X
Third
Paper on Animal Electricity
By
Sig. Don Alessandro Volta
24
November 1792
Two
weeks ago, on my arrival in Pavia, I got your letter of
22 October, where I was informed that the printer
Morelli of Milano would soon send me a copy of the
reprint of the Booklet by GALVANI, with some notes and a
Dissertation of yours.(a)
This book has not yet arrived but I have
been able to read the copy kindly lent to me by my
friend and colleague SPALLANZANI. I had the pleasure of
reading those notes and the Dissertation, which I found
not only erudite but also written with elegance.
Moreover, you paid too much honour to my little findings.
For that I very humbly thank you and also your most
learned and kind Uncle, Dr. GALVANI, for the regards as
well as for his appreciation of myself and my work.
§
1 I do not know whether You have seen and fully read two
papers of mine on animal electricity published in the Giornale
Fisico-Medico of Dr. Brugnatelli. GALVANI had not
yet delivered the last part of the second paper when You
published your Dissertation and the notes with the new
edition of the Commentary. In that part, I prove that
electricity, both artificial and animal, operates
directly on the nerves and on them only; that it is not
necessary for the electric fluid to flow through them up
to the muscles, much less that a discharge occurs
between nerve and muscle or between its internal and its
external face, as the praiseworthy Author believes. It
suffices that only the nerve be stimulated by the fluid
which can flow through only a small piece of it, in
order to excite the action of said nerve, so that it
produces by itself (in which way we confess we know not)
the contraction of the muscle; that, finally, the
electric fluid is not a non-mediated cause, even
as a stimulus, of muscular motion, but only a mediated
one, an occasional, remote cause, its proper action
being limited to stimulating and exciting the nerves. If
things are as just stated, and as the observations in my
quoted paper and many others contribute to proving, the
theory and the explanations of GALVANI that you are
trying to support, largely collapse and the whole
building is likely to fall down. The materials remain,
however, and these are the beautiful findings of his
original experiments, the new discoveries originating
from them. Yes, what remains are the materials for
another building, if not more beautiful, at least more
consistent, which it will be possible to build.
§
2 Among the many experiments showing that all depends on
the nerves and that, to obtain muscle contraction and
movement of an entire limb, it suffices that a weak
current of electric fluid invade a few points of the
controlling nerve, and only a portion, even a very small
portion thereof be included in its circuit, leaving
aside the rest of the nerve and in particular the muscle
or the dependant muscles. From the many experiments
showing this, I said, several were described in the
quoted second Paper from §§ 54 to 60. Permit me to
describe here some others of the same kind that appear
remarkable for their simplicity.
Let
us bare one (or both) of the crural nerves of a frog, or
the sciatic of a lamb (or of another animal), I touch
and squeeze the nerve with the edge of a gold or silver
plate e.g. with a coin. I see that nothing happens (by
chance some convulsion or movement of the limbs is
excited in the first moments when the bared nerve is
still so sensitive that it reacts to every touch or
shock, but very soon it doesn't give any sign when
touched or compressed in any way. Such is its state when
I attempt it in the ways that I am going to describe). I
touch or compress it with the edge of a blade of tin and
nothing happens. I touch it with the joined edges of
both blades and then very strong contractions of the leg
muscles are excited, and the leg trembles and writhes
furiously. Touching the tip of the tongue in the same
way a sharp taste is experienced, not felt at all when
touching with one or the other metal separately: I was
much surprised to learn that such an experiment was
reported by SULZER. Such tests on the nerves can be
varied in many ways, and one of the most beautiful is,
keeping the nerve compressed with the silver coin, to
apply to the latter a piece of tin or tin foil and slide
it over till it contact the same nerve: At the moment
when the double contact is reached, you will see violent
contraction of the muscles, being repeated if the
operation is repeated, or lasting as long as the double
contact is kept. The same happens with the taste
experienced in analogous experiments done on the tongue.
The spasmodic convulsions are at their maximum (showing
one of the strongest tetanus effects) if,
keeping one of the metals in a constant touch with the
nerve, the other one is detached for a short time and
then touches again, and this is done repeatedly with
some celerity. Instead of a single tin foil I often use
that kind of paper, improperly called "silver paper"
that is covered with a foil of tin (which, when really
bright and of good quality, usually behaves better that
a tag of ordinary tin), taking care that this foil
directly touch the silver blade or coin, as well as the
nerve (or the tongue, in the experiments thereon) being
touched by the gleaming tin foil, and not only by the
bare paper, as could happen if by chance this is not
properly bent. So in order to be safer, I obtain a
doubled paper by folding it so that that the metallic
side is all on the outside, and I apply it to the silver
coin in such a way that the bending (not sharp but
rather rounded) is against the nerve; so that then, by
sliding it down, the metallic foil touches at in several
points for better contact.
§
3 It is quite clear in all these experiments that only
the nerves are affected, moreover few points of them, in
the short passage traversed by the electric fluid from
the place at which the nerve touches the tin to the
other, very close by, where it touches the silver; and
that these metals are the cause of the electric current
because they are different: They are therefore in a
proper sense the exciters and motors,
while the animal organ and its nerves are only
passive. Now these nerves, excited in such a way by
the electric fluid, if they are those serving taste, on
the tip of the tongue, correspondingly arouse a
sensation of taste(b).
If, however, they are those directly influencing
muscular contraction, like the crural nerves, the
brachial, etc., according to their task these
contractions and movements will be excited. I say "excited"
not because the electric fluid flows to the flexor or
elevator muscles (this does not happen in our
experiments, since its flowing is limited, as just
stated and as it clearly appears, to only a very small
portion of those nerves) but by virtue and action proper
to those nerves that control all the muscles serving
voluntary movements in such a way that once those nerves
are stimulated, the muscles are also stimulated
accordingly to their irritability (though we do not
understand how this happens).
§
4. I have already said that I was not a little surprised
to find that experiencing of an acid taste on the tongue
has been known for some time, when on its tip both edges
of two blades, one of tin the other of silver, were
applied joined side by side. This experiment, reported
by SULZER more that 25 years ago(c),
was totally unknown to me, and I knew it fromYourself,
since in your Dissertation you mention it at § 21,
recalling almost the full text of the Author. Now this
amiable Swiss Philosopher and famous Academician of
Berlin whom I had the chance of knowing and of dealing
with in a friendly manner in the last years of his life,
in his metaphysical and physiological speculations had
totally different ideas and gave a completely different
explanation of the phenomenon, as can clearly be seen
from the cited text(d).
He did not even have any suspicion that the cause could
be the electric fluid moved by the contact of two
dissimilar metals flowing from part of the tongue
touched by one [metal] to the part touched by the other,
as I have discovered and demonstrated. On the other hand,
this was the only experiment known before my discoveries,
and performed in only that manner (since it was not
found to be changed), is one of the hundreds that I have
done in so many different ways. Nor did I start from
that experiment, as it seems that you suppose; on the
contrary, it was one of the last to which I came through
a series of many others suggested by the application of
my principles.
§
5 I started by fitting a large piece of tin foil to the
tip of my tongue, and putting further back on the flat
of it and close to its root, a silver coin. Making
communication between those metallic armatures by means
of an arc with a brass wire, or any other metal, a sharp
acid taste was excited on the tip of my tongue. This was
the first discovery, to which I soon added another
giving quite a different taste, harsh and burning, and
if not decisively alkaline, close to it, which is felt
(more difficult to detect, usually being very weak and
sometimes imperceptible) when the experiment is done
inversely, i.e. applying the silver to the tip and the
tin to the back [of the lower surface] or some other
part of the tongue. (e)
Now, considering that the brass
wire, or any other intermediate metal used as a
conducting arc, was not really necessary, since it is
possible to use for this task, i.e. serving as a
communication between the two armatures, one end of the
same silver strip, or one of tin foil, I used very soon
this easy arrangement in one or in the other form; or
e.g. applying to the back of the tongue the wide, convex
part of a silver spoon, and touching with its handle the
tin foil placed on the tongue’s tip; or bending around
the spoon the same tin foil, or so-called silver paper,
then applied to the tongue in such a way that the handle
was used only partially – or in other ways. Performing
the experiment repeatedly, I observed that having placed
one armature on the tip of my tongue, the other could be
placed even very close to the preceding one, on the
tongue or gum or inside a lip, touching in a few points
being sufficient. In conformity with what I had already
found, it suffices to use even very small armatures of
tin and silver as usual, or of other metals provided
they were different, placed on a nerve and even on the
bare muscle, being one close to the other. It suffices,
I say [to use] such very small and very close armatures,
placing between them a communication, mediated or
not-mediated, for exciting the contractions, etc. So,
then, even on the tongue the experiment of taste
succeeded very well using no matter how small a coin or
other small tag of silver, gold, copper or brass, and
touching any point of the tongue with the edge of these
little tin or lead armatures, covering similarly few
points at the tip of the tongue, and continuing this one
metal touched the other one. This suggested trying to
overlay a silver blade with a little ribbon of tin foil
or the usual silver paper, and having applied said
ribbon to the silver tag, either edge-to-edge or in a
transversal line, to put the tongue’s tip and pressing
it against the two metals on that edge line, so that
some points of the tongue could touch the tin, other
points the silver. The successful result corresponded to
expectation: i.e. I felt a sharp acid taste(f).
This is how I came, after a series of attempts, to
coincide with the old experiment reported by Sulzer.
This experiment, unique and isolated being unknown to
me, as I already said, could not give me any help.
§
6 You recognise, by citing this experiment, that I have
been led to mine, which are so much more extended, and
to the explanation of the same, totally different from
the old [explanation] by SULZER based on other
principles and conjectures. Anyway the real rationale
that pushed and guided me to such investigation is not
the one that you suppose, i.e. that nerves in touch with
conducting bodies emanate electric steam which, if
returned to the muscles to which it tends, excites some
contraction or impression. That we should look in the
human body for those nerves which, being almost at the
surface, could easily be armed with metal foil (such
nerves are provided by the tongue, etc.) No, this was
not my rationale, nor could it be, since, considering
the armatures, any time they are of different metals,
not as simple conductors but as true exciters and motors
of the electric fluid, I believed that animal organs
were only passive, and as the parts contiguous or
close to those armatures were dissimilar, that no
movement to the electric fluid could be given by them,
nor by the nerves nor the muscles. However, since metals
have their own proper virtue and force for pushing or
attracting the electric fluid, and one of them more than
the other and being of different species, e.g. tin and
silver, the armatures could break the natural
equilibrium and calm, and set the fluid in motion.
§
7 This seems [true] with no doubt at least for all those
experiments in which, as I discovered already many
months ago and published in the two papers cited,
muscular motion can be obtained even without baring any
nerve, by applying to single and even coupled muscles,
and even to two parts of the same muscle the dissimilar
armatures and immediately making them communicate
directly or with the interposition of a third metal. It
seems indubitable, I repeat, for all these experiments:
because in the others made with baring and isolating the
nerves in the GALVANI style, and then adding a
communication between them and the dependant muscles by
means of a conducting arc, it is yet undecided, and in
my opinion very dubious, that what You believe with the
cited Author happens in all cases is what happens
sometimes in the early moments, i.e. after preparation
when the vital forces are still at full strength, i.e.
that the flow of electric fluid causing the violent
muscular movement, derives really from a discharge of
the fluid that abounds either in the nerves or muscles
and tend naturally by its own strength to re-establish
balance. I say sometimes and in the early moments
when convulsions and movements are excited by even
touching, here the nerves and there the muscles, with
metals of the same species, and even touching sometimes
with a single metal. Then (after a few moments and
subsequently lasting much longer) it becomes necessary,
in order to get contractions and muscle movement, to use
different metals or dissimilar armatures. It must be
believed, and I consider it as certain, that the
electricity originates from these metals, and that
animal organs are here purely passive, as stated before.
Such is my constant opinion, for these cases and even
specimens with bared nerves, that in order to excite the
usual convulsions what is necessary is that the touching
metal must be different from the metal touching the
muscle. No matter about those very few cases where metal
and armatures seem similar; but perhaps they are not
entirely similar (I could make many remarks here, but I
will make them elsewhere). In all other cases without
exception muscular movements are obtained by applying
both armatures, always of different metals, to some
external part, without baring any muscle and without
arming separately nerve and muscle in GALVANI style. And
that was the situation until before the writing of my
second paper on animal Electricity, published
then in the June and July issues of the Giornale
Fisico Medico of Pavia.
§
8 It was, then, rather different rationale from the one
You ascribe[1] to me that led me to the new
experiments on the tongue; and it derived just by
analogy with previous experiments of mine, independently
from any explanation. I hope that it will not be
displeasing to You if I expose them as I did in a letter
written in French last August to Mr. Tiberio CAVALLO to
be presented to the Royal Society in London.
"Having
managed to excite tonic convulsions and violent movement
in the muscles and limbs not only of small animals but
also big ones, without baring any nerve, and through the
simple application of armatures of different metals to
muscles stripped of integument; I soon wondered if one
could not obtain the same results with man. I conceived
that those results could be obtained on amputated
members. But how to do those things on a complete,
living man? It would be necessary to remove the skin,
make a deep incision, take out maybe some flesh in the
places on which metal blades had to be placed, as I
often did in the fleshy parts of big animals. Happily it
came to my mind that we have in the tongue a bare muscle,
without skin covering its external parts, a very humid
muscle, very mobile and obedient to the commands of the
will. There are then all the conditions required for
exciting lively movements by means of the usual
different armatures. I then performed on my tongue the
experiment that I am going to describe.
Having
dressed the tip of the tongue and part of its upper face
with tin foil (so-called "silver paper" is
very suitable) I applied the convex part of a silver
spoon on the back of the tongue, and bent the spoon
until its handle was in contact with the tin foil. I was
expecting to see the tongue trembling, for that purpose
I was doing the experiment in front of a mirror. But the
trembling that I had dared to predict did not happen.
Instead, I had a sensation that I did not expect: it was
a very strong bitter taste on the tip of the tongue.
I
was surprised by that; but reflecting on the matter I
could easily understand that the nerves terminating on
the tip of the tongue have the function of taste and not
at all of movement of that muscle. It was quite natural
that the irritating power of the electric fluid, set in
motion by the usual arrangement of different metallic
armatures, here excited taste and nothing else. To
arouse the movements in the tongue which it is capable
of, it would be necessary to apply an armature close to
its root, where the nerves for exciting its movement are
situated. I was soon able to test this with the
following experiment.
I
cut out the tongue from a just recently killed lamb,
close to its root, and applied tin foil close to the cut
and a silver spoon to one of the surfaces. I then
established communication, as is necessary, between the
two metals. I had the pleasure of seeing the all tongue
tremble violently, in particular raising its tip, or
twisting from one side to the other. And this
every time I made the two metals communicate. I repeated
this experiment on the tongue of a calf; having covered
its root with tin foil, I put the tongue on a silver
plate as the second metal part. It worked with equal
success. I then repeated the same experiment with the
tongue of other small animals, such as rats, chickens
and rabbits, obtaining the effect almost every time. I
say ‘almost’, since sometimes it did not work on the
tongue of small animals, either because the tin foil
could not be applied properly and in the right place or
because the nerves for tongue movement could not be
reached, or because the tongue was already cold and had
lost its vitality, which does not last for a long time
in the muscles of warm-blood animals, particularly in
the tongue."
I
wanted to transcribe here this long quotation from that
letter in order to show you what I was thinking already
several months ago, and the direction followed in my
experiments which led me to new discoveries. Now I will
finish this letter, already too long, to tell you about
a little discovery of the past few weeks.
§
9 I have found that charcoal, already known as an
excellent conductor not inferior to metals, behaves like
them as an electricity exciter and motor, when used as
an armature, i.e. when conveniently touching animal
parts or any very humid body, or, even better, water
itself. What seems more striking is that charcoal is, in
relation to that virtue, not in the class of metals that
I have called inferior (comprising tin and lead, to
which I have subsequently added zinc); and not even in
the middle [class] where we find iron, copper, brass,
and also antimony, bismuth, and cobalt; but in the
superior class, comprising silver, gold, platinum and
mercury. With these goes charcoal, which is, moreover,
even better than all of them, even than silver, which I
had put on top. Consequently the sharpest taste felt on
the tongue is not obtained with tin and silver any more;
but with tin and charcoal (that must be perfect; since
not all pieces of charcoal taken at random succeed well).
The taste is as usual acidic if the tongue’s tip
kisses and presses the tin; alkaline, and very harsh and
burning if it kisses and presses the charcoal.
Conforming to this, charcoal is superior to silver, gold
and much more to the other metals, when used to excite,
instead of the taste on the tongue, the contractions and
the movements on the other voluntary muscles. In these
muscles and limbs, even truncated and detached (when any
vitality could be believed to be quenched), such
contractions and movements can be obtained much more
easily than taste, particularly the alkaline taste, on
the complete, living tongue. Such metals, even silver,
is inferior (and much inferior) to charcoal, as brass
and iron are inferior to gold and silver. This moreover
is proved by the fact that even the acid taste (though
weak) is experienced by touching the silver, e.g. a coin,
with the tip of the tongue, while a piece of charcoal is
placed on the back of the tongue, and it is moved until
it touches the coin. The same acid taste is felt, and
about the same strength, with brass and with iron when
used in the same manner as silver, etc.
Many
more things I have to tell you concerning your beautiful
Dissertation in Latin[2], as well as on other
experiments and observations. I will do it in one or
more letters to follow[3].
Meanwhile,
I am, etc.
[Translated
from Italian and French by Luigi Dadda, Politecnico di
Milano, October 2000] [Revised and completed by John
Coggan, Oxford University, March 2002]
