420 LIVING TORPEDOS IN BERLIN. 



I 



3. Method of leading-off Malapterurus shocks into an 

 experimental circuit. 



By the term experimental circuit I designate as before a circuit 

 however arranged, whether continuous or otherwise, into which the 

 shock is led for the purpose of testing- any of its actions 1 . One of 

 the first problems in the experiment is obviously to arrange this 

 conduction as favourably as possible. When the animal is taken 

 out of the water this is not difficult ; but even when you have a 

 living animal at your disposal, it is undesirable to risk its life for 

 one observation ; moreover, fish that have been taken out of water 

 are usually so violent that it is disadvantageous to experiment 

 with them. It is therefore necessary to obtain a solution of the 

 problem which is applicable to animals which are still in the water. 



Faraday in his researches on Gymnotus used for this purpose 

 special arrangements. He applied to the fish two saddles of thin 

 copper, covered externally with indiarubber. The further these 

 saddles were apart from one another, the stronger was the derived 

 current. If very strong actions were required, he placed glass plates 

 on the bottom of the trough to which the indiarubber border of the 

 saddle was so attached, that the part of the fish grasped by it was 

 almost as completely insulated as if in the air 2 . Faraday does not 

 appear to have thought of insulating the fish between the saddles, 

 indeed, it would be hardly possible to apply a cover so as to enclose 

 the whole of so long and wriggling a fish. In consequence of the 

 great intensity of the Gymnotus shock Faraday's contrivance 

 answered for almost all purposes, it was, however, difficult to obtain 

 discharge shocks 3 . I was not able to recommend any better 

 arrangement to Dr. Sachs for leading off the shocks. The saddle 

 employed by him differed from that of Faraday in this respect, that 

 instead of being made of copper coated externally with indiarubber, 

 it was made of guttapercha lined with tin, after the model of the 

 leading-off plates which I used for the Malapterurus. On the left 

 side of the figure the lacquered strip of tin is shown which serves 

 to connect the lining with the leading-off wire. 



In working with the small and relatively weak Malapterurus, 

 I found that the application of the saddles to the ends of the organ 

 was insufficient, and that it was necessary also to insulate the fish 

 between the saddles from the water. This was easily effected by 



1 Gesammelte Abhandlungen, vol. ii. p. 612. a Loc. cit. p. 5. nos. 1758-1760. 

 a Loc. cit. p. 7. no. 1767, note 2. Comp. Untersuchungen, p. 158. 



