212 SECONDABY ELECTROMOTIVE PHENOMENA IN 



density of current, or greater density but longer time of closure, 

 negative action follows in both directions, though weaker in the 

 direction of the shock. With greater current density and shorter 

 time of closure positive action appears, but is stronger in the 

 direction of the shock. As the shock in the electrical organ is 

 directed from the head to the tail we may describe the polarising 

 current in that direction as a descending one, and the one in the 

 opposite direction as ascending. Thus a purely negative after- 

 current often follows a momentary ascending current, though the 

 descending one generates a strong positive after-current. The 

 latter is distinguished by its longer duration from a shock of the 

 organ, however induced. While the shock deflects the needle in 

 the same way as a momentary volta-electric current, the positive 

 after-current actually holds it pressed against the stop for some 

 time. At the same time the primary current is also stronger in 

 the direction of the shock than in the opposite direction. From the 

 great electromotive force which the primary current must possess in 

 order to obtain positive polarisation, the electromotive force of this 

 polarisation is relatively considerable. As it will probably be a 

 long time before any one finds an opportunity of making such 

 experiments again, I will communicate a few particulars and a few 

 numbers to show what magnitudes we have to do with. 



I had already made polarisation experiments on the smallest of 

 the three fishes, sent to me by Goodsir, and which were killed on 

 the 23rd November, 1857, in which however the primary current had 

 not been observed. But I convinced myself, by their means, of the 

 agreement of the secondary electromotive behaviour of the organ 

 with that of muscle and nerve. For further experiments I used 

 strips of the organ of the largest specimen, which was 233 mm. 

 long. On the morning of the 1 2th of January the animal was found 

 dead, yet the organ still gave reflex shocks on irritation of the skin 

 with a forceps, so that a frog's leg, the nerve of which was applied 

 to the fish, contracted. As its death was unexpected, the necessary 

 galvanometrical apparatus was unfortunately not at hand. The 

 only available galvanometer had to be kept for the primary 

 current. The nerve multiplier was employed for the secondary 

 actions. It soon proved to be too sensitive ; but after the experi- 

 ment was begun with it, it could not be exchanged for another in- 

 strument without sacrificing the comparableness of the result 1 . Had 

 I then known the astonishing tenacity of life which the organ 



1 Gesammelte Abhandlungen, vol. ii. p. 718. 



