436 LIVING TORPEDOS IN BERLIN. 



before me undertook so many times iodide of potassium electrolysis, 

 both with Gymnotus and Torpedo, should have mentioned the 

 secondary spot not even Faraday, who made use of this means for 

 the purpose of studying- in the fish the distribution of tensions. 

 Perhaps in Gymnotus the shock is too strong 1 to allow the formation 

 of the secondary spot. Even Sachs, on whom I pressed the clearing 

 up of this point, failed to obtain the secondary spot in Gymnotus 1 . 



I was extremely curious to see what the result would be of my 

 experiments on Torpedo. Nothing being- needed for the experiment 

 except the iodide of potassium electrolyser and the frog-alarum, I was 

 able, through the kindness of Dr. Hermes, to undertake it as early 

 as the summer of 1881 in the Berlin Aquarium (see p. 418). Since 

 then I have often repeated it, and without exception have always 

 seen the secondary spot, very black and at the moment of its appear- 

 ance sharply defined, and I have also shown it to several other 

 observers. In the first instance the electrodes applied to the fish 

 were merely a couple of zinc plates, but afterwards the dorsal and 

 ventral shields above described were used. It need not be said that 

 care was taken that they should be homogeneous. The spots only 

 appeared at the moment when the frog-alarum struck. Both spots 

 seemed to me to be fainter than in the case of Malapterurus. 

 I endeavoured by the use of platinum electrodes to make the 

 secondary spot the larger of the two. In this I was not successful, 

 although the spot was brought more distinctly into view. It was, 

 however, easy to hinder the formation of the secondary spot by 

 means of the frog-interrupter. An overweighting of 30 grammes 

 delayed the opening of the circuit sufficiently to permit the forma- 

 tion of a primary spot, which was not appreciably smaller, without 

 any secondary one. If the frog-interrupter was partly short 

 circuited the secondary spot reappeared with the next shock. 



Thus as regards the matter in hand all is clear with regard to the 

 Torpedo, and the only obscurity which remains is why the secondary 

 spot escaped the observation of all earlier observers, and especially 

 of Matteucci, who led off with platinum electrodes as well as with 

 platinum points, by which means the secondary spot is certainly 

 strengthened if not always made the stronger of the two. I cannot 

 imagine that the Torpedo-shocks by which John Davy and Mat- 

 teucci decomposed iodide of potassium, exceeded in strength the 

 powerful shocks of my Malapterurus to such an extent that the 

 secondary spot did not appear in consequence of the larger quantity 

 1 Untersuchungen, p. 163. 



