ANIMAL ELECTRICITY. 



83 



power. No irritation has ever produced a dis- 

 charge after death. The intensity of the elec- 

 trical power seems to bear no relation to the 

 size of the fish, at least after it has attained 

 mature age ; small fish are almost always ac- 

 tively electrical. 



The torpedo sometimes bears great irritation, 

 even the firm grasp of a hand, without dis- 

 charging. In these circumstances it writhes 

 and twists itself about for some time, using 

 strong efforts to escape, before it emits its 

 electricity. In a few instances it has been 

 found impossible by any means to excite even 

 vigorous torpedos to discharge. Both Lace- 

 pede and Reaumur handled and irritated the 

 most lively torpedos, even while yet in their 

 native element, without experiencing any shock. 

 But generally the shocks are stronger when the 

 skin of the fish is in any way irritated. All 

 electrical fishes soon become exhausted and 

 die, even in sea-water, when they are excited 

 to give a continued succession of discharges. 

 But fishes much exhausted by frequent dis- 

 charges recover their electrical energy after a 

 few hours' rest. The torpedo seems to possess 

 electrical power even in the earliest periods of 

 its existence. Spallanzani relates that he found 

 within a female torpedo two living foetuses, 

 which gave distinct shocks on being removed 

 from their coverings. Dr. Davy, also, once 

 received a sharp although not a strong shock, 

 in extracting foetal fish from the uterine cavities 

 of a dying torpedo. 



When the Gymnotus is grasped by the hand, 

 the intensity of the discharge is moderate at 

 first, but is increased if the pressure be conti- 

 nued. The torpedo discharges whenever it is 

 taken out of the water ;, and Walsh found that 

 a vigorous fish repeats the discharge as often 

 as it is lifted out, and again on being re-im- 

 mersed ; also that it gives more violent shocks 

 in air than in water. Spallanzani found the 

 shock to be more severe when the fish was laid 

 on a plate of glass. The following observation, 

 reported by Walsh, seems to prove that the 

 Gymnotus can distinguish at some distance 

 between substances capable of receiving and 

 conducting its discharge, and those which can- 

 not conduct ; and that (excepting when it is 

 much irritated) it discharges only when con- 

 ducting bodies are presented to it. Two wires 

 were put into the water of the vessel in which 

 a Gymnotus was swimming ; these wires were 

 of some length, and stretched; they termi- 

 nated in two glasses filled with water placed 

 at a considerable distance from each other. 

 Whilst the apparatus remained in this state, 

 and the circulation was of course interrupted, 

 the animal did not prepare to exercise his 

 power, but whenever any conducting substance 

 filled the interval, and rendered the circle 

 complete, it instantly approached the wires, 

 arranged itself, and gave the shock. 



The same fish, according to the observations 

 of Messrs. Humboldt and Bonpland, appears 

 to have the power of transmitting its discharge 

 in any direction it pleases, or towards the 

 point where it is most sharply irritated; and 

 further, it seems to be able to discharge, some- 



times rora a single point, at other times from 

 the whole of its surface. Dr. Davy has satis- 

 fied himself that the Torpedo also has the 

 power of discharging its electricity in any 

 direction it chooses. 



The shock produced by the discharge of the 

 Gymnotus is most severely felt when one hand 

 seizes the head and the other the tail. When 

 two persons take hold of a Gymnotus, the one 

 by the head or by the middle of the body, and 

 the other by the tail, both standing on the 

 ground, shocks are felt, sometimes by one 

 alone, sometimes by both. It has been ob- 

 served that when metals are placed in the 

 vessel or pond containing a Gymnotus, the fish 

 appears much agitated, and discharges very 

 frequently. 



II. Motions of the fish in the aft of dis- 

 charging. These have been particularly ob- 

 served only in the Torpedo and Gymnotus. At 

 the time of discharging, according to some ob- 

 servers, the Torpedo generally becomes some- 

 what tumid anterior to the lateral fins, retracts 

 its eyes within their orbits, and moves its 

 lateral fins in a convulsive manner. When 

 the fish begins to lose its plumpness, after 

 having given frequent shocks, " a little tran- 

 sient agitation" is perceptible along the carti- 

 lages which surround the electrical organs at 

 the time of the discharge. Dr. Davy, how- 

 ever, states that he has never seen the Torpedo 

 of the Mediterranean retract its eyes at the 

 time of discharging ; and that he has not been 

 able to associate any apparent movement of the 

 fish with the electrical discharge. 



The Gymnotus sometimes emits the strongest 

 discharges without moving any part of its sur- 

 face in the slightest perceptible degree. But, 

 at other times, it seems to arrange itself so as 

 to bring the side of its body into a parallel 

 with the object of its attack before discharging. 

 When a small fish is brought near a Gymno- 

 tus, it swims directly up to it, as if about to 

 seize it ; on approaching close, however, it 

 halts, seems to view the fish for a few seconds, 

 and then, without making the smallest move- 

 ment discoverable by the eye, emits its dis- 

 charge ; should the small fish not be killed by 

 the first, the Gymnotus gives a second, and a 

 third shock, until its object is accomplished. 

 It continues to kill a large number in close 

 succession, if they be supplied to it, but it 

 eats very few. 



III. Physiological effects of the discharge. 

 The effects of the discharge' on man vary ac- 

 cording to its intensity and the extent of the 

 surface of the fish which is touched. A vigo- 

 rous torpedo causes a momentary shock, which 

 is felt through the arm even as far as the shoul- 

 der, and leaves a degree of painful numbness 

 in the finger and hand, continuing for a few 

 seconds, and then going off entirely. Some 

 observers have compared the sensation pro- 

 duced to that felt in the arm when the elbow is 

 struck so as to compress strongly the ulnar 

 nerve; and others (even such as have been 

 much accustomed to receive electric shocks) 

 have declared the sensation to be extremely 

 painful ; Gay Lussac and Humboldt say that 



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