48 THE SIGNS OF LIFE [LECT. 



27. Polarisation. But I have been using the galvanometer 

 " at low power," much shunted, in the knowledge that the blaze- 

 currents in the main experiment would be very strong. And to 

 see whether or not there is any trace of response, a " high power " 

 of the galvanometer must be taken by unshunting it. Which 

 has now been done (and you notice by the way that an exact 

 compensation is a little more troublesome to effect), and I repeat 

 the test, right and left. There is just a trace of after-effect to 

 your left ( ) after excitation to your right ( + ), to your right 

 ( + ) after excitation to your left ( ) and this is not a physio- 

 logical response, it is only the ordinary polarisation counter- 

 current exhibited by any electrolyte. I will show it you in 

 more pronounced form with a couple of wires dipping in salt 

 solution, but not now after lecture, when I shall also test 

 these unpolarisable electrodes. 



28. Experiment IV. You have just witnessed the third 

 experiment in one form, demonstrating to you physiological 

 after-effects, and you will have no difficulty now in following 

 the steps by which I am about to make it in another form, to 

 demonstrate to you these same after-effects inclusive of their 

 earliest visible manifestations, which I have referred to as the 

 effects. I do not think that the distinctive words are justified 

 by any distinction of phenomena ; their use has, however, been 

 pressed upon me by the necessity of distinguishing between 

 the results of two methods. 



A fresh eyeball (that has just been tested by the assistant 

 and found to respond normally to light) is set up between elec- 

 trodes, and I intend to send through it and through the gal- 

 vanometer a break induction shock of suitable strength, first in 

 one, then in the other direction. The strength taken as suitable 

 is one that gives through a circuit of resistance equal to that 

 formed by eyeball electrodes and galvanometer, a distinct and 

 equal swing of the spot to the right and to the left, and that if 

 sent through the eyeball is fully adequate to arouse a normal 

 (positive) blaze. 



I now send a break shock through the eyeball (and galvano- 

 meter) in the positive direction, and you see the galvanometer 



