160 GENERAL PROPERTIES OF LIVING TISSUES 



contraction when the cathode is on the central 

 side of the painted zone. Painting the cathodal 

 region directly also prevents excitation. 



The failure of the induction current to stimu- 

 late at the anode, on opening the current, is due 

 to the exceedingly brief duration of the induced 

 current ; there is not time for a sufficient anelec- 

 trotonic alteration in excitability. If the current 

 is shortened still more (if it be less than 0.0015 

 sec.), the cathodal excitation also disappears. 

 With very strong currents, however, opening the 

 current stimulates as well as closure. 



3. Additional evidence of polar action is 

 secured by connecting the electrodes with the 

 capillary electrometer through a closed short- 

 circuiting key. The meniscus is brought into 

 the field, the nerve is stimulated repeatedly 

 with maximal break currents, and then stimu- 

 lation is stopped, and the short-circuiting key 

 in the electrometer circuit opened. The menis- 

 cus will move in a direction indicating a higher 

 potential at the anode (positive anodal polariza- 

 tion current). 



4. Finally, it may be added that the galvanic 

 current may increase the stimulating effect of the 

 induced current as pointed out on page 80, but only 

 when the cathode of the induced current falls in 

 the cathodal region of the polarizing current. 



