Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 2 - By Alexander Von Humboldt And Aime Bonpland.
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When A Leyden Jar Is Placed On A Wet Woollen Cloth
(Which Is A Bad Conductor), And The Jar Is
Discharged in such a manner
that the cloth makes part of the chain, prepared frogs, placed at
different distances, indicate
By their contractions that the current
spreads itself over the whole cloth in a thousand different ways.
According to this analogy, the most violent shock given by the
gymnotus at a distance would be but a feeble part of the stroke which
re-establishes the equilibrium in the interior of the fish.* (* The
heterogeneous poles of the double electrical organs must exist in each
organ. Mr. Todd has recently proved, by experiments made on torpedos
at the Cape of Good Hope, that the animal continues to give violent
shocks when one of these organs is extirpated. On the contrary, all
electrical action is stopped (and this point, as elucidated by
Galvani, is of the greatest importance) if injury be inflicted on the
brain, or if the nerves which supply the plates of the electrical
organs be divided. In the latter case, the nerves being cut, and the
brain left untouched, the torpedo continues to live, and perform every
muscular movement. A fish, exhausted by too numerous electrical
discharges, suffered much more than another fish deprived, by dividing
the nerves, of any communication between the brain and the
electromotive apparatus. Philosophical Transactions 1816.) As the
gymnotus directs its stroke wherever it pleases, it must also be
admitted that the discharge is not made by the whole skin at once, but
that the animal, excited perhaps by the motion of a fluid poured into
one part of the cellular membrane, establishes at will the
communication between its organs and some particular part of the skin.
It may be conceived that a lateral stroke, out of the direct current,
must become imperceptible under the two conditions of a very weak
discharge, or a very great obstacle presented by the nature and length
of the conductor.
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