324 THE OUTGO OF ENERGY 



capillary electrometer. Let one observer watch 

 each meniscus, while a third experimenter 

 manages the polarizing current. Note the posi- 

 tion of each meniscus. Open the short-circuiting 

 keys. In each electrometer, the meniscus will be 

 displaced by the demarcation current. It should 

 be noted that the demarcation currents are of 

 opposite direction, flowing in the nerve from the 

 cross-section towards the lor gitudinal surface. 

 Make the polarizing current. 



When the polarizing current enters the nerve, 

 there will be a twitch in each electrometer, 

 caused by the negative variation of the demar- 

 cation current; this may be neglected. Each 

 meniscus will be displaced; on the side of the 

 anode of the polarizing current, the demarcation 

 current will be reinforced, but on the side of the 

 cathode it will be diminished. 



Thus the passage of the galvanic current 

 through a part of the nerve has polarized the 

 nerve on both sides of that part. The extra- 

 polar region on the side of the anode becomes 

 positive ; the extrapolar region on the side of the 

 cathode becomes negative ; similar changes prob- 

 ably occur in the intrapolar region. In short, an 

 electrotonic current is set up, having the same 

 direction as the polarizing current. This electro- 

 tonic current augments the demarcation current 



