ANIMAL ELECTRICITY. LECTURE V. 



Here is von FleischTs experiment. 



Fig. 49. 



Nerve, galvanometer, and secondary coil are in one 

 circuit. Without the nerve in circuit {i.e., with a short 

 circuiting- key down) I test for the direction of the make 

 and the break induction currents in the secondary coil 

 and galvanometer. The make deflection is to your 

 right, the break deflection is to your left, and, as you 

 see, the two deflections are equal and opposite, so that 

 if a series of rapidly alternating make and break 

 currents is passed through the galvanometer there is 

 no deflection. But when I open the nerve-key so as 

 to put the nerve in circuit, keeping up the alternating 

 currents, there is a deflection to your left, i.e., in the 

 direction of the break current. 



To what is this deflection due } Is it physical or 

 is it physiological ? It is in any case due to a polari- 

 sation counter current ; a few years ago I should have 

 answered that it is physical, not physiological, and I 

 might have illustrated the answer by reproducing^- the 

 experiment on a polarisation cell without any nerve at 

 all. But I should have had to take stronger currents, 



