Having placed four gymnoti, of unequal
strength, in such a manner as to receive the shocks of the most
vigorous fish by contact, that is to say, by touching only one of the
other fishes, I did not observe that these last were agitated at the
moment when the current passed their bodies. Perhaps the current did
not penetrate below the humid surface of the skin. We will not,
however, conclude from this, that the gymnoti are insensible to
electricity; and that they cannot fight with each other at the bottom
of the pools. Their nervous system must be subject to the same agents
as the nerves of other animals. I have indeed seen, that, on laying
open their nerves, they undergo muscular contractions at the mere
contact of two opposite metals; and M. Fahlberg, of Stockholm, found
that his gymnotus was convulsively agitated when placed in a copper
vessel, and feeble discharges from a Leyden jar passed through its
skin.
After the experiments I had made on gymnoti, it became highly
interesting to me, on my return to Europe, to ascertain with precision
the various circumstances in which another electric fish, the torpedo
of our seas, gives or does not give shocks. Though this fish had been
examined by numerous men of science, I found all that had been
published on its electrical effects extremely vague. It has been very
arbitrarily supposed, that this fish acts like a Leyden jar, which may
be discharged at will, by touching it with both hands; and this
supposition appears to have led into error observers who have devoted
themselves to researches of this kind. M. Gay-Lussac and myself,
during our journey to Italy, made a great number of experiments on
torpedos taken in the gulf of Naples. These experiments furnish many
results somewhat different from those I collected on the gymnoti. It
is probable that the cause of these anomalies is owing rather to the
inequality of electric power in the two fishes, than to the different
disposition of their organs.
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. The fish may with impunity be touched with a
key, or any other metallic instrument; no shock is felt when a
conducting or non-conducting body is interposed between the finger and
the electrical organ of the torpedo. This circumstance proves a great
difference between the torpedo and the gymnotus, the latter giving his
strokes through an iron rod several feet long.
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.
