LIVING TORPEDOS IN BERLIN. 535 



However that may be, the instance of internal adaptation to 

 which we have been now led, far surpasses all earlier ones in 

 ingenuity. It would certainly have demanded the profoundest 

 reflection of a clever brain, to hit upon the idea of making each 

 column as good a conductor for its own shock as any other animal 

 tissue can be, but comparatively a non-conductor for the current of 

 all other columns. In connexion with the extremely transitory 

 nature of the shock, it is not a little remarkable, that it is only 

 currents of extremely short duration that the organ conducts 

 irreciprocally. Of what service would it have been to the fish, if it 

 had become a perfect non-conductor for continuous heterodromous 

 currents also * ? 



15. Positive polarisation in its dependence upon the density of 

 the polarising current. A case of relatively positive polar- 

 isation by the heterodromous current. 



By the establishment of irreciprocal conduction, a foundation 

 hitherto wanting, has been gained for the investigation of the 

 phenomena of polarisation in the electrical organ, in one direction 

 at least. We no longer require to attribute a clearly quite incon- 

 ceivable strength to the relatively positive polarisation produced by 

 the homodromous current, nor an equally unaccountable transitoriness 

 in the first moments after opening the polarising circuit, which is 

 entirely at variance with its later persistence. From the circum- 

 stance that when the period of closure is lengthened, the homodro- 

 mous current is stronger than the heterodromous, we cannot draw the 

 conclusion which we held to be good in the first communication 

 (p. 456), on the assumption that there is no such thing as 

 irreciprocal conduction. Such conduction does exist, consequently 

 that superiority may be the result of it ; and as a further conse- 

 quence, it does not prove that positive polarisation and the shock 

 are different processes. 



1 It should be remembered, in regard to the history of the subject, that irreciprocal 

 conduction has been brought into connexion with the shock of electrical fishes once 

 before in a remarkable way. P. Erman's unipolar conductors, flame, soap, white of 

 egg, and other animal substances, in a certain degree of dryness presented the 

 earliest known instance of irreciprocal conduction. ' Noch frage man mich nicht,' 

 he says in his somewhat curious language, ' ob ich wohl am Ende zu glauben vermag 

 dass die erwahnte isolirende Eigenschaft der unipolaren Leiter . . . mit dem Me- 

 ohanismus der Spontaneitat der vorzugsweise sogenannten elektrischen Thiere einen 

 denkbaren Zusammenhang habe. Ich kann diese Frage zur Zeit nicht beantworten, 

 aber gestehen will ich dass ihrer Losung mein Augenmerk bei dieser Untersuchung 

 war.' Gilbert's Annalen der Physik, 1806, vol. xxii. pp. 44, 45. 



