ANIMAL ELECTRICITY. LECTURE \T. I 39 



The Spot flies off scale to the rioht. I brino- it back 

 on scale by a considerable movement of the controlling 

 magnet, and when it' is steady, excite the nerve by 

 closing the key of the induction coil. The deflection 

 during excitation is to the right, i.e., the polarising 

 current is increased. 



This is precisely as you might have foretold, never 

 having seen the experiment before. The nerve 

 at e is anodic, zincable, and during excitation it gives 

 current from e to e\ i.e., with the polarising current. 

 You may perhaps express this in terms of positive and 

 negative, but by no means so clearly ; in fact this 

 simple matter under the title of " polarisation incre- 

 ment " is one of the well known posers of honours 

 examinations in physiology. But I should not advise 

 any candidate to say "zincable" to his examiner, I 

 only advise him to think '' zincable " in order to under- 

 stand the subject. 



Let us fix the matter by repeating the two experi- 

 ments with a reversed polarising current. 



In the first experiment (of the electrotonlc decre- 

 ment) p Is Kathodic ; the electrotonlc deflection 

 (Kat.) Is from right to left; during polarisation the 

 nerve is less Kathodic at e than at e\ i.e., less zincative 

 and more zincable at e, and during excitation there is 

 current in the nerve from e to e\ i.e., the electrotonlc 

 current is diminished. 



The second experiment (of the polarisation incre- 

 ment) is obviously the same whichever way you take it. 



