342 ELECTRIC FISHES I TORPEDO. 



excellent food), and to make the rivers they infest passable 

 to travellers. A number of wild horses are collected in the 

 neighbourhood, and are driven into the water ; the Gymnoti 

 attack these, and speedily stun them, or even destroy their 

 lives by repeated shocks ; but their own powers of defence 

 and injury are exhausted in the same degree, and they then 

 become an easy prey to their captors. 



421. The shock of the Torpedo (fig. 177) is less powerful; 

 but it is sufficient to benumb the hand that touches it. From 

 its proximity to European shores, this fish 

 has been made the subject of observation 

 and experiment more completely than the 

 other ; and some curious results have been 

 attained. It seems essential to the proper 

 reception of the shock, that two parts of the 

 body should be touched at the same time ; 

 and that these two should be in different 

 electrical states. The most energetic dis- 

 charge is procured from the Torpedo, by 

 touching its back and belly simultaneously ; 

 the electricity of the back being posi- 

 :DO> tive, and that of the belly negative. When 

 two parts of the same surface, at an equal distance from the 

 electric organ, are touched, no effect is produced ; but if one 

 be further from it than the other, a discharge occurs. It has 

 been found that, however much a Torpedo is irritated through 

 a single point, no discharge takes place ; but the fish makes 

 an effort to bring the border of the other surface in contact 

 with the offending body, through which a shock is then sent. 

 This, indeed, is probably the usual manner in which its dis- 

 charge is effected. If the fish be placed between two plates 

 of metal, the edges of which are in contact, no shock is per- 

 ceived by the hands placed upon them, since the metal is a 

 better conductor than the human body ; but if the plates be 

 separated, and, while they are still in contact with the opposite 

 sides of the body, the hands be applied to them, the discharge 

 is at once rendered perceptible, and may be passed through a 

 line formed by the moistened hands of two or more persons. 

 In the same manner, also, a visible spark may be produced ; 

 but this is less easily obtained from the Torpedo than from 

 the Gymnotus. As to the uses of the electrical organs to the 



