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XII
(A)
FIRST LETTER
13 September
1792
Sources
| PRINTED |
MANUSCRIPT |
| Phil.
Tr. part I, 1793, p.
10
Ant. Coll. Vol II
Pt. I1, p.121 |
Cart. Volt
(Volta File) J 13, L 8, N 26, N 27 |
|
REMARKS
TITLE from Phil- Tr.
DATE from Phil. Tr.
J 13 contains various fragments, some repeated with
changes, in French
L 8 is a complete Ms- with published epistolary
introduction
In Cart. Volt N 26 there is a handwritten signed letter
by Sir J. Banks, President of the Royal
- Society,
London, dated London, 27 November 1792. He
thanks and congratulates V for his
- two letters and tells him they are being translated
into English.
In Cart. Volt. N 27 there is the official receipt from
the Secretary of the Royal Society, dated
, for the two letters communicated
to the Society at their 31 January 179
session. On the same sheet, signed at the bottom by
Tiberio Cavallo, he thanks for the
two communications and requests the third.
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XII (A)
FIRST LETTER
13 September
1792
I owe you thanks, Sir, and have for
more than a year now, for the gift you sent me of some fine
samples of what you call electrical impressions. I
received them together with the quite detailed description of
how to produce them, at the hands of the young man whom I
recommended to you, Doctor Scasso of Genoa. Since then, I have
not written to you as I had no remarkable experiments and no
discoveries to communicate to you, and because I believe your
taste is rather like mine in that you dislike mere courtesy
letters. I know not but that it may be my idleness that makes me
give these excuses for such a long silence
Anyway, it is time to break the silence.
So to make up for this deficiency I am going to write you not a
letter but such a lengthy dissertation that I fear you will have
more reason to complain about the so-called "making good"
than about the original fault. However, as I wish to share with
you some surprising discoveries and a host of new experiments,
no less important than they are curious, I hope that the length
of this letter will not appear excessive and that you will bear
with the few details which I could not omit without obscuring
clarity or without making it difficult for those wishing to
repeat these experiments. On the other hand, I have been as
succinct as possible in describing a great number of other
experiments, indicating only the main results, wherever I
thought that that would suffice to give a fair idea of the
outcome. In short, I have tried never to be verbose, which I
know you dislike.
The subject of the discoveries and
research with which I propose to entertain you, Sir, is Animal
Electricity. I know this is a keen interest of yours. I do
not know if you have yet seen the work by a professor from
Bologna, Mr. GALVANI, which appeared about
a year ago with this title: ALOYSII GALVANI de
Viribus Electricitatis in Motu Musculari Commentarius. Bononiae 1791,
58 pages in quarto, with four big plates, or whether you have at
least hear of it. It contains one of the most wonderful, most
surprising discoveries and the seeds of many others. Our Italian
newspapers have given various extracts, amongst which that from
Dr. BRUGNATELLI of Pavia, entitled Giornale
Fisico-Medico. I myself have provided two long memoirs, and
others will follow, since I have greatly extended the research
and experiments on this subject.
Now what I am about to give you here is
but a sketch both of Mr. GALVANI’s
admirable discovery and the progress I have been quite happy to
make in this new career. I hope you will show this letter to the
President of the Royal Society, Sir Banks*.
It is to be communicated, should he deem fit, to that august
company. It is but a poor token of my gratitude for the honour
they have bestowed on me by accepting me as a member. It
betokens also my eagerness to share with them the fruit of my
research.
1) Dr. GALVANI prepared
a dissected frog so that its leg, otherwise separate from
the rest of the body, were held on one side of the spinal
cord only by the bared crural nerves. Every time a spark was
drawn from the main conductor of the electric machine and
not from the animal’s body but from some other object and
in a completely different direction (when these animal
remains were a considerable distance from the conductor from
the machine, in particular circumstances which I shall
shortly explain), Dr. GALVANI observed
that the animal’s legs jerked and the muscles contracted
spasmodically. The required circumstances, then, were that
the thus dissected animal was in contact with or very close
to some metal or other quite sizeable good conductor.
Results were even better when the frog was between two
similar conductor, one of which was directed towards the end
of the legs and one of its muscles and the other towards the
spine or nerves. It was also of advantage when one of these
conductors, which the writer will designate nerve
conductor and muscle conductor, preferable the
latter, was free to communicate with the floor. It is
especially in this position that the legs of the frog
prepared as explained gave violent jerks, stretched out and
flailed about at every spark from the conductor from the
machine. This occurred though the frog was some distance
away and although the discharge was not via the nerve
conductor nor the muscle one but through another, which was
similarly some distance from them and had an entirely
different connection through which to transmit the discharge,
such as a person in the opposite corner of the room.
2)
This phenomenon surprised Mr. GALVANI
perhaps more than it should have done. For it was quite well
known that the force, not only of electric sparks striking
the animal’s muscles or nerves but of current from the
fluid going through them in some way or another with
sufficient rapidity, had the power to arouse shocks.
Moreover, it was evident in this experiment an all those of
similar type reported in the first and second parts of his
work, that his frog was indeed open to being traversed by
the current. One has but to retrace the action of the
electrical atmospheres or what is called pressure
electricity. Because of this, the fluid in deferent
bodies, placed within the sphere of activity of some
electrified body, is pushed and displaced by reason of the
force and extent of this sphere. The fluid is kept on the
move as long as there is electricity in the dominant body
but, once this is removed, it gradually returns to its place
from afar, if the electricity is dissipated little by
little; it return suddenly if the electrical force is
destroyed all at once by sudden discharge from the body
which was filled therewith. So it is this returning
current, this reflux of electric fluid in deferent
bodies touching or near to the frog, it is this sudden
passing from the muscle conductor to the nerve
conductor, or vice versa, through the frog’s
body, and especially where the current is squeezed into the
single narrow channel of the nerves, which excites spasms
and movement, in the experiments in question. Mr. GALVANI
appears not to have reflected sufficiently on this action of
electrical atmospheres. He did not yet know how prodigiously
sensitive his frog was when strangely prepared in the manner
described above. (I would add that I have found roughly the
same reaction in all other small animals like lizards,
salamanders and mice.) He was extremely struck by such an
effect, which will seem not so strange to other physicians.
However, this was the first step towards the fine, great
discovery of animal electricity, properly speaking,
which belongs not only to frogs and other cold-blooded
animals but equally to all warm-blooded animals, quadrupeds,
birds, etc.. This entirely new and very interesting
discovery formed the third part of his work. He has thus
opened up a vast field into which we propose to enter, to
continue researching, after having lingered a while longer
over the preliminary experiments concerning the action of
artificial or foreign electricity on nerve and muscle fibres.
3)
It was Chance that presented Mr. GALVANI
with the phenomenon we have just described and which,
I say again, surprised him more than it ought to have done.
However, who would have believed that an electric current so
weak as not to be revealed by even the most sensitive
electrometers could be capable of so violently exciting
movement in its members which had been severed some hours
previously, movements such as the legs stretching out,
jumping, etc., not to mention the most violent tonic spasms?
Now this is the current which fills the little animal lying,
for instance, on a table near to some metal or between two
good, non-insulated conductors, when someone draws a slight
spark from the big electric conductor hanging several feet
above and discharges it by a completely different route.
4)
I say sli ght, for if it is a
strong spark and if the distance from the large, strongly
electrified conductor to the bodies on the table is not
particularly great, small sparks will appear in between
these bodies – especially if they are metal – and at a
point where the frog completes the circuit between them. The
sparks are evidently produced by the returning electric
fluid we mentioned above (Sect. 2). Or, if things do not get
thus far, one may observe quite evident movement in
electrometers placed on the same table and at the same
places. Now in this case (where electrometers show signs),
and much more in the other (when the afore-mentioned sparks
are obtained), one can observe that even a complete, intact
frog or other small animal – a lizard, mouse or sparrow
– trembles throughout its body, especially the legs which
stretch out excitedly if the electric fluid (the returning
current) passes along the legs from one end to the other. So
far there is nothing surprising. The surprise comes when the
electric current is imperceptible even to the most sensitive
electrometers but yet excites the same convulsions, the same
movements and struggling, if not over the whole frog at
least in the several members prepared in Mr. GALVANI’s
way.
5)
I applied myself rather carefully to
finding out what the least electric power was that was
required to produce these effects, both in a whole frog full
of life and in one dissected and prepared in the manner
mentioned. Mr. GALVANI had failed to
investigate this. I chose the frog in preference to, say,
any other animal because it is endowed with most durable
vitality and is very easy to prepare. Besides, to this end I
have also made tests with other small animals, with
approximately equal success. In order to evaluate the power
of the electric current, I thought it necessary to submit
the animal intended for this particular experiment not to
returning current caused by the atmosphere (Sect. 2) but to
direct electrical discharge, sometimes from a simple
conductor, at other times from a Leyden jar, in such a way
that the entire current had to pass through the animal’s
body. For this purpose, I was careful to keep it insulated
in one way or another, most often by pinning it down to two
planks of soft wood supported on glass pillars.
6)
So I found that the electricity from
a medium-sized simple conductor, which managed to produce
only a feeble spark and to raise the HENLY
electrometer from 5 to 6 degrees, was wanted for a
complete live frog. If I used just a medium-sized Leyden
flask, the much feebler charge from that produced the effect,
so that, for example, although it gave no spark and did not
in the least register on a quadrant electrometer, it only
just registered on the CAVALLO
electrometer, moving its little pendulums only about one
line.
7)
That, as I have just shown, for a
whole, intact frog. A dissected one, especially prepared in
Mr. GALVANI’s
manner, where the legs are attached to the spine only
by the crural nerves, requires even weaker electricity from
the conductor or the Leyden flask (the fluid being forced
through the narrow passage of the nerves) to excite
convulsions, etc. – yes, a charge forty or fifty times
weaker, like a charge from the flask or which is entirely
imperceptible to the afore-mentioned CAVALLO
electrometer and even to the highly sensitive BENNET
one, a charge which I could make perceptible only by means
of my condenser, and which I think I can evaluate as five or
six hundredths of a degree on the CAVALLO
electrometer.
8)
So here, in the legs of a frog
attached to the spinal column solely by well-exposed nerves,
we have a new sort of electrometer; since electric charges,
which give no sign on other meters, appear not to exist,
whereas they give very marked signs on what we might call
this animal electrometer.
9)
When one has seen how this prepared
frog feels and mightily trembles at extremely weak
electricity, an imperceptible current, one should not be
surprised if it writhes in the same way, when another large
or small current of electric fluid different from the one
previously explained (Sect. 2), which is passed through deferent
bodies near the frog and becomes re-established, is
suddenly discharged via the main conductor from an electric
machine and passes rapidly through the nerves. Let us
suppose this returning current is just about equivalent to
that projected by a sufficiently large conductor, with
non-sparking electricity which is scarcely perceptible even
to a CAVALLO
electrometer, or a small Leyden flask charged to
scarcely ten degrees on this electrometer. Let’s suppose,
I repeat, that the electric current is no stronger than that;
it is still strong enough, as my above reported experiments
( Sects. 6 & 7) have shown , to arouse the movements we
are considering.
10)
But if after these experiments one
should not be surprised at those which Mr. GALVANI
describes in the first and second parts of his work,
how can one fail to be surprised by those quite new and
marvellous ones which he reports in the third part? In those
he got the same convulsions and violent movements from the
limbs without having recourse to any artificial electricity
or external stimulus; he simply applied any conducting
arc to one end of the muscles and the other end to the
nerves or spine of the frog prepared as described. This
conducting arc could be wholly metal or part metal and part
other (conducting) deferent bodies, like water or
several people, etc. Even woodwork, walls and floor could be
part of the circuit, provided that they were not too dry.
Only the insertion of non-conducting (cohibent)
bodies, like glass, silk or resin would prevent the effect
from occurring. Bad conductors, however, were not so much
use, and that only for a few minutes after the frog was
prepared and its life force was still at the peak. Beyond
that point none but good conductors could be used with
success, and shortly after that one could only succeed with
excellent ones, i.e. with entirely metal conducting arcs.
Moreover, great advantage was to be gained from applying a
completely metal arc to that part of the spine which he left
attached to the crural nerves, and to the nerves themselves,
especially when this part was covered with brass or lead
foil.
11)
Mr. GALVANI
did not stop there in his truly astonishing
experiments on frogs. He successfully extended them not only
to other cold-blooded animals but also to quadrupeds and
birds. He obtained the same results from these beasts, with
the same preparation, viz. he removed the covering of one of
the main nerves, where it joined a limb capable of movement,
and reinforced this nerve with a metal tag or foil to
establish communication via a conducting arc from this nerve
to the muscles depending thereon.
12)
Thus it is that he happily
discovered and showed us most clearly that in all or nearly
all animals there is real animal electricity. It
seems to be proved by his experiments that the electric
fluid tends to pass from one part to another of a living
organic body, even if dissected, as long as some vitality
remains, that it tends to pass from the nerves to the
muscles or vice versa, and that the muscle movements are due
to this more or less rapid transfusion. In truth it seems
that one can raise no objection to this, nor to the way Mr. GALVANI
explains it as a sort of discharge, like that from a
Leyden jar. However, a great number of experiments which I
have performed on this subject have shown that many provisos
must be made, both regarding the event and the conclusions
the writer has drawn therefrom. At the same time, they
greatly extend the amount of phenomena attributed to this animal
electricity and show them to us in a great number of
circumstances and fresh combinations.
13)
Following the idea he had as a
result of his experiments, and in order to follow at all
points the analogy with the Leyden flask and the conducting
arc, Mr. GALVANI
claims that there is a natural excess of electrical
fluid in the nerve or the interior of the muscle and a
corresponding lack in the exterior thereof, or vice versa
H consequently supposes that one end of this arc must be in
communication with the nerve, which he considers as the
conducting wire, and the hook of the Leyden jar, the other
end must contact the outer surface of the muscle. All the
figures in Plates 3 and 4, and all his explanations, come
down to that. But if he had varied his experiments a little
more, as I did, he would have seen that this double contact
with nerve and muscle, this circuit he imagines, is not
always necessary. He would have found what I found, namely
that one can excite the same convulsions, the same movements
in the legs and other limbs of frogs and any other animal,
by metal contacting two parts of a single nerve or two
muscles or even different parts of a single simple muscle.
14)
It is true that success is nowhere
near obtained, either one way or the other, without having
recourse to an artifice which we shall have occasion to
discuss more at length later. The trick is to use two
different metals. This artifice is absolutely not necessary
if the experiments are carried out following Mr. GALVANI’s
system described above (Sects. 10 & 11), at least while
the vitality in the animal or its severed limbs remains at
full strength. But since, when tags of different metals are
applied either to nerves alone or muscles only, one can
manage to make these last contract or limbs move, one must
conclude that if (and this may still be very doubtful) there
are cases when the supposed discharge between nerve and
muscle (Sects. 12 & 13) is the cause of muscular
movements, there are other more frequent cases also when the
same movements are obtained by an entirely different
stratagem, a completely different circulation of electric
fluid.
15)
Yes, it is a completely different
trick of the electric fluid which we can say disturbs the
equilibrium rather than re-establishing it, in that it flows
from one part of the nerve, muscle, etc. to the other, both
internally, through conducting fibres, and externally via
the metal conductors, applied not because of a surplus or
lack but because of the action of the metals themselves,
provided they are of different types. It is thus that I have
discovered a new law, which is not so much a law of animal
electricity as a law of normal electricity. To this law must
be attributed most of the phenomena which, according to Mr. GALVANI’s
experiments, and several others which I subsequently made,
seem to belong to true, spontaneous animal electricity, but
they do not. They are really effects of very weak artificial
electricity, aroused in the way I suspected, by applying
armatures of two different metals, as I have already shown
and which I will explain better elsewhere.
16)
I should say here that, discovering
this new law, this hitherto unknown artificial electricity,
I doubted all that had seemed to prove the existence of
animal electricity properly speaking, and I was about to go
back on that idea. However, re-examining all the phenomena
thoughtfully and repeating the experiments in this new
light, I found that some still support examination (those,
for instance, where no different armature is required,
indeed no armature at all, no simple metal wire nor other
deferent body functioning as a conducting arc between
insulated nerve and its dependent muscle, to make the muscle
contract)(Sects. 10, etc.), and that therefore natural,
proper, organic animal electricity does actually exist and
cannot be entirely rejected. The events supporting this,
although they are much more limited, cannot fail to be a
proof, as I have just shown and as will be seen better later.
17)
What may perhaps be considered more
unpleasant is that limits must now be set on one’s mastery
of understanding animal life. The fine ideas must be given
up which seemed to explain clearly all muscle movement. My
experiments, varied in as many ways as possible, show that
the movement of electric fluid excited in the organs does
not act immediately on the muscles. It only excites the
nerves, and it is they that in turn excite the muscles. But
what this nerve action is, how it spreads from one place to
another, how it passes to the muscles and then makes them
move, are still problems which we can no more resolve now
than before the discovery in question.
18)
Now I come to the experiments which
prove all that I have advanced in the last two paragraphs. I
will choose only a few of the myriad available, most of them
new and different from Mr. GALVANI’s,
which seem to me to establish certain principles. But first
let us say another word about that writer’s experiments. I
know not if he has done others but those which he tells us
about in his works are too limited. When he wants to make
muscle twitch and move by the action of the electric fluid,
he always strips and insulates the nerves, establishing a
connection with electricity-conducting bodies between nerves
and their dependent muscles (as can be seen in all the
figures on the Plates in this work). He therefore supposes
and explains quite clearly that in every case, either by
means of artificial electricity or natural animal
electricity, the resulting transfer of electric fluid must
occur from the nerves to the muscles or vice versa.
He affirms that at least these two extremes must be included
[in the circuit] for muscle movement to occur. And indeed
all the experiments he describes to us seem to prove that.
But, as I said, they all revolve in too narrow a circle,
from which he has never or hardly ever stepped. By varying
this type of experiment in several ways, as I have done, I
have shown that neither one nor other of these conditions (baring
and insulating the nerves, and simultaneously putting them
in contact with each other) is absolutely necessary (Sect.
13). When one has bared, for instance, the sciatic nerve of
a dog, a sheep, etc., all that is required is to pass
electric current from one part of the nerve to another, even
quite close, leaving all the rest intact and free,
particularly the whole leg; that is what is necessary, I say,
to see the leg convulse and move most vigorously. This
happens either with exterior, artificial electricity or by
setting in movement the electrical fluid inherent in the leg.
Here is how I performed these experiments.
19)
EXPERIMENT
A. I squeeze the sciatic nerve with tweezers, just
above where it is inserted into the thigh, and a few lines
above I apply a coin or other metal piece to the same nerve,
which is carefully separated from its attachments and held up
by a thread or supported on a glass plate, a stick of Spanish
wax, dry wood or any other bad conductor. Then, with the belly
of a weakly charged Leyden flask touching the tweezers, I
touch the hook to the other piece of metal. And there we have
the discharge, even though it is not strong enough to give the
slightest spark, convulsing the muscles of the thigh and the
leg which is shaken and stretches more or less excitedly. And
yet, as can be seen, the whole leg or even part of the nerve
coming from it were off the route traced by the moving
electric fluid which could irritate only a very small part of
the nerve. Nevertheless, that was enough to cause muscle
contractions.
20)
EXPERIMENT B. The
same thing occurs, i.e. convulsions and leg movements take
place, without recourse to external electricity, through the
discharge which, in a certain way, occurs naturally when,
having applied some tweezers or a metal piece, as above, to
one part of the nerve and a piece of entirely different metal,
especially tin and lead, to another part, we simply bring them
into contact with each other, either directly or via a third
piece of metal which functions as a conducting arc.
21)
And so there we have the same
effects, convulsions and most lively muscle movements,
without the discharge of electric fluid between nerves and
muscles, as Mr. GALVANI
still supposes, and without the need for one end of
the conducting arc to touch the nerve and the other end the
muscle. But neither is the other condition required, of
stripping any nerve and laying it bare, as the following
experiment will show.
EXPERIMENT
C.
I apply armatures or different metal tags (the difference is
important) (Sects. 14 & 15) to a whole, live frog,
complete in its skin – in a word, intact. I stick a piece of
tin foil, for instance, on its back or its lumbar region, and
put a silver coin on its thigh or under its belly, and press
it somewhat. Having done that, I slide the coin until it makes
contact with the tinfoil or I put the two armatures in contact
using a brass wire or any other piece of metal. Spasms are
thus excited in all the muscles of the belly, thighs and back,
with violent jerking of the legs, contraction and curving of
the spine, etc.. Although the spasms and convulsions be almost
all over the animal, they are most marked in the muscles and
limbs touching or adjoining the armatures and even more in
those which directly depend on the main nerves close to said
armatures.
22)
These experiments succeed with other
beasts too, fish and especially eels whose skin need not be
removed, though it does somewhat hinder the action. This is
why removing it partially, especially in the case of the
frog, we are surer to get the effects and they are much
greater. In this respect one gains even more by cutting the
frog’s head off and finally killing it by inserting a
large pin into its spinal cord. Then by using different
metal armatures, as described, we excite stronger movement
or which seems more evident since it cannot be confused with
movements the animal makes when alive.
23)
In order to succeed in these
experiments, it is of advantage, as we have seen, to remove
the frog’s skin, although it is thin and quite damp, it is
even more so, indeed necessary, to remove it from almost all
other animals, lizards, salamanders, snakes, tortoises, and
especially from quadrupeds and birds, endowed with much
drier, thicker skin. This is how I proceed.
EXPERIMENT
D.
Using a few big pins I attach the lizard, mouse, hen, etc. to
a table. I make an incision down its back in the skin and
other integuments right down to the bare flesh of the animal
thus incapacitated and open up the integuments on both sides.
I do likewise with the thigh or the leg. After that I apply
the two armature to the naked parts: here tinfoil, there the
spoon or coin. Now every time I create a connection between
the two armatures the adjacent muscles contract sharply,
especially the thigh and leg muscles which move and thresh
about very strongly. This jerking is much more violent
depending on how near the tinfoil is to the sciatic nerve and
how well applied the silver one is to the muscle called gluteus
or the other called gastrocnemius. The movement is
always more intense if we actually bare the nerve in question
and cover it with tinfoil, if we remove all other attachments
and leave it fastened only to the muscles into which it enters,
and if, finally, we remove the limb, complete with its pendant
nerve, from the rest of the body and then subject it to the
experiments.
I am, etc.
Sept. 13, 1792.
Translated by John Coggan, Oxford
University
Notes
*
Translator’s note: Volta is referring to Sir
Joseph Banks
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