Account of the Electrical Eels, and of the Method of catching them in South America by means of Wild Horses.

Abridged from Humboldt's Personal Narrative.

Real Gymnoti or Electrical Eels, inhabit the Rio Colorado, the Guarapiche, and several little streams, that cross the missions of the Chayma Indians.

They abound also in the large rivers of America, the Oroonoko, the Amazon, and the Meta; but the strength of the current, and the depth of the water, prevent their being caught by the Indians.

They see these fish less frequently than they feel electrical shocks from them when swimming or bathing in the river.

In the Llanos, particularly in the environs of Calabozo, between the farms of Morichal, and the missions de arriba and de abaxo, the basins of stagnant water, and the confluents of the Oroonoko, (the Rio Guarico and the Canos of Rastro, Berito and Paloma), are filled with electrical eels.

We at first wished to make our experiments in the house we inhabited at Calabozo; but the dread of the electrical shocks of the gymnoti is so exaggerated among the vulgar, that during three days we could not obtain one, though they are easily caught, and though we had promised the Indians two piastres for every strong and vigorous fish.

Impatient of waiting, and having obtained very uncertain results from an electrical eel that had been brought to us alive, but much enfeebled, we repaired to the Cano de Bera, to make our experiments in the open air, on the borders of the water itself.

We set off on the 19th of March for the village Rastro de abaxo; thence we were conducted to a stream, which, in the time of drought, forms a basin of muddy water, surrounded by fine trees.

To catch the gymnoti with nets is very difficult, on account of the extreme agility of the fish, which bury themselves in the mud like serpents.

We would not employ the barbasco, that is to say, the roots of the Piscidea erithryna and Jacquinia armillaris, which, when thrown into the pool, intoxicate or benumb these animals.

These means would have enfeebled the gymnoti; the Indians therefore told us, that they would "fish with horses.

We found it difficult to form an idea of this extraordinary manner of fishing; but we soon saw our guides return from the savannah, which they had been scouring for wild horses and mules.

They brought about thirty with them, which they forced to enter the pool.

The extraordinary noise caused by the horses' hoofs makes the fish issue from the mud, and excites them to combat.

These yellowish and livid eels, resembling large aquatic serpents, swim on the surface of the water, and crowd under the bellies of the horses and mules.

A contest between animals of so different an organization furnishes a very striking spectacle.

The Indians, provided with harpoons and long slender reeds, surround the pool closely; and some climb upon the trees, the branches of which extend horizontally over the surface of the water.

By their wild cries, and the length of their reeds, they prevent the horses from running away, and reaching the bank of the pool.

The eels, stunned by the noise, defend themselves by the repeated discharge of their electric batteries.

During a long time they seem to prove victorious.

Several horses sink beneath the violence of the invisible strokes, which they receive from all sides in organs the most essential to life; and stunned by the force and frequency of the shocks, disappear under the water.

Others, panting, with mane erect, and haggard eyes, expressing anguish, raise themselves, and endeavour to flee from the storm by which they are overtaken.

They are driven back by the Indians into the middle of the water; but a small number succeed in eluding the active vigilance of the fishermen.

These regain the shore, stumbling at every step, and stretch themselves on the sand, exhausted with fatigue, and their limbs benumbed by the electric shocks of the gymnoti.

In less than five minutes two horses were drowned.

The eel, being five feet long, and pressing itself against the belly of the horses, makes a discharge along the whole extent of its electric organ. It attacks at once the heart, the intestines, and the plexus coeliacus of the abdominal nerves.

It is natural, that the effect felt by the horses should be more powerful than that produced upon man by the touch of the same fish at only one of his extremities.

The horses are probably not killed, but only stunned.

They are drowned from the impossibility of rising amid the prolonged struggle between the other horses and the eels.

We had little doubt, that the fishing would terminate by killing successively all the animals engaged; but by degrees the impetuosity of this unequal combat diminished, and the wearied gymnoti dispersed.

They require a long rest , and abundant nourishment, to repair what they have lost of galvanic force.

The mules and horses appear less frightened; their manes are no longer bristled, and their eyes express less dread.

The gymnoti approach timidly the edge of the marsh, where they are taken by means of small harpoons fastened to long cords.

When the cords are very dry, the Indians feel no shock in raising the fish into the air.

In a few minutes we obtained five large eels, the greater part of which were but slightly wounded.

Some were taken by the same means toward the evening.

The Indians assured us, that when the horses are made to run two days successively into the same pool, none are killed the second day.

The temperature of the waters in which the gymnoti habitually live, is about 86° of Fahrenheit.

Their electric force, it is said, diminishes in colder waters.

The gymnotus is the largest of electrical fishes.

I measured some that were from five feet to five feet three inches long; and the Indians assert, that they have seen them still longer.

We found, that a fish of three feet ten inches long weighed twelve pounds.

The transverse diameter of the body was three inches five lines.

The gymnoti of Cano de Bera are of a fine olive-green colour.

The under part of the head is yellow, mingled with red.

Two rows of small yellow spots are placed symmetrically along the back, from the head to the end of the tail.

Every spot contains an excretory aperture.

In consequence, the skin of the animal is constantly covered with a mucous matter, which, as Volta has proved, conducts electricity twenty or thirty times better than pure water.

It is in general somewhat remarkable, that no electrical fish, yet discovered in the different parts of the world, is covered with scales.

We yet know with certainty only seven electrical fishes:

Torpedo narke, Risso, t. unimaculata, t. marmorata, t. galvanii, Silurus electricus, Tetraodon electricus, Gymnotus electricus.

It would be temerity to expose ourselves to the first shocks of a very large and strongly irritated gymnotus.

If by chance you receive a stroke before the fish is wounded, or wearied by a long pursuit, the pain and numbness are so violent, that it is impossible to describe the nature of the feeling they excite.

I do not remember having ever received from the discharge of a large Leyden jar, a more dreadful shock than that which I experienced by imprudently placing both my feet on a gymnotus just taken out of the water.

I was affected the rest of the day with a violent pain in the knees, and in almost every joint.

To be aware of the difference, which is sufficiently striking, that exists between the sensation produced by the pile of Volta and an electrical fish, the latter should be touched when they are in a state of extreme weakness.

The gymnoti and the torpedoes then cause a twitching, which is propagated from the part that rests on the electric organs as far as the elbow.

We seem to feel at every stroke an internal vibration, that lasts two or three seconds, and is followed by a painful numbness.

Gymnoti are neither charged conductors, nor batteries, nor electromotive apparatuses, the shock of which is received every time they are touched with one hand, or when both hands are applied to form a conducting circle between two heterogeneous poles.

The electric action of the fish depends entirely on its will; whether because it does not keep its electric organs always charged, or by the secretion of some fluid, or by any other means alike mysterious to us, it be capable of directing the action of its organs to an external object.

We often both tried, both insulated and uninsulated, to touch the fish, without feeling the least shock.

When Mr Bonpland held it by the head, or by the middle of the body, while I held it by the tail, and, standing on the moist ground, did not take each other's hand, one of us received shocks, which the other did not feel.

It depends upon the gymnotus to act toward the point where it finds itself the most strongly irritated.

The discharge is then made at one point only, and not at the neighbouring points.

If two persons touch the belly of the fish with their fingers, at an inch distance, and press it simultaneously, sometimes one, sometimes the other, will receive the shock.

In the same manner, when one insulated person holds the tail, and another pinches the gills, or pectoral fin, it is often the first only by whom the shock is received.

It did not appear to us, that these differences could be attributed to the dryness or dampness of our hands, or to their unequal conducting power.

The gymnotus seemed to direct its strokes sometimes from the whole surface of its body, sometimes from one point only.

Nothing proves more strongly the faculty which the gymnotus possesses, of darting and directing its stroke according to its will, than the observations made at Philadelphia, and recently at Stockholm, on gymnoti rendered extremely tame.

When they had been made to fast a long time, they killed from afar small fishes put into the tub.

They acted at a distance; that is to say, their electrical stroke passed through a very thick stratum of water.

We need not be surprised, that what was observed in Sweden, on a single gymnotus only, we could not see on a great number of individuals in their native country.

The electric action of animals being a vital action, and subject to their will, it does not depend solely on their state of health and vigour.

A gymnotus, that has made the voyage from Surinam to Philadelphia and Stockholm, accustoms itself to the imprisonment to which it is reduced; it resumes by degrees the same habits in the tub which it had in the rivers and pools.

An electrical eel was brought to me at Calabozo, taken in a net, and consequently having no wound.

It ate meat, and terribly frightened the little tortoises and frogs, which, not knowing the danger, placed themselves with confidence on its back.

The frogs did not receive the stroke till the moment when they touched the body of the gymnotus.

When they recovered, they leaped out of the tub; and when replaced near the fish, they were frightened at its sight only.

We then observed nothing that indicated an action at a distance; but our gymnotus, recently taken, was not yet sufficiently tamed to attack and devour frogs. On approaching the finger, or metallic points, within the distance of half a line from the electric organs, no shock was felt.

Perhaps the animal did not perceive the neighbourhood of this foreign body; or, if it did, we must suppose that the timidity it felt in the commencement of its captivity, prevented it from darting forth its energetic strokes, except when strongly irritated by an immediate contact.

The gymnotus being immersed in water, I approached my hand, both armed and unarmed with a metal, within the distance of a few lines from the electric organs; yet the strata of water transmitted no shock, while Mr Bonpland irritated the animal strongly by an immediate contact, and received some very violent shocks.

If I had plunged the most delicate electroscopes we know, prepared frogs, into contiguous strata of water, they would no doubt have felt contractions at the moment when the gymnotus seemed to direct its stroke elsewhere.

The electrical organ of the gymnoti acts only under the immediate influence of the brain and the heart.

On cutting a very vigorous fish through the middle of the body, the fore part alone gave me shocks.

The shocks are equally strong, in whatever part of the body the fish is touched; it is most disposed, however, to dart them forth when the pectoral fin, the electrical organ, the lips, the eyes, or the gills are pinched.

Sometimes the animal struggles violently with a person holding it by the tail, without communicating the least shock.

Nor did I feel any when I made a slight incision near the pectoral fin of the fish, and galvanized the wound by the simple contact of two pieces of zinc and silver.

The gymnotus bent itself convulsively, and raised its head out of the water, as if terrified by a sensation altogether new; but I felt no vibration in the hands which held the two metals.

The most violent muscular movements are not always accompanied by electric discharges.

The action of the fish on the organs of man is transmitted and intercepted by the same bodies that transmit and intercept the electrical current of a conductor charged by a Leyden vial, or Volta's pile.

In wounded gymnoti, which give feeble but very equal shocks, these shocks appeared to us constantly stronger on touching the body of the fish with a hand armed with metal, than with the naked hand.

They are stronger also, when, instead of touching the fish with one hand, naked, or armed with metal, we press it at once with both hands, either naked or armed.

These differences, I repeat, become sensible only when you have gymnoti enough at your disposal, to be able to choose the weakest; and the extreme equality of the electric discharges admits of distinguishing between the sensations felt alternately by the hand naked or armed with a metal, by one or both hands naked, and by one or both hands armed with metal.

It is also in the case only of small shocks, weak and uniform, that the shocks are more sensible on touching the gymnotus with one hand (without forming a chain) with zinc, than with copper or iron.

Resinous substances, glass, very dry wood, horn, and even bones, which are generally believed to be good conductors, prevent the action of the gymnoti from being transmitted to man. I was surprised at not feeling the least shock on pressing wet sticks of sealing-wax against the organs of the fish; while the same animal gave me the most violent strokes, when excited by means of a metallic rod.

Mr Bonpland received shocks when carrying a gymnotus on two cords of the fibres of the palm-tree, which appeared to us extremely dry.

A strong discharge makes its way through very imperfect conductors.

Perhaps also the obstacle which the conducting arc presents, renders the discharge more painful.

I touched the gymnotus with a wet pot of brown clay without effect; yet I received violent shocks when I carried the gymnotus in the same pot, because the contact was greater.

When two persons, insulated or not insulated, hold each other's hands, and one of these persons only touches the fish with the hand, either naked or armed with metal, the shock is most commonly felt by both at once.

It happens, however, also, that, in the most painful shocks, the person who comes into immediate contact with the fish alone feels the shock.

When the gymnotus is exhausted, or in a very weak state of excitability, and will no longer emit strokes on being irritated with one hand; the shocks are felt, in a very vivid manner, on forming the chain, and employing both hands.

Even then, however, the electric shock takes place only at the will of the animal. Two persons, one of whom holds the tail, and the other the head, cannot, by joining hands and forming a chain, force the gymnotus to dart his stroke.

In employing very delicate electrometers in a thousand ways, insulating them on a plate of glass, and receiving very strong shocks, which passed through the electrometer, I could never discover any phenomenon of attraction or repulsion.

The same observation was made by Mr Fahlberg at Stockholm.

This philosopher, however, has seen an electric spark, as Walsh and Ingenhousz had done before him at London, by placing the gymnotus in the air, and interrupting the conducting chain by two gold leaves pasted upon glass, and a line distant from each other.

No person, on the contrary, has ever perceived a spark issue from the body of the fish itself.

We have irritated it for a long time during the night, at Calabozo, in perfect darkness, without observing any luminous appearance.