Regarding the effects of the discharges of the other electrical fishes, we know very little. The shock given by the Malapterurus of the Nile and Niger (Silurus, Linn.) is said to be more feeble than that of the Torpedo, and yet very painful, attended with trembling, and followed by soreness of the limbs. In attempting to take an individual of Tetraodon electricus in his hand, Lieutenant Paterson (its discoverer) received so severe an electrical shock that he was obliged to quit his hold.
The effects of the discharge of the Gymnotus on the larger animals cannot be better illustrated then by the account which Humboldt has given of the method of capturing the fish adopted by the South American Indians. This method consists in irritating the fish by driving horses into the pools which it inhabits. It directs its electricity in repeated discharges against these horses until it becomes exhausted, when it falls an easy and harmless prey into the hands of the fishermen. Humboldt saw about thirty wild horses and mules forced into a pool con taining numerous Gymnoti. The Indians sur rounded the banks closely, and being armed with harpoons and long reeds, effectually pre vented the escape of the horses. The fishes were aroused by their trampling, and, coming to the surface, directed their electrical discharges against the bellies of the intruders. Several horses were quickly stunned, and disappeared beneath the surface of the water. Others, ex hibiting signs of dreadful agony, hurried to the hank, with bristled mane and haggard eye, but there they were met by the wild cries and violent menaces of the lndians,which forced them again to enter the water. And when, at last, the sur vivors were permitted to leave the pool, they came out enfeebled to the last degree, and their benumbed limbs being unable to support them, they stretched themselves out upon the sand completely exhausted. In the course of five minutes two horses were drowned. By degrees, the discharges from the Gymnoti becoming less intense, the horses no longer manifested the same signs of agony, and the wearied fishes ap proached the margin of the pool, almost lifeless; and then they were easily captured by means of small harpoons attached to long cords. The fishes left in a pool thus disturbed were found scarcely able to give even weak shocks at the end of two days from the time of their combat with the horses. Humboldt concluded from what he saw and heard, that the horses which are lost in the course of this singular fishery are not killed, but merely stunned, by the dis charge. Their death is occasioned by the con sequent submersion.
In this way many mules are destroyed in at tempting to ford rivers inhabited by the Gyrnno tus. So great a number of mules were thus lost within the last few years at a ford near Uritucu, that the road by it was entirely abandoned. When small fishes receive the discharge of a Gymnotus, they arc immediately stunned, turn upon their backs, and remain motionless. They however, for the most part, recover after being removed to another vessel. Reaumur reports that he once saw a duck killed by the repeated discharges of a torpedo ; but both Ingenhousz and Dr. John Davy kept small fishes in the same vessel with torpedos, without observing that the former showed any symptoms of suffering from the shock of the latter. Ilumboldt saw one Gymnotus receive the discharge of another with out giving any evidence of feeling it. Galvani, havingplaced some frogs' thighs, skinned, on the back of a torpedo, saw them convulsed when the fish was excited to discharge.
It is said that the discharge of the torpedo is used medicinally by the Arabians of the present day, particularly in fevers. The patient is placed
naked on a table, and the fish applied to all the members of the body in succession, so that each should receive, at least, one shock. This treat ment causes rather severe suffering, but enjoys the reputation of being febrifuge.
IV. Magnetieal effects of the discharge.— Schilling asserted that he had seen the magnetic needle set in motion by the discharge of a Gym notus;* also, that the fish was attracted by a magnet, and adhered to it ; and that it became so languid when detached from the magnet, that it gave no shock when irritated. Ingenhousz, Spallanzani, Flagg, lIumboldt, and lionpland obtained no such results in repeating the expe riments of Schilling. Professor Hahn of Ley den suggests that the fish examined by Schilling may have been coated with particles of ferrugi nous sand, which frequently forms the beds of the American rivers inhabited by the Gymnotus; and that these, adhering to its glutinous skm, may have given rise to the phenomena observed by Schilling. In quoting the contradictory statements of the above-mentioned observers, Treviranus remarks,* " it is a striking circum stance that so good an observer as Schilling was should have been convinced that he saw such magnetic phenomena in connexion with the fish, and still more remarkable is it that Humboldt and lionpland should have found a belief in the possession of magnetic properties by the Gymnotus prevalent amongst the inhabitants of the Savannas of Caraccas." Sir llumphry Davy passed many strong dis charges from a torpedo through the circuit of an extremely delicate magnetic electrometer, with out perceiving the slightest deviation of, or effect on, the needle. Ile explained this negative result by supposing, that the motion of the electricity in the organ of the torpedo is in no measurable time, and that a current of some continuance is necessary to produce the devia tion of the magnetic needle.t Under more favourable circumstances than those in which Sir H. Davy investigated the properties of the electricity of the torpedo, Dr. John Davy re sumed the enquiry at Malta, and ascertained, in the most satisfactory manner, that animal elec tricity. is capable of producing magnetic effects. He not only saw the needle of a magnetic elec trometer very much affected by the discharge of a torpedo, but he found needles, previously free from magnetism, converted into magnets by the same. In one experiment, he placed eight needles within a spiral, formed of fine copper wire, one inch and a half long, and one tenth of an inch in diameter, containing about one hund red and eighty con vol u tio ns,an d weighingfour grains and a half. A single discharge from a torpedo, six inches long, having been passed through this, the contained needles were all converted into magnets, each one as strong if only one had been used. It was found that the ends of the needles which were nearest the ventral sur face of the fish had received southern polarity, and of course the other extremities northern po larity. The discharges from fish, only four hours after they were taken from the uterine cavities of their mother, were sufficiently strong to magne tize needles through the medium of a spiral, al though but feebly. The same kind of result was obtained with the multiplier; the needle of which, when subjected to a torpedo's discharge, indicated that the electricity of the dorsal surface corresponded with that of the copperplate of the voltaic pile, and the electricity of the ventral surface with that of the zinc plate.