t bodies, the phenomena
of electricity would seem to show, and some late experiments
render it by no means improbable, that this fluid or influence,
acts a conspicuous part in the nervous system. That it exists in
great quantity in animal bodies, is evident on gently rubbing the
back of a cat in the dark; and it would seem that, in some
instances, it may be given out or secreted by the nerves. We shall
afterwards see that the seat of vision is a delicate expansion of
a large nerve which comes from the brain, and is spread out on the
bottom of the eye; and flashes of light, or a kind of sparkling,
is often seen to dart from the eyes of persons in high health, and
possessed of much nervous energy. These luminous flashes are very
apparent in the dark in some animals; such as the lion, the lynx,
and the cat; and it is difficult to account for this appearance
unless we suppose it electrical.

The experiments of Galvani and others, have however proved beyond
all doubt, that this fluid, when applied to the nerves and
muscles, is capable of exciting various sensations and motions. To
produce this fluid by the application of two metals, it is
necessary that one of them should be in such a situation, as to be
easily oxidable, while the other is prevented from oxidation. If a
piece of zinc be put into water, no change will take place; but if
a piece of silver be put along with it, the zinc will immediately
oxidate, by decomposing the water, and a current of electricity
will pass through the silver. If the upper and under surfaces of
the tongue be coated with two different metals, one of which is
easily oxidable, and these be brought into contact, a sensation is
produced resembling taste, which takes place suddenly, like a
slight electrical shock. This taste may likewise be produced by
applying one part of the metals to the tongue and the other to any
part of the body deprived of the cuticle, and bringing them in
contact.

The sensation of light may be produced in various ways; such as by
applying one metal between the gum and the upper lip, and the
other under the tongue; or by putting a silver probe up one of the
nostrils, and a piece of zinc upon the tongue; a sensation
resembling a very strong flash of light is perceived in the
corresponding eye, at the instant of contact.

But the experiments which tend most strongly to prove what I have
hinted, are made in the following manner. Lay bare a portion of a
great nerve leadin