THE ELECTRIC EEL.
If the rational basis of legend and fable is worth exploring at all, we may well ask why the possession of electric power, the most strange, and until recently the most inexplicable, attribute of any of the inhabitants of the water, does not play a greater part in the marvellous narratives of ancient voyages? The remora, or sucking-fish, magnified a thousand times in imaginations excited by a world of strange and new experience, was the besetting foe of mariners in Northern waters. Clinging to the keel, it kept their barques for weeks in the mare pigrum, the sluggish sea of drifting ice. Whales, rising like sandbanks above the waves, tempted the weary crews to make fast to their treacherous bulk, and then plunged to the bottom, carrying with them both ships and sailors. Gigantic squids thrust their slimy arms down the hatchways, and plucked sleeping seamen from their berths and strangled them before their comrades’ eyes. But the “torpedo”—the paralyzer—though as well known then to the fishers of the Mediterranean as it is now known, under the name of the “crampfish,” or electric ray, to the trawlers of Cornwall or the Channel, seems to have appealed less to the fancies of the sailors of old, than the new though less mysterious powers of the monsters, great and small, which rushed beneath their keels in hyperborean seas. Possibly the powers of the “torpedo” were too well known to excite curiosity, though it is difficult to believe that a creature which sometimes reaches a bulk of 100 lbs. weight, and can emit an electrical discharge strong enough to kill a duck, or to cause in the human arm a “creeping sensation felt in the whole limb up to the shoulder, accompanied by a violent trembling, and sharp pain in the elbow,” followed by loss of sensation for an hour, was not as suggestive to sailors’ fancies as the tentacles of the cuttle-fish, or the sucking-discs of the remora. But if the fabulous terrors of the last were enough to deter the boldest mariners who sailed beyond Thule, it is matter for congratulation that early explorers were unacquainted with the powers and proportions of a monster of still more formidable mould, the electric eel of Southern America. Its mere aspect is lurid, sombre, and repulsive. Its belly glows like red-hot iron, as if fresh from the lake of living fire. Its back is dark and shiny, as if tinged by inky Cocytus. Around its lips and jaws are glowing spots like bubbles of hot metal. The colours meet in a line along the side; and the creature, when drawn from the water, looks as though formed of two welded portions of iron, the one hot, the other cold, just plunged into the blacksmith’s cistern. Small eyes, blue and bleared, are set in the top of a blunt ferocious head, from which the strong and muscular body tapers gradually to a point at the tail. Such, at least, is the appearance of the two electric eels at the Zoo, of whose power the writer, with curiosity stimulated by Baron Humboldt’s unique description of these creatures in the inland pools of tropical America, recently made trial. Neither the size of the fish, nor their physical condition in the small tank in which they exist at present, could reasonably be expected to produce such results as the great traveller witnessed in the stagnant pools of the llanos of Caraccas, when the Indians drove a herd of horses into the water to face the electric discharges of the fish. “These yellowish livid eels,” he writes, “resembling large aquatic snakes, swim near the surface of the water, and crowd under the bellies of the horses and mules. The struggle between animals of so different an organization affords a very interesting sight. The Indians, armed with harpoons and long slender reeds, closely surround the pool, and by their wild shouts and long reeds prevent the horses from coming to the bank. The eels seek to defend themselves by repeated discharges of their electric batteries, and for a long time it seems as if theirs would be the victory. Several horses sink under the violence of the invisible blows which they receive in the most vital parts, and, benumbed by the force and frequency of the shocks, disappear beneath the surface. Others, with mane erect and haggard eyes, raise themselves and endeavour to escape, but are driven back by the Indians. Within five minutes a couple of horses are killed. The eel, which is five feet long, presses its body against the belly of the horse, and attacks at once the heart, the viscera, and the group of abdominal nerves. It is natural,” the author adds, “that the effect which a horse experiences should be more powerful than that produced by the same fish on man, when it touches him only at one of the extremities. The horses are probably not killed, but stunned, and are drowned amid the confusion of the struggle between the other horses and eels.”
The truth of Humboldt’s account of the taking of the electric eels is sometimes doubted. But apart from the credit due to the deliberate utterances of one of the greatest minds of modern days, the accuracy of whose views, even when he put them forward as mere probable surmise, is being constantly verified by later experience, the powers of the creatures, even of the small specimen brought to this country, are so astonishing as to make Humboldt’s account not err on the side of the marvellous.
It would be difficult, unless the opportunity existed of taking a plunge into a tank large enough to swim in, and well stocked with electric eels, to realize by personal experience the precise effect of the shocks upon the horses; but a record of the writer’s sensations when in personal contact with these uncanny creatures may perhaps give some notion of the strength of their electric power. The largest of the pair in Regent’s Park, about 4½ ft. in length, thick and deep, and probably weighing from 16 lbs. to 18 lbs., was moving sluggishly on the bottom of the tank, and was slowly raised to the surface by a landing-net. As its side became visible, its resemblance to a “cooling cast” was even closer than when seen from above. When grasped in the middle of the back, there was just time to realize that it had none of the “lubricity” of the common eel, when the first shock passed up the arm with a “flicker” identical with that which a zig-zag flash of lightning leaves upon the eye, and, as it seemed, with equal speed. A second and third felt like a blow on the “funny-bone,” and the hand and arm were involuntarily thrown back with a jerk which flung the water backwards on the pavement and over the keeper who was kindly assisting in the enterprise. This slight mishap recalled a far less agreeable result of a shock inflicted on a previous inquirer, whose recoiling hand had struck the assistant a severe blow in the face. Unwilling to be baffled by a fish less in size than the salmon which form the common stock of a fishmonger’s window, the writer once more endeavoured to hold the eel at any cost of personal suffering. But the electric powers were too subtle and pervading to be denied. The first muscular quiver of the fish was resisted; but at the second, the sense of vibration set up became intolerable, and the enforced release was as rapid and uncontrollable as the first. The smaller eel was neither so vigorous nor so resentful as its fellow. But though the first and second shocks did not compel the grasp to relax, a third was equally intolerable with that given by the larger fish. The electrical power seems to increase rapidly in the heavier eels. One of 5 ft. in length, which appeared to be nearly dead when it arrived at the Gardens, and was therefore handled without ceremony, inflicted a shock which, as the keeper stated, “nearly sent him on his back;” and the same fish, when being carried by hand in a tub up to the rooms of the Royal Society, sent a shock through the water which nearly caused the downfall of fish and bucket alike. This power of projecting its electric discharge, either through the water or by means of any conductor, to the object which it desires to paralyze, may be well observed at the Zoo. The usual way in which the shocks are received is by grasping a copper-rod, which is placed in contact with the fish’s back. But it is when in pursuit of the small fish which form its food that the “range” of the eel’s battery is best seen. On the last occasion on which the writer was present at the eel’s feeding-hour, eight or ten lively gudgeon were taken from a pail, and placed in the eel’s tank. The small fish at once dived to the bottom, as is their habit, and sought refuge in the corners, or at the angle made by the meeting of the base and sides of the stone cistern. Every one of the fish was killed by electric shock before being eaten; but in the case of those in the corners, it was impossible for the fish to bring the electric organ, which lies on each side of the lower part of the tail, into direct contact. The eel, therefore, swam past them, like a torpedo-boat which intends to discharge its broadside torpedoes, and as the battery came opposite, the fish gave a slight quiver, which instantaneously produced a violent shock in the gudgeon, and turned it belly upwards. After three had been killed and eaten, the shocks became weaker, and the other gudgeon seemed only partly paralyzed by the first shock, and sometimes recovered and swam away in a crippled condition until benumbed by a second shock. One fish which was “shocked” and left for dead while the eel went in pursuit of more, recovered after a few minutes, and was subsequently pursued, received a direct shock from the eel’s side, and was killed. The inference suggested by the writer’s own experience of the violence of the shocks inflicted, though with different degrees of intensity, is that the eel controls the power of the electrical discharge at will, just as it controls any other function which has its initiative in muscular action; and that the gudgeons received enough, and no more, than was sufficient to paralyze them, and make them easy victims for the slow-moving eel.
DEEP-SEA LAMPS.
The possibility of exhibiting the powers of electrical fishes in the tanks at the Zoo, suggests the question whether, in the progress of marine aquariums, we shall ever see the luminous creatures of the deep seas exhibited alive before air-breathing mortals in this upper world. Virgil’s Sybil set the depth of Tartarus at twice the skyward gaze to the summit of Olympus. But the profundity of the ocean abyss is such that in the deep Atlantic Olympus might be imposed upon itself, and Ossa piled above, without rising to break the surface. The imagination almost refuses to grasp the physical conditions in an abyss so profound as the ocean bed off the coast of Porto Rico, wrapped, by a weight of waters five miles deep, in perpetual darkness and everlasting cold, and under a pressure of which figures can convey no practical conception. Even at the average depth of 2,500 fathoms sunlight can never penetrate. The temperature is only a few degrees above freezing-point, the water is without movement, there is no plant-life, and the pressure is two and a half tons on the square inch, or about twenty-five times greater than that which drives a railway train. Yet it is now certain that where the fancy painted a survival of the sterile and lifeless plains of an unformed world, or at most the rude survivals of primitive fossils, the bed of the deep sea teems with animal life, and the clinging darkness of its waters is peopled by myriads of fragile and fantastic forms, and lighted into a blaze by the effulgence from their bodies. Hard as it is to conceive the bare existence of life under the conditions of the ocean abyss, the mind pauses in astonishment at the completeness of the triumph by which creatures apparently doomed to live in eternal night are supplied not with mere slimy secretions of luminosity, but with rows of bright and ever-burning lamps, in organs fitted with lenses and reflectors, which shoot their beams sidelong through the circumfluent ocean, or project shafts of light before their eyes to illuminate their path.
The results of recent deep-sea exploration have been summarized by Mr. Sydney J. Hickson, Fellow of Downing College, Cambridge, in a short work on The Fauna of the Deep Sea, published in the “Modern Science Series.”[[1]] Though the bulk and specialized character of the reports of separate expeditions organized by the English, French, German, Italian, and Norwegian governments, makes such a task one of no ordinary difficulty, Mr. Hickson has succeeded in his wish to “give in a small compass the more important facts of this great mass of literature in such a form as may interest those who do not possess a specialist’s knowledge.” The main conclusions are clearly presented with examples and excellent illustrations, in number sufficient to convince without bewildering. On one point we could desire a little more information. There is no suggestion of the means by which creatures differing so little in bodily frame and tissue from the shallow-water species, from which they are apparently derived by migration into the deeps, support the enormous pressure in their present home. Some explanation seems to be required, though an incident in the recent erection of the Forth Bridge seems to suggest that the modification of tissue to endure high pressure may be acquired more rapidly than is supposed. The men employed in the steel shells or caissons sunk to form the foundations of the piers, worked in a pressure of air rather greater than the pressure of the water outside, which would otherwise have penetrated between the rims of the caissons and the ground. On those days on which they were not employed, and came to the surface, they felt such pain in the joints from the expansion of the air, which had been absorbed at high pressure, that they begged to be allowed to go down into the caissons and spend their off hours in the pressure to which they had grown accustomed. This instance of partial migration into conditions of high pressure, seems worthy of a place among the facts of deep-sea exploration. Yet it must remain among the strangest features of life in the ocean abyss, that its inhabitants show so little visible change of structure to meet what seems the first and most overwhelming change of physical conditions. The angler-fish and eels, crabs and prawns, star-fish and zoophytes of the shallow waters are represented in the abyss by forms almost similar in structure, though that some difference must exist is shown by the fact that when brought up by the dredge from the depths of the ocean they are killed and distorted by the diminution and disappearance of the vast pressure in which they habitually live. “The fish which live at these enormous depths,” writes Mr. Hickson, “are liable to a curious form of accident. If, in chasing their prey, or for any other reason, they rise to a considerable distance above the floor of the ocean, the gases of their swimming-bladder become greatly expanded, and their specific gravity reduced. If the muscles are not strong enough to drive the body downwards, the fish, becoming more and more distended as it goes, is gradually killed on its long and involuntary journey to the surface of the sea. The deep-sea fish, then, are exposed to a danger that no other animals in this world are subject to—namely, that of tumbling upwards.”
[1]. The Fauna of the Deep Sea, by Sydney J. Hickson, M.A., D.Sc. London: Kegan Paul and Co.
But however obscure the structure which enables the deep-sea creatures to withstand the pressure of the waters, the means by which they combat the plague of darkness is evident and astounding. It is well known that the number of phosphorescent animals, even in shallow tropical seas, is such that they can illuminate not only the waters, but the air, to a considerable distance. Sir Wyville Thompson states, that near the Cape Verde Islands he saw the sea in such a blaze of phosphorescence that, though there was no moon, “it was easy to read the smallest print, sitting at the after-port in the cabin; while the bows shed, on either side, rapidly widening wedges of radiance, so vivid as to throw the sails and riggings into distinct lights and shadows.” But, great as is the number of luminous creatures in the shallow waters, the percentage among those dredged from the deeps is greater, though their brilliant glow, when lying upon the decks of the exploring ships, is no guide to the possible intensity of their light in the pressure under which they live. Many of the deep-sea species possess light-projecting organs in numbers and perfection unrivalled by the shallow-water forms. Some of the fish have double rows of tiny lamps running the whole length of their bodies, like the rows of port-holes in an ocean steamer’s sides. These are supplemented by other sets of less clearly divided light-organs, arranged in clusters and groups of fifty or a hundred. Other deep-sea fishes have bull’s-eye lanterns set beneath their eyes, projecting their light “full-a-head.” Sections cut through these extraordinary organs show that above the phosphorus-burning vessel lies first a layer of “reflectors,” and lastly, a lens for concentrating the beams. Perhaps the strangest development of this power of illumination is in an angler-fish, found at a depth of 14,700 feet. Like the other “anglers,” it has a huge mouth armed with long uneven teeth, and a pendent “fishing-rod” tentacle which attracts other fish like a bait. In the shallow-water “anglers” this tentacle resembles something edible by fish. In the deep-water species it is fitted with an organ which is supposed to be a phosphorus lamp, and to play the part of a “Will-o’-the-Wisp” in attracting little fishes to the angler’s jaws.