LESSON III. THE REVOLVING DRUM. THE 

 MUSCLE CHAMBER. NERVE MUSCLE PREPARA- 

 TION. LATENT PERIOD OF MUSCULAR CON- 

 TRACTION. 



1. The revolving drum. Tracings are taken on 

 smoked paper covering a revolving drum. The rate of 

 revolution can be varied in two ways: (1) by shifting 



the belt on two sets of pulleys, one on the shaft con- 

 nected with the motor, the other on the stand of the 



