VIII
(A)
TWO
LETTERS TO MARTIN VAN MARUM
FIRST
LETTER
Como,
30 August 1792
Dear Sir,
Since
your last letter arrived during our vacation, when I am
usually out on excursions, I have not been able to reply
sooner. I am sorry about that, and even more sorry that
I have to defer the commission I gave you to construct
for me the Gasometer which you have invented. The reason
is that, I have not yet been authorised to incur this
expense for the Pavia University [Physics] Cabinet, as
this year’s expenses are already quite high. Yet I
hope to obtain it by renewing the request, and as soon
as I get it, which could be in the next two or three
months, I will hasten to let you know. I beg you to
excuse me for the unnecessary trouble which I put you to,
and for my delay in replying to your letter and thanking
you for the new drawing you sent me along with the
description of your simplified machine.
I do not
know, Sir, if you are aware of the fine discovery of
Mr.GALVANI, Professor at Bologna,
on Animal Electricity. I have eagerly entered the
new field he has opened up for us and I have made some
fresh discoveries, some of which I have already
published in two Memoirs on the subject, included in the
Giornale Fisico-Medico edited by Dr BRUGNATELLI
of Pavia (May, June and July), and which will be
followed by others. I propose to give you a brief
summary of the sequence of these discoveries and add a
few reflections.
Mr.GALVANI
dissects a frog so as to retain the hind legs
attached only by the crural nerves to a part of
the spinal cord otherwise detached from the body. Then
applying the end of a metal wire, or conducting arc, to
some point on these nerves, or else to the portion of
the vertebral column where they join, causes convulsions,
jerking and violent movement in the legs: they jump and
writhe most surprisingly. This effect is obtained every
time contact is made. The results are even better and
over a longer period if, with a metal blade attached
either to the vertebral column or to the extremities of
the crural nerves which end there, one touches this sort
of armature on the one hand and the leg muscles on the
other.
Our
Bologna Professor did not stop at these experiments on
the frog. He extended them to other animals, even
warm-blooded ones, quadrupeds and birds. He had the same
success using the same artifice of stripping out the
main nerve of a limb from its surrounding attachments, the
brachial, sciatic, etc. He then wrapped it in metal
foil and by means of a conducting arc he established a
connection between the "armed" nerve and the
dependent muscles. He varied these experiments in
different ways but always so that he established a
connection between nerves on the one hand and muscles on
the other. He considers this an essential condition, at
least so that the current of electric fluid can spread
via the nerves to the muscles and strike them somehow,
thus arousing their irritability.
But as I
varied the experiments much more and multiplied the
research, I found that the afore-mentioned conditions
hardly necessary. When the nerve is bared and
unencumbered as above, one can limit the inrush of or
distance covered by the electric fluid to two
more-or-less neighbouring parts by applying armatures to
two designated points on the nerve etc. The dependent
muscles will equally convulse and the limb will writhe
as usual even though all its muscles are outside the
circuit covered by the electric current. This works
especially well with the sciatic nerve and leg of a dog,
lamb, etc. If one strips quite a long section of this
nerve and covers part of it (e.g. three or four lines)
with tin foil, and puts a silver strip on another part,
leaving some one or two lines between these armatures,
every time one establishes communication between tem,
either directly, by moving the silver piece into contact
with the tin, or indirectly by interposing a third
metal, one excites jerking movements in the leg, even
though none of its muscles was touched. One cannot
imagine how the electric fluid set in movement in only
one small part of a nerve leaving the muscles can in any
way strike them. So then, it is not at all necessary for
muscles to be directly influenced by the electric fluid
flowing into them; it is the nerves that must be excited.
That is all it requires and no more, to give rise to
movement of the muscles controlled by these nerves.
As these
experiments succeed equally well in limbs cut off from
the animal, and for quite a long time, when the
sensitivity of the dominant nerve would seem to have
been extinguished, seeing that it is impossible to
excite violent movement in said limb by pushing, cutting
or tearing it, but that it is so easy to arouse movement
by a light shock from the electric fluid, one might
reasonable conclude that this same fluid is the most
appropriate stimulant for the nerves. One might think it
entirely natural and that it is through its
ministrations that the animal’s nervous system
functions. Assuming this, the soul has but to impress a
certain movement on the electric fluid, call up, slow
down or invert the movement it already has in the nerves
it controls, in order to bring about the movements it
desires in this or that stiffening or flexing muscle in
the limbs – in short, all those which obey its will.
The more one considers these experiments, the conditions
and circumstances surrounding them, as I shall show
hereafter, the more one will be persuaded of what I am
suggesting here on quite well-founded hypotheses.
Although
it is the nerves that are the parts directly affected by
the action of the electric fluid, and though muscle
contraction is only a secondary effect arising (at
present we know not how and are still no more advanced
than before these experiments) from the action of nerves
thus excited, as we have just seen, it is not at all
necessary, in order to succeed in the experiments
question, to strip and insulate these nerves in
accordance with the system described and practised by GALVANI;
one can leave them in place, covered and hidden by flesh,
and apply the metal armatures straight on the nerves and
muscles, one on one muscle, the other on another one or
even two parts of the same muscle, provided the nerves
are not buried under too thick a layer of integument.
Thus for a frog which has very thin skin full of
moisture, you can leave the skin on, if you wish, and
apply tin foil [directly] to, for instance, its back or
lumbar region and a silver coin under its thighs. When
connection is made between these two armatures, by means
of a third metal, the whole body of the intact frog will
be seen to quiver, writhe and shoot out its hind legs
violently. The same happens if the frog is already dead
and decapitated, when a big needle is pushed into its
spinal cord
In truth,
these movements are obtained more strongly and more
easily if the armatures are applied to the naked muscle
flesh, once the frog’s skin has been removed, but, as
I said, it is not absolutely necessary to skin it. Just
as it is not essential to remove the skin from eels and
other fish, to excite in them all sorts of movements and
contortions, using the same artifice of armatures. I
have [, however,] found it necessary with other animals
whose skin is drier and not so thin: lizards,
salamanders, snakes, etc. As for birds, mice and other
small quadrupeds, which have even thicker integuments,
it is absolutely necessary to remove all the fat,
cellular tissue and other membranes surrounding the
muscles. All these integuments must be removed to
uncover the bare flesh on which one wants to put
armatures. Without so doing, it is very difficult to get
muscle contractions and trembling, and quite impossible
to get limbs to move and jerk as we want. In bigger
animals (cats, dogs, rabbits, sheep, etc) and in the too
adipose parts, the main nerves helpful to movement, i.e.
those controlling the flexing muscles, are too covered
and buried. So, apart from certain membranes that may
cover the flesh, it is necessary to remove a certain
amount, until the intervening layer is thin enough
between the armature and the nerve we want to irritate,
so that the expected movements can occur. It is not that
we do not get any muscle quivering and spasms, more or
less, without cutting and thinning down the fleshy parts;
but if we do, the muscles are near the surface and
roughly limited to the area of the armatures, if this is
not very big. If, instead, the armatures cover a wider
area and are applied in the right way to the places
controlled by the sciatic or brachial
nerves, and if from this area both the integuments and
enough flesh have been removed to leave very little
between the nerve and the armature, whole limbs will
manage to shake, for instance an entire leg, a complete
arm, a dog’s or lamb’s paw, etc. In this case, it is
almost as if the nerve had been uncovered and the
armature had been applied directly, since quite a thin
layer of wet flesh does not prevent the moving electric
fluid from penetrating to the nerve and arousing it to
action.
One can
therefore see from these experiments that, properly
speaking, it is the irritation of the nerves into which
the electric fluid flows that causes muscle movement,
not the action of the fluid directly on the muscles, as
Dr.GALVANI thinks and as I myself
thought at first. That if, without uncovering any nerve,
one simply applies the two armatures to the muscles
themselves, left where they are or completely detached
from the animal, or to one single muscle or even a
little piece of muscle, if, I say, by applying the tin
foil and silver tag to two external parts, either of one
single muscle or of two, one causes jerky contortions,
palpitations, etc., whenever and every time one makes
communication between these armatures, the reason is
that each of these muscles (and their smallest parts) is
filled with a network of nerves of which there are an
infinite number underneath all the parts covered by said
armatures.
There is
one thing, though, that is worth considering more and it
is this: despite the fact that all limbs are supplied
with nerves, there are some, nevertheless, which are
controlled by the will, the muscles which move
spontaneously and produce the phenomena described, viz.
contractions, etc., by the action of electric fluid
transmitted from one place to another. At lease, I have
not managed to get any reaction from the muscles of the
ventricle, intestines, even the heart (all of which,
especially the last, are highly excitable), even when
they have seemed still full of life and reacted to any
other chemical or physical stimulus. I have, I repeat,
managed to get nothing from the heart, intestines, etc.,
by the electrical artifice described, whereas all the
stiffening and flexing muscles in limbs, and most of
those in the back, chest and stomach (in a word, all
those which are subject to the will) do not fail to rise
to the test in question, even long after the physical
and chemical stimuli have stopped having an effect. In
this perspective I have tried the diaphragm muscles and
obtained results as expected, since these muscles are
controlled by the will. So there appears to remain no
doubt on this point.
Now, if
the electric fluid can make contractions, etc., through
the slightest movement caused by applying armatures,
only in muscles governed by the will – and vice versa
– cannot we conclude that it is only by the will that
such reactions are produced, in other words, through
movement similar to what it can give to the electric
fluid? Does one not have reason to believe that it is by
the ministry of the will that the soul acts, as I have
already suggested, and that said fluid acts not directly
on the muscles but on the nerves which, excited by this
their appropriate stimulus, act on the former, as my
experiments have shown? I say no more, since how this
passing from one action to another occurs is still not
clear, as I have admitted. We have no idea how this
nervous power produces muscle contraction. It is,
however, certain – and my experiments alone prove it
– that movement in the voluntary muscles comes from
action thereon by the nerves. And it is more than likely
that the agent, the exciter of these nerves governed by
will, is the same in all cases, viz. the electric fluid
in which we see the same effects operating so easily.
As for
other muscles whose movement depends not on the will nor
can it be excited by the gentle flow of electric fluid
causes by applying armatures, etc., one may believe that
such non-voluntary movements, such as that of the heart
and the worm-like movements of the intestines, are not
carried out by the nerves but by some other mechanism.
Consequently the nerves in these muscles have a
completely different function. One may thus understand
well why the electric fluid in the experiments in
question merely stimulates the nerves a little and
causes not the convulsions and twitching in
non-voluntary muscles that it causes in those governed
by the will.
But what
are we to say of those animals none of whose parts
reveal those movements we would expect to arouse by the
above-mentioned artifice, however otherwise likely they
are to produce spontaneous motions? I have come across
several of these what might be called "rebellious"
creatures, in the worm class, like leeches, slugs,
snails, earthworms and others, which, despite my
numerous tests, varied in as many ways as possible, give
no reaction. I would add, they held out against
artificial electricity discharges strong enough to spark
and give my arm a shock; no part of these small animals
showed any movement – they seemed entirely unaffected,
which much surprised me. Would this be for lack of
nerves? But can we say these creatures have none?
Certainly not, and indeed slugs have them in abundance.
But probably the office of these nerves is not to create
movement in any part, and, although these movements be
spontaneous, they are caused by an entirely different
mechanism, like the non-spontaneous movements in other
animals. There are indeed water and earth worms whose
real movement mechanism has been discovered and
described. However it may be, there is an essential
difference in the animal economy between those and other
animals.
But if,
as we have just seen, many types of worm refuse to react
to our experiment, I would not rush to the conclusion
that this is the reaction of all worms in general, let
alone of al insects. On the contrary, I must say I have
had considerable success with many of them, like
crayfish, beetles, grasshoppers, butterflies and even
flies. Here is how I most surely got the effect from
those creatures so difficult to experiment with because
of their small size or because of the scales that cover
them. Having decapitated the fly, butterfly, beetle,
etc., I cut them right down the cuticle with a knife or
fine scissors. I push a piece of tinfoil or silver paper
– which is properly speaking paper with a layer of tin
– deep into the gap near the neck. Somewhat further
down, I similarly push in, edgewise, a silver tag, e.g.
a small coin. Moving the latter until it contacts the
tinfoil, I see the feelers and legs bend and writhe, and
the body itself tremble, etc.
I now
come (1)
To the experiments which I performed
on my tongue, and to others which showed me new
phenomena, as curious as they are instructive. I apply
to the tip of my tongue a very clean tin strip and,
further forward (2)
a gold or
silver coin to its flat [surface]. I immediately feel a
more or less sharp reaction on the tip: a clearly acrid
taste, which continues and even increases as long as
communication between the two metals lasts. Instead of a
solid strip of tin, it is better when I use a thin sheet
of this metal (3)
or a piece of tin foil, as mentioned above.
This is a striking phenomenon. What is more striking is
that if I conduct the experiment in reverse, i.e.
putting the tin foil on the flat and the silver on the
tip of the tongue (4)
, one gets
here (5)
an entirely
different taste, a burning flavour tending to bitter, in
short a rather more alkaline bitterness than acid.
There is
no doubt that this different sensation comes (6)
from
the fact that the electric fluid in one case enters the
tip of the tongue and in the other case comes out
therefrom. So it is the acid taste that comes when
entering and the alkaline or almost alkaline (7)
one
when said fluid comes out. Therefore, tin causes the
electric fluid to pass to that part it covers, whereas
silver draws out the fluid from the parts with which it
is in contact (8). To decide that, I had recourse to
artificial electricity. I touched the tip of my tongue
to the main conductor from the machine, with sometimes
positive and sometimes negative charge, and clearly
tasted the two different flavours, acidic for positive
electricity and the other bitter, almost alkaline one
for negative (9) . To properly obtain these two
distinguishable tastes, one must not excite sparks on
the tongue, for these would irritate it too much and
produce more or less painful sensations rather than
those of taste. What is needed is not sudden jerky
irritation but gentle continuous irritation (10)
, such as one
has when receiving on the tip of the tongue a tickling
breath or electric wind at a suitable distance from the
blunt conductor of the electrical machine. Alternatively,
one can apply the tip of one’s tongue itself to the
conductor whilst turning the machine over. Do you wish
to remove all suspicion that the taste one feels is
actually that of the metal? Do not put your tongue
directly thereon (11)
but on to a piece of wood, damp
cloth, etc., which you have connected to the
conductor (12)
. It is also good to let a chain hang from
the conductor to the table or the floor, so that, if
accidentally removing your tongue from contact, you do
not get stabbing sparks. Then the conductor is no longer
insulated and gives quite free passage to the electric
fluid whose course is not blocked when the Machine is
set in motion. By this continual flowing away, the
electricity can never rise to considerable tension, so
that a very sensitive electrometer touched to the
conductor gives nought but a weak signal. However, since,
when the tongue is applied to this same conductor, a more
or less (13)
large amount of the moving (14)
electric
fluid has to drain away by this (15)
route, this is precisely
what is needed to tickle the tongue gently, i.e. the
taste nerves (16)
, and arouse the sensation in question,
viz. the acid taste or the other bitter, burning one,
according to whether the fluid comes in or goes out.
However, so that these sensations can be felt quite
noticeably, especially the alkaline one which (17)
is more
difficult to excite (though when one manages to arouse
it, it becomes sharper and more unpleasant because of
its bitterness), the electric fluid which flows so
gently must, I say, on the other hand, flow copiously.
That is why the Machine must work well and supply
abundantly.
With all
that, one can (18)
never manage to arouse a taste as strong
as that provided by two silver an tin contacts simply
applied to the tongue and communicating with each other.
The reason is probably that this movement of electric
fluid is even slower, stopping, so to speak, at the end
of the nerves (19)
and distributing action of exciting
the sense of taste to better advantage. Thus, one can
believe that the amount of electric fluid set in motion
in this manner is not small, though its current is
slower (20).
But of this I shall talk later.
I will
have to write you, Sir, a second letter to continue this
one, for I still have much to communicate to you. Accept
in the meanwhile and until I know what you think about
it*. I am most respectfully and with all
possible friendship
Yours,
etc.
EDITORS’
NOTES AND
ADDITIONS FROM VOLTA’S MANUSCRIPTS
Summary
of comments by I. Bosscha, secretary of the Dutch
Scientific Society, on Volta’s letter of 30 August
1792.
Volta’s
two letters of 30 August and 11 October probably make up
one single letter. They were copied from minutes and
form one Memoir, intending to continue in a third letter
that was never written.
Van Marum’s
reply to Volta never arrived, because of the 1792 war,
and Volta waiting for it in vain never wrote the third
letter. The correspondence remained broken off until
1796. Volta was meanwhile engaged in the struggle
against supporters of animal electricity, and only in
his letter to Vassalli from Como dated 24 October 1795
did he free himself of the obligation to reply to the
Galvanists.
The
Commentary (q.v.) contains information on Galvani’s
works.
Galvani
sent a copy of the Commentary to D. Bassano Carminati, a
Professor of Medicine at Pavia, who passed it on to
Volta, encouraging him to repeat the experiments. Volta
diffidently started experimenting in the last week of
March and his incredulity soon changed to enthusiasm. He
then repeated the experiments at the Anguissola building
in Milan and on 3 April he wrote letter to Baronio
included in Br. Ann., in Ant. Coll. and translated into
German by Meyer.
Carminati
reported Volta’s results to Galvani who replied to
Carminati. This reply was published by Aldini in Galvani’s
Commentary, p. 67, and translated into German by Meyerr on
In
the second Memoir on animal
electricity followed at once and was put in Br. Ann., in
Ant. Coll. and translated into German by Meyer. In this
Volta gave free rein to criticism and demolished Galvani’s
theory.
In the
third Memoir on Animal Electricity, Volta said that the
second part of his second memoir had not been published
when the second edition of Galvani’s Commentary was
brought out by Aldini. The 30 August letter to Van Marum
must have immediately followed the second Memoir. The
third memoir is contained in a letter to Aldini.
__________________________
In Cart.
Volt. E 24 there is a draft on the subject of both
letters, quite faithfully containing all the first and
most of the second, without repetitions, whereas the two
letters as published have one section in common. Bosscha
explains this fact by supposing the two letters were
drawn from one draft and written at two different times
with an interval between (during which Volta went on a
journey).
Translated
by John Coggan, Oxford University
