METHODS OF ELECTRICAL STIMULATION 75 



be no static electrification. Further, the appear- 

 ance of positive and negative electricity during 

 the period of stimulation must be provided 

 against, especially if that period is at all pro- 

 tracted, for it must not be forgotten that the 

 bridge of nerve, which completes the secondary 

 circuit by uniting the two electrodes, possesses 

 very high resistance, and thus affords but an 

 imperfect closure of the ends of the secondary 

 wire. This provision is made by connecting the 

 positive electrode with the earth by a good con- 

 ductor, for example by a copper wire leading 

 from the electrode to the gas or water pipe 

 In case of doubt, a control experiment should 

 be made. The nerve should be severed between 

 the stimulated point and the muscle, and one 

 end laid on the other. Excitation through the 

 passage of a nerve impulse along the nerve is 

 thereby made impossible. If the muscle still 

 contracts when the nerve is stimulated above 

 the section, it is because of unipolar stimulation. 



An additional reason for care is that the insu- 

 lation of the secondary spiral is injured by leav- 

 ing the secondary circuit open while the hammer 

 of the indue torium is in action. 



It may be stated that the direction of the uni- 

 polar discharge is of importance. Excitation 

 takes place only where the positive charge enters 



