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 act 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 sale 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 scent:cis, 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 Ilumboldt say that it is more so than the shock produced by the Leyden phial ; and Configliachi compares it to that caused by the contact of two poles of the voltaic pile. Ingenhousz thus describes Iris sensations under the discharge of the tor pedo. " I took a torpedo in my hand, so that my thumbs pressed gently on the upper surface of the lateral fin, whilst my forefingers pressed the opposite side. About one or two minutes after I felt a sudden trembling in my thumbs, which extended no further than my hands ; this lasted about two or three seconds. After
sonic seconds more, the same trembling was felt again. Sometimes it did not return in several minutes, and then came again at very different intervals. Sometimes I felt the trem bling both in my fingers and my thumb. These tremors gave me the same sensations as if a great number of very small electrical bottles were discharged through my hand very quickly one after the other. Sometimes the shock was very weak, at other times so strong that I was very near being obliged to quit my hold of the animal." Walsh ascertained that the same torpedo has the power of discharging in two different manners, so as to produce at one time the effect described by Ingenhousz as a trembling, and at another time a sharp instan taneous shock closely resembling that produced by the discharge of a Leyden phial.t Accord ing to Sir II. Davy, " whoever has felt the shocks both of the voltaic battery and of the torpedo must have been convinced, as far as sensation is concerned, of their strict ana logy.1 Sometimes the torpedo buries itself in the sand left dry at ebb-tide ; and it has occasionally happened, according to some naturalists, that persons walking across the sand, and treading upon the spot beneath which the electrical fish lay concealed, have received his discharge so fully as to be thrown down.§ The effects produced by the discharge of the Gymnotus are more severe. When it is touched with one hand, a smart shock is generally felt in the hand and fore-arm ; and, when both hands are applied, the shock passes through the breast. The discharges of large fish (they grow to the length of twenty feet in their native rivers) sometimes prove sufficient to deprive men, while bathing, of sense and motion. Fermin found that a strong one had power to give a shock to fourteen persons at the same time ; and other experimenters have seen twenty seven persons simultaneously receive its shock. Ilumboldt states that, having placed his feet on a fresh Gymnotus, he experienced a more dreadful shock than he ever received from a Leyden phial, and that it left a severe pain in his knees and in other parts of his body, which continued for several hours. Sometimes the discharge occasions strong contractions of the flexor muscles of the hand which grasps the fish, so that it cannot he immediately let go ; and then, the shock being repeated still more severely, painful sensations are experienced thoughout the whole body, and headache with soreness of the legs remains for some time after.* Paralytic affections, as well as giddiness and dimness of sight, are said sometimes to have followed the reception of strong discharges.-I It is stated by some observers that there are men who are as insusceptible of the shocks of electrical fishes as others are of those from the Leyden phial ; and that women affected with nervous diseases are seldom conscious of receiving the discharge. Kwmpfer asscrtedt that, by sup pressing respiration for a short time, any man may render himself insensible to the torpedo's discharge; but this has been disproved by Walsh and other observers.