Digitale Ausgabe

I was impatient, from the time ofmy arrival at Cumana, to procureelectrical eels. We had been pro-mised them often, but our hopes hadalways been disappointed. Moneyloses its value as you withdraw fromthe coast; and how is the impertur-bable phlegm of the vulgar to be van-quished, when they are not excitedby the desire of gain? The Spaniards confound all elec-trical fishes under the name of tem-bladores, (producers of trembling, lite-rally tremblers.) There are somein the Caribbean sea, on the coast ofCumana. The Guayqueria Indians,who are the most skilful and indus-trious fishermen in those parts,brought us a fish, which, they said,had benumbed their hands. Thisfish ascends the little river Manza-nares. It is a new species of theray, the lateral spots of which arescarcely visible, and which much re-sembles the torpedo of Galvani.The torpedoes, furnished with anelectric organ that is externally visi-ble, on account of the transparencyof the skin, form a genus or subge-nus, different from the rays properlyso called. The torpedo of Cumanawas very lively, very energetic in itsmuscular movements, and yet theelectrical shocks it gave us wereextremely feeble. They becamestronger on galvanizing the animal |Spaltenumbruch|by the contact of zinc and gold.Other tembladores, real gymnoti orelectrical eels, inhabit the Rio Co-lorado, the Guarapiche, and severallittle streams that cross the missionsof the Chayma Indians. Theyabound also in the large rivers ofAmerica, the Oroonoko, the Ama-zon, and the Meta: but the strengthof the current, and the depth of thewater, prevent their being caught bythe Indians. They see these fishless frequently than they feel elec-trical shocks from them when swim-ming or bathing in the river. Inthe Llanos, particularly in the envi-rons of Calabozo, between the farmsof Morichal and the missions de arri-ba and de abaxo, the basins of stag-nant water, and the confluents of theOroonoko (the Rio Guarico and the Canos of Rastro, Berito, and Paloma)are filled with electrical eels. Weat first wished to make our experi-ments in the house we inhabited atCalabozo; but the dread of the elec-trical shocks of the gymnoti is sogreat, and so exaggerated among thevulgar, that during three days wecould not obtain one, though theyare easily caught, and we had pro-mised the Indians two piastres forevery strong and vigorous fish. Thisfear of the Indians is the more extra-ordinary, as they do not attempt toemploy means in which they professto have great confidence. When in-terrogated on the effect of the tem-bladores, they never fail to tell thewhites that they may be touchedwith impunity, while you are chew-ing tobacco. This fable of the influ-ence of tobacco on animal electricity |322| |Spaltenumbruch|is as general on the continent ofSouth America, as the belief amongmariners of the effect of garlic andtallow on the magnetic needle. Impatient of waiting, and havingobtained very uncertain results froman electrical eel that had beenbrought to us alive, but much enfee-bled, we repaired to the Cano deBera, to make our experiments inthe open air, on the borders of thewater itself. We set off on the 19thof March, at a very early hour, forthe village of Rastro de abaxo; thence we were conducted by theIndians to a stream, which, in thetime of drought, forms a basin ofmuddy water, surrounded by finetrees, the clusia, the amyris, and themimosa with fragrant flowers. Tocatch the gymnoti with nets is verydifficult, on account of the extremeagility of the fish, which bury them-selves in the mud like serpents. Wewould not employ the barbasco, thatis to say, the roots of the piscideaerithryna, jacquinia armillaris, andsome species of phyllanthus, which,thrown into the pool, intoxicate orbenumb these animals. Thesemeans would have enfeebled thegymnoti; the Indians, therefore,told us, that they would “fish withhorses,” embarbascar con cavallos. We found it difficult to form an ideaof this extraordinary manner of fish-ing; but we soon saw our guides re-turn from the savannah, which theyhad been scouring for wild horsesand mules. They brought aboutthirty with them, which they forcedto enter the pool. The extraordinary noise causedby the horses’ hoofs makes the fishissue from the mud, and excites themto combat. These yellowish andlivid eels, resembling large aquaticserpents, swim on the surface of thewater, and crowd under the belliesof the horses and mules. A contestbetween animals of so different anorganization furnishes a very strikingspectacle. The Indians, provided |Spaltenumbruch|with harpoons and long slender reeds,surround the pool closely; and someclimb upon the trees, the branchesof which extend horizontally overthe surface of the water. By theirwild cries, and the length of theirreeds, they prevent the horses fromrunning away, and reaching the bankof the pool. The eels, stunned bythe noise, defend themselves by therepeated discharge of their electricbatteries. During a long time theyseem to prove victorious. Severalhorses sink beneath the violence ofthe invisible strokes, which they re-ceive from all sides in organs themost essential to life; and stunnedby the force and frequency of theshocks, disappear under the water.Others, panting, with mane erect,and haggard eyes, expressing anguish,raise themselves, and endeavour toflee from the storm by which theyare overtaken. They are drivenback by the Indians into the middleof the water; but a small numbersucceed in eluding the active vigi-lance of the fisherman. These re-gain the shore, stumbling at everystep, and stretch themselves on thesand, exhausted with fatigue, andtheir limbs benumbed by the elec-tric shocks of the gymnoti. In less than five minutes twohorses were drowned. The eel,being five feet long, and pressingitself against the belly of the horses,makes a discharge along the wholeextent of its electric organ. It at-tacks at once the heart, the intes-tines, and the plexus cœliacus of theabdominal nerves. It is natural, thatthe effect felt by the horses shouldbe more powerful than that produ-ced upon man by the touch of thesame fish at only one of his extremi-ties. The horses are probably notkilled, but only stunned. They aredrowned from the impossibility ofrising amid the prolonged strugglebetween the other horses and theeels. We had little doubt, that the fish- |323| |Spaltenumbruch|ing would terminate by killing suc-cessively all the animals engaged;but by degrees the impetuosity of thisunequal combat diminished, and thewearied gymnoti dispersed. Theyrequire a long rest, and abundantnourishment, to repair what theyhave lost of galvanic force. Themules and horses appear less fright-ened; their manes are no longerbristled, and their eyes expressless dread. The gymnoti approachtimidly the edge of the marsh, wherethey are taken by means of smallharpoons fastened to long cords.When the cords are very dry theIndians feel no shock in raising thefish into the air. In a few minuteswe had five large eels, the greaterpart of which were but slightlywounded. Some were taken by thesame means toward the evening. The temperature of the waters inwhich the gymnoti habitually live,is from 26° to 27°. Their electricforce diminishes, it is said, in colderwaters; and it is remarkable, that ingeneral, as a celebrated naturalisthas already observed, animals endow-ed with electromotive organs, theeffects of which are sensible to man,are not found in the air, but in a fluidthat is a conductor of electricity.The gymnotus is the largest of elec-trical fishes. I measured some thatwere from five feet to five feet threeinches long; and the Indians assertthat they have seen still longer. Wefound that a fish of three feet teninches long weighed twelve pounds.The transverse diameter of the body,without reckoning the anal fin, whichis elongated in the form of a keel,was three inches five lines. Thegymnoti of Cano de Bera are of afine olive green. The under partof the head is yellow, mingled withred. Two rows of small yellowspots are placed symmetrically alongthe back, from the head to the endof the tail. Every spot contains anexcretory aperture. In conse-quence, the skin of the animal is |Spaltenumbruch|constantly covered with a mucousmatter, which, as Volta has proved,conducts electricity twenty or thirtytimes better than pure water. It is,in general, somewhat remarkable,that no electrical fish, yet discover-ed in the different parts of the world,is covered with scales. The gymnoti, like our eels, arefond of swallowing and breathing airon the surface of the water; but wemust not thence conclude with Mr.Bajon, that the fish would perish ifit could not come up to breathe theair. Our eels wander a part of thenight upon the grass, while I haveseen a very vigorous gymnotus, thathad sprung out of the tub, die onthe ground. Mr. Provençal andmyself have proved, by our re-searches on the respiration of fishes,that their humid bronchiæ can exe-cute the double function of decom-posing the atmospheric air, and ofappropriating the oxygen dissolvedin water. They do not suspendtheir respiration in the air; but theyabsorb the gazeous oxygen, like areptile furnished with lungs. It isknown that carp may be fatten-ed by being fed out of the water,and wetting their gills from time totime with humid moss, to preventtheir drying. Fish separate theirgill covers wider in oxygen gas, thanin water. Their temperature, how-ever, does not rise; and they live thesame length of time in pure vital air,and in a mixture of ninety parts azot,and ten oxygen. We found, thattench (cyprinus tinca) placed underinverted jars filled with air, absorbhalf a cubic centimetre of oxygen inan hour. This action takes place inthe gills only; for fishes, on which acollar of cork has been fastened,and leaving their head out of thejar filled with air, do not act uponthe oxygen by the rest of theirbody. It would be temerity to exposeourselves to the first shocks of a verylarge and strongly irritated gymno- |324| |Spaltenumbruch|tus. If by chance you receive astroke before the fish is wounded orwearied by a long pursuit, the painand numbness are so violent that itis impossible to describe the natureof the feeling they excite. I do notremember having ever received fromthe discharge of a large Leyden jar,a more dreadful shock than thatwhich I experienced by imprudentlyplacing both my feet on a gymnotusjust taken out of the water. I wasaffected the rest of the day with a vio-lent pain in the knees, and in almostevery joint. To be aware of the dif-ference, which is sufficiently strik-ing, that exists between the sensa-tion produced by the pile of Voltaand an electrical fish, the lattershould be touched when they are ina state of extreme weakness. Thegymnoti and the torpedoes then causea twitching, which is propagatedfrom the part that rests on the elec-tric organs as far as the elbow. Weseem to feel at every stroke an in-ternal vibration that lasts two or threeseconds, and is followed by a pain-ful numbness. Accordingly, theTamanac Indians call the temblador, in their expressive language, arimna, which means something that deprivesof motion. The sensation caused by the fee-ble shocks of an electrical eel ap-peared to me analogous to that pain-ful twitching, with which I havebeen seized at each contact of twoheterogeneous metals applied towounds, which I had made on myback by means of cantharides. Thisdifference of sensation between theeffects of electrical fishes and thoseof the pile, or a Leyden vial weaklycharged, has struck every observer;there is, however, nothing in thiscontrary to the supposition of theidentity of electricity and the galva-nic action of fishes. The electricitymay be the same; but its effectswill be variously modified by thedisposition of the electrical apparatus,by the intensity of the fluid, by the |Spaltenumbruch|rapidity of the current, and by aparticular mode of action. In Dutch Guyana, at Demerary,for instance, electrical eels were for-merly employed to cure the paraly-tic. At a time when the physiciansof Europe had a great confidence inthe effects of electricity, a surgeonof Essequibo, Mr. Vander Lott, pub-lished in Holland a treatise on themedical properties of the gymnoti.These electrical cures are foundamong the savages of America, aswell as among the Greeks. We aretold by Scribonius Largus, Galen,and Dioscorides, that torpedoes curethe headache and the gout. I did nothear of this species of remedy inthe Spanish colonies which I visited;but I can assert, that, after havingmade experiments during four hourssuccessively with gymnoti, Mr. Bon-pland and myself felt till the nextday a debility in the muscles, a painin the joints, and a general uneasi-ness, which was the effect of a strongirritation of the nervous system. Gymnoti are neither charged con-ductors, nor batteries, nor electro-motive apparatuses, the shock ofwhich is received every time theyare touched with one hand, or whenboth hands are applied to form aconducting circle between two hete-rogeneous poles. The electric ac-tion of the fish depends entirely onits will; whether because it do notkeep its electric organs alwayscharged, or by the secretion of somefluid, or by any other means alikemysterious to us, it be capable of di-recting the action of its organs to anexternal object. We often tried,both insulated and uninsulated, totouch the fish, without feeling theleast shock. When Mr. Bonplandheld it by the head, or by the middleof the body, while I held it by thetail, and, standing on the moistground, did not take each othershand, one of us received shockswhich the other did not feel. It de-pends upon the gymnotus to act to- |325| |Spaltenumbruch|ward the point, where it finds itselfthe most strongly irritated. Thedischarge is then made at one pointonly, and not at the neighbouringpoints. If two persons touch thebelly of the fish with their fingers,at an inch distance, and press itsimultaneously, sometimes one,sometimes the other, will receivethe shock. In the same manner,when one insulated person holds thetail of a vigorous gymnotus, andanother pinches the gills, or pec-toral fin, it is often the first onlyby whom the shock is received. Itdid not appear to us that these dif-ferences could be attributed to thedryness or dampness of our hands,or to their unequal conducting power.The gymnotus seemed to direct itsstrokes sometimes from the wholesurface of its body, sometimes fromone point only. This effect indi-cates less a partial discharge of theorgan composed of an innumerablequantity of leaves, than the facultywhich the animal possesses, perhapsby the instantaneous secretion of afluid spread through the cellularmembrane, of establishing the com-munication between its organs andthe skin only, in a very limited space. Nothing proves more strongly thefaculty which the gymnotus pos-sesses, of darting and directing itsstroke according to its will, than theobservations made at Philadelphia,and recently at Stockholm, on gym-noti rendered extremely tame. Whenthey had been made to fast a longtime, they killed from afar smallfishes put into the tub. They actedat a distance; that is to say, theirelectrical stroke passed through avery thick stratum of water. Weneed not be surprised, that what wasobserved in Sweden on a single gym-notus only, we could not see on agreat number of individuals in theirnative country. The electric actionof animals being a vital action, andsubject to their will, it does not de-pend solely on their state of health |Spaltenumbruch|and vigour. A gymnotus that hasmade the voyage from Surinam toPhiladelphia and Stockholm, accus-toms itself to the imprisonment, towhich it is reduced; it resumes, bydegrees, the same habits in the tub,which it had in the rivers and pools.An electrical eel was brought to meat Calabozo, taken in a net, and, con-sequently, having no wound. It atemeat, and terribly frightened the lit-tle tortoises and frogs, which, notknowing the danger, placed them-selves with confidence on its back.The frogs did not receive the stroketill the moment when they touchedthe body of the gymnotus. Whenthey recovered, they leaped out ofthe tub; and when replaced near thefish, they were frightened at its sightonly. We then observed nothingthat indicated an action at a distance; but our gymnotus, recently taken,was not yet sufficiently tamed to at-tack and devour frogs. On ap-proaching the finger, or metallicpoints, within the distance of half aline from the electric organs, noshock was felt. Perhaps the animaldid not perceive the neighbourhoodof this foreign body; or, if it did,we must suppose, that the timidity itfelt in the commencement of its cap-tivity, prevented it from dartingforth its energetic strokes, exceptwhen strongly irritated by an imme-diate contact. The gymnotus beingimmersed in water, I approached myhand, both armed and unarmed witha metal, within the distance of a fewlines from the electric organs; yetthe strata of water transmitted noshock, while Mr. Bonpland irritatedthe animal strongly by an immediatecontact, and received some very vio-lent shocks. If I had plunged the mostdelicate electroscopes we know, pre-pared frogs, into contiguous strataof water, they would no doubt havefelt contractions at the moment whenthe gymnotus seemed to direct itsstroke elsewhere. Prepared frogs,placed immediately on the body of a |326| |Spaltenumbruch|torpedo, experience, according toGalvani, a strong contraction at everydischarge of the fish. The electrical organ of the gymnotiacts only under the immediate influ-ence of the brain and the heart. On cut-ting a very vigorous fish through themiddle of the body, the fore partalone gave me shocks. The shocksare equally strong, in whatever partof the body the fish is touched; it ismost disposed, however, to dart themforth when the pectoral fin, the elec-trical organ, the lips, the eyes, orthe gills, are pinched. Sometimesthe animal struggles violently with aperson holding it by the tail, withoutcommunicating the least shock. Nordid I feel any when I made a slightincision near the pectoral fin of thefish, and galvanized the wound bythe simple contact of two pieces ofzinc and silver. The gymnotus bentitself convulsively, and raised itshead out of the water, as if affright-ed by a sensation altogether new;but I felt no vibration in the handswhich held the two metals. Themost violent muscular movementsare not always accompanied by elec-tric discharges. The action of the fish on the or-gans of man is transmitted and inter-cepted by the same bodies that trans-mit and intercept the electrical cur-rent of a conductor charged by aLeyden vial, or Volta’s pile. Someanomalies, which we thought we ob-served, are easily explained, whenwe recollect, that even metals (as isproved from their ignition when ex-posed to the action of the pile) pre-sent a slight obstacle to the passageof electricity; and that a bad con-ductor annihilates the effect of a fee-ble electricity on our organs, whileit transmits to us the effect of a verystrong electricity. The repulsiveforce that zinc and silver exercisebetween each other, being far supe-rior to that between gold and silver,I have found, that when a frog, pre-pared and armed with silver, is gal- |Spaltenumbruch|vanized under water, the conductingarc of zinc produces contractions assoon as one of its extremities ap-proaches the muscles within threelines distance; while an arc of golddoes not excite the organs, when thestratum of water between the goldand the muscles is more than half aline thick. In the same manner, byemploying a conducting arc composedof two pieces of zinc and silver sol-dered together endwise, and restingas before, one of the extremities ofthe metallic arc on the ischiaticnerve, it is necessary, in order toproduce contractions, to bring theother extremity of the conductingarc nearer and nearer to the mus-cles, in proportion as the irritabilityof the organs diminishes. Towardthe end of the experiment, theslightest stratum of water preventsthe passage of the electrical current,and it is only by the immediate con-tact of the arc with the muscles, thatthe contractions take place. I dwellon these effects, dependent on three variable circumstances: the energyof the electromotive apparatus, theconductibility of the medium, and theirritability of the organs that receivethe impressions; as it is because ex-periments have not been sufficientlymultiplied with a view to these threevariable elements, that, in the actionof electrical eels and torpedoes, theaccidental circumstances have beentaken for absolute conditions, with-out which the electric shocks arenot felt. In wounded gymnoti, which givefeeble, but very equal shocks, theseshocks appeared to us constantlystronger on touching the body of thefish with a hand armed with metal,than with the naked hand. Theyare stronger also, when, instead oftouching the fish with one hand,naked, or armed with metal, we pressit at once with both hands, eithernaked or armed. These differences,I repeat, become sensible only whenyou have gymnoti enough at your |327| |Spaltenumbruch|disposal to be able to choose theweakest; and the extreme equalityof the electric discharges admits ofdistinguishing between the sensa-tions felt alternately by the handnaked or armed with a metal, by oneor both hands naked, and by one orboth hands armed with metal. It isalso in the case only of small shocks,weak and uniform, that the shocksare more sensible on touching thegymnotus with one hand (withoutforming a chain) with zinc, than withcopper or iron. Resinous substances, glass, verydry wood, horn, and even bones,which are generally believed to begood conductors, prevent the actionof the gymnoti from being transmit-ted to man. I was surprised at notfeeling the least shock on pressingwet sticks of sealing wax against theorgans of the fish, while the sameanimal gave me the most violentstrokes, when excited by means of ametallic rod. Mr. Bonpland receiv-ed shocks when carrying a gymnotuson two cords of the fibres of the palm-tree, which appeared to us extreme-ly dry. A strong discharge makesits way through very imperfect con-ductors. Perhaps, also, the obsta-cle which the conducting arc pre-sents, renders the discharge morepainful. I touched the gymnotuswith a wet pot of brown clay, with-out effect; yet I received violentshocks when I carried the gymnotusin the same pot, because the contactwas greater. When two persons, insulated ornot insulated, hold each other’shands, and one of these persons onlytouches the fish with the hand, eithernaked or armed with metal, theshock is most commonly felt by bothat once. It happens, however, also,that in the most painful shocks, theperson who comes into immediatecontact with the fish alone feels theshock. When the gymnotus is ex-hausted, or in a very weak state ofexcitability, and will no longer emit |Spaltenumbruch|strokes on being irritated with onehand, the shocks are felt in a veryvivid manner, on forming the chain,and employing both hands. Eventhen, however, the electric shocktakes place only at the will of theanimal. Two persons, one of whomholds the tail, and the other the head,cannot, by joining hands and forminga chain, force the gymnotus to darthis stroke. In employing very delicate elec-trometers in a thousand ways, insu-lating them on a plate of glass, andreceiving very strong shocks, whichpassed through the electrometer, Icould never discover any phenome-non of attraction or repulsion. Thesame observation was made by Mr.Fahlberg at Stockholm. This philo-sopher, however, has seen an elec-tric spark, as Walsh and Ingenhouszhad done before him at London, byplacing the gymnotus in the air, andinterrupting the conducting chain bytwo gold leaves pasted upon glass,and a line distant from each other.No person, on the contrary, has everperceived a spark issue from thebody of the fish itself. We have ir-ritated it for a long time during thenight, at Calabozo, in perfect dark-ness, without observing any lumi-nous appearance. Having placed fourgymnoti of unequal strength in sucha manner as to receive the shocks ofthe most vigorous fish by communi-cation, that is to say, by touching onlyone of the other fishes, I did not ob-serve that these last were agitated atthe moment when the current passedby their bodies. Perhaps the currentestablished itself on the humid sur-face of the skin. We will not, how-ever, conclude from this, that thegymnoti are insensible to electricity;and that they cannot fight with eachother at the bottom of the pools.Their nervous system must be sub-ject to the same agents as the nervesof other animals. I have, indeed,seen, that, on baring their nerves,they undergo muscular contractions |328| |Spaltenumbruch|at the simple contact of two hetero-geneous metals; and Mr. Fahlberg,of Stockholm, found, that his gymno-tus was convulsively agitated whenplaced in a copper vessel, and feebledischarges from a Leyden vial passedthrough its skin. After the experiments I had madeon gymnoti, it became highly inte-resting to me, at my return to Eu-rope, to know with precision the va-rious circumstances in which anotherelectrical fish, the torpedo of ourseas, gives, or does not give, shocks.Though this fish had been examinedby a great number of natural philo-sophers, I found all that had beenpublished on its electrical effects ex-tremely vague. It has been veryarbitrarily supposed that this fishacts like a Leyden vial, which maybe discharged at will, by touching itwith both hands; and this supposi-tion appears to have led observersinto error, who have devoted them-selves to researches of this kind.Mr. Gay-Lussac and myself, duringour journey to Italy, made a greatnumber of experiments on torpedoestaken in the Gulf of Naples. Theseexperiments furnish many resultssomewhat different from those I col-lected on the gymnoti. It is proba-ble, that the cause of these anoma-lies proceeds rather from the ine-quality of electric power in the twofishes, than the different dispositionof their organs. Though the power of the torpedocannot be compared with that of thegymnoti, it is sufficient to cause verypainful sensations. A person ac-customed to electric shocks can withdifficulty hold in his hands a torpedoof twelve or fourteen inches, and inpossession of all its vigour. Whenthe animal no longer gives any butvery feeble strokes under water, theshocks become more sensible if it beraised above the surface. I haveoften observed the same phenome-non in galvanizing frogs. The torpedo moves the pectoral |Spaltenumbruch|fins convulsively, every time it emitsa stroke; and this stroke is more orless painful, according as the im-mediate contact takes place by agreater or less surface. We haveabove observed, that the gymnotusgives the strongest shocks withoutmaking any movement with the eyes,head, or fins. Is this differencecaused by the position of the elec-tric organ, which is not double inthe gymnoti? or, does the movementof the pectoral fins of the torpedodirectly prove, that the fish restoresthe electrical equilibrium by itsown skin, discharges itself by itsown body, and that we generallyfeel only the effect of a lateralshock? We cannot discharge at will eithera torpedo or a gymnotus, as we dis-charge at will a Leyden vial or aVoltaic pile. A shock is not alwaysfelt, even in touching the electricfish with both hands. We must irri-tate it to make it give the shock.This action in the torpedoes, as wellas in the gymnoti, is a vital action; it depends on the will only of theanimal, which, perhaps, does not al-ways keep its electrical organscharged, or does not always employthe action of its nerves to establishthe chain between the positive andnegative poles. This is certain,that the torpedo gives a long seriesof shocks with astonishing celerity:whether it be, that the plates or la-minæ of his organs are not whollyexhausted, or that the fish rechargesthem instantaneously. The electric stroke is felt whenthe animal is disposed to give it,whether we touch with a single fin-ger only one of the surfaces of theorgans, or apply both hands to thetwo surfaces, the superior and in-ferior at once. In either case, it isaltogether indifferent, whether theperson who touches the fish withone finger, or both hands, be insulat-ed or not. All that has been saidon the necessity of a communication |329| |Spaltenumbruch|with the damp ground, to establish acircuit, is founded on inaccurate ob-servations. Mr. Gay-Lussac made the import-ant observation, that, when an insu-lated person touches the torpedo withone finger, it is indispensable thatthe contact be immediate. The fishmay with impunity be touched witha key or any other metallic instru-ment; no shock is felt when a con-ducting or nonconducting body is in-terposed between the finger and theelectrical organ of the torpedo. Thiscircumstance furnishes a great dif-ference between the torpedo and thegymnotus, the latter giving hisstrokes through an iron rod severalfeet long. When the torpedo is placed on ametallic plate of very little thickness,so that the plate touches the inferiorsurface of the organs, the hand thatsupports the plate never feels anyshock, though another insulated per-son excites the animal, and the con-vulsive movement of the pectoralfins denotes the strongest and mostreiterated discharges. If, on the contrary, a person sup-port the torpedo, placed upon a me-tallic plate, with the left hand, as inthe foregoing experiment, and thesame person touch the superior sur-face of the electrical organ with theright hand; a strong shock is thenfelt in both arms. The sensation isthe same when the fish is placed be-tween two metallic plates, the edgesof which do not touch, and the per-son applies both hands at once to theseplates. The interposition of onemetallic plate prevents the communi-cation, if that plate be touched withone hand only, while the interposi-tion of two metallic plates does notprevent the shock when both handsare applied. In the latter case, itcannot be doubted, that the circula-tion of the fluid is established by thetwo arms. If, in this situation of the fish be-tween two plates, there exist any |Spaltenumbruch|immediate communication betweenthe edges of these two plates, noshock takes place. The chain be-tween the two surfaces of the elec-tric organ is then formed by theplates; and the new communicationestablished by the contact of the twohands with the two plates, remainswithout effect. We carried the tor-pedo with impunity between twodishes of metal, and felt the strokesit gave only at the instant when thedishes no longer touched each otherat the edges. Nothing in the torpedo, or in thegymnotus, indicates that the animalmodifies the electrical state of thebodies by which it is surrounded.The most delicate electrometer is noway affected, in whatever manner itis employed, whether bringing itnear the organs, or insulating thefish, covering it with a metallic plate,and causing the plate to communi-cate by a conducting wire with thecondenser of Volta. We were atgreat pains to vary the experimentsby which we sought to render theelectrical tension in the organs ofthe torpedo sensible; but they wereconstantly without effect, and per-fectly confirmed what Mr. Bonplandand myself had observed respectingthe gymnoti during our abode inSouth America. Electrical fishes, when very vigo-rous, act with the same energy underwater and in the air. This observa-tion led us to examine the conduct-ing property of water; and we foundthat when several persons form thechain between the superior and in-ferior surface of the organs of thetorpedo, the shock is felt only whenthese persons have united theirhands. The action is not intercept-ed if two persons who support thetorpedo with their right hands, in-stead of taking one another by theleft hand, plunge each a metallicpoint into a drop of water placed onan insulating substance. On substi-tuting flame for the drop of water, |330| |Spaltenumbruch|the communication is interrupted,and is only re-established, as in thegymnoti, when the two points imme-diately touch each other in the inte-rior of the flame.