72 LABOR A TOR Y G VIDE IN PHYSIOL OGY. 



the positions of the secondary coil at that point in 

 the tracing. 



(5) Still leaving the short-circuiting key open make 

 and break the primary current as rapidly as it is pos- 

 sible to close and open the key in the primary circuit. 

 Take tracing. 



(6) So adjust the apparatus that the Neef hammer is 

 brought into the primary circuit, thereby making 

 and breaking that circuit with each vibration of the 

 hammer. Mount a fresh gastrocnemius, adjust the 

 kymograph for slow or medium rotation. 



Close the short circuiting key; close the key in 

 the primary circuit. The Neef hammer should start 

 to vibrating and continue to do so as long as the 

 primary circuit is closed. Start the kymograph. 

 After an abscissa a few centimeters in length has 

 been traced upon the drum, open the short-cir- 

 cuiting key. If the experiment is successful the 

 muscle will be tetanized. Allow the tetanizing cur- 

 rent to operate until a tetanus tracing several centi- 

 meters in length has been traced. Close the short- 

 circuiting key. 



After a few moments the muscle may be again 

 tetanized, and repeatedly so until exhausted. 



