ELECTRIC ORGANS OF FISHES. 357 



of the Gymnoti, employed by the Indians of South America, 1 and 

 all its circumstances establish the close general analogy between the 

 Gymnotus and Torpedo in the vital phenomena attending the ex- 

 ercise of their extraordinary means of offence. It is voluntary and 

 exhaustive of the nervous energy ; like voluntary muscular effort, 

 it needs repose and nourishment to produce a fresh accumulation. 

 In the experiments performed by Professor Faraday on a large 

 living Gymnotus, 2 the most powerful shocks were received when 

 one hand grasped the head and the other hand the tail, of which 

 I had painful experience ; especially at the wrists, the elbows, 

 and across the back. But the nearer the hands were together 

 within certain limits, the less powerful was the shock. It was 

 demonstrated by the galvanometer that the direction of the elec- 

 tric current was from the anterior parts of the animal to the pos- 

 terior parts, and that the person touching the fish with both hands 

 received only the discharge of the parts of the organs included 

 between the points of contact. Needles were converted into 

 magnets : iodine was obtained by polar decomposition of iodide 

 of potassium ; and, availing himself of this test, Faraday showed 

 that any given part of the organ is negative to other parts before 

 it, and positive to such as are behind it. Finally, heat was 

 evolved, and the electric spark obtained. The delicate plates 



1 They rouse the Gymnoti by driving horses and mules into the ponds which those 

 fish inhabit, and harpoon them when they have exhausted their electricity upon the 

 unhappy quadrupeds; ' I wished,' says Humboldt, 'that a clever artist could have 

 depicted the most animated period of the attack: the groups of Indians surrounding 

 the pond, the horses with their manes erect arid eyeballs wild with pain and fright, 

 striving to escape from the electric storm which they had roused, and driven back by 

 the shouts and long whips of the excited Indians : the livid yellow eels, like great 

 water-snakes, swimming near the surface and pursuing their enemy: all these objects 

 presented a most picturesque and exciting ensemble. In less than five minutes two 

 horses were killed. The eel, being more than five feet in length, glides beneath the 

 body of the horse, and discharges the whole length of its electric organ. It attacks, 

 at the same time, the heart, the digestive viscera, and, above all, the gastric plexus of 

 nerves. I thought the scene would have a tragic termination, and expected to see 

 most of the quadrupeds killed; but the Indians assured me the fishing would soon be 

 finished, and that only the first attack of the Gymnoti was really formidable. In fact, 

 after the conflict had lasted a quarter of an hour, the mules and horses appeared less 

 alarmed ; they no longer erected their manes, and their eyes expressed less pain and 

 terror. One no longer saw them struck down in the water; and the eels, instead of 

 swimming to the attack, retreated from their assailants, and approached the shore.' 

 The Indians now began to use their missiles; and, by means of the long cord attached 

 to the harpoon, jerked the fish out of the water, without receiving any shock so long 

 as the cord was dry; but a less cautious assailant, who had climbed an overhanging 

 bongh, was brought down into the water, amidst the laughter of his companions, by 

 the shock sent upwards from the wounded Gymnotus, along the wetted cord attached 

 to the harpoon, cvn. p. 55. 



2 LXXXIII. 



