894 SPECIAL PHYSIOLOGY. 



part than a nerve, still retain their electric power. Destruction of the electric 

 lobe in the Torpedo completely destroys the electric power. The discharge of 

 electricity in the Gymnotus may be caused, by touching different points on the 

 same side of the body, or different points on opposite sides of the body ; in the 

 Torpedo, it is exeitecl by touching the upper and under surface of the animal. 

 But it is said, that when exactly corresponding points on the two sides, or on 

 the same surface of the body, are touched, no shock occurs, and that not even 

 a current passes through a galvanometer. Contact with one point only in- 

 duces no shock, and a Gymnotus instinctively endeavors to bring a second 

 point into near relation with anything which touches it. The back of the 

 Torpedo is electrically positive ; the ventral surface is negative ; the strongest 

 currents are obtained over the electric organ. In the Gymnotus, however, the 

 most powerful shocks are obtained by touching the two extremities of the 

 body, which here present opposite electric states, the head being positive, and 

 the tail negative. 



The electric discharge from these Fishes not only produces shock to the 

 living nerves of one individual, or even of a chain of persons touching each 

 other's hands, but it affects the galvanometer, magnetizes needles, acco"m- 

 plishes chemical decompositions, and even produces a spark in a properly 

 devised circuit. (Faraday. ) There can be no doubt, therefore, of its perfect 

 identity with the electricity developed by physical means. 



The energy of the electric discharge depends on the size and strength of the 

 animal. If is exhausted by too frequent use ; sometimes a powerful discharge 

 precedes death. Torpedoes, in which the electric nerves have been divided, 

 appear to live longer than those the electric organs of which are subject to re- 

 peated irritation. The electric energy, like that of the vital processes gen- 

 erally, is greater, and less easily exhausted, in young Torpedoes than in older 

 ones^ and shocks have been felt even from the foetal Fish, as it has been ex- 

 tracted from the abdomen of the parent. Just as the embryo of the Snapping 

 Turtle has been seen to snap its jaws whilst still in the egg, so the foetal Tor- 

 pedo has been seen to try and bring its surfaces in proper contact with foreign 

 bodies, so as to pass the shock through them. The electric power is first ex- 

 cited, and then destroyed, by strychnia and morphia. A temperature of 32 

 suspends the power, which is again restored by immersion of the Fish in water 

 at a temperature of from 58 to 68 ; at 86, rapid and strong discharges take 

 place, and the Torpedo soon dies. 



The use of this remarkable power, beyond that of serving for protection, or 

 for obtaining food, is not evident ; indeed allied Species, exposed to the same 

 enemies, and living on the same food, flourish without such organs. More- 

 over, the Gymnotus kills many more fishes than it eats, and Torpedoes, kept 

 in confinement, have been found to destroy small fishes without eating them. 

 The electric discharge has been supposed to assist indirectly in the digestive 

 process, inasmuch as animal substances subjected to powerful electric currents, 

 undergo ready decomposition ; the intestine of the Torpedo is very short, but 

 so also is the digestive canal of the allied Species. It has also been imagined 

 that oxygen may be supplied to the gills, by decomposition of the water near 

 them by these organs ; but this is improbable. Lastly, it has been thought 

 that they may render the Fish galvanometric, and thus enable it to recognize 

 changes in the electric condition of the surrounding medium. The chief use, 

 however, must surely be protective. It has been said that certain Molluscs 

 and Insects are able to emit feeble shocks of electricity, but this is doubtful. 

 The Coelenterata, as the Sea-Anemones and others, irritate and destroy their 

 prey by stinging organs, which act suddenly, but are not really electric. 



The great size of the nerves distributed to the electric organs, the special 

 distribution of the extremities of the nerves upon the membranous walls of 

 the cells, the results of division of those nerves, and of destruction of the so- 

 called electric lobe, the excitement of the organs by irritation of the brain, 

 and, lastly, the apparent subjection of the whole apparatus to the will of the 

 animal, show, that in some way the electric phenomena developed in these 

 living galvanic batteries, are largely dependent on the nervous system. Ac- 

 cording to one view, the electric force may be developed and accumulated in the 

 electric organ, and may be merely discharged under the influence of the nerves. 



