When the torpedo is placed on a metallic plate of very little
thickness, so that the plate touches the inferior surface of the
organs, the hand that supports the plate never feels any shock, though
another insulated person may excite the animal, and the convulsive
movement of the pectoral fins may denote the strongest and most
reiterated discharges.
If, on the contrary, a person support the torpedo placed upon a
metallic plate, with the left hand, as in the foregoing experiment,
and the same person touch the superior surface of the electrical organ
with the right hand, a strong shock is then felt in both arms. The
sensation is the same when the fish is placed between two metallic
plates, the edges of which do not touch, and the person applies both
hands at once to these plates. The interposition of one metallic plate
prevents the communication if that plate be touched with one hand
only, while the interposition of two metallic plates does not prevent
the shock when both hands are applied. In the latter case it cannot be
doubted that the circulation of the fluid is established by the two
arms.
If, in this situation of the fish between two plates, there exist any
immediate communication between the edges of these two plates, no
shock takes place. The chain between the two surfaces of the electric
organ is then formed by the plates, and the new communication,
established by the contact of the two hands with the two plates,
remains without effect. We carried the torpedo with impunity between
two plates of metal, and felt the strokes it gave only at the instant
when they ceased to touch each other at the edges.
Nothing in the torpedo or in the gymnotus indicates that the animal
modifies the electrical state of the bodies by which it is surrounded.
The most delicate electrometer is no way affected in whatever manner
it is employed, whether bringing it near the organs or insulating the
fish, covering it with a metallic plate, and causing the plate to
communicate by a conducting wire with the condenser of Volta. We were
at great pains to vary the experiments by which we sought to render
the electrical tension of the torpedo sensible; but they were
constantly without effect, and perfectly confirmed what M. Bonpland
and myself had observed respecting the gymnoti, during our abode in
South America.
Electrical fishes, when very vigorous, act with equal energy under
water and in the air. This observation led us to examine the
conducting property of water; and we found that, when several persons
form the chain between the superior and inferior surface of the organs
of the torpedo, the shock is felt only when these persons join hands.
The action is not intercepted if two persons, who support the torpedo
with their right hands, instead of taking one another by the left
hand, plunge each a metallic point into a drop of water placed on an
insulating substance.
