch as it shortens. The triceps 

 thus acts as a weak spring, opposing the biceps, and it gently 

 returns to its natural length when the contraction of the biceps 

 ceases. By their mere elasticity the muscles are kept tense and 



