g to any muscle or limb of an animal, for
instance, the leg of a frog separated from the body. Touch the
bared nerve with a piece of zinc, and the muscle with a piece of
silver, and strong contractions take place the instant these
metals are brought into contact. The same effect may be produced
by placing a piece of silver on a larger piece of zinc, and
putting a worm or a leech on the silver; in moving about, the
instant it touches the zinc it is thrown into strong convulsions.

These phenomena have been clearly proved to be electrical; for by
a number of pieces of these metals, properly disposed, strong
shocks can be given, the electrometer can be affected, a Leyden
vial charged, the electric spark seen, and combustible bodies
inflamed.

Some animals likewise possess the power of accumulating this
influence in a great degree; for instanc the torpedo, and
electrical eel, which will both give strong shocks; and if the
circuit have a small interruption a spark may be seen, as was
shown by Mr. Walsh. On dissecting these fish, Mr. Hunter found an
organ very similar to the pile of Volta; it consists of numerous
membranaceous columns, filled with plates or pellicles, in the
form of thin disks, separated from each other by small intervals,
which intervals contain a fluid substance; this organ, like the
pile of Volta, is capable of giving repeated shocks, even when
surrounded by water.

It is not absolutely necessary to use two metals to produce the
galvanic phenomena; for if one side of a metal be made to oxidate,
while the other is prevented from oxidation, these appearances
will still be produced. It is not indeed necessary to use any
metal; for a piece of charcoal, oxidated in the same way, produces
galvanism; so does fresh muscular fibre, and perhaps any substance
capable of oxidation. The most striking circumstance in galvanism,
is, that it accompanies oxidation, and is perhaps never produced
without it. But oxidation is always going on in the body by means
of respiration and the circulation of the blood. We shall
afterwards find reason to believe, that the oxygen, received from
the atmosphere by the lungs, is the cause of animal heat, and
probably of animal irritability; and it is perhaps not
unreasonable to suppose, that the nervous influence or electricity
may be separated by the brain, and sent along the nerves, which
seem the most powerful conductors of it, to stimulate the muscles
to action.

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