Digitale Ausgabe

The phænomena of electric fish ought to be the subject ofour renewed researches, with a view to the opinion of manyphilosophers, who conceive that they are capable of beingexplained upon the principles of that beautiful theory withwhich Volta has enriched science. You well know, myrespected friend, what must have been our anxiety to pro-cure the torpedo; and you will perhaps be astonished thatI should be so long in writing to you respecting it. AtGenoa we found some of them, but we were then withoutinstruments. At Civita Vecchia we searched for them invain. At last, during our stay at Naples, we procuredthem very frequently, of great size, and very vigorous. Ishall relate to you, in this letter, the series of experimentswhich M. Gay-Lussac and I have instituted upon the actionof the torpedo (Raja Torpedo of Linnæus). M. de Buch,a German mineralogist, was present at our experiments. Ipresent to you the results which they afforded, and relatethe facts without introducing any theoretical notions. Our experiments were principally intended to discoverthose conditions in which the torpedo is unable to commu-

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† From Annales de Chimie, no. 166.|357| nicate those shocks termed electric, although the feeling isvery different from that which is occasioned by the dis-charge of a Leyden phial. Having at hand no other workbesides that of Aldini, in which he has combined into oneview the beautiful researches of Geoffroy with those of Spallanzani and Galvani, we shall not have it in our powerto compare our own labours with those of preceding phi-losophers. 1. Although the power of the torpedo cannot be com-pared to that of the gymnotus, it is not less capable of oc-casioning disagreeable sensations. A person much in thecustom of receiving electric shocks, supports with somedifficulty the shock of a torpedo 14 inches long, and in astate of perfect vigour. The gymnotus communicates itsinfluence under water, unless when much weakened. M. Gay-Lussac has observed, that the action of the tor-pedo in this condition is not perceptible until it is raisedabove the surface of the water. It is with this fish, as withfrogs on which Galvanic experiments are made: the cir-cumstances under which the contraction takes place, varyaccording to the degree of excitability in the organs. 2. I have remarked, while in South America, that thegymnotus gives the most frightful shocks without makingany external motion of the eyes, head, or fins: it moves nomore than one person communicating an idea or sensationto another. But the torpedo, on the contrary, moves itspectoral fins in a convulsive manner before each shock;and the violence of the stroke is always proportioned to theextent of the surface of contact. 3. The organs of the torpedo, or gymnotus, cannot bedischarged by us at will, like a Leyden phial or a Galvanic pile; nor does the electric fish uniformly communicate ashock when touched. It must be irritated that it may giveits stroke; for this action depends upon the will of theanimal, which in all probability does not always keep itselectric organs charged: it charges them, however, withastonishing celerity, and is thus able to give a long seriesof shocks. 4. The shock is felt, provided the animal is disposed togive it, when a single finger is applied to a single surface ofthe electric organs; or when the two hands are placed oneon the upper and the other on its under surface at the sametime. And in either of these cases the shock is equallycommunicated, whether the person be insulated or not. 5. If a person while insulated touches the torpedo withhis finger, it is indispensably necessary that the finger be in |358| immediate contact; for no shock is communicated when aconducting body, such as a piece of metal, is interposedbetween the finger and the organs of the fish. Thus wemay touch the animal with a key, or other metallic instru-ment, and experience no shock in consequence. 6. M. Gay-Lussac having observed this important fact,we placed the torpedo on a plate of metal, so that the in-ferior surface of its electric organs was in contact with themetal. The hand which supported the plate felt no shock,although another person in a state of insulation irritated theanimal, and when the convulsive motions of its pectoralfins plainly indicated very powerful discharges of its elec-tric fluid. 7. If on the contrary a person support the torpedo placedon a metallic plate, with his left hand as in the precedingexperiment, and with his right touches the upper surface ofthe electric organ, then a violent shock is felt in both armsat the same moment. 8. The same feeling is experienced when the fish isplaced between two plates of metal, the edges of which donot touch, and the person applies a hand to each plate atthe same instant. 9. But if in the preceding experiment there exists animmediate communication between the edges of the twoplates, no shock is felt in the arms; for in this case thechain of connection between the two surfaces of the organis formed by the plates, and the new communication esta-blished by applying the two hands to the plates becomes al-together inefficient. 10. The most delicate electrometer does not indicate thestate of electricity of the organs of the torpedo: it is noway affected by any method which we can have recourse to,either by bringing it near to the organs, or by insulatingthe fish, covering it with a plate of metal, and then form-ing a communication by means of a wire between the plateand the condenser of Volta. Nothing shows here, as inthe gymnotus, that the animal can modify the state ofelectricity of surrounding bodies. 11. As electric fish act while in a state of health withthe same power under water as in the air, we examined theconducting properties of this fluid. A number of personshaving formed a circle of connection between the upper andunder surfaces of the organs of the torpedo, no shock wasexperienced till they had moistened their hands with water.The shock is equally felt when two persons who have theirright hands applied to the torpedo, instead of taking hold of |359| each other’s left hands, plunge a pointed piece of metal intoa drop of water placed upon an insulating body. 12. By substituting flame instead of a drop of water, thecommunication is interrupted, and no sensation is expe-rienced until the two pieces of metal touch each otherwithin the flame. 13. We must also observe that no shock will take placeeither in air or under water, unless we immediately touchthe body of the electric fish. They are unable to give theirstroke through a layer of water, however thin; a factwhich is the more remarkable, as we know that in Galvanic experiments, where the frog is placed under water, it issufficient to bring the silver forceps near to the muscles,and that the contraction takes place when the layer of waterinterposed is one or two millimetres in thickness. Such, my respected friend, are the principal observationswhich we have made upon the torpedo. Experiments 4thand 10th prove that the electric organs of these animalsmanifest no tension or excess of charge. We should ratherbe inclined to compare their action to a chain of smallLeyden phials than to the pile of Volta. As some commu-nication is always necessary for the occurrence of a shock,and having received strokes from the gymnotus throughvery dry cords, I conclude that in the case where thispowerful animal appeared to give these violent shocks with-out the existence of any communication, it must havearisen from my imperfect insulation. If the torpedo actsby poles, by an electrical equilibrium which tends to re-establish itself, experiments 5th and 6th seem to prove thatthese poles exist near one another upon the same surface ofthe organ: for we feel the shock by touching a single sur-face with the finger. A plate interposed between the handand the organ (6.) re-establishes of itself the equilibrium,and the hand which supports this plate feels nothing, be-cause it is out of the current of the electric influence. Butif we suppose a number of poles of different descriptionsupon each surface of the organ, why is it that, by cover-ing these with two metallic plates the edges of which donot touch, and placing the hands upon these plates, theequilibrium is re-established through the medium of thearms? Wherefore, it may be asked, does not the positiveelectricity of the inferior surface seek, at the moment ofexplosion, the negative electricity of the neighbouring pole?and wherefore does it find it only in the superior surface ofthe electric organ? These difficulties are perhaps not in- |360| sumountable, but the theory of these vital actions requiresstill further research. Geoffroy * has proved that rays,which do not exhibit any marks of electricity, possess or-gans very analogous to those of the torpedo. The leastinjury of the brain of this animal prevents its electricalaction. The nerves, therefore, without doubt, act thechief part in the production of these phænomena; and thephysiologist, who takes a general and enlarged view of thevital actions, would with reason oppose the ideas of thephilosopher, who conceives he can explain the whole bythe contact of the albumino-gelatinous pulp with the ten-dinous septa which nature has combined in the formationof the organs of the torpedo.