THE MECHANICAL CHANGES OF MUSCLE 219 



sent into the muscle or nerve, which contracts, and a curve is obtained 

 similar to that shown in Fig. 62. Since the rate of the pendulum is constantly 



K\ 

 FIG. 53. Simple form of pendulum myograph. 



varying throughout its course, it is necessary to have a tuning-fork, or time-marker 

 actuated'electrically by a tuning-fork, writing just below the muscle-lever. 



FIG. 54. Diagram of spring myograph, or ' shooter.' 



In the spring myograph, otherwise known as the trigger or shooter myograph 

 (Fig. 54), a smoked glass plate is also used. " The frame supporting the glass 

 plate slides on two horizontal steel wires. To make the instrument ready for 

 use, the frame is moved to one side, which compresses a short spring. When 



