Though the power of the torpedo cannot be compared with that of the
gymnotus, it is sufficient to cause very painful sensations. A person
accustomed to electric shocks can with difficulty hold in his hands a
torpedo of twelve or fourteen inches, and in possession of all its
vigour. When the torpedo gives only very feeble strokes under water,
they become more sensible if the animal be raised above the surface. I
have often observed the same phenomenon in experimenting on frogs.
The torpedo moves the pectoral fins convulsively every time it emits a
stroke; and this stroke is more or less painful, according as the
immediate contact takes place by a greater or less surface. We
observed that the gymnotus gives the strongest shocks without making
any movement with the eyes, head, or fins.* (* The anal fin of the
gymnoti only has a sensible motion when these fishes are excited under
the belly, where the electric organ is placed.) Is this difference
caused by the position of the electric organ, which is not double in
the gymnoti? or does the movement of the pectoral fins of the torpedo
directly prove that the fish restores the electrical equilibrium by
its own skin, discharges itself by its own body, and that we generally
feel only the effect of a lateral shock?
We cannot discharge at will either a torpedo or a gymnotus, as we
discharge at will a Leyden jar or a Voltaic battery. A shock is not
always felt, even on touching the electric fish with both hands. We
must irritate it to make it give the shock. This action in the
torpedos, as well as in the gymnoti, is a vital action; it depends on
the will only of the animal, which perhaps does not always keep its
electric organs charged, or does not always employ the action of its
nerves to establish the chain between the positive and negative poles.
It is certain that the torpedo gives a long series of shocks with
astonishing celerity; whether it is that the plates or laminae of its
organs are not wholly exhausted, or that the fish recharges them
instantaneously.
The electric stroke is felt, when the animal is disposed to give it,
whether we touch with a single finger only one of the surfaces of the
organs, or apply both hands to the two surfaces, the superior and
inferior, at once. In either case it is altogether indifferent whether
the person who touches the fish with one finger or both hands be
insulated or not. All that has been said on the necessity of a
communication with the damp ground to establish a circuit, is founded
on inaccurate observations.
M. Gay-Lussac made the important observation that when an insulated
person touches the torpedo with one finger, it is indispensible that
the contact be direct.
