IX
NEW
OBSERVATIONS
ON
ANIMAL ELECTRICITY
Communicated
by Dr. Cav. D. ALESSANDRO VOLTA
November
1792
Not
having yet fully finished the third Paper on Animal
Electricity, I want meanwhile to tell You and the Public
in advance about some new discoveries.
I
found that charcoal, well cooked, is an exciter and
motor of electricity as are metals. Moreover it stands
above all of them, even above silver that I had put on
top, so that the most vivid taste that can be excited on
the tongue is not with tin and silver but with tin and
charcoal. Equally, charcoal is much better than silver
and gold in exciting, instead of the taste on the tongue,
the contraction and motion of other muscles.
I
have also succeeded in exciting the sensation of light
with the same arrangement of the two dissimilar metallic
armatures used to excite taste. This is how I proceed: I
apply first to one eye bulb one extremity of a tin
ribbon (tin foil, improperly called silver paper, is
very effective). Then I put a silver coin or spoon in my
mouth. I then touch it with the other extremity of the
tin strip. This is sufficient, every time I renew the
contact, to create the sensation of a dim light or a
transient flash, which is more or less vivid depending
on the condition of contact of the two metallic
armatures, or the two eyelids being well closed, or on
being in a dark environment. This sensation is certainly
produced by the electric fluid going from the eye
surface, to which the tin is applied, to the back of the
eye and then to the silver pieces in the mouth; it flows
through the retina and a more or less lengthy section of
the optic nerve, so exciting it. The result of this
experiment improves if the tin is applied to one eye and
the silver to the other one, instead of placing it in
the mouth, so involving both retinas. But, in order to
avoid damaging such a delicate part as the eye, by
direct contact with the metals, I have tried to perform
this experiment in another way, and I succeeded with a
good, even better result by pressing a feather, well
soaked with tepid water, onto the eye and applying to it
the metallic part. I did the experiment in several other
ways, even replacing the silver with charcoal, with good
success. The first and most curious is to apply the tin
foil to the tongue and the silver tag to the feather
over the eye. With this arrangement we get, at the
closing of communication between both metals, two
distinct sensations, the first being the usual acid
taste on the tongue, the other one the brightness in the
eye.
I
have tried with similar arrangements to excite the sense
of smell and the sense of hearing, with no results up to
now.
From
all these experiments, where the sensation of light as
well of taste are excited, as in the majority of those
in which strong, lively contraction of muscles is
obtained, it is certainly not possible to derive
argument for true animal electricity proper to these
organs which appear purely passive. Instead metals are
active any time they are of different species or differ
for some other property, and, being suitably applied to
humid parts, move the electric fluid and, when
communication is established between them, they start it
circulating. I made experiments showing equally the
transport of electric fluid when two dissimilar metals
applied to bodies that are not at all animal but are
just humid, such as paper, leather, cloth soaked with
water and even better simply water. It just appears that
all is the effect of the contact of metals. In these
circumstances they are not simply carriers but true
motors and exciters of electricity, and this is a
capital discovery. It remains to be discovered whether
in some cases the muscular contractions and movements,
excited in animals prepared and tickled in Sig. GALVANI’s
way, can be attributed to electricity proper to animals,
to a natural imbalance of the fluid in them, as I, too.
used to believe in the beginning, but I have now serious
doubts. The more I go ahead with my experiments the more
these doubts increase, to the point that now I am
certain that the electric fluid can never be moved and
transported from one part of the animal to another by an
action proper to the organs or by any vital force, but
being determined and compelled by virtue of the impulse
received in the places in contact with metals. It is
then expelled from one part and attracted by the other
one. I am now, I say, certain about this, in particular
on observing that nothing, or almost nothing, is
obtained without the contact of some metals, more
precisely of two [metals] of different species or which
are in some way dissimilar, i.e. for hardness,
cleanliness, brightness, etc. I have then been driven to
conjecture that even when some convulsion or movement is
obtained through the contact of metals that look alike (such
a situation is very rare, and it occurs in the first
moment after the preparation, when the sensitivity of
the nerves is at its maximum) the effect, even in such a
case, is due to an imperceptible difference between the
metals.
If
things are such, what remains of the animal electricity
claimed by GALVANI and demonstrated by his beautiful
experiments? Nothing other than the prodigious
excitability of the nerves serving the sensations and
movements, especially voluntary ones, due to the
stimulus of the electric fluid set flowing by external
causes; which means a purely passive disposition with
regard to electricity that is external or artificial.
[The nerves] are excited like, let us say, simple
Electrometers; [they are] in effect Electrometers of a
new kind, incomparably more sensitive than any other
Electrometer.
[Translated
from Italian by Luigi Dadda, Politecnico di Milano,
October 2000 Revised by John Coggan, Oxford University,
March 2002]
*
See
previous translator’s notes
