THE THEORY OF ELECTRIC ORGANS 265 



the positive A'. We may next take a flat strip of lead, of 

 which the lower surface B is brominated. 1 On mechanical 

 stimulation of both surfaces by vibration it will now be 

 found that the resultant responsive current flows across the 

 strip, from the negatively- responding B to the positively- 

 responding A (fig. 1 66). It will be seen that here as the 

 molecular disturbance 

 on which excitation 

 depends is caused by a 

 non-electrical form of 

 stimulus the electrical 

 character of the response 



obtained is unexcep- FIG. 166. Flat Strip of Lead, of which 



tional in its freedom lower Surface is Brominated 



from any Complication Response of upper surface positive, of lower 

 * surface negative. Resultant response 



by the polarisation- from lower to upper. 



factor. 



Let us next consider what would be the effect of sending 

 induction shocks across such a strip. If inorganic bodies 

 be really inexcitable, then we can here obtain only the 

 counter-polarisation current as the after-effect. That is to 

 say, on sending a shock from below to above in an ascending 

 direction, we should observe only negative polarisation as 

 an after-effect, or a descending current from above to below. 

 A descending shock should, on the other hand, give rise to 

 an ascending after-current. But if inorganic substances 

 should prove to be excitable, and if B were to become on 

 excitation relatively negative to A, as we found in the 

 experiments on mechanical stimulation, then, whatever the 

 direction of the shock, we should have a uni-directioned 

 response, from below to above, exactly like the excitatory 

 discharge of the electrical organ of Torpedo, from the ventral 

 surface to the dorsal. 



1 In order to brominate this surface as required, it may be held exposed to 

 vapour of bromine. Or an electrical deposit may be made by electrolysis, in a 

 bath of potassium bromide solution. A certain depth of deposit and time of 

 formation are important to the successful preparation of the plate. When these 

 are secured, the proper condition of responsiveness is found to be long-enduring 

 as will be seen from the photographic records. 



