Observations respecting the Gymnotes, and other Electric Fish.

[From Baron Humboldt's Historical Relation of his Voyage in America.]

In his last voyage in America, Baron Humboldt made many original observations respecting the gymnotus and torpedo, which are highly interesting to the physiologist expressly, as well as to the naturalist in general; and, as the history of the Voyage of this philosopher is, from its great price, perhaps not in the possession of many of our readers, we shall give some extracts from it, relating to the animals above designated.--Edit.

The Spaniards confound, under the name of tembladores (tremblers), all electric fish.

They exist in the sea of the Antillas, on the coasts of Cumana.

The Indians of Guayqueries, who are the most skilful fishers and most industrious people of those regions, brought us a fish which, as they said, benumbed their hands.

This fish rises up the little river of Manzanares.

It was a new species of raja, the spots on the sides of which are but slightly visible, and which much resembles the torpedo of Galvani.

The torpedoes, provided with an electric organ, which is visible externally from the diaphanous state of the skin, form a genus or sub-genus different from the rajas, properly speaking.

The torpedo of Cumana was very lively, and extremely vigorous in his movements, and yet the electric shocks he gave us were but very weak.

They became stronger on galvanising the animal by the contact of zinc and gold.

Other tembladores, real gymnotes, or electric eels, inhabit the Rio Colorado, the Guarapiche, and many rivulets which traverse the Chaymas Indies.

They enter also the great rivers of America,--the Oroonoko, the Amazon, and the Meta; but the force of the current and depth of the water in those parts prevent the Indians from catching them.

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

It is in the Llanos, especially in the environs of Calabozo, between Morichal and Aniba and Abaxo, that the ponds of stagnant water and the overflowings of the Oronooko (the Rio- Guarico, the Canos of the Rastro, Berito, and Paloma), are filled with gymnotes.

We wished at first to make our experiments in the house we inhabited at Calabozo; but the fear of the electric shocks of the gymnotus is so great, and their effects so much exaggerated by the people, that for three days we could not procure any of these animals, although they may be caught with facility, and we had promised the Indians two piastres for each large and vigorous fish they would bring us.

This fear of the Indians is the more extraordinary, because they do not resort to a means for preventing the shocks, in which, they state, they have much confidence.

They tell white men, when they are interrogated respecting the effects of the tembladores, that they may be touched with impunity, if we chew tobacco.

This fable of the influence of tobacco on the electric powers of these animals, is as general on the continent of South America, as the belief of sailors is in the effect of garlic and suet on the magnetic needle.

Cuvier.

Regne Animal, t. ii. p. 156. There are in the Mediterranean, according to Risso, four species of electric torpedoes, which were formerly confounded under the name of raja torpedo: namely, torpedo narke, torpedo unimaculata, torpedo galvani, and torpedo marmorata.

The torpedo of the Cape of Good Hope, on which Mr.

Todd has recently made some experiments, is undoubtedly a nondescript species.

Impatient of this long delay, and obtaining only very indeterminate results from our observations on a living gymnotus very much weakened, which they had brought us, we went to Cano de Bera, to make our experiments in the open air on the side of the water. We sat out on the 19th of March early in the morning, for the little village called Rastro de Abaxo; whence the Indians led us to a small river, which, in seasons of great drought, forms a pool of muddy water, surrounded by beautiful trees, clusia, amyris, and mimoses with odoriferous flowers.

The catching of the gymnotes with a net is very difficult, because of the extreme agility of these fish.

We would not employ the barbasco, that is to say, the roots of the piscidia erithryna, the jacquinia armillaris, and some species of phyllanthus, which, thrown into a pond, intoxicate or stupify the fish: this measure would have weakened the gymnotes.

The Indians told us, they would fish with horses.

We could not imagine what this extraordinary way of fishing could be; but we soon saw our guides return from a savannah, where they had collected several wild horses and mules, which they drove before them into the pool.

The noise made by the splashing of the horses made the fish rise from the bottom of the water, and prepare for the combat.

These yellowish and livid eels, similar to large water-snakes, were then seen swimming on the surface of the water, and pressing themselves against the bellies of the horses and mules.

A battle between animals so different presented a very picturesque scene.

The Indians, armed with harpoons and long sharp canes, closely surrounded the pool; some of them, too, climbed up the trees whose branches hung over the water, and, by their cries and weapons, prevented the horses from escaping from the water.

The eels defended themselves by repeated discharges of their electric batteries.

For a long time they seemed likely to become victorious.

Many horses sunk under the violence of the shocks they received over all the organs most essential to life; benumbed by the force and frequency of them, they disappeared under the water.

Others, panting for breath, with erect mane, haggard eyes, and signs expressive of extreme anguish, rose again, and endeavoured to escape from the storm around them; but the Indians drove them back again into the middle of the water.

Some, however, escaped the vigilance of the fishermen, and gained the shore, stumbling at every pace, and stretching themselves on the sands, apparently benumbed by the electric shocks of the gymnotes.

In less than five minutes, two horses were drowned.

The eel, being five feet in length, pressing itself along the belly of the horse, makes a discharge from the whole extent of his electric organ, and thus attacks at once the heart, the coeliac plexus, and the whole of the abdominal nerves.

It is obvious that the effect in the horse must be greater than what it is in a man, when he only touches the animal by one of his extremities.

The horses are, probably, not killed, but merely benumbed, and are drowned, from their inability to raise themselves during the combat between the rest with the gymnotes.

We at first had no doubt but that the battle would end with the death of all the horses engaged in it; but the impetuosity of it gradually diminished, and the gymnotes, fatigued, dispersed.

They have occasion for a long repose and an abundance of nutrition, to repair what they have lost of their galvanic power.

They timidly approached the margin of the pool, when they were taken by means of little harpoons attached to long cords.

When the cords were perfectly dry, the Indians drew them up without receiving any shocks.

In a few minutes we had obtained five large gymnotes, most of which were but slightly wounded.

Several others were taken towards the evening by the same means.

The temperature of the water in which the gymnotes usually live, is about 26° or 27° Reaumur, (90° or 92° Fahrenheit.)

They assured us that their electric power diminished in colder water; and it is very remarkable, as a celebrated naturalist has observed, that animals, generally, endowed with organs productive of electric powers, the effects of which are sensible to man, are not found in the air, but in an electro-conductive fluid.

The gymnotus is the largest of the electric fish.

I have seen some of them which were from five feet to five feet three inches in length.

The Indians declared that they had seen still longer.

We found that a fish which was three feet ten inches long weighed twelve pounds.

The transverse diameter of the body was, without including the anal fin, three inches and five lines, (very nearly four inches English measure.)

Amyris lateriflora, A. coriacea, Laurus pichurin, Myroxilon secundum, Malpighia reticulata.

Embarbascas con cavallos: properly, make the fish intoxicated or sleepy by means of horses.

The Indians assured us, that, when a troop of horses were driven into that pool two days in succession, no horse is killed on the second day.

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

The part below the head is yellow, mingled with red.

Two rows of small yellow spots are placed symmetrically along the back, from the head to the point of the tail: each spot surrounds an excretory opening; and the skin of the animal is constantly covered with a mucous matter, which, as Volta proved, conducts electricity twenty or thirty times more powerfully than pure water.

It is very remarkable, that no electric fish hitherto discovered is provided with scales.

The gymnotus, like the common eel, likes to respire the air on the surface of the water.

The latter is known to creep during the night on the grassy banks of rivers; but we must not conclude, with M. Bajon, that the fish would die if it were not to come and respire air without the water.

I have seen a very vigorous gymnotus die on the dry ground, after having darted out of the adjacent pool. M.

Provencal and myself have proved, by our researches on the respiration of fishes, that their gills, when wet, are capable of performing the functions, both of decomposing atmospheric air, and of abstracting the oxygen dissolved in water.

They do not suspend their respiration in the air, but absorb gaseous oxygen, like a reptile provided with lungs.

It is well known that carps are fattened by feeding them out of water, taking care to moisten from time to time their gills with some wet moss, to prevent them from becoming dry.

Fish open their bronchial valves more in oxygen gas than in water; but their temperature is not raised, and they live as long in vital air as in a mixture of 90 parts of azote and 16 of oxygen.

We have found that tenches, placed under bell-glasses filled with air, absorb in an hour half a cubic centimetre (about one-sixth of a cubic inch English measure) of oxygen.

This action takes place in the gills alone; for, fish having cork-collars adapted to them, and placed thus with their head outwards and the rest of the body in a vessel filled with air, do not absorb the oxygen by the rest of the body.

It appears, that respiration of air is effected by the medium of an extremely thin layer of water over the surface of the gills.

The swimming-bladder of the gymnotus is two feet five inches long in a fish three feet ten inches in length.

It is separated from the skin by a mass of fat, and is situate on the electric organs, which fill more than two-thirds of the animal. The same vessels that are insinuated between the laminae of these organs, give also numerous branches to the exterior surface of the bladder just mentioned.

One hundred parts of the fluid contained in this bladder, I found to be constituted of 96 parts azote and 4 oxygen.

The medullary substance of the brain presents but a slight analogy with the albuminous and gelatinous matter of the electric organs, but these two substances have this in common,--they receive a large quantity of arterial blood, which is deprived of its oxygen in them.

We stop, at present, at the conclusion of these preliminary observations, because we wish to give an account of Baron Humboldt's experiments on the electric powers of the gymnotes in an uninterrupted manner, and the limits of the Journal will not permit us to do this in the present Number.--Edit.