342 ELECTRIC FISHES :—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 Zorpedo (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- — 
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 
Fig. 177.—ToRPEpo. 
