CHAPTER III. 



Kecord of muscular contraction (muscle- 

 twitch). Muscular contractions are recorded 

 upon a metal drum covered with highly glazed 

 paper, and caused to revolve by clockwork, or some 

 other form of motor, at a regular rate. With a drum 

 of six inches diameter one revolution in a second 

 is a convenient speed. The glazed paper is 

 blackened by holding a gas flame against it while 

 the drum is revolving. The paper must fit evenly 

 and tightly, or it will become burnt. 



The contraction of the muscle is amplified by a 

 lever (myograph lever), which may be straight, but 

 which may also very conveniently take the crank 

 form (Sanderson's myograph). In this form of 

 myograph the lever is fixed at the end of a frog- 

 cork, to which the muscle is fastened by a pin 

 passed through the knee joint ; the tendon is 

 attached to the short arm of the lever by means of 

 a thread and hook. The lever should be weighted 

 with a ten-gramme weight, attached to it near the 

 fulcrum, and should be so adjusted that when nearly 

 horizontal, but with the point a little lower than 

 the fulcrum, the muscle is stretched by the weight 

 and the connecting thread is taut. Arrange the 

 drum in the primary circuit of the induction coil 

 (Fig. 26), so that, as it revolves, a pin which pro- 



