ON LIVING MALAPTERURUS. 



383 



they are soldered to the small copper plates in which the wires end. 

 These wires, after an insulated course, come to view (', s) at the 

 upper end of the handle. The cover is open before and behind in 

 order to leave the barbels and the tail free. 



In using this contrivance, one waits for the moment when the 

 fish is lying nearly across the experimental tub. The cover is 

 then held horizontally over it, until it settles in the most 

 favourable position, and is then quickly placed upon it. In 

 order that the air between the tinfoil lining and the fish may 

 escape, two holes are bored in the cover at its inner edge with a 

 hot punch. Almost at the instant that the cover touches the fish, 

 it gives a shock ; but as it is insulated in every direction excepting 

 where the head and tail are exposed, a considerable strengthening 

 of the discharge is produced, as the following experiment teaches. 



I prepared a cover, which differed from another intended for the 

 same fish in this respect, that the guttapercha wall between the 

 two lined ends was removed and was replaced by three glass rods. 

 The results in divisions of the scale were as follows : 



The insulation of the fish, by means of the cover, doubles therefore 

 the strength of the shock in the experimental circuit. The covers 

 would undoubtedly have worked still better, if they had also in- 

 cluded the tail. That the covers often enclosed the fish before it 

 discharged, is shown by the observation that when they were applied, 

 the frog-alarum not unfrequently remained inactive from the in- 

 sufficiency of the branch current in the excitation tube. If the fish 

 discharges, as it generally does, several times after the excitation, the 

 leading-off cover has also the advantage, that the following shocks 

 are sure to be led through the experimental circuit, whereas the fish 

 cannot be held firmly with the loose saddles, without hurting it. 



Between every two experiments, the cover is put in another tub 

 of water, in order that inequalities in the tinfoil linings may be 

 removed. They are not put in the same tub, because the fish is 

 thereby disturbed, and, probably taking the cover for another fish, 

 discharges frequent electric shocks at it (see above, p. 376). 



