In two previous letters, and particularly in the last one, I
have described, perhaps in too much detail, the methods to excite convulsions in
frogs by means of second-class conductors only. However, it was appropriate to
erase the impression in many physicists resulting from the objections made to
the aim not really to support animal electricity, in the real meaning of an
electric change due to imbalance of electric fluid from one organic part to
another as a consequence of the vital forces, but rather to deny the other
intrinsic source of Electricity, which I support, strictly related to the
contact between different conductors. From the different ways to excite a
current of electric fluid by using only 2nd class conductors, all
methods that essentially consist in having at least three different types of
conductors in the circuit, let us now pass to the various methods of obtaining
that electrical current, and thus the convulsions in the frog etc., again with
three conductors which are different (this is always required) but with two
belonging to the 2nd class and one of the first class: in other words
to put one of the latter class, for instance a piece of silver, in between two
conductors of the 2nd class and different from each other, such as
water and blood, pure water and saline water [1] etc.
I have already mentioned such a new method or trick in more
than one part of the 3rd letter, specifically towards the end. Really
I have written, clearly though concisely, its essential points, so that it is
almost useless to add any more, particularly to you, as you are no less skilful
in carrying out experiments than in dealing with applications. In any case I do
not really think that it is useless, at least in order to save the great study
and fatigue that could drive you to carry out many new attempts without any
specific direction, I do not think it useless, I say, to offer you, my very
distinguished colleague, such a hint and the appropriate clarifications, letting
you know not about all the many attempts and experiments I carried out according
to that point of view but only about the principal results that more directly
support my principles.
These experiments are less easy and more satisfactory than
the ones with 2nd class conductors only, since they can excite
convulsions in weak frogs, even in frogs prepared long ago and even in ones not
properly prepared, namely frogs only skinned or disembowelled. In summary, this
other trick of using two 2nd class conductors of different types with
one first class conductor between them is much more efficient than the one
involving three conductors, albeit different, of the same class. It is not much
less efficient than that first used in this kind of experiment, or at least that
which Physicists have been interested in, namely the one with two different
metals or first class conductors , with one of 2nd class between them
and with one or more wet conductors.
Let us now come to the
experiments.
Take a metallic arc with two ends perfectly similar not only
as regards their intrinsic properties, namely the type of metal or alloy, but
also for hardness, temper, polish, etc.; since also these incidental differences
considerably affect the electric fluid in the contact of the metal with the wet
conductor, as I have clearly demonstrated in the first letter. Then, with one
end of the metallic arc let us touch the muscles of the legs and with the other
the muscles of the back of the properly, recently prepared frog. The well known
convulsions and beating about will not happen, except very seldom, where the
muscle touched by the arc is wet with water and the other muscle to which the
second end of the arc is applied is dirty with blood or other liquids different
from water. In such a case, a first class conductor, namely the metallic arc, is
between and in contact with two 2nd class and different conductors,
such as water on the one hand and another wet medium or saline solution on the
other.
That this result depends on the different character of the
two liquids will be clear after the observation that convulsions no longer occur
even though one touches both sides of the same muscles with the same metallic
arc, after having carefully washed them in water, removing any bloody or slimy
humour or stains of , blood, dissolved soap or any saline solution. In that case
the first class conductor, the homogeneous metal, is caught in between two 2nd
class conductors both of the same type. The action on the electric fluid arises
from the contacts being opposite and equal. Therefore they cannot induce any
current or circulation of the fluid.
In these
experiments, in which the arc of one single metal
does not cause any motion or convulsion even in the best prepared and most
excitable frog, when one side is applied to muscles or to fleshy legs and the
other end to any similarly fleshy part of the body. I am assuming that the parts
touched by the arc, besides being absolutely clean, are approximately of the
same consistency and their surfaces neither very rough nor very polished.
Sufficiently
similar, usually, are the naked flesh of the
thighs and of the frog’ back, after being prepared and well washed of blood
and any other slimy humour, rewashed, if required, and moderately dried. Then it
is that after the application of the arc made of the same metal to those parts
no convulsions are observed, unless some wet conductor different from water
should replace one or other contact, as we have discussed [2].
However, in the event that the parts of the metallic arc
should considerably differ in hardness and consistency or polish or in other
properties, then the muscles could exhibit convulsions even without interposing
blood or other slimy liquid or saline solution; this is what happens on some
rare occasions. This happens more easily when instead of applying one end of
that homogeneous metallic arc to the soft, fleshy parts of the thighs one
applies it to the more compact , sleek muscles of the legs, particularly to the
gastrocnemius, and with the other end one touches the naked sciatic nerves or
the soft, partially torn flesh on the back. It happens better if the contact
with the gastrocnemius muscle occurs in its lower part, where it displays a
clear white, pearl-coloured surface and transforms into hard tendon. I have
already shown in two previous letters that this tendon is very different from
the soft, fleshy parts with a rougher surface, just like the naked sciatic
nerves, as regards - the properties we are dealing with. Bringing it to a direct
contact by interposing a thick or thin layer of blood or of other slimy or
saline humour (since there must be at least three different conductors, as I
have explained in those Letters and I will better explain soon), produces an
electrical current, not so powerful, indeed, but rather valuable anyway, capable
of inducing convulsions in all the leg muscles of the frog, provided that it is
well prepared and very sensitive. Then, if one interposes a piece of metal,
instead of one or other of the liquids mentioned, between the afore-mentioned
gastrocnemius muscle and the naked sciatic nerves or another fleshy part of the
body if the connection is completed and the circuit is made, with our
single-metal arc, by properly applying one end to the tendon and the other end
to the nerves already described, or to any fleshy part of the body.
Alternatively, when (and this is practically the same) one applies a plate of
any metal to the same part or to the nerves and then it is brought into contact
with the great tendon, this action will give rise to an electric current; and
this will be as strong as the activity of a first-class motor and conductor
vis-à-vis second-class ones, however different their species. In this way, in
fact, it will be possible to excite convulsions even in frogs prepared some time
ago and already so languid that they are no longer sensitive even if the tendon
itself is connected to the back muscles, wet with a strongly alkaline solution,
which is, as far as my experiments show, the most effective experiment using
only second-class conductors.
Many times, to tell you the truth, just the opposite happens,
namely that convulsions in frogs are more easily excited by connecting the legs
with the body, i.e. connecting the tendon to the body wet with alkaline liquid,
rather than establishing the same connection with an entirely metal arc without
interposing any liquid of the type mentioned above. But this happens just by
chance, when the parts of the animal touched by the arc are not wet enough, in
particular on the outside, and therefore scarcely deferent. One can remedy this
fault by experimenting in another way, namely by introducing saline liquid
between the two parts, the tendon of the leg and the sciatic nerve or any other
fleshy part of the body. This establishes the required connection between the
two parts while it provides adequate wetting.
In order to get good success in the experiments with a single
piece of metal touching the legs and the sciatic nerves of the frog or its body
(and this is much better than using only second-class conductors, even though,
for the best ones in this class, it is better that those parts of the animal be
well wetted, not only inside but also on the outside, and that the liquid
wetting the surface of the body, at least at the points where the contact is
going to occur, is noticeably different from the one which wets the part of the
legs that is going to be touched; and the more different they are, the better it
is.
Therefore if one humour is going to be pure or almost pure
water, and the other slimy blood , saliva, mucus or saline water, namely the one
which is wetting any part of the legs, and the one with which all or part of the
body is soaked, since any metal will be used in a way that it touches the legs
on one side and the body on the other, just in the places where there are the
various liquids, strong convulsions will be excited in all the muscles of the
legs, even should the frog not be one that appears to have the best sensitivity,
provided that it is properly prepared: In the event that the liquid which is
used to soften the legs be not very different from water and the one which wets
the body be saline water or dissolved soap or acid liquid, one will be able to
excite convulsions more easily and still more strongly even in frogs prepared
long before as well as in others not fully prepared, namely only disembowelled.
To this extent one never gets results by trying with 2nd class
conductors only, regardless how much they differ.
Moreover, if the saline liquid is a well saturated alkaline,
for instance oil of tartar (according to the old nomenclature) and the metal
which is interposed between it and the liquid conductor is zinc (this metal by
itself as well as in conjunction with other metals appears to be the most
powerful in its ability to excite the electric fluid through various contacts),
it will be possible to excite muscular contractions even in frogs which are not
really disembowelled but just killed and skinned. In short by means of just zinc
in between an alkaline liquid and a liquid conductor, it is possible to induce
an effect stronger that the one obtained by means of a conducting arc of two
different metals, but not very different, scubas silver and brass, copper and
iron, tin and lead, between which the frog is placed Even by means of these one
can hardly trigger convulsions in a frog where only the muscles and not the
nerves have been bared; and it is scarcely possible with metals which are much
more different in regard to the quality we are dealing with, like silver and
iron, brass and lead, or tin, lead or zinc.
Then what I have claimed since the beginning is really true,
namely that this new artifice of using just one metal or first class conductor
placed in between two wet or 2nd class conductors , provided that
they are very different gives almost as effective results as the other known
long ago: that of two first - class very different conductors with one or more
of the second class between them This, I claim, is almost as much effective,
because with two metals which are not only much but very much different, like
silver and certain [3]……
EDITORIAL BOARD NOTES
AND ADDITIONS FROM A. VOLTA’S MANUSCRIPTS
[1]
In Cart. Volt. J 39 and J 50 there are
various sheets with very many notes on these experiments that V. mentions also
in letters 3 and 4 to Vassalli and in the 1st. to Gren (§ 35)
[2]
Ms. L 17 stops here. The
continuation is from J 33.
[3]
Ms. J 33 stops here. In Ms. L
17, which follows a similar line to J 33, the letter continues as follows:
In order to shake, for instance, a whole intact frog, or one merely
decapitated and skinned without further dissection, in order to excite tonic
spasms with only two metal pieces applied one to the back or stomach and the
other to its legs, and thus raise convulsions in either leg or both by forming
contact between the two metals, it is not sufficient to have some tiny diversity
between these metals, though that is all that is needed when applied in the
usual way to a completely prepared frog. No mediocre difference [4]
is required but a big one. Those between silver and iron, between brass and lead
or tin are not big enough, or only just so. To be really successful, we need to
go from silver, which is at one extreme of the scale, to lead or zinc which are
at the other end. Even with a single metal, best if it is zinc, I manage to
arouse convulsions in a whole, intact frog, or one merely decapitated and
skinned, applying a strip of the same metal to one leg – very wet, of course,
or which I soak well with water – or to its back. The leg or back I previously
dried thoroughly of any aqueous humour and blood, and then drenched in oil of
tartar.
[4]
The reading of letter 5,
published by Cantoni, ceases here. The little that follows is to be found on
another sheet discovered by Prof. A. Volta Junior".
Revised by John Coggan, Oxford University
