So you ask for a
prompt summary of the experiments I have made in the last eight
or ten days since I began work on Animal Electricity,
following the wonderful discoveries by Mr GALVANI,
of which I showed you a short demonstration this evening on a
few frogs, in the house of Count ANGUISSOLA.
You ask for this summary and you ask me to leave it here in
Milan before I leave for Como. Here is what I have been able to
draw up in a great hurry.
ACTION
OF ARTIFICIAL ELECTRICITY ON THE MOTION OF MUSCLES THROUGH
NERVES.
Very weak electricity
is sufficient to shake and drive into convulsions a whole,
living frog, and particularly its hind legs, driving the
discharge i.e. the course of the electrical fluid, from the head
to the feet or vice versa - the charge of a small Leyden flask,
reaching 4 or 5 degrees on the HENLY electrometer, or Quadrant
electrometer, is sufficient.
Having decapitated
the frog and driven a needle or small metal hook into spinal
column, then a smaller charge is enough, e.g. 1 or 2 degrees on
the same electrometer, driving the weak electrical flux from the
backbone to the feet, or vice versa.
Having severed the
whole body of the frog and kept only its hind legs attached to
the backbone or to a section of it by the (carefully isolated)
crural nerves, far weaker electricity, not detectable by the
quadrant-electrometer but only by the very sensitive jar
electrometers by CAVALLO, BENNET
and myself (or even undetectable by them), produces the
usual effect and also strong contractions of muscles, tonic
convulsions and spasms, which often exhibit a true tetanus.
Finally, having
covered that backbone section and (which is very useful) also a
section of the nerves with thin metal foil, the muscles react
prodigiously to electricity which is almost undetectable even by
the BENNET electroscope, the most
sensitive one (made of two small strips of very thin gold or
silver leaf). They react to a charge from the Leyden flask which
hardly reaches one tenth of a degree on that electrometer. To
detect that charge and to measure it, my Condenser is
required.
Consequences
All these experiments
show the role of the nerves and how the frog’s muscles are
easy to contract (and also those of other animals, since similar
effects are observed) in response to electrical stimulus.
Given such influence,
which cannot be questioned, it is easy to understand how
different frog preparations contribute to making it more and
more sensitive to very weak electricity. This occurs in
proportion as the electric fluid follows better (and more
contained) the path of the nerves.
Indeed, since such
fluid is divided into as many different paths as provided by the
different parts of the body (integuments, vessels, humours,
etc.), which are also deferent [conductive], less fluid
goes through the nerves to the leg muscles, so that they react
only to electricity of moderate force.(1)
Having cut off the
head and driven the needle into the spinal cord, the electric
fluid goes more directly to the muscles of the legs through the
said nerves, and less is diverted. Therefore, weaker electricity
produces the effect. (2).
Leaving only the
backbone, or a section of it with the crural nerves, only these
nerves are available to communicate to the leg muscles, and thus
very weak electricity, of which none is dispersed through other
conductors (3).
Finally, having
applied the metal plate or foil to the spine and the
afore-mentioned foil to the nerves (34), further weak
electricity is sufficient: Indeed, since such foil provides a
very perfect conductor at many points of the spine and nerves,
which are not sufficiently deferent (good conductors) in
themselves, it makes the flow easier for a large dose of
electrical fluid.
SPONTANEOUS
ANIMAL ELECTRICITY WHICH APPERTAINS EVEN TO SEVERED LIMBS WHILE
SOME VITALITY LASTS
Such electricity,
which is peculiar and native to Animals, not external nor
introduced from outside, is observed especially in frogs
prepared in the above-described manner (3.4.). By the very
artifice of isolating nerves and coating them with metal foil,
there is observed in other animals, not only cold-blooded but
also warm-blooded, there is observed, I say, this native animal
electricity, in the form of the rising of the muscle itself,
contractions, convulsions and spasms, which have been observed
to be produced by artificial electricity, without really
employing it, either weak or strong, but simply by establishing
communication between electrical conductors, especially
metal ones, not interrupted by any non-conductor between
muscle and nerve.
And since that conducting
arc really possesses neither more nor less than its natural
dose of electrical fluid, it cannot give or take anything from
the animal (prepared or not) which equally possesses its natural
dose of fluid uniformly distributed (i.e. balanced between its
parts). If, then, such a conducting arc (made for example of a
piece of folded, C-shaped metal wire), applied to the muscle on
one side and the nerve on the other, gives motion to the
electrical fluid and gives rise to said convulsions, it is
evident that such fluid is somewhat unbalanced between those
parts of the animal, and that the conducting arc, or discharger,
acts so as to repair such imbalance, since this is its proper
and sole duty. In a word, such an arc cannot force the electric
fluid to motion, if it does not tend to move; it can only
provide a path for it.
For the freshly
prepared frog, and as long as its vital strength is fully
present, it is possible to include in the circuit, i.e.
to include in the conducting arc, also non-perfect
deferents, such as a body of water, one or more people, and even
bodies which are known as very bad conductors, such as a wooden
or marble table, somewhat moistened, a carpet, part of the floor,
of the wall, etc. Only true non-conductors, i.e. glass,
resins, silk, etc., avoid the discharge and then prevent the
effect of convulsions.
As the strength of
the animal or of the severed limbs dies down (i.e. shortly after
preparation), bad conductors (stones, walls, wood, cloth, etc.)
have the effect that they reduce or delay the free course of the
electric fluid, coming from one of the two parts of the animal
(and which tend to pass from nerves to muscles, or from the
latter to the former) so much that muscle contraction no longer
takes place. For that to happen, a prompter, quicker movement,
the violent incursion (violent, I mean, in proportion) of such
electric fluid is required.
Later such a course
is obstructed, or very much delayed (and thus convulsions do not
arise), even by passably good conductors, such as two or more
people holding hands, then even a single person, and then water
itself. Finally the experiments do not succeed but with
conducting arcs that are wholly polished and clean, and with
very well-fitted metal armatures, and somewhat extended ones, on
the muscle and nerve, but especially on the nerve.
GENERAL
RESULTS OF THESE EXPERIMENTS ON INTRINSIC ANIMAL ELECTRICITY
The frog prepared
as explained (3.4.) behaves in the same way as a Leyden
flask.
However, its charge
(supposing it can be so defined) is so weak that it cannot be
detected even by the most sensitive jar electrometer, since it
does not reach one tenth of a degree, and perhaps not even 5
or 6 hundredths of a degree on my own thin straw electrometer.
Assuming that
charge, which implies, as is well known, an excess on
one side and correspondingly a shortage on the other, I
maintain that, on the side of the nerves or inside the muscles
where they terminate, there is the shortage and in the
most external parts of said muscle there is an excess.
This fact, which
could not be discovered by means of any electrometer, even the
best, because of the extreme weakness of such electricity, was
discovered by me by another means. I thought that by employing
very weak charges, it would not be negligible which part of
the flask I would apply to the nerve and which to the muscle:
that where there is the excess or that where there is the
shortage; because approaching two flasks by the homologous
parts, i.e. excess to excess, shortage to shortage, both
discharges are prevented, whereas they trigger each other when
the opposite electricities are made to approach. Now, then,
after performing the experiment several times, I have noticed
that if the part of the flask which touches the nerve is
positive, or plus, a charge of 5 or 6 hundredths of a
degree on my thin straw electrometer is sufficient to produce
convulsions; on the other hand, if it touches the muscles, and
the nerve corresponds to the negatively charged part, or minus,
20, 25, 30 hundredths of a degree on the same electrometer are
not sufficient. So I have concluded that the nerve presents
negative and the muscles positive electricity.
Whatever the
analogy claimed with the Leyden jar, what is directly proved
by my experiments is that an extremely weak electric force is
sufficient to produce the effect of convulsions, if it is
applied so that the electric fire is drawn out of the exterior
of the muscles and is pushed into the nerves; and that, on the
other hand, if it is drawn out of the nerves and taken to the
exterior of the muscles, the electric force that is required
to give rise to the same convulsions is, though still weak, at
least four times larger than the previous one. Then, even when
no artificial electricity is employed, but the electricity of
the organ is released by the mere application of the
conducting arc, if this intrinsic electricity is, as
everything shows, very weak and yet it excites convulsions, it
must be concluded that here the direction of the fluid is the
same that produces such effects by the minimum force, i.e.
from the muscle to the nerve, or from the exterior to the
interior of the muscle through the nerve.
Accordingly, it is
logical to believe that, if, in the living, whole animal,
muscles - especially those controlled by the will - are
excited to contract and make their own movements and functions
by means of the electrical fluid, as everything seems to
demonstrate, it is natural, I conclude, that such fluid then
keeps the same path and direction, i.e. that it descends from
nerves to muscles, since, though it can produce the same
effect even running in the opposite direction, it does so with
far greater force.
[Translation by Vito
Svelto and Valerio Annovazzi-Lodi of Pavia University]
[Revised and
completed by John Coggan of Oxford University]
NOTE
BY THE EDITORIAL BOARD
&
ADDITIONS FROM VOLTA’S OWN MANUSCRIPTS
______________________
To
give an idea of what Physicists, and particularly Volta, thought
about animal electricity a few years before Galvani’s
discovery, we consider it worth publishing the following, clear,
brief and painstaking letter as evidence.
LETTER
FROM A. VOLTA
TO M.ME
LE NOIR
DE
NANTEUIL.
Madam,
I make no excuses for
not having sent you this short article on animal electricity on
the day I promised you I would. You would no doubt have expected
this, recalling that I was short of time that day, the eve of my
departure. However, the best excuse I can make is to send you
this very paper from London, where I arrived on the third of
this month and immediately thought of fulfilling my undertakings.
On
Animal Electricity
( ) When you rub a
cat’s back, brush a horse down or comb your hair (when dry) ,
you hear crackling and see sparks. The hairs standing up reject
each other, whilst they attract and are attracted by other
bodies. In a word: all the signs of electricity are there, and
are even very strong, when the weather is cold and the air very
dry.
The same phenomena
occur in the same circumstances, when one pulls up one’s
sleeves, or pulls on stockings, a woollen or beaver skin jacket,
and especially when one pulls off two new silk stockings, one
black and one white, and separates them.
( ) The electricity
is sometimes so lively that streaks of light appear instead of
sparks, so that people have reported seeing light flames flying
about the head of a person and the bodies of horses. These were
probably no more than little electric darts, which surprise and
our love of the marvellous have made people exaggerate.
( ) People wanted to
call this electricity animal electricity, like that which
arises as if spontaneously in the feathers of living parrots.
But these people were wrong, given that the living or dead
creature contributes nothing to this electricity, which is not
connected to any vital function, since produced by merely
rubbing hairs, silk, wool, and even underwear. When they are
perfectly dry, they are just as excellent idioelectric
bodies as dry wood, paper, etc.
( ) The animal
carrying or wearing such things can at most encourage their
electrification in that it keeps them warm, which is a great
advantage for things like this. This is so true that a piece of
equally hot wood or metal, onto which one lays a lock of hair,
fur, silk stockings, etc., will encourage the electricity in
these bodies just as much as a living person, given that there
is no dampness of perspiration.
( ) To call it animal
electricity it must be such as is connected to life, it must
have something to do with the functions of animal life. But does
such electricity exist? Yes. It has been discovered in the Torpedo
Fish and in the Electric Eel of Surinam, which
Naturalists following Linneus have called Gymnotus electricus.
The first of these is a flatfish to be found in the
Mediterranean, rarely in the Ocean; the second is a freshwater
fish, living in the rives of Surinam and Cayenne.
( ) The ancients knew
the Torpedo Fish very well, and the strange stunning effect it
produces in arms which touch it directly or indirectly. It is
this stunned feeling which the fish produces that caused it to
be given the Latin name Torpedo.
( ) Several
hypotheses have been advanced, some more ingenious than others,
to explain this extraordinary phenomenon, but nothing more.
After the discovery of the main electrical phenomena, some
Physicists, particularly sGravesande and Musschenbroek,
sensing that all these merely mechanical explanations were
insufficient, and noticing a close resemblance between the
effect produced by the fish in question and the Leyden flask,
judged that these two phenomena could be of the same type and
produced by the same cause, i.e., electricity. But it was left
to Mr. Walsh, a member of the London Royal Society, to
demonstrate their absolute identity by irrefutable experiments. Mr.
Bayen, the King’s doctor in Louisianna, had already proved
as much by a few experiments on the Electric Eel. He had shown
that the stunning was only spread through good conductors of
electricity and absolutely stopped by insulating bodies, that a
chain of people holding hands and forming a circuit were
immediately affected, etc.; in short, everything just as with
the Leyden jar. He showed that the slightest interruption in the
chain of conductors stops the discharge of electricity and
thereby prevents ever getting a spark. This is his explanation:
( ) Seeing that all
this happens just the same with the discharge from a large electric
battery under low charge, which always gives a big shock on
immediate impact but no visible spark, we may consequently
believe that the Torpedo Fish discharges a large amount of
electric fluid, as does such a battery, but with little energy
i.e. low tension (as I call it). Neither of these forms
of discharge can suffer even the slightest interruption.
( ) Mr Walsh found
that the electric Eel gave a much greater shock than the Torpedo
Fish and deduced that the former could discharge not only a
greater quantity of electric fluid but also with much greater
energy. He compared the Eel to the same electric battery charged
to a more perceptible degree of force (or, as I call it, tension).
He immediately hoped to get a spark, which he easily did. This
is how he performed that experiment:
( ) With a knife, he
cut across a piece of metal stuck to a strip of glass, so that
there was the smallest break in continuity. He put this glass
strip into the circuit. The moment when the end of the
conducting arc touched the head of the Eel, the other end of the
arc being attached to the tail, the place, where said
interruption was marked by the knife cut, sparked.
( ) It is highly
surprising that an animal could move electric fluid at will,
condense it in one part of its body, remove it from another part,
and finally propel it through conductors, which, if the animal
is in the air, form the circuit, and thereby restore it to
equilibrium. It is even more astonishing that this charge and
discharge can operate under water, which is itself a conductor,
and that the electric current strikes just the arm of a man
dipped in to touch the eel or another fish swimming close by (which
is so struck that it cannot extract itself from the devouring
mouth of the electric animal).
( ) It is true that
this can be explained perfectly well by assuming similarly a
large quantity of electric fluid discharged at that moment and
that the fluid must preferably move to better conductors than
water, like metals and animals. This is what happens with the
discharge from a large battery, however little tension there is.
It still remains to be discovered how and by what means a little
animal can move such a big quantity of electric fluid at will.
( ) There is no doubt
but that the Torpedo Fish and the Electric Eel both have a
special organ for this purpose. The same Mr. Walsh went even
further. He discovered in the Eel what may properly be called an
electric sense. If one, two or several good conductors
not in a circuit are plunged into the tub of water where the Eel
is, the animal seems entirely unaffected. But as soon as
communication is established between two of these submerged
conductors, to form a circuit, and even joins the parts outside
the tub, the animal moves its head up to the end of the conducting
arc, as if to smell it, and discharges its electricity which
strikes the person or people in between, presuming they are
forming a chain joining both conductors.
( ) That is the point
which discoveries on animal electricity have reached. The
could doubtless be pushed further. Mr. Walsh has not even
published everything we have reported hers regarding an
explanation of these problems; he has only reported the most
important experiments. Mr. Cavendish, also a member of
the Royal Society, has added in some way by an excellent memoir
published in the Philosophical Transactions, where he even
describes what might be called an Artificial Torpedo which he
made. He sets it working by moving the discharge from a big
electric battery towards it while it is immersed in water. Since
this is how a large quantity of electric fluid moves in the
Torpedo Fish, a hand immersed in the water near it receives a
great shock, etc. Our explanation based on the great quantity of
electric fluid, but with very low tension or energy,
completely agrees with Mr. Cavendish’s explanation and
experiments. He in turn agrees with Mr. Walsh, from whom
I have this statement and many details which he gave me in a
recent conversation.
Just a couple more
words, Madam , to finish this letter now I have started it. I
beg you, if it be possible, to get a copy of the documents I
dictated to you to Marchioness Doria Villani, Hôtel d’Hambourg,
rue Jacob. I had quite a good journey here, having spent only 14
hours at sea between Ostend and Margate, and being seasick only
one hour. I am very pleased with London, where I shall stay
until half-way through June. I am counting on having the time to
visit Bath, Oxford, Birmingham and Manchester, to see all the
Factories. I have already made the acquaintance of several
Academics here, but no Ladies. The post is about to leave and I
have not got the time to reread all I have written. Kindly
convey my very humble greetings to your Father, Madam, to your
other half, to the Marquis of Bullion, and remember sometimes
him who caused you to waste many evening hours writing. He will
always consider it time gained which he spends in your service.
In addition, Madam, he has the honour, with profound respect, to
be
Your very humble,
most obedient servant,
Alessandre***
Volta
To Madame de Nantueil,
rue des Capucines
Hotel de la Police,
in Paris.
In the Brit. Journ.,
the above letter from V. to Dr. BARONIO on
“Animal Electricity” is preceded by a letter - from Don BASSANO
CARMINATI, Professor of Medicine at the
University of Pavia, to Dr. GALVANI, of
the Bologna Institute (3 April 1794) and another letter from DR..
LUIGI GALVANI to
Prof. Don BASSANO CARMINATI
(8 May 1792) on the same subject as Volta’s letter.
