71 



When all is in readiness close the connection by means of 

 the key by raising or lowering its lever. Or in other words 

 "making" or "breaking" the current. Gradually move 

 the secondary coil along the scale while making and break- 

 ing the current. The current is made when the connection 

 is complete and broken when the connection is interrupted. 

 N'ote at what point on the scale the first result appears and 

 whether it be from "make" or "break". Make a table 

 of your results as follows : In one column indicate the dis- 

 tance of the secondary coil from the primary. In another, 

 Response at Make, and the last column, Response at Break. 

 This is electrical stimulation in the form of single induction 

 shocks. 



(b) Remove the wires from the primary coil and connect 

 them with the sockets leading to the vibrating hammer. On 

 applying the electrodes to the nerve or muscle the latter is at 

 once thrown into a state of rigid spasm or continuous con- 

 traction called tetanus. Compare this tracing with that of 

 (a). This form of stimulation is known as the interrupted 

 current or repeated shocks. 



(c) Remove the induction coil and use only the battery 

 with its wires and the key. Make and break the current as 

 in (a). Notice that if the key be so arranged as to permit 

 the current to flow continuously through the nerve, no con- 

 traction occurs provided there be no variation in the intensity 

 of the current. Rapidly make and break the current by . 

 opening and closing the key ; a mere or less perfect tetanus 

 is produced. This is the constant current form of stimula- 

 tion. Scratch your name on the above tracings to identify 

 them. The tracings may be made permanent by drawing 

 the paper through a pan of shellac. 



