_General reflections on the action and influence which Galvanism,
considered in a medical point of view, exercises on the animal
œconomy._
I shall not here speak of the variation in insensible perspiration,
and of the increase of circulation, which, according to the
observations of several physicians, are found to be produced by
Galvanism. Similar phænomena, as is well known, take place during the
administration of common electricity. I shall therefore confine myself
to those effects which hitherto have been produced only by the action
of Galvanism. I shall observe in the first place, that Galvanism, as
already shown in the Experiments detailed in the Second Part, is
capable of effecting a separation of the fluids, and even sometimes of
protruding the fæcal matters from the body. In the case of the
decapitated malefactor, I found that when the arc was applied to one
ear and to the lips, a very sensible portion of saliva was discharged
from the mouth. This observation was confirmed at Genoa on the head of
an ox, and in several other places on the heads of sheep. The
phænomenon of the extrusion of the fæcal matters from the trunk of an
ox, by means of Galvanism, was observed also by Professor Mojon of
Genoa, and his brother, to take place in human bodies. Considering the
animal fluids separately, I have found that very great variations are
produced in them by Galvanism. But before I give an account of the
experiments which I made on this subject, I shall describe the
apparatus I employed.
The animal fluid destined to be exposed to the action of Galvanism is
put into a glass vessel (Plate III. fig. 6.) covered by a wooden lid,
having in it two holes equally distant from the centre. Two wires, one
of brass and the other of plated copper, the upper extremities of
which are bent into the form of a hook, pass through these holes in
such a manner, that the lower extremities of them reach nearly to the
bottom of the vessel, where they are bent at right angles, so that
only a very small interval is left between them. The upper extremity
of one is made to communicate with the bottom of the pile, and the
other with the summit. In consequence of this arrangement the Galvanic
fluid is obliged to traverse the animal fluid, by which means it
exercises an action on it according to the distance of the wires, and
by its action separates from its different strata sometimes one
principle and sometimes another; and this secretion will be effected
with more ease and in greater abundance, according as the action of
the pile is stronger, and the capacity of the conductors more
considerable.
EXPERIMENT I.
Having put into glass vessels four ounces of blood recently drawn from
the vein of a person in good health, I left one of them exposed to the
contact of the atmospheric air, and subjected the other to the action
of the pile. In both these portions I observed a speedy coagulation of
the crassamentum, and at the end of twenty-four hours the serous part
was separated. The blood exposed to the action of the pile adhered so
strongly to the two wires immersed in it, that it was difficult to
separate them from the clot which was thus suspended in the aqueous
fluid, but in the other vessel the clot remained at the bottom.
EXPERIMENT II.
I put two equal portions of bile, still warm, taken from the
gall-bladder of an ox, into two glass vessels, exposed one of them to
the contact of the air, and subjected the other to the action of the
pile. After ten hours had elapsed, I observed that the bile in the
latter had become so opake as no longer to afford a passage to the
light; while the other portion, exposed to the atmosphere, retained
its transparency and colour. I observed also a considerable
disengagement of air, the nature of which I have not yet had an
opportunity of examining.
EXPERIMENT III.
I took four ounces of urine, voided by a man in good health, exposed
it to the action of the pile, and at the end of twenty-four hours
found that the greater part of its constituent principles was
separated. A portion of them was collected around the wires in such a
manner as to form cylindric bodies of a considerable diameter, of
which the wires were the axes. As the mass of the attracted matters
increased, a portion fell to the bottom by its own weight. The
cylinders were soon entirely destroyed, and the substances which
formed them were precipitated by the least shock given to the vessel.
I repeated this experiment lately in Mr. Wilson’s anatomical theatre
in Windmill-street; and I observed, at the end of eighteen hours, a
great quantity of the moleculæ furnished by the urine adhering to the
two wires. But at length, not being able to withstand the effect of
its gravitation, it began to fall down, forming a sort of wedge, the
apex of which was at the surface of the urine, and the base at the
bottom of the vessel.
EXPERIMENT IV.
Instead of putting the urine into a common apparatus, if a glass
syphon with two platina wires be employed (Plate III. fig. 5.), the
urine becomes limpid on the one side, and turbid on the other. The
substance detached from the urine afterwards appears in the form of
flakes, which are attracted by the platina wires. I observed this
phænomenon for the first time in the company of those celebrated
chemists Fourcroy and Vauquelin, while they were performing Galvanic
experiments in their own laboratory.
EXPERIMENT V.
The substance above mentioned, which was precipitated to the bottom,
when separated by filtration and dried, weighed about the fourth of a
grain, and the fluid separated from it was of a greenish colour. On
examining the earthy deposit of this urine, we obtained sulphate of
lime by adding to it sulphuric acid.
EXPERIMENT VI.
Having exposed to the action of the pile, in the same manner, four
ounces of urine voided by a person with jaundice, I obtained an earthy
sediment, the weight of which was nearly equal to that above
mentioned. The liquor separated from it was transparent, inclining a
little to black. By the same chemical process I obtained sulphate of
lime, though the sediment of the urine was somewhat dark, and afforded
a portion of carbon and bile which inflamed in the fire.
EXPERIMENT VII.
Having repeated the above experiments with different kinds of urine, I
observed in general, that Galvanism, by a peculiar attraction,
separates from urine the sulphates and muriates united to a portion of
the bile, and also to carbon, which in a great part are precipitated
to the bottom of the vessel: the other part, which remains attached to
the wires, exhibits a regular saline crystallization, of so singular a
form that it seems worthy of becoming an object of further research to
chemists.
The examination of urine voided by persons labouring under different
kinds of disease, seems to be an object sufficient to excite the
curiosity of physicians. To expose to the action of Galvanism
artificial aëriform fluids, analogous to those which act a part in the
animal œconomy, might also be attended with advantage. For this
purpose it will be convenient to employ the apparatus represented in
Plate III. fig. 7, which was lately constructed, with great precision,
by M. Dumoutier at Paris. The whole artifice consists in a vertical
metal tube, which can be raised up or pushed down. It is furnished
with a stop-cock, and the tub in which the apparatus is placed has
another. If the inverted bell be filled with water, and connected, by
means of the vertical tube, with the apparatus which is to supply the
gas, on opening the lower cock, the water will descend in the bell,
and its place be supplied by the gas intended to be subjected to
experiment.
From all the observations hitherto made, there seems to be reason to
conclude, that the effects produced on the animal œconomy by common
electricity and by the Galvanic pile are different. The phænomena of
artificial Galvanism give us some right to suppose, that a similar
action is exercised by the Galvanic fluid circulating in the fluids
and in the organs of living animals. In this point of view Galvanic
researches may one day throw great light on the nature of secretion;
and it may perhaps be found necessary, when remedies are administered,
to take its influence into consideration: for it is possible that the
action of these remedies in the animal œconomy may depend on the
establishment of such an arc between the system of the nerves and that
of the muscles, as may not alter the natural state of the Galvanic
fluid proper for the constitution of the individual to whom these
remedies are administered. All this however is mere conjecture, and
must be classed with many other things in the theory of Galvanism
which are still involved in obscurity, and which we can hope to see
explained only by new researches and new experiments.
Taking a general view of this Third Part, I must observe that the
administration of Galvanism, when the above experiments are carefully
examined, seems to appear in a much more advantageous point of view
than before. I have indeed proved:
1st. That Galvanism, on many occasions, exercises an influence
different from that of common electricity, and that it may be
administered in various cases with great ease and safety.
2d. That the action of Galvanism manifests itself by a sensible
attraction between the nervous and muscular parts; which seems to
confirm the hypothesis of Humboldt, who supposes a Galvanic atmosphere
peculiar to these parts when in a state of perfect vitality.
3d. That the strong impression made by Galvanism on the brain seems to
explain its power on the organ of hearing; and therefore the
physicians of Berlin, and other parts of Germany, are entitled to
great praise for their researches on this subject.
4th. That though medicine is capable of affording considerable aid in
cases of drowning and of asphyxia, it presents us with no means so
powerful as Galvanism. The experiments made at London, Jan. 17, 1803,
on the body of Forster, executed for murder, have fully convinced me
of the activity of this stimulant.
5th. That in cases of melancholy madness, when other remedies fail,
Galvanism may be employed with the greatest hopes of success, provided
the disease does not proceed from a vitiated constitution, or a
general derangement in the animal machine.
6th. That the current of the Galvanic fluid produces a great
alteration in the animal fluids; separates a great many of their
principles, and produces this effect in a particular manner in urine.
It is however much to be wished, that in addition to the knowledge
already acquired in regard to Galvanism, some convenient method could
be discovered of increasing or lessening its action on the animal
fluids; by which means the advantages of the medical administration of
this subtle agent would be rendered more certain and more effectual.
DISSERTATION
ON
_ANIMAL ELECTRICITY:_
READ IN THE
INSTITUTE OF BOLOGNA,
IN THE YEAR 1793,[3]
BY J. ALDINI.
I. While our Academy was congratulating itself on the progress made by
the doctrine of animal electricity, its exultation was in some measure
checked by an objection brought against it, which did not attack any
one part of it, but the whole theory. If the contractions in animal
bodies, said its opponents, are produced merely by the electricity of
metals, how degraded is that electricity which at first was supposed
to reside in animal bodies, since it is now found to be subservient to
the electricity borrowed from metals! I heard repeated objections of
this kind while labouring under a severe indisposition; but being
restored to health by the skill and attention of Galvani, I took the
earliest opportunity to inquire after the success of his animal
electricity, and at the same time promised him every assistance in my
power in the prosecution of his researches, for which I always
entertained a great fondness. He accepted my offer; and as I had now
recovered my former strength and vigour, I was anxiously desirous to
defend the cause of animal electricity, attacked and almost exploded,
amidst a variety of contradictory opinions, and with this view to
undertake a new series of experiments.
II. The theory of animal electricity had scarcely been proposed, when
a suspicion was entertained that it might be produced by some external
agent excited by the arming or by the arc. This suspicion Galvani
endeavoured to obviate in various ways. By using an insulated arc, it
was impossible that the person who performed the experiment could
communicate any of his electricity to the animals. In preparing the
frogs he employed no conducting bodies; he neither touched them with
his fingers nor with a knife; he uncovered the muscles and nerves with
idio-electric bodies, and still the usual contractions took place.
Nay, Galvani carried his attention so far as to exclude even the air.
Having immersed a frog with an insulated arc in a glass vessel filled
with oil, and having made a communication by means of an arc between
the muscles and nerves, muscular contractions were immediately
produced. This electricity, the animal being thus surrounded by
idio-electric bodies, could not certainly be furnished by the
atmosphere, from which it was entirely separated. While engaged in
these experiments, the celebrated Spallanzani stopped a few days at
Bologna on his way to Pavia, and during a short conversation which he
had with Galvani on his new system, expressed some suspicion that the
electricity observed in animals might be acquired from external
bodies. After some discussion however on this subject, Spallanzani
acknowledged that the experiment made on the frog immersed in oil was
so conclusive, that nothing could be better calculated to satisfy all
his doubts. I mention this circumstance, because the approbation of so
eminent a man was of the utmost importance to the cause of the theory
of animal electricity.
III. Having proposed the before-mentioned series of experiments, I was
led into various reflections on this subject. As the same electricity
exercises an extensive action in the different parts of animals—some
becoming electric through an excess, and others through a deficiency
of it—I could not comprehend why there should not be an electrical
movement even when the end of a very long arc was covered by a
non-conducting body; and why the same arc touched by the same person,
in the same atmosphere, should sometimes become charged with a very
small quantity of electricity, only capable of exciting motion in the
legs of a frog, and sometimes with a large quantity sufficient to
produce contractions in the leg of a lamb or a calf. This circumstance
appeared to me to be involved in a considerable degree of obscurity. I
conjectured also that internal electricity might have been implanted
in animal bodies for the purpose of defending the animal œconomy, and
protecting it against any injury which it might sustain from an excess
of the external atmospheric electricity. Were not this the case, there
might be reason to apprehend that the electricity of the clouds, in
the time of storms, might attack the human body and destroy it.
IV. But though the suspicion of electricity being communicated from
the air, or from the person who performed the experiment, was lessened
or removed, there were still some who thought that the objection in
regard to metals could not be obviated in the same manner. The idea
generally entertained, that all the contractions ascribed to animal
electricity were to be ascribed only to external electricity,
proceeding from the armatures, and not to any electric virtue in the
animals, seemed to be strengthened. Carradori, who had made this
objection, afterwards altered his opinion, and became a strenuous
advocate for animal electricity; but the celebrated Volta still
entertained great doubts. These he communicated to me in a long
letter, and they were afterwards published in the Pavian Journals. All
his doubts were founded on this circumstance: heterogeneous metals are
required to produce contractions; one of which becomes charged
positively and the other negatively; and it is only in the act of
restoring an equilibrium between them that muscular contractions are
excited.
V. This simple and ingenious idea was no doubt highly captivating; but
the experiments made by Galvani and by myself prevented me from
adopting it entirely; for it is evident from Galvani’s Dissertation,
and from my own observations, that if the muscles and nerves of a frog
be immersed in two vessels filled with water, contractions will be
produced on the application of a metallic arc. Here then we have
muscular contractions with one arc and with one metal. Living frogs
subjected to the action of rarefied or of condensed air, and
afterwards dissected in the usual manner, exhibit contractions without
any armature, and merely by a silver arc applied to the muscles and
nerves; and this is always the case, whether the frogs be large and
strong, or small and weak. While engaged with these experiments,
Galvani informed our academy that he had obtained contractions in
large and vigorous frogs, which had been recently dissected, without
the help of the air pump and without armatures, merely by the
application of an arc. The same thing occurred to Carradori, who,
though he at first entertained doubts on this subject, was afterwards
convinced of the truth of the phænomenon. It still however appeared to
me, notwithstanding the results obtained by Galvani and Carradori,
that the animal electricity of frogs was excited in more abundance by
the action of the air pump, even without the application of armatures.
VI. But that the series of experiments I had undertaken might be
better calculated to establish the theory of animal electricity, and
as it was difficult to find any of the solid metals homogeneous
throughout, I had recourse to mercury, which, by the help of
chemistry, may be brought to a very considerable degree of purity. For
the greater convenience in the employment of this substance, I
invented the following apparatus:—Two glass vessels are so arranged
(Plate IV. fig. 1.) that the one stands above the other: the upper one
is filled with mercury, and the spinal marrow of a prepared frog is
placed in it; and by means of a hole in the bottom of it, which may be
opened at pleasure, the mercury can be made to fall on any part of the
muscles of the same animal placed in the lower vessel. The stream of
mercury occasions convulsive movements to take place in the muscles;
and yet in this case the mercury forms both the armature and the arc:
consequently the electricity in both is the same, and can exercise no
action. When contractions therefore take place, they cannot be
ascribed to the electricity of the metal. Should it be said that the
mercury as it runs down may excite electricity from the sides of the
glass vessel, as is the case with the mercury in the upper part of a
barometer, which, when in the least agitated, shines with an electric
light, any doubt on this subject may be easily removed by substituting
vessels of wood instead of those of glass.
VII. When these vessels are used, care must be taken to pay attention
to one circumstance, which may prevent the success of the experiment.
As the spinal marrow is exceedingly light, it will float on the
surface of the mercury; whereas it ought to be immersed in that metal.
It will be necessary therefore to press down the spinal marrow below
the surface of the mercury, by means of a glass rod, or any other
non-conducting body, so that it may be entirely immersed; otherwise
some irregularity may take place, and the experiment fail. To perform
it with the greatest convenience, provide a glass vessel consisting of
two branches in the form of a syphon, as represented in Plate IV. fig.
2., one of which is wide, and has its edges reflected inwards, so as
to form an inverted cone, ending in an aperture that can be opened and
shut at pleasure. If mercury be poured into the narrower branch, so as
to fill the interior part of the vessel around the inverted cone, it
will not be able to rise up into the latter, until the aperture in its
apex be opened. When this arrangement has been made, immerse the
spinal marrow of a frog in the mercury contained in the smaller branch
of the vessel, and place the muscles in the conical part, which is
empty: if the aperture be then opened, the mercury, endeavouring to
bring itself into a state of equilibrium, will come in contact with
the muscles, and contractions will be produced; as an arc of
quicksilver will thus be speedily formed between the nerves and the
muscles.
VIII. But the experiment may be performed in a manner still more
simple. Provide a glass vessel (Plate IV. fig. 10.) filled with
mercury, and let the muscles of a prepared frog be laid to float on
the surface of the metal; then suspend the spinal marrow by a silk
thread in such a manner, that by letting down the thread the marrow
can be made to touch the mercury at pleasure. As soon as the spinal
marrow is brought into contact with the surface of the metal,
contractions will take place in the muscles; and the same will be
observed if a plate of gold or silver be substituted in the room of
the mercury. This phænomenon will be exhibited not only by a whole
frog, but by half a frog divided longitudinally; which, as soon as it
touches the mercury, by the method above described, will be violently
convulsed. Having mentioned these experiments to Galvani, to whom I
often had recourse for instructions, he regretted that I had confined
my researches to frogs only, and advised me to try warm-blooded
animals. I therefore took the leg of a lamb or a chicken, and holding
it in my hand in a vertical position, in such a manner that the bare
muscles were in communication with the mercury, I then raised the
crural nerve without any armature, so that, by being left to itself,
it could be made to touch the mercury at pleasure. As soon as it did
so, I observed a violent agitation and contraction in the whole limb,
and likewise when I used the before described apparatus, Plate IV.
fig. 2.
IX. While I made these experiments, I was well aware that the
contractions produced in the limb might by some be ascribed to the
impulse of the mercury, acting on it like a kind of stimulus, or to
electricity received from the surrounding bodies, rather than to the
innate electricity of animals. I would advise those who entertain such
an opinion to hold the hind legs of a frog in their hand, in a
vertical position, and to press only the spinal marrow against the
surface of the mercury. Let them immerse also the spinal marrow in
salt water, or in vinegar: no contraction will take place, though in
this case there is still a mechanical impulse; and though the saline
or acid quality of these liquids is exceedingly proper for acting as a
stimulus. To this I may add, that in the apparatus already described
(Plate IV. fig. 2.) there is no impulse from the mercury, which
acquires only that gentle motion necessary to enable it to put itself
into a state of equilibrium. In a word, I have observed (Plate IV.
fig. 1.) that when both the upper and lower vessels are filled with
mercury, if the aperture be opened so that the metal which falls down
shall not strike against the muscles; yet the same contractions take
place: which indeed ought to serve as a proof that mechanical impulse
has no share in producing the effect.
X. But I had no reason to apprehend the action of any stimulus, as I
had before found by experience, that a very strong impulse applied to
the nerves or to the muscles excited no contractions. I made
experiments for this purpose, not on living but on dead animals, when
the irritability was feeble and almost extinct; and I found that it
could be excited neither by pricking with a needle, by acids, nor by
the most powerful stimulants. It seemed to be entirely dead; but I
observed both in cold and in warm-blooded animals, provided the
experiment was performed within a certain period, that the
irritability was always obedient to the power of the Galvanic arc,
though no effect was produced by any mechanical impulse. As frogs were
most convenient for my experiments, I tried them with every possible
kind of mechanical stimulants. I immersed the spinal marrow or the
nerves in acids; pierced them with a needle; cut the nerves, and even
sometimes scooped out the whole medullary substance from the vertebral
canal; still no motion was produced. But the same nerves and muscles
which had withstood such powerful mechanical stimulants, when metallic
armatures and an arc were applied in the gentlest manner, immediately
exhibited contractions.
XI. Having obviated every objection that might be made in regard to
the action of stimulants, I shall now endeavour to remove any doubt
that may remain of external electricity. Provide a glass cylinder
terminating in a neck, and introduce into it a prepared frog with a
little mercury; incline the cylinder in such a manner, that the
mercury may occupy the lower part of it, and form an armature to the
muscles. If the extremity of the neck of the cylinder be applied to an
enameller’s lamp, and sealed hermetically, all communication between
the inclosed frog and the external air will be cut off. Now, if the
cylinder be removed from its inclined to a horizontal position, the
mercury, which was in contact only with the muscles, must touch also
the spinal marrow; and a mercurial arc being thus formed, contractions
will immediately follow. If the experiment be repeated with the glass
cylinder immersed in oil, the same contractions will take place; but
in this case it will be necessary to remove the immersed cylinder a
little from its position by means of a silk thread, in order that you
may be enabled to make the mercury flow from the nerves to the muscles
at pleasure.
XII. There is no reason, therefore, in this case, for ascribing the
contractions either to the arc or to the armatures, which, as they
consist of mercury alone, cannot produce the two kinds of electricity
necessary for exciting contractions. But even if we should allow, with
those who form the most absurd suppositions, that mercury alone
possesses both kinds of electricity, one contraction only could be
expected, and not several in succession. In a word, there is no reason
to apprehend that any external electricity is obtained either from the
glass vessel which receives the mercury, or from the surrounding
atmosphere, which is separated from the spinal marrow by three strata
of non-conducting bodies; namely, air, glass, and oil. The simplicity
of this process may not be fully apparent to the reader; but I can
with truth assert, that simplicity was an object which I had always in
view. Having prepared a frog, I laid it to float in mercury immersed
in oil, and then endeavoured to excite contractions by the application
of an insulated arc. Owing to some inaccuracy in the experiment,
however, it did not succeed; and my attachment to simplicity, while
endeavouring to discover the least complex method of exciting
contractions, was the cause of my not obtaining the desired result.
This want of success was perhaps owing to the mercury not being in
proper contact with the nerves, in consequence of the oil adhering to
them. That I might exclude all suspicion of atmospheric air having any
share in the phænomenon, I was obliged to adopt that method of
performing the experiment which I have already described.
XIII. I however readily foresaw, that the advocates of external
metallic electricity might object, that no contractions were obtained
but by the application of armatures, or, when armatures were excluded,
by using in their stead an arc, which is itself an armature. And I
must indeed acknowledge that we are as yet acquainted with no
substances but metals capable of exciting animal electricity, though
nature, so abundant in resources, may no doubt furnish a great
many[4]. But I shall here observe that metals are not the cause of the
contractions produced in animal bodies, but merely a condition
requisite for calling forth the latent innate animal electricity which
exists in them. For though armatures are necessary to render
non-conducting bodies electric, there is no reason why the shock given
by the Leyden flask should be ascribed to the arc or to the armatures;
as a charged magic square, or a Leyden flask, when freed from the
armatures, exhibits a great quantity of electricity. If you charge a
Leyden flask filled with water, pour the water from it, then pour in
other water, and form a communication by an arc between the opposite
surfaces, you will experience a shock. This very simple experiment
agrees with some made by Mr. Wilson, Mr. Cavallo, and others.
Armatures, therefore, have a powerful effect in attracting
electricity, and confining it in non-conducting bodies; but they do
not supply electricity themselves.
XIV. If this mode of reasoning be admitted in regard to common
electricity, it ought not to be rejected when applied to the phænomena
of animal electricity. For, as an explosion is produced by a magic
square, or Leyden flask, even when the armatures are removed, the case
is the same in regard to the contractions in animals. But to prove in
a more evident manner that metals have no action in such cases, the
following experiment was made. An insulated person, holding in his
hand a metallic arc, and a prepared frog, furnished with heterogeneous
armatures, was electrified, as well as every thing about him, by means
of an electrical machine. The person, the frog, the armatures, and the
arc, being all electrified positively, none of the metals employed in
this experiment, as their electricity was reduced to a state of
equilibrium, could produce contractions. As these are produced only by
applying the arc to the armatures, they cannot be ascribed to external
electricity, but to the innate electricity of the frog. If only one of
the armatures be touched, no contractions take place; but if the arc
be applied to both, they are immediately produced; which is a strong
proof that the arc possesses the power of exciting the electricity
inherent in animal bodies. Those philosophers would reason very
incongruously who should ascribe the cause of these contractions to
electricity communicated from the person, since they would thus allow
to the person that animal electricity which they deny to the frog; a
conclusion which few will admit. But in attempting to remove every
suspicion of communicated electricity, it was necessary that the
experiments undertaken should be free from all influence of artificial
electricity.
XV. I therefore endeavoured to obtain an equilibrium in the armatures
by mutual contact. This simple method was borrowed from the principles
adopted by philosophers, who, while they endeavour to produce an
equilibrium, are accustomed to apply a body electric by excess to one
in a contrary state. Immerse in water the spinal marrow of a prepared
frog, without armature, and let the muscles rest on a non-conducting
body. The vessel must be somewhat in the form of a syphon, and the
spinal marrow introduced into the smaller branch must not float on the
liquid, but be totally immersed in it: this arrangement is of great
importance in regard to the success of the experiment: a small piece
of tin foil must be made to float on the surface of the water at a
considerable distance from the spinal marrow: if you then touch the
muscles with one of your hands moistened a little with water, and with
the other apply a silver arc to the tin foil, a contraction will
immediately take place. While struck with the constancy of this
phænomenon, I could not help reasoning in the following manner:
Muscular motion is produced though the frog is in contact with no
metallic body: every thing metallic is separated from the frog; and
even if it possessed contrary kinds of electricity, they are in a
state of equilibrium. What then is the external agent which produces
contractions in the frog? Though the metals, while they acquire an
equilibrium, come into contact, which is followed by contractions,
there certainly can be no fear of external electricity from them. This
is sufficiently proved by the metals themselves being brought into
equilibrium before the contractions take place. If you touch the
muscles with one hand moistened with water, and with the other immerse
into water a piece of gold coin, a small part of which is covered with
tin foil, contractions will immediately ensue. Yet both the metals,
before the contraction, were brought to a state of equilibrium by
being in contact: they can therefore have no share in the
contractions, which must arise from innate electricity. If salt water,
milk, serum, or the crassamentum of the blood, be substituted for
common water, there will still be contractions; and the case will be
the same if a bit of gold, silver, or brass, or even iron, covered
with tin foil be employed. Here then we have tin brought into a state
of equilibrium with various metals before the contractions take place,
without these contractions being impeded. Nor is it of any consequence
that the metals be touched with the hand. For, if the tin foil be
applied to the tip of the tongue, or to the lips, and if a piece of
silver wire be made to touch the tin foil on the one side, and the
spinal marrow covered by no metal on the other, contractions will be
produced as often as an arc is made to the muscles by means of the
moistened hand.
XVI. The object of our researches hitherto has been muscular motion;
we shall now direct them to the phænomena of the senses. Let an
insulated person be electrified by means of a common electrical
machine, and let him apply a silver arc to the tip of his tongue
covered with tin foil. The armature and the arc will both become
electrified by this new accession of electric matter. We cannot
therefore suppose one armature to be positively and the other
negatively so; and for this reason no transmission of electricity, and
no sensation of taste, can be expected. As the tongue, however,
experiences a sensation of acidity, it must have been excited not by
the armatures or by the arc, but by the innate electricity of the
muscles and nerves. But the necessity of an internal arc, which
appears in the above phænomena, is an argument in favour of innate
electricity. In order, however, to excite the taste by animal
electricity, the application of different metals to the tongue is not
sufficient: the arc must be conveyed to the muscles of the tongue, or
to others at a distance from it. When I first made this experiment, it
gave me no small pleasure to find that it was confirmed and enriched
with new observations by the celebrated Volta[5].
XVII. That the phænomena already mentioned arise from an interior arc,
will be proved, in my opinion, by the following experiment: If an
insulated metallic arc, or a piece of charcoal, be applied to the tip
of the tongue with the moistened hand, no taste will be produced; but
if the same hand be applied to the same metallic arc or charcoal, a
taste will be experienced. In both cases of this experiment dissimilar
armatures were brought into contact, and reduced to that state of
equilibrium to which they tended. Why then should the result of the
experiment be so different? When the metals or charcoal touch the
moistened hand, a speedy and uninterrupted communication is formed
even between the remote muscles and the nerves of the tongue, which
when intercepted by the non-conducting body prevents all sensation of
taste. It may therefore be established as a principle, that to excite
a sensation of taste, it is necessary besides the application of
external armatures to have an internal arc, which may bring the
internal electricity to a state of equilibrium. This observation is
confirmed by Carradori, who, while endeavouring to excite a sensation
of taste in two persons at the same time, found that it was necessary
to establish an arc between them, either by making them join hands, or
by moistening the plane on which they stood[6].
XVIII. I shall conclude this dissertation with an account of some
later experiments on this subject. Volta, in a letter which I received
from him, requested I would try to produce contractions without any
metallic application, and recommended charcoal, which in his first
experiments he had found to be the best armature for animal
electricity. I therefore took the earliest opportunity of attempting
to produce contractions in the beforementioned manner without the aid
of metals. I was encouraged in this design by Aloysius Laghi,
professor of chemistry; who having analysed our fossil coal in
consequence of a public decree for that purpose, was desirous that
chemical processes might be made subservient to my researches. It was
well known, that every kind of vegetable charcoal formed the best
armature, so that when this coal was used there was no need for
metallic armatures. Hence, in that Galvanic experiment called the
animal alarum, a charcoal plane substituted for one of silver produced
the same effect: charcoal arcs also were used instead of metallic. The
coal employed in this manner was vegetable coal: but the English
fossil coal, and that dug up in our territories, did not produce the
same effect. I employed the different principles extracted from our
fossil coal, namely, calcareous earth saturated with the acetous acid,
siliceous earth semi-vitrified by fixed alkali, and argillaceous
earth. All these, however, formed bad armatures for animal
electricity; and the case was the same with the ashes of our fossil
coal, and of the English coal.
XIX. None of these phænomena, however, afforded any grounds for
objecting against the theory of electricity in general; as that
bituminous substance which is always found combined with fossil coal,
deprives it of the power of being a conductor of animal electricity.
This conjecture was confirmed by experience; for, having employed our
own fossil coal and the English in the state of coke, they formed
excellent armatures, as by the action of the fire they had been freed
from those idio-electric principles which opposed the development of
animal electricity, A phænomenon in the mean time occurred, which
tended to throw great light on the nature of this electricity. Having
placed the spinal marrow upon a piece of coke, and formed an arc from
the muscles to the coke, contractions always took place in certain
parts, while in others there was no appearance of them. The reason of
this seemed to be, that the action of the fire had made some parts of
the same coal conductors, and left others idio-electric, in
consequence of the large quantity of the bituminous principle which
they contained. But though torrified fossil coal acquired a conducting
property, vegetable charcoal was still found to be much fitter for
conveying animal electricity. Hence I conceived a hope, that I should
be able to excite contractions, in the manner before described,
without any metallic arc, and by the application of charcoal alone.
For these new experiments, I employed the largest frogs, and I
selected on purpose such pieces of charcoal as seemed the least fitted
for being conductors of animal electricity. I placed the prepared
muscles of a frog on the charcoal, and suspended the unarmed spinal
marrow, by a silk thread, in such a manner that the marrow could be
made to touch the charcoal at pleasure. When large frogs were
employed, contractions always took place; and Galvani found the case
to be same in his experiments. Here then we have contractions produced
without the intervention of any metallic substances: why then ascribe
to the different power of metals, effects which can be produced by
bodies which certainly have nothing of the metallic quality? If the
spinal marrow or muscles be made to communicate separately with the
charcoal, there will be no contraction; and it appears that to produce
contractions, the arc and the armature must consist of homogeneous
charcoal. Having given an account of my experiments, it remains that I
should collect in a few words the inferences which may be deduced from
them.
XX. In the first place, it is certain that to produce contractions it
is not necessary to employ two different kinds of metal, and that one
is sufficient. In vigorous animals this result may be obtained by
silver, and particularly by gold.
2d. If any suspicion of heterogeneity should arise, in regard to the
solid metals, this difficulty may be easily obviated by employing a
fluid metal, that is to say, mercury purified by chemical means.
3d. Contractions are excited when one of the armatures and the arc
consist of mercury, by making the mercury to run down on the muscles
placed below it. There is no reason here to suspect that the stimulus
produced by the impulse of the mercury has any share in the
phænomenon, as it is sufficiently proved by experiments that this is
not the case.
4th. That when there is no reason to suppose a want of equilibrium in
the electricity of the armatures and of the arc, animal electricity is
excited, and produces contractions.
5th. That when the armatures and arc are formed of charcoal, the same
results will be obtained; which evidently proves that the animal
electricity is not produced by the metals.
[3] The title of the work from which this and the following
dissertation are translated is, _Joannis Aldini de Animali
Electricitate Dissertationes duæ_. Bononiæ 1794.
[4] There seems here to be some mistake, as the author says,
towards the end of this Dissertation, that he produced
contractions in a frog by employing coals, both as an arc
and as armature. T.
[5] The celebrated Volta, in a letter which I received from
him, announcing that he had observed the same phænomena as
those described in my Dissertation, published the preceding
year, § xxii. p. 19. added the following remarks: “The best
and easiest method of performing this experiment, is to
immerse in a large earthen or glass vessel, filled with
water, a silver dish, in such a manner that a part of it
remains above the surface of the water; to apply to the tip
of the tongue a small bit of tin foil, so that part of it
shall hang out of the mouth; to bring this tin foil into
contact with the silver vessel, either immediately or by
means of a third piece of metal; lastly, to immerse the hand
in the same water gradually, if you are desirous of
perceiving gradually on the tongue the acid taste; or
suddenly, and at once, if you are desirous of perceiving it
at once and in the highest degree. A silver spoon half
immersed in the water, or instead of the dish, if not too
small, will produce nearly the same effect as I have already
mentioned. The case is not the same with a slender silver
rod or wire, which if gradually immersed will scarcely
produce any taste at all. If the vessel which contains the
water be itself of silver, a dish or spoon will then be
unnecessary. This vessel forms the best armature for the
water; and to perceive the taste very strongly, it will be
sufficient to immerse the hand in the water, or to bring the
tin foil which hangs from the mouth into contact with the
vessel.
[6] As convulsions are excited in two frogs, when one end of
an arc is made to touch the uncovered crural nerves of the
one, while the other end of the arc is applied to the crural
nerves of the other, covered by an armature; I have observed
that the sensation of two tastes, one acid and the other
alkaline, can be excited at the same time in the tongues of
two persons, one of which is armed with tin foil, and the
other with silver, if a communication be formed between the
two armatures. It is necessary, however, that a
communication also should exist between the two persons. If
the floor on which they stand be wet, and their shoes moist,
this will be sufficient. _Sig. Dottore Giovachino Carradori
Lettera quinta sull Ellettricità Animale, diretta al
Chiarissimo Sig. Cav. Felice Fontana._
SECOND DISSERTATION
ON
ANIMAL ELECTRICITY:
READ IN THE
INSTITUTE OF BOLOGNA,
IN THE YEAR 1794,
By J. ALDINI.
I. The philosophers of the present period are so sanguine in their
expectations, that when a new theory is proposed, unless it be
presented to them perfect and fully proved, they either attack it in
part, or entirely reject it. Such has been the case with animal
electricity, discovered by Galvani. It is urged against it by its
opponents, that it is subject to variations; and because they do not
find it obedient to all those laws established by the laborious
researches of a Franklin, a Beccaria and an Æpinus, they assert either
that it has no foundation, or that it is contrary to nature. It has
therefore been conceived that an accurate comparison of animal and
common electricity, in order to ascertain whether there be any
difference between them, might be the best means of obviating such
objections. For this purpose I made various experiments in animal
electricity under the air pump, employing proper conductors, and I
compared its phænomena with those exhibited by the Leyden flask. In a
word, while I endeavoured to pursue my researches agreeably to the
general theory of common electricity, my principal object was to prove
the constancy of animal electricity, by discovering, if possible, an
agreement in the physical laws of both.
II. As it had been proved by a great many experiments, that common
electricity could be obtained from non-conducting bodies in the most
perfect vacuum possible to be formed by means of an air pump,
experiments were undertaken in order to ascertain whether the same
phænomenon was common also to animal electricity, and with this view
attempts were made to excite the latter in vacuo[7]. Muscati indeed
had deprived animals of life in vacuo, and afterwards found them
susceptible of Galvanism in the open air; but he made no attempt to
determine whether the animal electricity could be manifested in vacuo.
I employed for my experiments a glass vessel; Plate IV. fig. 6.,
furnished with a metallic rod, which could be, raised up or pushed
down at pleasure. To the extremity of the rod, within the receiver,
was affixed at right angles a metallic wire, from one end of which an
armed frog was suspended by the muscles, and from the other a small
metallic chain a little longer than the frog, a plate of silver being
placed below both the frog and the chain. When as perfect a vacuum as
possible had been obtained, the metallic rod was pushed down, so that
the small chain and the spinal marrow of the suspended frog were made
to touch the silver plate, and by these means the latter formed an arc
in the exhausted receiver. In this experiment, the power of Galvanism
was found to be the same as in the open air, so that as often as the
rod was pushed down contractions were excited in the frog. By this
method it was easy to ascertain what repeated contact could produce by
forming new arcs: for though the small chain and the extremity of the
spinal marrow touched the silver plate; yet, when removed from that
position ever so little, by moving the rod new contractions took
place, which could not have been expected unless new contact on moving
the rod had produced as it were new arcs. This kind of apparatus
seemed the most convenient for performing in vacuo all those
experiments which Galvani had performed in the open air.
III. But it was as yet difficult to determine, whether the
contractions which took place were stronger in rarefied than in common
air; for the difference between the electricity was so small, that it
was impossible to say which was the more powerful. I therefore
resolved to clear up this point by other experiments. For this
purpose, having cut in two a prepared frog, I placed in vacuo one part
of it, by means of the above apparatus, and after a short period drew
it out, and compared it with the half which had not been subjected to
the action of a vacuum. On applying an arc, the one exhibited strong
and the other faint contractions; from which it appeared that the
vacuum had occasioned some loss of the animal electricity; as the
muscular and nervous parts subjected to experiment belonged to the
same frog, this evidently showed that the whole difference arose from
the action of the vacuum.
IV. It is well known that a vacuum absorbs common electricity; and
therefore it need not excite any wonder that in the present experiment
it should have dispersed some of the animal electricity. As this loss
took place by insensible degrees, strong contractions were not to be
expected; and the case is nearly the same in a Leyden flask loaded
with aqueous vapours, which produces no remarkable explosion. But
though convinced of the truth of this circumstance, I resolved to
confirm it by a new experiment. I therefore charged two Leyden flasks
armed in the same manner, applying them at the same time to the same
conductor, and by the same number of turns of the machine. One of
these flasks was introduced into the glass receiver of the air-pump,
and the other was exposed to the atmosphere. At the end of five
minutes after the air had been exhausted as much as possible, the
flask in the receiver was taken out, and, being discharged by a
metallic arc, emitted a weak spark, while the other flask exhibited
strong signs of electricity. I again charged two flasks by the same
turns of the machine till the electrometer indicated in both the same
degree of electricity, and kept one of them for half an hour beneath
the receiver. When the latter was taken out, it afforded a weak and
almost exhausted spark; while the other, which had remained in the
open air, emitted a strong one. Had the first flask remained longer
under the receiver, it would no doubt have entirely lost its
electricity; while the other without the machine retained that with
which it was charged.
V. In this experiment every possible care was taken to observe the
variations produced by the vacuum. The receiver which covered the
Leyden flask was of a large size, and the flask, being placed in the
middle of it, was at a considerable distance from its sides: the
receiver was well fitted to the plate of the machine, and not by means
of moist leather, as is usual, so that all communication with the
external air was prevented; and therefore there is no reason to
suppose that any aqueous vapour introduced into the machine, when the
pressure of the air was withdrawn, could perform the office of an arc.
That the electricity might not immediately bring itself to a state of
equilibrium, the conductor of each flask terminated in a ball: had not
this been the case, the whole electricity would soon have been
dispersed; for, when the conductors terminate in a point, if the
chamber be darkened, coruscations of light will every where be seen on
the glass receiver, and afford a most agreeable spectacle. A conductor
terminating in a ball seemed therefore to be most convenient for my
purpose, that, by rendering it more difficult for the electricity to
bring itself to an equilibrium, I might be able to produce a greater
imitation of the intimate manner in which animal electricity adheres
to the animals. But though in the above experiments I ascribe some
part of the phænomena to the animal electricity being weakened in
vacuo, I am of opinion that more is to be ascribed to the violent
perturbation of the principles which the vacuum must have excited in
the muscular and nervous parts.
VI. As it was now established, that animal electricity could be
excited in vacuo, I endeavoured to ascertain whether that excited
without the vacuum, and conveyed to the receiver, could be made to
pass through a very small space in vacuo. For this purpose I placed
the metallic rod at a small distance from a silver plate resting on
the bottom of the air pump: the limbs of a chicken or lamb, prepared
in the usual manner, were then deposited near it; and the muscles, by
means of a metallic chain, were made to communicate with the plate of
the machine, while an armed nerve was made to communicate by means of
an insulated arc with the metallic rod. The air being exhausted, the
rod was pushed down, and gradually brought as near as possible to the
plate without coming into actual contact with it. In this state no
contractions were produced; but they immediately took place when the
rod was brought into contact with the plate. It appears therefore that
animal electricity is considerably impeded in its progress by a
vacuum; and that, like artificial electricity, it does not readily
suffer itself to be dissipated, unless transmitted through good
conducting bodies. For, when a small quantity of the electric fluid is
accumulated in the Leyden flask, either none of it proceeds from the
metallic wire to a less perfect conductor, or, if any is transmitted,
it must be with difficulty, and with great violence. Common
electricity, indeed, is seen to pass quietly through metals or water
separately; but a strong electric spark, in proceeding from one
metallic conductor to another, if it pass through water interposed
between them, does so with such violence, that the glass vessel which
contains the water is in danger of being broken to pieces. That
electricity, therefore, may be conveyed from a conducting body, to one
less endowed with that property, it must be in such abundance as to be
able to overcome the resistance of the body through which it has to
pass: hence, it need excite no surprise, that the small quantity of
electricity which produces contractions should not be able to pass
over a very small space in vacuo. Here then we have a proof that
animal electricity is not only subject to the laws of non-conducting
bodies, but that it is affected different ways by the smallest
obstacles of conducting bodies, and by different kinds of them. It is
indeed so evident that a vacuum from its nature is unfit for conveying
electricity, that, even if one be produced, not by the usual method,
which is always attended with some defects, but in the most accurate
manner possible, it is totally improper for being a conductor of the
electric fluid. This is sufficiently proved by the following
experiment of Walsh: If two barometers be joined, and the upper part
or bend be carefully deprived of air, when one of these barometers is
electrified, the electric fluid will not be communicated to the other,
in consequence of the resistance opposed by the intervening vacuum.
Adams, however, exhibited by means of a single barometer the same
phænomenon as Walsh did with a double one[8]; for, having extracted
the air entirely from the upper part of the barometer, no electric
light was observed; but on introducing a very small quantity of air
the whole barometer became luminous. These observations are sufficient
to show that animal electricity, in regard to the property of not
being able to pass through a small space in vacuo, is subservient to
the general laws of common electricity. But let us proceed to other
phænomena respecting animal electricity excited in vacuo.
VII. If a prepared frog, furnished with two armatures, be placed in a
horizontal position on a non-conducting body, under a glass receiver,
(Plate IV. fig. 11.) and if an arc be formed by pushing down a rod, so
as to join both the armatures without touching the frog, contractions
will immediately take place; but if the smallest non-conducting body
intervene, none will be produced. I found it no very difficult matter
to exhibit in vacuo, by an apparatus somewhat similar, what may be
called an animal alarum. A horizontal arm fixed to a vertical moveable
rod (Plate IV. fig. 5.) was adapted to the inside of a glass receiver,
in such a manner that, when the receiver was exhausted, any body
resting on the horizontal arm could be made to fall down. The leg of a
prepared frog was then fixed to the vertical rod; while the other
rested on the horizontal arm, and the spinal marrow, with an armature
of tin foil, touched a silver plate in the bottom of the receiver. The
horizontal arm being turned round a little, by means of the vertical
rod, the leg of the frog resting on the arm fell down on the plate
below: an arc being thus formed, contractions immediately took place,
and were incessantly repeated, until all the animal electricity was
restored to an equilibrium.
VIII. These experiments were made on dead frogs; but I shall here show
that living ones also may be made to exhibit signs of electricity
under the same circumstances. A piece of tin foil was applied to the
back of a frog tied to a silver plate by means of silk strings, (Plate
IV. fig. 4.) and two metallic chains were suspended in such a manner,
that by pushing down the rod the extremity of the one chain could be
made to touch the silver plate, and the extremity of the other the tin
armature: when an arc was by these means formed, contractions
instantly took place. The frog began to breathe with difficulty, to be
agitated with convulsive movements, and to be seized with an universal
tremor, so that its last moment seemed to be approaching; but on air
being admitted into the receiver, it recovered and appeared as lively
and active as before. On examining more closely the changes which had
taken place in the animal while in this state, which was certainly
contrary to nature, I found the muscles red with a superabundance of
blood: but when dissected in the usual manner, they exhibited strong
signs of animal electricity; for, on applying an arc to the nerves or
muscles, without any armature, violent contractions were produced, and
continued for a long time, provided care was taken that there should
be no deficiency of animal moisture. That such a quantity of
electricity should be excited, will not seem astonishing to those who
have seen more violent electric commotions excited in the animal
machine by the action of a needle. This indeed has been placed beyond
all doubt by an observation of Gardini, who says “that having made
some experiments with a large torpedo, he remarked that stronger
convulsions were produced when the animal was subjected to great pain
by any means, such as pricking it with a needle[9].” The phænomena
exhibited by a vacuum or rarefied air, were exhibited also by
condensed air, so that very powerful contractions were produced by one
homogeneous arc. For, if the same apparatus described in Plate IV.
fig. 4. be adapted to a condensing machine, a dead frog introduced
into it will readily be contracted. Live frogs also, after being kept
for half an hour or a whole hour in air twice as dense as that of the
atmosphere, exhibited strong signs of electricity without any
armature, and merely by the application of a silver arc to the nerves
and muscles.
IX. Having made these experiments in vacuo and condensed air, it was
of some importance to try also what effect would be produced on animal
electricity by the action of the aëriform fluids. The apparatus
employed for this purpose was as follows: I provided a glass vessel
(Plate IV. fig. 3.), terminating at the upper extremity in a neck, to
which could be closely fitted, when necessary, a metallic cover,
having a perforation in the centre to receive a moveable rod, which
was connected with a transverse metal conductor supporting a frog
prepared in the usual manner. Having filled the vessel with water, or
mercury, which was still better, I placed it on the shelf of a
pneumatic tub, and introduced into it, according to Priestley’s
method, any particular gas. Some water or mercury was put into the
dish to which it was afterwards removed; and the metal cover, having a
frog suspended from it, being then fitted to the neck of the vessel,
the frog by means of this apparatus could be immersed at pleasure in
carbonic acid gas, hydrogen, or any other kind of gas; so that the
constancy of animal electricity might be tried in either. It is
evident that, by letting down the spinal marrow of the frog, and the
end of the conductor to the surface of the water or mercury, by means
of the rod, an arc will be formed, and that muscular contractions must
then be produced. The same experiment may be performed by means of a
bottle (Plate IV. fig. 6.) furnished with a cover like the former.
After being filled with water or mercury, it is inverted on the shelf
of the pneumatic tub, and the gas is then introduced in the usual
manner; but care must be taken not to displace the whole of the water
or mercury, as a portion must be left to cover the bottom when the jar
is turned up. This experiment I tried only with oxygen gas, reserving
the other kinds of air till a more convenient opportunity.
X. To give more weight to these experiments in vacuo, I endeavoured to
prevent all those errors which arose, or might be suspected to arise,
from the introduction of air; for I supposed that some opponent of the
theory of animal electricity, while endeavouring to find out
objections against it, since there was no foundation for asserting
that the vacuum afforded any electricity to the animals, might pretend
that, the plate of the pneumatic machine being metal, according to
custom, some electricity from the atmosphere might be attracted by it,
and be thus conveyed even through a vacuum to the animals. On this
account it was necessary that a vacuum should be formed, without
placing the receiver on a metallic plate; without the contact of any
conducting bodies, and in such a manner as to show that the
electricity excited was that really existing in the animals. I
therefore employed a glass receiver (Plate IV. fig. 9.) cut into two
parts above its middle, between which was placed a horizontal
partition, in order that the upper part might be filled with oil, or
some non-conducting body. The partition was perforated with a large
aperture, the superior edges of which projected a little upwards; and
the lower, projecting downwards, were furnished with small circular
grooves, so that the hole could be shut by a piece of bladder tied
over it with thread. A sharp-pointed rod was placed over the hole, so
that, being let down by a non-conducting handle, it could be made to
pierce the bladder. This, however, was to be done only when the lower
part of the receiver was exhausted of air; for the oil, when the air
is withdrawn, speedily falls down: by these means a vacuum is formed
in the upper part, and, in consequence of the interposed stratum of
the oil, remains insulated, as it can receive no electricity from the
metallic plate of the machine, nor from other conducting bodies. But
it will be in vain to attempt to form a vacuum in this manner, unless
the parts of the cut glass be so fitted as to prevent entirely the
admission of external air. A very simple and ingenious apparatus, for
the same purpose, was invented by F. Borelli: in order to stop the
efflux of the oil at pleasure, he adapted to the hole a glass cone, by
which means he was enabled to produce an insulated vacuum of greater
or less capacity in the upper part of the receiver. Here then I had a
vacuum every where surrounded with non-conducting bodies, so that, if
animal electricity were excited in it, there could be no reason for
ascribing it to electricity borrowed from the atmosphere.
XI. I adapted to a glass rod, in a longitudinal direction, a metallic
plate, (Plate IV. fig. 7.) which at the upper extremity was bent into
a right angle, and supported the spinal marrow of a frog, so that it
might be considered as a lengthened conductor of the nerves. This
plate was inserted into a glass receiver, so as to move in it with
ease; and by means of a screw could be fixed at any altitude whatever.
An accurate representation of this apparatus, with the glass rod
annexed, is seen in Plate IV. fig. 8. Iron hooks fixed to the feet of
the suspended frog acted the part of a conductor to the muscles; and
the upper part of the receiver being exhausted of air, as above
described, a stratum of oil was still left to separate the frog from
the partition. To guard against all danger from the action of any
internal metallic body, a strong magnet was applied to the iron
conductor of the muscles, which, immediately obeying the power of
attraction, fell upon the conductor of the nerves; and thus a circuit
of animal electricity from the muscles to the nerves being speedily
effected[10], contractions were immediately produced. When I
communicated this experiment to the Institute, I was extremely
desirous that the apparatus I had here invented for the purposes of
animal electricity might be of some advantage to the science of
philosophy in general, of which I was always fond, and which formed
the chief object of my study. But it is necessary that I should
mention to what I more particularly allude.
XII. Such bodies as had hitherto been put into the air pump were
gradually subjected to the action of a vacuum. Hence it appeared that
the apparatus above described might be attended with a considerable
degree of utility; as in future, any body whatever, whether solid or
fluid, might be subjected to this action at once. For, the lower part
of the receiver being deprived of its internal air, if the bladder be
burst by means of the glass rod, the fluid will run down and occupy
the space emptied of air, leaving a vacuum in the upper part. When the
fluid has thus fallen to the lower part of the receiver, solid bodies
even, if any were immersed in it while in the upper part of the
receiver, will also experience the action of the vacuum. But liquid
bodies are of such a nature, that they have united with them certain
aëriform fluids, which, when the pressure of the air is removed,
readily expand. A fluid, therefore, when it has fallen to the lower
part of the receiver, being agitated and thrown into a state of
perturbation by the motion, its most subtle principles will be
extricated, and fill the capacity of the bell. The vacuum will then be
disturbed by the evaporation, which, acting on the mercury in the
barometer connected with the air pump, will cause it to fall. But
every one acquainted with the principles of philosophy must know, that
the depression of the mercury in the barometer will be greater,
according as a greater quantity of aëriform fluids has been disengaged
in the receiver; and if the degree of pressure in the barometer varies
according to the variety of aëriform principles, it may be readily
seen, that this method may be employed to determine the quantity of
them, or their elasticity, since they are cut off from all
communication with the surrounding atmosphere, though it still
exercises its pressure upon them.
XIII. The vacuum here obtained in the upper part of the bell, seems to
be far superior to that produced in the lower part, according to the
usual method. For it has long been a complaint among philosophers,
that by working the air pump the air is only rarefied, till it no
longer possesses elasticity capable of raising the valve, so that it
is impossible to produce a complete vacuum by this method. If we can
credit the followers of Euler, that subtle fluid, which they call
ether, and which permeates every thing, still remains; for, adopting
the opinion of the antient Peripatetics, they consider a vacuum as
beneath the dignity of nature. But, setting aside this question, I
shall only observe, that if a vacuum be formed in the upper part of
the receiver, by the method above described, it does not appear that
it can be disturbed by any thing from without, and the gravity of the
falling fluid will not suffer itself to be overcome by the subtle
ether, if any really exists. Should it be apprehended that the air
contained in the oil may be disengaged, and disturb the vacuum, you
may substitute in its stead mercury or water, which can be deprived of
air either by boiling or by long exposure to the action of a vacuum.
But before any thing certain on this subject can be said, new and
repeated experiments will be necessary. As every objection that could
be made in regard to a vacuum seems now to be obviated, since a space
perfectly free from common air can be produced, and cut off from all
communication with the atmosphere, or with conducting bodies, I shall
return to animal electricity, from which I was led by a desire of
contributing towards the improvement of natural philosophy in general.
XIV. Those who attempt to determine the velocity of the nervous fluid
in a given time, undertake a matter of great difficulty, respecting
which nothing certain can be known. Haller rejected the suppositions
of those who, comparing the tenuity of the nervous tubes of the heart
with the large branch of the aorta, were of opinion, that the velocity
of the nervous fluid must be two thousand eight hundred and eighty
times greater than that of the blood. This celebrated physician,
distrusting hypothesis, had recourse to experiment, and found that the
velocity of the nervous fluid would be no less than nine thousand feet
in the first minute. But in this determination of the velocity of the
nervous fluid there seems to be some difficulty, which perhaps ought
to be ascribed rather to the period when that celebrated man lived,
than to his want of sagacity or accuracy. Had Haller possessed the
means of conveying the nervous fluid with his own hands to different
parts at pleasure, he would no doubt have given us some more certain
ideas respecting its rapid motion. I resolved, therefore, not to
neglect those advantages with which the modern philosophy has been
enriched, and to employ very long metallic arcs, by which I could
direct the animal electricity as I pleased. A staircase which reached
from the top to the bottom of the house, with many windings, presented
me with an iron plate, exceedingly convenient for the transmission of
animal electricity. A metal wire, brought down from the top of the
staircase, was connected with the iron plate, and by these means I
obtained an arc, the length of which was above one hundred and fifty
feet. When this arrangement was made, the two extremities of this very
long arc were applied to the armed nerves and muscles of a frog; and
the animal electricity being thus excited, instantly proceeded with so
much velocity from the one extremity of the arc to the other, that no
difference could be perceived between the time when the frog touched
the arc, and that when it began to be agitated. But to show that this
result was not owing entirely to the metallic conductor, I employed
long ropes dipped in salt water, and always with the same effect. This
circumstance seems to prove, in a striking manner, a great similarity
between the nervous fluid and common electricity, and to overturn the
opinion of Haller, who, according to his calculations, makes the
nervous fluid require a second for passing over the space of 150 feet.
XV. According to Beccaria, a celebrated observer of the propagation of
the electric fluid, there are two ways of its being transmitted; one
when it flows through conducting bodies only, and the other when,
being collected in non-conducting bodies, it proceeds from the coating
electric by excess to that which is in the contrary state. In the one
case, Beccaria establishes a certain time for its passage; in the
other he allows none. This celebrated man observed, that the electric
matter was conveyed from the conductor of a machine, along a metallic
wire 500 feet in length, in the course of a second; in its passage
along a hempen rope of the same length, it employed seven seconds; but
when the rope was moistened with water, it required only two or nearly
three vibrations of a pendulum. When he discharged a Leyden flask by
the longest conductor, he was never able to observe the least interval
of time. The same thing was remarked by Jallabert, Sigaud de la Fond,
and other philosophers, who performed their experiments, not in an
apartment but in the open air; and conveyed the electric fluid in this
manner for a considerable distance along the banks of large rivers.
Monnier extended two iron wires[11] in an open field, parallel to each
other, for the distance of 5107 feet; and a man placed between them
held in his hands the extremity of the conductors, keeping them at a
little distance from his body. “But the man, who was in the middle of
the arc,” says the author, “while he saw the spark issue from the jar,
received the shock: he could have distinguished the smallest interval
of time between the explosion and the shock; and if it had amounted to
the fourth part of a second, it could have easily been remarked.”
XVI. While reflecting on these facts, I formed a conjecture from the
great celerity with which animal electricity is conveyed, respecting
the manner in which it is evolved. If the animal electricity were
conveyed from a muscle to a nerve, or vice versa, in the same manner
as the common electric fluid is conveyed from the machine by the
chain, it would have been observed to employ some time, however small,
in its passage. As I at first ascribed this to the shortness of the
conductor I had used, I extended it to more than 250 Parisian feet,
and applied the nerves and muscles of a frog to this new conductor in
the manner above described, without observing the least obstacle to
the passage of the electric fluid. As this arc formed a half of that
employed by Beccaria, the space of half a second would have been
required, if we consider in this passage only one kind of electricity.
But the half second required according to the observations of Beccaria
was not observed: it therefore appears, that this propagation of
animal electricity ought not to be referred to the first-mentioned
case, but to that where equilibrium is restored between the negative
and positive state.
XVII. This rapid conveyance of animal electricity, however, is
entirely stopped, if the metallic arc be intercepted, not only by
non-conducting but by certain conducting bodies. Here then we have
again occasion for the action of two contrary kinds of electricity.
For the electric matter, whether positive or negative, when conveyed
from the machine to the chain, pervades all bodies in the same manner,
provided they be conductors. Thus the metallic conductor of the
machine, the insulated person, and all other bodies that may be
connected with it, become electric in the same manner. But the same
electric matter collected in non-conducting bodies requires, before it
can be discharged, certain conditions in the conducting bodies by
which it is discharged. When the metallic arc is interrupted by a
little water, the Leyden flask, if it contain a moderate quantity of
electricity, cannot be discharged; for the two contrary kinds of
electricity to be discharged require that every part of the arc should
be equally endowed with the property necessary for conducting the
electric fluid. But in the case of only one kind of electricity, it
would pass with great readiness either through water or metal. Let us
now apply these phænomena of general electricity to the theory of
animal electricity. In the experiment mentioned in the sixth section,
if only one kind of electricity proceeded from the nerves or the
muscles, it would be immediately conveyed from the nerve to the metal,
then to the vacuum back to the metal, and thence to the muscle, as
being the place from which it issued. Besides, the electricity
propagated in this manner would have produced contractions, which
however were not observed. The progress of the animal electricity,
therefore, experienced considerable obstacles, not only from
non-conducting but also from conducting bodies; which affords a strong
proof that electricity exists and is collected in the muscular fibre,
in the same manner as in non-conducting bodies. But the remarkable
quickness of the progress of animal electricity leads me to the Leyden
flask; and therefore I shall here say a few words respecting the
analogy between the phænomena it exhibits, and those of animal
electricity; and give an account of the reasons which first induced me
to enter on this comparison.