54 PRACTICAL PHYSIOLOGY 



upper end of the preparation is rigidly fixed in a clamp and to the 

 lower end is attached by a short thread or pin a brass mm. scale, 

 having its zero at the bottom. The lower end of the scale has a small 

 tray to carry weights or a hole by which weights can be hooked on. A 

 pointer carried by a separate stand is placed opposite the zero of the 

 scale. A weight of 10 grms. is attached to the scale and the amount 

 of extension read off; then another 10 grms. is added and so on until 

 the load is 100 grms. or more. It will be found that the length to 

 which the muscle is extended is not proportional to the weight used, 

 but that, by each increase of weight the muscle is stretched rather less, 

 the greater the previous extension. By removing the weights one by 

 one the elasticity of the muscle is observed ; it is not complete ; for 

 when all the weights have been removed the muscle does not at once 

 return to its original length. An * extension-remainder ' is present, and 

 this is the more marked the more the muscle is fatigued by the degree 

 and duration of the extension. Therefore the observations should be 

 made as rapidly and on as fresh a muscle as possible. It is probable 

 that muscle in the body with its circulation intact is completely elastic. 



If the muscle is replaced by a suitable piece of rubber band and the 

 same observations are repeated on it, it will be found that the series of 

 elongations are more nearly proportional to the weights used, thus con- 

 forming nearly to Hooke's Law, which states that the successive 

 increments in length produced by equal increments of weight are, in 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 ' exten- 

 sion-remainder ' does appear and only gradually disappears. 



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



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. 



