ANIMAL ELECTRICITY. 



85 



there they were met by the wild cries and violent 

 menaces of the Indians, 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 Gymno- 

 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 are 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. Humboldt saw one 

 Gymnotus receive the discharge of another with- 

 out giving any evidence of feeling it. Galvani, 

 having placed 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. Magnetical 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, Humboldt, and Bonpland 

 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; 



* Mem. de 1'Acad. de Berlin, 1770. 



and that these, adhering to its glutinous skin, 

 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 Bonpland should have found a belief in 

 the possession of magnetic properties by the 

 Gymnotus prevalent amongst the inhabitants 

 of the Savannas of Caraccas." 



Sir Humphry 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. He 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.f 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, containingabout one hundred 

 and eighty convolutions,and 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 as 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. 



In 1827, before Dr. Davy performed his ex- 

 periments, similar magnetic effects were observed 

 by means of the multiplier, by MM. De 

 Blainville and Fleuriau, at La Rochelle. They 



* Biologie, v. 145. 



t Phil. Trans. 1829. 16. Similar experiments 

 were made with the discharge of the Gymnotus by 

 Messrs. Rittenhouse and Kinnersly with the same 

 results. They saw no effect produced on the elec- 

 trometer. Philadelphia *Med. and Phys. Journal, 

 i. 15. 



