Part 11
XXI. Some, perhaps, will object to this analogy, that in the above experiments the flask destitute of electricity forms the arc; while, on the contrary, both flasks ought to be charged to represent properly the muscles and nerves of frogs, which both possess electricity. But the very same phænomenon is observed in two charged flasks, provided one of them is charged with more electricity than the other. Hence, in support of our analogy, we need only assume, that the quantity of electricity in the one frog is a little different from that of the other; a supposition which, in forming an hypothesis, the severest philosopher may allow. I shall say nothing of the great variety and connection of the elements of which animal bodies are composed, and which on this account require a difference in the quantity of the animal electricity. It appears by some late experiments of Valli[13], that animal electricity is discharged in the same manner as that which is collected in non-conducting bodies. It is likewise proved, that the same arc and the same armatures, according to the various consensus and connection of the nerves, and according to the different positions in which they are applied, elicit a larger or smaller quantity of electricity, and sometimes none at all. Those indeed who consider these observations will hardly think it possible, when animal Leyden flasks consist of so many different parts, that there should not be some difference in the electricity collected. But there is no need of employing conjecture in regard to a point, which is confirmed not only in regard to animals, but in all conducting bodies, by the ingenious observations of Coulomb[14]; for it is fully established that the electric matter is communicated and accumulated different ways on the surface of conducting bodies. But if this phænomenon takes place in conducting bodies the parts of which are homogeneous, there is no reason to deny that it may appear in animals in which provident nature has so intermixed conducting with non-conducting parts, in order that the action of animal electricity might not be short and transient, but constant and durable.
XXII. But if the diversity in the structure of animal bodies require that the force and power of the animal electricity, collected in the corresponding muscles, should be different, a singular agreement will appear between the phænomena of the Leyden flask and those of animal electricity. If an insulated person touch two flasks containing equal quantities of electricity, however great, he will experience no shock; but if one of the flasks contain a greater charge than the other, he will receive a shock according to the ratio of the difference of the electricity of the flasks. Though the frogs therefore represent two Leyden flasks, one of them may act the part of an arc, and produce an equilibrium, provided it be allowed that there is a difference between the quantities of the electricities collected. I have here endeavoured to establish the proposed analogy, not because I suppose the muscles to be so many Leyden flasks, such as they are exhibited to us by the ingenuity of philosophers, but in order to show that many phænomena are common to both; nor have I applied animal electricity to explain all the phænomena of muscular motion, with a view of obtaining applause from those who are zealous advocates for this theory. I must also observe, that if in the prosecution of this object I have met with any anomalies, I do not on that account despise the agreement of the laws of philosophy which have been established by so much labour. Several of the phænomena observed by Galvani and others have served me as a foundation for the proposed analogy, and induced me to extend, if possible, its boundaries. But going back to the origin of animal electricity, since it belongs to the subject, I shall here take a general view of the whole, and express the substance of it in a few corollaries.
XXIII. The corollaries I propose will follow the order of time in which they arose, and therefore will express the gradual improvement of animal electricity.
1. Animal electricity passes freely through bodies which possess nearly the same degree of conducting power, but it does not pass through non-conducting bodies.
2. It is affected by the obstacles which occur, not only in non-conducting but in conducting bodies, as well as by their varieties; and if these obstacles be numerous, its passage is stopped: but if it be possible to overcome them, the impediment causes it to make a more powerful effort to attain to a state of equilibrium. Hence, unlike armatures and arcs are of great effect in exciting a moderate degree of electricity, when the same electricity resists the power of a homogeneous metal.
3. Animal electricity obeys the law of equilibrium; for, when the muscles have been brought to a state of equilibrium with the corresponding nerves, no contractions are produced by the application of an arc; but if that which produces the equilibrium be removed, the contractions immediately take place.
4. Poisons, mephitic air, aëriform fluids, and condensed air, do not prevent animal electricity from being excited.
5. The influence of a vacuum on animal electricity is various. In dead animals, if kept a long time in vacuo, the animal electricity is weakened: in living animals it is considerably increased.
6. Though a vacuum does not prevent the electricity from being excited, it will not serve as a conductor of it when it has been excited: if an arc from the nerves to the muscles be intercepted by the smallest vacuum, no contractions take place.
7. As metallic armatures are of great effect in attracting and collecting artificial electricity, the case is the same with animal electricity; but care must be taken not to ascribe to them that electricity which the muscles naturally possess.
8. Though unlike armatures have a great effect in calling forth animal electricity, we have reason to conclude from several experiments, that they do not contain two kinds of electricity capable of producing muscular motion.
9. As natural electricity issues with great force from sharp-pointed bodies, and proceeds to them more readily than to others, the case is the same in regard to animal electricity, as it issues more readily from the pointed parts of the metallic arming applied to the nerves and muscles.
10. The nervo-electric fluid is propagated with that rapidity which is required in restoring to an equilibrium two opposite kinds of electricity.
11. The same conditions which cause two flasks to be discharged when an arc is established from the exterior coating of the one to the interior coating of the other, excite contractions in two frogs, when an arc is formed from the nerve of one to the muscles of the other.
12. The arc applied as above mentioned to the interior coating of two phials, and to the nerves of two frogs, seems to give more force to the proposed analogy; for the electric explosions have a great similarity to the muscular motions excited in the frogs.
I might have enlarged the number of these corollaries, had not the well-known fate of various opinions, now consigned to oblivion, rendered me more timid in hazarding conjectures. I, however, did not allow myself to think that I ought so far to give way to my timidity as to check the spirit of inquiry, or to abandon the hope of one day attaining to the truth. But it would be unreasonable to expect in animal electricity, which is yet in its infancy, that precision and those satisfactory results which can be the work only of time, and of the continued labour of philosophers.
[7] As this term is improperly used by philosophers, I must here observe, that I shall in future understand by it air highly rarefied by the usual means.
[8] In the description of a new air-pump of his invention, where he shows that electricity cannot pass through a vacuum, he adds: “There can be little doubt, from the above experiment, of the non-conducting power of a perfect vacuum; and this fact is still more strongly confirmed by the phænomena, which appear upon the admission of a very minute particle of air into the inside of the gauge. In this case, the whole becomes immediately luminous upon the slightest application of electricity; and a charge takes place, which continues to grow more and more powerful, in proportion as fresh air is admitted, till the density of the conducting medium arrives at its maximum. _An Essay on Electricity, explaining the Theory and Practice of that useful Science._ Third edit. London, 1787.
[9] Josephi Gardini de Electrici Ignis Natura Dissertatio, Regiæ Scientiarum Academiæ Mantuanæ exhibita, Mantuæ 1792, p. 100.
[10] This may be accomplished in a much more simple manner, without the aid of a magnet, by connecting a wire with the lower part of the nerves, and applying the wire to the muscles by turning the rod round.
[11] Précis historique et expérimental des Phénomènes électriques, par M. Sigaud de la Fond, Paris 1781, sect. i. art. 4.
[12] Aloysii Galvani de Viribus Electricitatis in Motu musculari Commentarius, Mutinæ iterum editus, p. 29.
[13] M. Valli Cinquième et Huitième Lettre sur l’Electricité Animale, dans Observations sur la Physique, par M. l’Abbé Rozier, tom. xlii. Paris, 1792.
[14] Recherches sur la Distribution de Fluide Electrique entre plusieurs Corps Conducteurs, et la Détermination de la Densité Electrique dans les différens Parties de la Surface de ces Corps. _Mem. de l’Acad. Royale des Sciences, An. 1788._
CONCLUSION.
I publish my experiments respecting muscular contractions produced by one metal with the greater confidence, as they were repeated different ways by the celebrated Humboldt, who has adopted my opinion. In his work on Galvanism, under the head which he entitles “Answer to the Objections made by Volta to the Experiments of Aldini,” he says, “J. Aldini of Bologna invented a very ingenious apparatus, by means of which he was enabled to refute the supposition of Professor Volta. For this purpose he had recourse to mercury: every thing relating to his experiments is very well represented in the plate which accompanies his memoir. Volta, in reply to these experiments, observes, that they can impose only on those who have not thoroughly examined them. He denies the facts related by Aldini, and persists in his opinion that the phænomena of Galvanism may all be referred to the laws of heterogeneity. In regard to the experiments made with mercury, he says that there is a great difference between the surface of this metal and the interior of its mass; because the surface becomes oxidated by the contact of the atmospheric air; that consequently, in the experiment of Aldini, the conducting arc is not really but apparently homogeneous, the organs being immersed to different depths in the metal: besides, that the mercury in these experiments produces a shock; and that, as this shock is not the same at both extremities of the arc, the result is an unequal development of electricity. Volta, therefore, opposes to the phænomena described by Aldini nothing but hypothesis. We might reply in the same manner; but as it is much better in philosophical disputes to have recourse to experiments, I undertook some researches for the purpose of removing all doubt in regard to this subject.
“I purified mercury by all the known means employed for that purpose. I strained it several times through a piece of chamois leather; I washed it with water and soap, with vinegar and with alcohol. It appeared to me that it contained neither lead nor tin; and that it was free from oily particles and dust: it was perfectly fluid, and divided itself into small, very round globules, which did not adhere to each other, and which left behind them no traces. Its surface was as brilliant as that of glass, without any pellicle or spot; and a small quantity of it being stirred in a mortar with water, did not communicate to it any sensible colour. It dissolved in nitric acid without sensible effervescence, and without giving any precipitate. A large quantity of mercury thus purified was poured into three porcelain vessels; and as I was aware that, if I performed several experiments with the same quantity of mercury, it might be objected, that the metal had contracted some impurity by the mere contact of the animal substances, I made only one experiment with the mercury in each of the vessels.
“I prepared several legs of frogs in such a manner that a portion of the crural nerve and a part of the muscle of the same length were left dependent. I placed a glass tube in a horizontal direction above a vessel containing mercury; made fast to it two silk threads, and suspended from it the thigh of the leg in such a manner that the nerve and muscle could be made to descend at pleasure. I brought the leg of the frog within two lines of the vessel, and then lengthened the thread till the nerve touched the surface of the metal. No contractions took place; but as soon as the nerve also was brought into contact with the metal, by lengthening the silk thread, the whole limb experienced a convulsive shock. I repeated this experiment with the same precaution, employing the two other vessels, and the same results were obtained.
“The muscle and nerve touched the mercury only at the surface; they were in no manner immersed in the metal; and care had been taken to lower them so gently, that it was impossible to suspect there could be any impulse, as in the experiment where Aldini had caused the mercury to flow down by employing a vessel shaped somewhat like a syphon.”
APPENDIX.
No. I.
_An Account of the Experiments performed by J. Aldini on the Body of a Malefactor executed at Newgate Jan. 17th 1803._
INTRODUCTION.
The unenlightened part of mankind are apt to entertain a prejudice against those, however laudable their motives, who attempt to perform experiments on dead subjects; and the vulgar in general even attach a sort of odium to the common practice of anatomical dissection. It is, however, an incontrovertible fact, that such researches in modern times have proved a source of the most valuable information, in regard to points highly interesting to the knowledge of the human frame, and have contributed in an eminent degree to the improvement of physiology and anatomy. Enlightened legislators have been sensible of this truth; and therefore it has been wisely ordained by the British laws, which are founded on the basis of humanity and public benefit, that the bodies of those who during life violated one of the most sacred rights of mankind, should after execution be devoted to a purpose which might make some atonement for their crime, by rendering their remains beneficial to that society which they offended.
In consequence of this regulation, I lately had an opportunity of performing some new experiments, the principal object of which was to ascertain what opinion ought to be formed of Galvanism as a mean of excitement in cases of asphyxia and suspended animation. The power which exists in the muscular fibre of animal bodies some time after all other signs of vitality have disappeared, had before been examined according to the illustrious Haller’s doctrine of irritability; but it appeared to me that muscular action might be excited in a much more efficacious manner by the power of the Galvanic apparatus.
In performing these experiments, I had another object in view. Being favoured with the assistance and support of gentlemen eminently well skilled in the art of dissection, I proposed, when the body should be opened, to perform some new experiments which I never before attempted, and to confirm others which I had made above a year ago on the bodies of two robbers decapitated at Bologna.
To enlarge on the utility of such researches, or to point out the advantages which may result from them, is not my object at present. I shall here only observe, that as the bodies of valuable members of society are often found under similar circumstances, and with the same symptoms as those observed on executed criminals; by subjecting the latter to proper experiments, some speedier and more efficacious means than any hitherto known, of giving relief in such cases, may, perhaps, be discovered. In a commercial and maritime country like Britain, where so many persons, in consequence of their occupations at sea, on canals, rivers, and in mines, are exposed to drowning, suffocation, and other accidents, this object is of the utmost importance in a public view, and is entitled to every encouragement.
Forster, on whose body these experiments were performed, was twenty-six years of age, seemed to have been of a strong, vigorous constitution, and was executed at Newgate on the 17th of January 1803. The body was exposed for a whole hour in a temperature two degrees below the freezing point of Fahrenheit’s thermometer; at the end of which long interval it was conveyed to a house not far distant, and, in pursuance of the sentence, was delivered to the College of Surgeons. Mr. Keate, master of that respectable society, having been so kind as to place it under my direction, I readily embraced that opportunity of subjecting it to the Galvanic stimulus, which had never before been tried on persons put to death in a similar manner: and the result of my experiments I now take the liberty of submitting to the public.
Before I conclude this short introduction, I consider it as my duty to acknowledge my obligations to Mr. CARPUE, lecturer on anatomy, and Mr. HUTCHINS, a medical pupil, for the assistance they afforded me in the dissection. I was also much indebted to Mr. CUTHBERTSON, an eminent mathematical instrument maker, who directed and arranged the Galvanic apparatus. Encouraged by the aid of these gentlemen, and the polite attention of Mr. KEATE, I attempted a series of experiments, of which the following is a brief account.
EXPERIMENT I.
One arc being applied to the mouth, and another to the ear, wetted with a solution of muriate of soda (common salt), Galvanism was communicated by means of three troughs combined together, each of which contained forty plates of zinc, and as many of copper. On the first application of the arcs the jaw began to quiver, the adjoining muscles were horribly contorted, and the left eye actually opened.
EXPERIMENT II.
On applying the arc to both ears, a motion of the head was manifested, and a convulsive action of all the muscles of the face: the lips and eyelids were also evidently affected; but the action seemed much increased by making one extremity of the arc to communicate with the nostrils, the other continuing in one ear.
EXPERIMENT III.
The conductors being applied to the ear, and to the rectum, excited in the muscles contractions much stronger than in the preceding experiments. The action even of those muscles furthest distant from the points of contact with the arc was so much increased as almost to give an appearance of re-animation.
EXPERIMENT IV.
In this state, wishing to try the power of ordinary stimulants, I applied volatile alkali to the nostrils and to the mouth, but without the least sensible action: on applying Galvanism great action was constantly produced. I then administered the Galvanic stimulus and volatile alkali together; the convulsions appeared to be much increased by this combination, and extended from the muscles of the head, face, and neck, as far as the deltoid. The effect in this case surpassed our most sanguine expectations, and vitality might, perhaps, have been restored, if many circumstances had not rendered it impossible.
EXPERIMENT V.
I next extended the arc from one ear to the biceps flexor cubiti, the fibres of which had been laid bare by dissection. This produced violent convulsions in all the muscles of the arm, and especially in the biceps and the coraco brachialis even without the intervention of salt water.
EXPERIMENT VI.
An incision having been made in the wrist, among the small filaments of the nerves and cellular membrane, on bringing the arc into contact with this part, a very strong action of the muscles of the fore-arm and hand was immediately perceived. In this, as in the last experiment, the animal moisture was sufficient to conduct the Galvanic stimulus without the intervention of salt water.
EXPERIMENT VII.
The short muscles of the thumb were dissected, and submitted to the action of the Galvanic apparatus, which induced a forcible effort to clench the hand.
EXPERIMENT VIII.
The effects of Galvanism in this experiment were compared with those of other stimulants. For this purpose, the point of the scalpel was applied to the fibres, and even introduced into the substance of the biceps flexor cubiti without producing the slightest motion. The same result was obtained from the use of caustic volatile alkali and concentrated sulphuric acid. The latter even corroded the muscle, without bringing it into action.
EXPERIMENT IX.
Having opened the thorax and the pericardium, exposing the heart _in situ_, I endeavoured to excite action in the ventricles, but without success. The arc was first applied upon the surface, then in the substance of the fibres, to the carneæ columnæ, to the septum ventriculorum, and lastly, in the course of the nerves by the coronary arteries, even with salt water interposed, but without the slightest visible action being induced.
EXPERIMENT X.
In this experiment the arc was conveyed to the right auricle, and produced a considerable contraction, without the intervention of salt water, but especially in that part called the appendix auricularis: in the left auricle scarcely any action was exhibited.
EXPERIMENT XI.
Conductors being applied from the spinal marrow to the fibres of the biceps flexor cubiti, the gluteus maximus, and the gastrocnemius, separately, no considerable action in the muscles of the arm and leg was produced.
EXPERIMENT XII.
The sciatic nerve being exposed between the great trochanter of the femur and the tuberosity of the ischium, and the arc being established from the spinal marrow to the nerve divested of its theca, we observed, to our astonishment, that no contraction whatever ensued in the muscles, although salt water was used at both extremities of the arc. But the conductor being made to communicate with the fibres of the muscles and the cellular membrane, as strong an action as before was manifested.
EXPERIMENT XIII.
By making the arc to communicate with the sciatic nerve and the gastrocnemius muscle, a very feeble action was produced in the latter.
EXPERIMENT XIV.
Conductors being applied from the sciatic to the peronæal nerve, scarcely any motion was excited in the muscles.
EXPERIMENT XV.