DISSERTATIONONANIMAL ELECTRICITY:READ IN THEINSTITUTE OF BOLOGNA,IN THE YEAR 1793,[3]ByJ. ALDINI.I.Whileour 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 supposedto 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 anarc 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 sometimeswith 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 onlyin 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 (PlateIV.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 preventthe 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 inPlateIV.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 (PlateIV.fig. 10.) filled with mercury, and let the muscles of a prepared frogbe 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,PlateIV.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 surroundingbodies, 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 (PlateIV.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 (PlateIV.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 Iobserved 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 mercurialarc 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 theleast 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 takeplace; 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 tinfoil, 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 withthe 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 confirmedand 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 resultof 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 recommendedcharcoal, 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 conductorof 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 inhis 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.
ON
ANIMAL ELECTRICITY:
READ IN THE
INSTITUTE OF BOLOGNA,
IN THE YEAR 1793,[3]
ByJ. ALDINI.
I.Whileour 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 supposedto 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 anarc 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 sometimeswith 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 onlyin 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 (PlateIV.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 preventthe 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 inPlateIV.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 (PlateIV.fig. 10.) filled with mercury, and let the muscles of a prepared frogbe 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,PlateIV.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 surroundingbodies, 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 (PlateIV.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 (PlateIV.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 Iobserved 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 mercurialarc 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 theleast 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 takeplace; 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 tinfoil, 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 withthe 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 confirmedand 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 resultof 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 recommendedcharcoal, 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 conductorof 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 inhis 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.