96 PRACTICAL PHYSIOLOGY 



a perfectly elastic body, equal. Also, as the weights are successively 

 removed, it will be found that the elasticity of rubber is more nearly 

 perfect. But, if the extension be great and of long duration, an 

 " extension-remainder " does appear and only gradually disap- 

 pears. 



Another method of demonstrating the same properties is to fix the 

 upper end of a muscle -preparation in the clamp of a simple myograph 

 and to attach its lower end to the lever by a bent pin. Attached to 

 the lever vertically below the muscle is a scale-pan or hook to which 

 weights can be suspended. The writing point of the lever is brought 

 on to the surface of a stationary smoked drum and a zero line 

 described by rotating the drum by hand. The drum is rotated 

 back so that the point of the lever is 5 mm. from the beginning of 

 the zero line, a weight of 10 grms. is attached to the lever, the muscle 

 will be extended and the writing point will record a new vertical 

 line on the drum. Turn the drum by hand so that the writing point 



FIG. 98. Curve of extensibility and elasticity of gastrocnemius. 

 The figures on the curve are weights in grms. Temp., 15 C. (A.P.B.) 



will describe a horizontal line 5 mm. long, 1 attach another 10 grms. 

 and repeat the process until 100 grms. or more are extending the 

 muscle. In the same way reverse the process and remove the 

 weights of 10 grms. one by one. If now the lower ends of the vertical 

 lines drawn by the fall and rise of the lever are joined, a curved line 

 will be formed, showing that the extension of the muscle becomes 

 less and less for each additional weight. Further, when all the 

 weights have been removed, the writing point will be below the 

 original zero line, showing an " extension-remainder " (Fig. 98). 

 It will also be seen that the line corresponding to the elasticity of the 

 muscle is a flatter and more gradual curve than that corresponding 

 to the extension ; this is caused by the long continued load impairing 

 the elasticity of the muscle. 



If the experiment be repeated on a piece of rubber band, the line 



1 By thrusting the points of a pair of fine forceps through a thin piece of 

 cork a means of measuring off equal distances is obtained ; there is a mm. 

 scale on the induction-coil. 



