STIMULATION OF MUSCLE AND NERVE 123 



Write now three other pairs of curves: one 

 while a galvanic current passes through the non- 

 polarizable electrodes in a descending direction 

 (cathode nearer the muscle) ; a second while an 

 ascending current passes (anode nearer the mus- 

 cle) ; and a third, after the galvanic current has 

 been some minutes broken, as a control. During 

 the writing of these curves measure the velocity 

 of the drum with the tuning fork as before. 



The speed of the nerve impulse will be found 

 to be greater than normal when the nerve im- 

 pulse starting at the second pair of metal elec- 

 trodes passes through an extrapolar cathodal 

 area (i. e. stimulation during descending current), 

 and less than normal when that region is made 

 anodal by reversing the galvanic current. In 

 other words, the conductivity of the nerve has 

 been increased by cathodal and diminished by 

 anodal stimulation. 



2. Conductivity is diminished by strong or pro- 

 tracted currents in the cathodal as well as in the 

 anodal region. Place two non-polarizable elec- 

 trodes upon the nerve about 3 cm. apart. Con- 

 nect them through a pole-changer with two dry 

 cells (Fig. 33). In the middle of the intrapolar 

 region place two stimulating electrodes close 

 together. Connect one of the stimulating elec- 

 trodes directly to the secondary coil of an indue- 



