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XIII
Letter to Sir
Joseph Banks
President of
the Royal Society, London
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Pavia, 30 March 1795
SOURCES
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MANUSCRIPT |
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Cart. Volt E 27. |
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REMARKS
TITLE from E 27.
DATE " " .
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E 27 is an almost complete draft of this letter. |
XIII
LETTER TO SIR JOSEPH BANKS
PRESIDENT OF THE ROYAL SOCIETY, LONDON.
Pavia 30 March 1795
Sir,
Two months ago I received the letter which you did me the
honour of writing to me and I have not yet recovered from the
pleasant surprise you [thereby] gave me. You had already told
me, Sir, of the favourable welcome which the Royal Society
gave to my papers on the action of electric conductors in
muscular movement and certain sensations dependent [on(1)]
the nerves, and I confirmed this by giving other public
witness. But I had not expected such an outstanding recompense,
for me most flattering, as the medal which has just been
awarded me. I could have hoped for it all the less even
despite the encouraging of hope which you gave me last year
since I have not yet finished my promised task of
reporting the progress of my research and developing numerous
other things to which I have been led.
In truth I am somewhat ashamed of this delay, which has,
moreover, been to my disadvantage. For in this interval,
several discoveries I made for over two years ago*
(and which I can justly claim as mine, having shown all the
experiments therewith connected to several people, both
foreign and national) have been published by others. What is
more, they were right to claim the honours if their own
research led to these new discoveries they did not know
that I had got there before them and had been showing the
experiments to everybody for a long time. I am therefore
careful not to accuse any one of them of publishing
plagiarised material; I merely reserve the right to claim as
mine the discoveries where indisputably, and as is well-known,
my experiments preceded theirs, although they beat me to
publishing. I shall also speak hereafter in my Memoirs of all
my new discoveries straight from the source
(2)
,
my source
(2)
embarrassing myself with what
others have published.
I could adduce several reasons for this long delay but I
cannot claim to excuse myself completely. The main reasons are
the questions and doubts I felt I had to resolve first.
Various objections have been raised to what I had put forward:
that one can excite contractions normally by means of metal
conductors applied to parts and brought into mutual contact,
only in the voluntary muscles, the erector and flexor
muscles, and not at all in the non-voluntary muscles, however
excitable they are otherwise, particularly the heart muscles.
To contradict me, people have produced experiments making the
heart beat twice as fast or even wake up when it was entirely
(2)
by applying two different metals, one to the heart itself an
the other to a few of the nerves leading thereto. Having
repeated and varied the tests in as many ways as possible and
determined under what circumstances one can obtain the effect
in question, I therefore rectified my proposition, which I had
probably stated too generally. But I discovered at the same
time that a great difference, an essential difference, exists,
as I had suspected, between the voluntary and non-voluntary
muscles and the nerves connected to either, or the nerves and
muscles of one type and the nerves and muscles of the other.
This is so, as long as muscle excitability remains great and
when using
(2)
in that, apart from it being
much more difficult to excite the later latter by the means
indicated, to the extent that the effect only occurs with the
most active metals (i.e. two that are very distant on the
scale I had drawn up, like lead and tin, or better zinc and
silver or gold), in addition, these two different metals, or
one of them, must be applied directly to the heart itself or
at least that heart must be placed so that all or a
considerable part of it be in the circuit and consequently be
traversed by the electric current excited by the two metals.
In a word, the electrical stimulus must affect the
muscle directly
(2)
ly if the electric
current is not applied to the muscle itself, if it does not
substantially enter it, I suppose that if it only encourages
it and penetrates only a small section of the nerves lying
between the two metals, or if the heart is placed in any
manner within the conducting arc, excluding the muscle, this
muscle will not be aroused. Now, it is a completely different
situation with the voluntary muscles, which react and convulse
most strongly when, having applied two metals (not even the
most active) at two different places, not even very distant
from each other, to the main nerves, e.g. the sciatic nerve,
inserted in the muscle, I bring the two metals into
communication, which creates an electric current going through
only this intercepted part of the nerve. All that is required,
for instance, is gentle squeezing of this nerve just above
where it enters the leg muscles it controls, squeezing, e.g.
the crural nerve of a prepared frog, with tweezers of which
one leg is silver ant the other tin, or better zinc, for all
the subject muscles or the entire leg to writhe, when all
other pressure, any other mechanical or chemical stimulant
applied to the same nerve, has no effect. So, the irritation
of a nerve alone or only part of the nerve by stimulating it
with a feeble electric current is very efficient for exciting
contractions in the voluntary muscles depending thereon and
more efficient than any other stimulus. Whereas this
irritation serves not for the heart and the other
non-voluntary muscles; for them, on the other hand, mechanical
and chemical stimulation is much more appropriate than
electricity, so much so that, even when the electric fluid
strikes such muscles hard and acts upon them directly and
manages to excite them, one can believe that it is acting as a
necessary stimulus. It being firmly established, as my
experiments prove, that electric fluid is the most appropriate
of all stimuli for creating contractions in voluntary muscles,
either because its current goes substantially right through
the muscles or flows
(3)
or that it affects
only the nerve, going through only a small stretch of same;
and on the other hand [the electric fluid is but a weak
stimulus, inferior to mechanical stimulus for non-voluntary
muscles and even totally ineffective when applied to the
nerves of those muscles](4), I have discovered a
very remarkable difference between the organs of movement, a
difference which led us to classify into two classes not only
the muscles but also their respective nerves, in relation to
their functions, not to mention the sense nerves which are yet
another class.
The explanation I have given as to how different metal
conductors excite the sense of taste on the tongue, light in
the eye, pain in very delicate parts, in wounds, as well as
contractions in voluntary muscles, the explanation which
considers them not a mere conductors but as motors of
electricity, each endowed with different strength according to
the type of metal and other accidental differences, when these
metals are applied to those of another class of moist
conductor and thereby complete the circuit, considering such
contact as the active cause of the electric current
moving in the circuit and continuing as long as the circuit is
not broken, so that the animals nerves and muscles included
in the circuit are merely passive, simply aroused by
extrinsic electricity, in a word electro-motors of a
different type and very sensitive; this explanation, which
totally upsets all that had previously been proposed, and
which I had believed, about animal electricity being inherent
in limbs, about an electrical charge or the natural balance
being upset between nerves and muscles or between the inside
and outside of same; this explanation, I say, generally
accepted by Physicists who have followed my steps in these
experimental fields, could hardly fail to meet with strong
opposition from GALVANIs disciples
and adherents, jealous of keeping the greatest glory for the
discovery by the acclaimed Professor from Bologna. They have
also tried their best to re-establish animal electricity a
totally useless effort, by comparison with what I have proved
by countless direct experiments, in the way they claim. Their
strongest argument is the convulsions excited in frogs,
prepared in the GALVANI manner, by
applying two pieces of the same metal, or even two ends of one
and the same metal strip. I already applied to these
objections more than a year ago in a Journal printed here in
Pavia. 1st, these convulsions are obtained only by
means of preparing the frog completely, while it still retains
considerable sensitivity; what is more, there are often no
such contractions even under these circumstances and, when
they do come, their strength is not comparable with what two
different metals arouse. 2nd, if the two pieces of
metal or the two ends of the same metal are not substantially
different, accidental differences are enough (like tempering,
density, more or less polished, gleaming or dull surface,
temperature, etc.) to make them exert different action or
force on the electrical fluid at points where these metals are
applied to moist conductors and determine the current. Indeed,
I have proved that by changing temper, polish or temperature
in one of the two pieces, or one of the two ends of the same
metal, one can excite contortions which cannot be obtained
when all aspects were otherwise perfectly equal. 3rd,
by choosing two pieces of a single metal, not subject to much
change, like gold or pure silver, cutting two pieces off the
same gold wire and pushing them like needles, one into the
spinal cord and the other into the leg of a recently prepared
frog, I never excited any convulsions when I connected these
two needles together, whereas I did arouse contortions with
two other pieces of gold or silver chosen at random, e.g. two
coins, etc. What can one say, then, but that there was some
accidental difference here between gold and gold, silver and
silver, since when there is no difference, there is no
reaction?
This, though, is a stronger objection: in the first few
moments after preparation and in certain cases, one can excite
convulsions in the frog without using any metal, by putting
one of its legs in contact with the spine or bared crural
nerves, and sometimes by making the connection via an expanse
of water or one or two people. It is therefore not, they say,
extrinsic electricity moved by metal conductors, for that is
missing here, but it is electricity which resides in the limbs,
a discharge of electrical fluid from these organs, nerves for
example, where it normally accumulates, to the part that is
lacking in it, e.g. to the muscles, the interior or exterior
of these muscles, by way of the nerves, as GALVANI
had thought.
These experiments carried very far some months ago by Mr. EUSEBE
VALLE, and with which GALVANIs
partisans thought they had triumphed, won over several who had
adopted my viewpoint which seemed incompatible with these new
facts. However, it is very easy to con[fute] them
(5)
As I maintain that upsetting the equilibrium, inciting the
electric fluid to run like a continuous stream through the
whole conducting circuit, comes from mutual contact between
two dissimilar conductors in this circuit, conductors which
are at the same time motors, i.e. they become instigators of
motion at points where a heterogeneous contact is made (somewhat
like what happens through friction) and this is what I have
shown by many different experiments; it happens in a very
marked way for metal conductors over against conductors of a
different class, which I call "humid" because they
owe their conductivity to water or some other humour which
they contain; I have but to add that other contacts between
heterogeneous conductors from only this last single class can
also act on the electrical fluid, disturb its calm and set it
flowing, with a force which is that much weaker in so far as
they are incomparably less perfect conductors than metals.
What I said about dry or metal conductors (in which I include
vegetable or animal carbon) must be extended, by analogy, to
humid conductors, viz. that what happens when one conductor of
this class contacts one of another, also happens
proportionally between two different conductors of the same
class. So, instead of saying the whole thing depends on the
difference between metal conductors, we can say it depends on
the difference especially between metal conductors. We
must not exclude the others from also possibly being motors.
A long time ago I had the idea that all conductors had this
activating ability to some extent; and I explained as much, in
the summer of 1792 to a few of my correspondents, especially
in two long letters to Mr. VAN MARUM,
the famous Dutch Physicist. Now experiments have confirmed
this hypothesis. They show that electric fluid is moved by
mere contact between two different humid conductors and
especially two different liquids. In subsequent Memoirs, I
shall report a number of these experiments. Here suffice it to
say that, if one fails to get the convulsions just by touching
the prepared frogs leg to its back to contact the spine,
one can sometimes get them again by moistening one or other of
these parts, in Mr. VALLEs way, with
saliva, saltwater, spirits of wine and other liquids, as Mr. VALLE
himself has proved. (*)
This one more experiment and I have done. Having put the
legs of a prepared frog in pure water contained in one glass
and its back in another glass of water, one can very
occasionally get one or two weak convulsions by putting two
fingers in the two glasses to complete the circuit. It happens
so rarely that I fail to succeed even with the best prepared,
freshest, strongest frogs, even in the first few moments
[after preparation]. I succeed no better by immersing two
perfectly homogeneous ends of gold or silver wire, but if I
repeat the experiment after moistening the end of my finger or
of the metal arc with a different liquid (brine, spirits of
wine, ink, vinegar, vitriolic acid or some animal humour like
milk, blood, saliva, or urine), I can excite muscle movement
when I make contact. This experiment is much more certain with
the metal conducting arc, but more decisive with my fingers;
which all proves that the effect is due to contact between two
heterogeneous liquids. After that, who cannot clearly see the
explanation of the phenomenon there has been so much noise
about, viz. weak convulsions in a carefully prepared frog
caused by merely contacting one of its legs to the bare crural
nerves or the back muscles? Even if saliva, etc. has not been
applied to one of the places, the mutual contact is always
made between two different conductors, at least as regards the
surface, which is smooth at the knee and the muscles covered
by the same smooth tissue, whereas, on the other hand, it is
rough and the flesh is torn and bleeding at the spine. It is
this difference, I declare, in contiguous conducting surfaces
which can be observed on the few occasions when Mr. VALLEs
experiment succeeds, which is normally when the flesh on the
back is touched, or contact is made with the nerves where they
leave the spine, not by any part of the leg but by the
gastrocnemius muscle and better still by the white muscle
tissue at the foot joint.
Let us conclude that no experiments have yet proved there
is an electrical discharge from animal
organs, as the supporters of GALVANI
claim, since
seeing
that everything can be explained by action
inherent in dissimilar conductors
brought into contact. I have personally proved this action and
in some way determined it by many other experiments especially
with metals (6).
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