132 EXTENSIBILITY AND WORK OF MUSCLE. [CH. xi. 



even in the body, and still more so after removal from the body, 

 when it begins to undergo degenerative changes culminating in 

 death, its elasticity is less perfect. The cohesion of muscular 

 tissue is less than that of tendon. E. Weber stated that a 

 frog's muscle one centimetre square in transverse section will 

 support a weight of a kilogramme (over 2 Ibs.) without rupture, 

 but this diminishes as the muscle gradually dies. 



The extensibility of any material may be studied and recorded 

 by measuring the increase of length which occurs when that 

 material is loaded with different weights. In Helmholtz' myograph 

 (fig. 140), different weights may be placed in the scale-pan beneath 

 the muscle, and the increase of length recorded on a stationary 

 blackened cylinder by the downward movement of the writing 

 point ; the cylinder may then be moved on a short distance, more 

 weight added, and the additional increase of length similarly 

 recorded, and so on for a succession of weights. 



If this experiment is done with some non-living substance, like 

 a steel spring or a piece of india-rubber, instead of a living 

 muscle, it is found that the amount of stretching is proportional 

 to the weight ; a weight = 2 produces an extension twice as 

 great as that produced by a weigh t= i ; in this way one obtains 

 a tracing like that seen on the left hand of figure 154, and the 

 dotted line drawn through the lowest points of the extensions is 

 a straight one. 



With muscle, however, this is different ; each successive ad- 

 dition of the same weight produces smaller and smaller incre- 

 ments of extension, and the dotted line obtained is a curve. 



A continuous curve of extensibility may be obtained by placing 

 a gradually and steadily increasing force beneath the muscle 

 instead of a succession of weights added at intervals. The most 

 convenient way of doing this is to use a steel spring, which is 

 gradually and steadily extended ; and the writing point connected 

 to the muscle inscribes its excursion on a slowly moving cylinder. 

 If, then, after the muscle has been stretched, the steel spring is 

 gradually and steadily relaxed, the muscle retracts and again writes 

 a curve now in the reverse direction, until it regains its original 

 length.* But in muscles removed from the body, unless they are 

 very slightly loaded, the return to the original length is never 

 complete ; the muscle is permanently longer to a slight extent, 

 which varies with the amount of the previous loading. 



* A mathematical examination of these curves shows that they are not 

 rectangular hyperbola, as they were once considered. They are very vari- 

 able in form and cannot be identified with anv knows mathematical curve. 



