THE THEORY OF ELECTRIC ORGANS 



267 



In taking these responses to homodromous and hetero- 

 dromous shocks, the counter-polarisation-current is super- 

 posed upon the excitatory effect For this reason we see, 

 in fig. 164, that the homodromous response, in which 

 negative polarisation was an opposing factor, is smaller than 

 the heterodromous, in which polarisation conspires with the 

 excitatory current. We have seen, in our experiments on 

 the leaf-organ, that when this negative polarisation is 

 annulled by taking responses under equi-alternating elec- 

 trical shocks, successive responses, giving the true excitatory 

 effect, become equal. I 

 give here (fig. 168) a series 

 of responses of the pre- 

 pared lead strip, under 

 these conditions of equi- 

 alternating shocks, in 

 which they are seen to 

 have become equal, the 

 resulting responsive cur- 

 rent being from the lower 

 surface to the upper, as 

 before. 



Having thus demon- 

 strated in various ways 

 the nature of that funda- 

 mental condition, which 

 determines the excitatory discharge of the electrical organ, 

 we may next take other organs which are known to be 

 differentially excitable, and observe whether they also, 

 under electrical excitation, give definite uni-directioned 

 responses. 



The differential excitability of the upper and lower 

 surfaces of the pulvinus of Mimosa are well known. On 

 subjecting this organ, then, to equi-alternating electrical 

 shocks, I obtained uni-directioned responsive currents, their 

 direction being from the more excitable lower to the less 

 excitable upper half, of which a photographic record is given 



FIG. 168. Photographic Record of Re- 

 sponses to Equi-alternating Electric 

 Shocks at Intervals of One Minute in 

 Prepared Lead Strip 



Responsive Current as before from lower 

 to upper surface. 



