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VII.
REPLY TO THE
QUESTIONS
OF ABBOT
TOMMASELLI.
Summer 1792.
SOURCES
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HANDWRITTEN. |
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Cart.
Volt. E 23; F
46 bis.
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REMARKS
TITLE: This
seems to be a letter sent to Abb. Tommaselli of
Verona ( See
New
Memo.
on Anim. Electr.
Letter III ,
as reported in Note).
DATE: Inferred from the above letter
The questions
referred to are clearly those written by an unknown hand
(Tommaselli?) on a sheet of
Cart.Volt . F 46 bis, and we insert them in a note
within the text.
Some passages
of this "Reply" recur in two notes written by
Volta in the above-mentioned Memo.
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REPLY TO THE QUESTIONS
OF ABBOT TOMMASELLI.
Reading
the questions
(1),
which Abb. TOMMASELLI of Verona addressed to me, it seems
that in the frog experiment, prepared in the manner of Dr. GALVANI, the
muscle with the outstanding nerve is also considered by him as a kind of Leyden
flask, whence an electric charge comes out, every time convulsions and movements
are excited by the various related devices, such as to determine a discharge of
electric fluid from inwards to outwards, and vice versa. Yet, I deem that
this experiment can be achieved, as a matter of fact, in a much simpler way by
means of artificial electricity. In my opinion, nothing else is necessary but an
ordinary flow of electric fluid, running from one extreme to the other of the
animal, or through those limbs which can usually be shaken in their internal
parts, chiefly through the nervous system. When the fluid runs in this way, from
the head or the back of the little animal under experiment straight to its legs,
or from these latter to the former, convulsions, jerks, etc. take place, every
time the electric current is fast and abundant enough: and such is its effect
even on a whole, intact frog, when the current is originated by a discharge,
hardly capable of raising a spark, coming from the ordinary Conductor of the
electric Machine, or by a discharge from a Leyden flask, not strong enough to
generate sparks. The same result can be obtained, directing such electric
current from one hind leg to the other. Besides, if the whole trunk is cut off
and the two hind legs are kept together, less electric force will be sufficient,
in other words a force with a lesser flood, to contort them, both of them being
passed through by more condensed fluid. it is known, indeed, that it acts and
irritates the sensitive fibres of the animal the more strongly, the narrower is
the passage offered to it.
Since
nerves are the internal parts of an animal which are more sensitive to stimulus,
as many experiments have already proved (every time they are indeed stimulated,
the contractions of the dependent muscles are accordingly excited), there is no
reason to be surprised, if the afore-mentioned convulsions and movements of the
animal’s limbs are so easily produced by such a low electric force, when that
fluid is impelled to flow exclusively through the narrow channels of nerves.
That is why the frog also tries to move under the slight effect of such an
imperceptible electric current, deriving for instance from a Leyden charge not
even perceived by the most delicate Electrometers. That is also why the animal
tries strenuously to move and, I dare say, to shake and kick its legs about,
when it is prepared in such a manner that its legs are tied to the back-bone
with the crural nerves, and the small quantity of electric fluid current flows
precisely through these very nerves. This fluid must not necessarily flow along
them and involve the muscles of the legs; it is enough that the wandering fluid
go through a part of those nerves, and try to prick and stimulate them. Yet,
when legs are out of circuit, it happens that convulsions as well as
moving and wriggling take place, because even in this case the Leyden flask can
discharge, for instance, on the two conductors: the first applied to the
back-bone, and the other to any one of the points of the bare crural nerves.
It
is therefore not absolutely necessary to use the muscle
Conductor, as GALVANI
has called it, as it is replaceable with the nerve conductor; and, in the same
way, even the moving of the electric fluid between the former and the latter, or
between the external and internal part of their substance, is not at all
required, as supposed before. In this procedure there is nothing that can look
like a Leyden discharge. And why should we strive to look for it where there is
no sign of it or need to find it?
Coming
now to the experiments, we proceed to discharge a great overhanging Conductor on
the frog, in order to attack its body with another completely invisible electric
current, in this way avoiding striking it directly with the electric fluid,
which could be thrown either from a simple conductor or from a flask. This
application is so easy to follow for everyone knows well the action of the Electric
atmospheres that there should be no need to add more information about it.
Yet, since not all, not even those who take delight in electric experiments, are
well informed, and very few can draw the right conclusions and also make the
required applications, it will be useful here to explain at least what is most
relevant and what fulfils our main purpose.
The
action of the electric Atmospheres, and of the so-called Electricity of
pressure, is such that the fluid of conducting bodies, plunged into the
sphere of activity of another over-electrified body, is moved and thrown
away in proportion to the force and the extent of that sphere. This area is
bigger than we can believe, and reaches to some feet in length, although it is
possible in truth to light sparks at a distance of a few inches. On the other
hand, if its electricity is shortcoming, the fluid is attracted and also
forced to remain in the vicinity of the electrified body. As we can see
hereafter, when most of the electricity of such a body is destroyed or removed
with the emanation of a great spark, and consequently the Atmosphere of the body
disappears or weakens, the fluid, which was removed from the other immersed
bodies, runs immediately to its destination, following a linear way, as is
typical of the best conductors.
Therefore,
when the electric current of that fluid goes back to its original place, passing
through the conductors to which the frog is attached, it is (as in the
expectations of Mr. GALVANI)
the rapid transit from the muscle Conductor to the nerve Conductor,
or vice versa through the body of the frog, and particularly through the
narrow way of the two crural nerves, that provokes those strange convulsions and
the more or less violent movements of the animal. There is no reason for
surprise in this experiment, except for the high impact of its effect, when the
frog is so prepared; and the same surprise arises equally in the above-described
experiments.
Furthermore,
it is possible to stimulate in the frog (as it is, entire and intact) or
likewise in other little animals, like lizards, salamanders, mice and little
birds, similar movements in all their limbs with the simple use of the electricity
of pressure, as in the described manner, without baring the nerves or
resorting to any other preparation. In this case, it is only necessary that the
electricity of pressure be stronger than usual and exert its influence at not
too great a dist. [distance]. Now put a whole frog on a table, between
two conductors, one of which has to reach the ground, and then place the animal
in a such way that it touches both of them or is just so near as to touch them:
the former with the head and the latter with the feet or the former with one
foot and the latter with the other foot. In this case we cannot call the former
a "muscle conductor" and the latter a "nerve conductor",
both of them being muscle conductors or, to be more exact, the fore and the hind
conductors. There is no concept of circuit in all that, in the sense of a system
which functions from muscles to nerves, or from the external to the internal
part; whereas every time a full and strong spark is discharged from the big
Overhanging conductor, provided that the distance is not so considerable, as we
explained, both of the frog legs will convulse. What else is possible to obtain
with this such preparation? As a matter of fact, what we can do is nothing else
but stimulate the same convulsions at a greater distance from the electrified
conductor and by means of weaker discharges from the same device. But this means
only that, once the nerves of the animal are bared and insulated, in order to
use them as channels for transit, a very small quantity of current of electric
fluid, imperceptible even to the most delicate
electrometers,
suffices to stimulate the nerves, and consequently to provoke
contractions
in the dependent muscles. This result is proved by my experiments on the
immediate electric discharges, as I have already pointed out.
These
few remarks, I think, can satisfy the questions of. Abb. TOMMASELLI,
and many others which will be asked on the activity of artificial electricity
applied in different ways, equally to a whole frog as to its cut limbs, prepared
in several manners, and to other animals too. He asked me nothing about the
electricity proper to animals, whereon I have made many discoveries. I have
observed many new phenomena which on the one hand do apparently extend the
effects of such animal electricity but on the other hand do enormously restrict
their influence and destroy most of Dr. GALVANI’s
explanations. Besides, they do equally prove that muscular movements, stimulated
by the device of the metallic armature are usually effects of a properly
extrinsic artificial electricity. But this does not happen always, as one might
be tempted to believe, since I have also proved, after rigorous examination of
all my tests, that the electric fluid which flows from the nerves to the muscles,
or from the internal to the external part of these limbs, is unbalanced and
moved simply by the same organic force; wherefore it follows that the important
discovery of GALVANI
about real and substantial animal electricity is true and
irrefutable However it must be restricted to a smaller number of phenomena and
therefore almost all of his hypotheses and explanations fail.
For
instance, when it is necessary to touch the muscle with a metal, and with
another different metal the nerve itself, in order to obtain the contractions
and movements with which we are dealing or, besides, to apply different
armatures (because in the case of armatures made of equal metal the effect is
not reached), it is neither possible to believe that any organic electricity is
able to work thereon nor that there is in those parts any natural alteration of
equilibrium which can move the electric fluid. It should be said rather that, if
transport of that fluid takes place by the mere application of two metals of
different kinds, the agents of that phenomenon are the metals themselves,
because they remove it from its quiet equilibrium, shift it from the places
where they are applied, and then transport it from one side to the other. This
is better proved in my experiments, whereby I obtain the same contractions and
movements, applying also the said dissimilar armatures to similar parts
of the animal, namely to the muscles only, without baring the nerves, or any
other part. If they are also applied to the same kind of muscles, for instance
to the gluteus muscles/buttocks of both legs, the frog jumps immediately,
if I let these two armatures of different metals (particularly if one is of tin
foil and the other is silver) communicate by means of a conducting arc,. What
else can I say? I could describe the capacity which the two metallic armatures
of different kinds have to move the fluid: the first for instance, made of
silver, attracts and sucks it in a certain way, whereas the second, made of tin,
pours it out and then sets it in endless circulation, every time and as long as
there is a communication between them, based on metallic affinity, or on good
conducting bodies. Besides, I have proved by direct experiments (for instance,
applying the armatures to bodies considered non-animal, to a wet cloth, etc.)
the specific capacity
and
power of action of dissimilar metallic armatures, even on those parts to which
they are applied and on the intermediate ones, when the fluid can flow with
sufficient freedom through them.
Metals
are therefore not only excellent Conductors, but also motors of
electricity: they indeed permit very easy passage to the electric fluid which,
being already unbalanced, is prone to move from the place where it is abundant
to the other where it is lacking . Furthermore they determine and support a lack
of equilibrium, by taking away or admitting the fluid itself, even where it is
equally shared. This happens when armatures are simply applied to any other kind
of conductor, and mostly when idio-electric
(*)
materials are rubbed
together. Since every metal prevails over any another in attracting or releasing
the fluid, what happens is that two armatures made of different metals are set
it in endless circulation, if they are applied in the explained manner and
communicate between them; and particularly, when the armature of silver is
connected to the armature of tin (these metals, as I have found out, are the
most favourably disposed), the former begins to attract the electric fluid
towards it and the latter to release it. This property of metals, which nobody
has till now suspected, is my new discovery, the result of my last experiments.
In truth I do not think that this property is only typical of metals but of all
conductors as well; and I deem it possible to maintain as a general principle
that this simple contact, or the fitting together of the conductors which have
different surfaces and are made most of all of different materials, is enough to
upset in some way the natural equilibrium of the electric fluid and to remove it,
as a matter of fact, with no need of rubbing. The rubbing action, like the
striking or simply pressing, is indeed much more efficacious, since it permits
the surfaces to fit together much better , thus allowing a greater number of
points to be in closer contact.
Leaving
these observations and considering the transport of electric fluid from one part
to of the animal to another as a mere action favoured by two armatures of
different metals applied to it, I underline again that, when such a condition is
respected, that is to say, when armatures are different and thus stimulate
convulsions and movements (whereas, if similar, movement cannot take place), it
is just possible to affirm that no animal electricity acts any important part.
The described effects can, and must also, be interpreted as necessarily produced
by an artificial electricity excited by the new device mentioned.
Yet
when, in a different case, the nerve is bared and isolated in the manner of Dr.
GALVANI,
and the same nerve and the relative muscle, from which it comes out, are
connected with the two extremes of the same metal, or the nerve and the muscle
are connected to the same metal in the same manner, convulsions can be anyway
excited. Oh, in this case, we could surely affirm that such phenomena are the
effect of a real , proper animal electricity! And whence could the movement of
the electric fluid derive then, if there is no other possible source? The
armatures being completely similar, each to other, it cannot derive, initially,
but from the same organic parts to which they are applied, exactly where the
fluid is unbalanced, that is to say between the
nerve
and the muscle, or between the internal and the external part of the muscle,
wherein it pierces and spreads the nerve. Such a condition of natural
electricity does not last very long after the death of the animal and the
dissection of it. Therefore, a frog tested thus stops contorting in a couple of
minutes; whereas, if it is arranged in the other manner, I mean with the device
of different armatures, the little animal goes on kicking its legs about for
some hours; and so it goes on, even when we apply both armatures to the external
part of the muscles, without baring any nerve.
I
have other proofs, besides, on the natural lack of balance of the electric fluid
in organs, or rather of its disposition to shift from one part to the other; and
these proofs show me exactly to which direction it tends, that is to say, from
the nerve to the internal part of the muscle. Yet, I have neither time nor space
to extend now the treatment of this subject; and I cannot even do it on the
other discoveries I have described in two Memoirs on animal Electricity
already published in the Giornale Fisico-Medico of Dr. BRUGNATELLI, respectively in the
issues of May, June and July; nor on other discoveries to which I am attending.
Since I fear that it could be difficult for Abb. TOMMASELLI
to get these small tomes, I think I may not be doing him a disservice by sending
him the sheet which the editor inserted in the first volume, wherein my
discoveries are shortly described.
(1)
Here are the collected questions of
Tommaselli [Editors’ note]:
To Mr. Chev. VOLTA from Abb. TOMMASELLI,
in Verona.
"When the Frog with its own
conductor attached to nerves
is subjected to electric atmosphere,
I ask: 1. Whether the Frog shakes, when
the spark from the great
Conductor is lighted, since the electric fluid is discharged outwards from the
muscle, or alternatively since it flows from the nerve into the muscle; or,
finally, since it goes back from the muscle to the conductor attached to
nerves, through the tunic of the tube or the nervous duct.
Supposed that the electric fluid
discharges outwards from the muscle, without the use of any nerve,
I ask: 2. Whether the contraction takes
place at the beginning of sparking,
after the Frog has been already charged and the conductor of nerves is put away.
As concerns
the objection whether You cannot consider as electricity what is discharged
outwards from the muscle, since it could be continually discharged (like that),
the answer is clear and plain, being inferable from Your interesting
observations made on the minimum amount of electric charges, which are deemed
sufficient to give a shock to the Frog with the Conducting
arc."
(*)
Translator’s note: V. is talking about
non-metals which create static electricity by friction.
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