Page:The New International Encyclopædia 1st ed. v. 06.djvu/862

* ELECTRIC BURGLAR ALARMS. 750 ELECTRIC FISH. ELECTRIC BURGLAR ALARMS. See Alarm. ELECTRIC CLOCK. See Clock. ELECTRIC COLUMN. See Dky Pile. ELECTRIC DISCHARGE. See Electricity. ELECTRIC FISH. A fish whidi possesses the jjower i)f (lisclmri.'ing electricity at will. Elec- tric organs are well developed in tlirce sorts of tislies: (1) Most strongly in the Brazilian elec- tric eel; (2) in a genus (ilalapterurus) of Af- rican catfishes; and, (3) most weakly, in the torpedo family of rays. Electric organs are ]>resent, but developed to a much slighter degree, in some other fishes, which are spoken of as pseudo-electric. The organs are modified muscu- lar tr.ict.H and nerve-connections, by means of which the fish are able to give an electric shock. They lie, in the case of the torpedo, in the head and gill region; in the South American eel they are on the ventral surface of the long tail ; and in Malapterurus they practically incase the en- tire body, or occur in lateral lines under the skin on each side of the tail. The electro-motive force seems to be under the infiuence of the central nervous system, and the nerves supplying the organs are enormously developed. In the tor- pedo the "electric plates' are arranged vertically, and the current passes in the same direction from the lower to the upper side. In the other two they are arranged longitudinally, and the cur- rent in Gymnotus passes toward the head and in Jlalapternrns toward the tail. The discharge, when the animal is at its best, may stun an ani- mal as large as the horse. This power is of use, doubtless, in defense, and probably in capturing smaller prey. Electric Eel. This fish (G^i/mnoius. or Electro- phonic, clectricus) inhabits the rivers of the basin of the Amazon and Orinoco, wherever they are warm and sluggish. It is in shape like a thick, stout, blackish, scaleless eel. and may grow to be six feet long; but it difTers .so much in structure from ordinary eels that it has been set apart as a separate family or other group by Cope, Gill, and other ichthyologists. It is abundant, and seems to have the general food and habits of an eel, Init little is known in regard to its generation or the use of its l)attery, except that it habitually kills more fish than it can consunu The fiesh is filled with bones, but is said to be ])alatable, and is not only eaten, but is regarded by the native South Americans as having medicinal value. Electric Catfish. These shock-giving catfish compose the subfamily Malapterurina>. of which the best known is the raash (Malapterurus elec- tricus) of the Nile. It grows to a length of four feet, with the ordinary rayed dorsal fin replaced by a fatty dorsal fin just in front of the rounded tail. It is said to give a shock like that from a I.eyden jar, which may be communicated by touching the creature with a conductor. Two other species are known. The ToKPicno. The electric rays, or torpedoes, constitute a family closely allied to the true rays. They embrace about six genera and fifteen species of the warmer seas of the world, and two species which approach nur southern shores. They have rounded, disk-like bodies, with powerful tails, and may weigh 80 pounds: swim close to the bottom, and are dark-colored above and light beneath, like other fishes of their class. The best- known species is Torpedo marmoraius of south- ern Europe, uixm which Ur, Gunther, ichthyolo- gist of the British iluscuin, made the foUouiiis; observations: He found that the phenomena at- tending the exercise of this extraordinary faculty closely resembled muscular action. The power is exhausted after sonic time., and it needs repose and nourishment to restore it. If the electric nerves are cut and divided from the brain, the cerebral action is interrupted, and no irritant to the body has any effect to excite electric dis- cliarge; but if their ends be irritated the dis- charge takes place, just as a muscle is excited to contraction under similar circumstances. And, singularly enough, the application of strychnine causes simultaneously a tetanic state of the muscles and a rapid succession of the involuntary electric discharges. The strength of the dis- charges depends entirely on the size, health, and energy of the lish. It seems to be "essential ami necessary to them for overpowering, stunning, or killing the creatures [fish of various kinds] on which they feed, while incidentally they use it as the means of defending themselves from their enemies." Anatomical Features. The electric organs in all the above-named fishes are to be regarded, according to W'iedersheim, as metamorphosed muscular tracts, and the nerve-endings belonging to them as homologues of the motor end-plates which arc ordinarily found on muscles. As re- gards the minute structure of the electric organs, the same essential arrangements are met with in all the forms. The framework is formed of fibrous tissue, which gives rise to numerous polygonal or more or less rounded chambers ( see Plate), Xii- nierous vessels and nerves ramify in the connec- tive tissue lying between these coni])artiuents, the nerves being inclosed in very thick sheaths, and having a great variety of origin, according to the species. In torpedo they arise from the 'electric lobe' of the medulla oblongata, a single branch coming also from the trigeminal; in all jiseudo-electric fishes, as well as in tlymnotus, in uhi<-h over 200 nerves pass to the electric organ, they arise from the spinal cord. The electric nen-es of Malapterurus arise on each side from a single enormous nerve-cell, which, lying in the neighborhood of the second spinal nerve, is con- tinued into a very large primitive fibre, which passes toward the end of the tail, dividing as it goes. The end-organs in which the nerves terminate are disks, called 'electric plates,' formed of mus- cle-sul)stance over one or the other side of which, according to the species, the terminal filaments of the nerve spread out. The side of the elec- tric plate on which the nerve branches out is negative at the moment of discharge, while the op])osite side is positive, and thus the difVerent arrangements of the jiarts in (iymnotus and in Malapterurus render it clear that the electric shock must pass in dilTereiit directions in these fishes — thus, in Malapterurus it passes from the head to the tail, but in the contrary direction in G.minotus. In torpedo the discharge passes from below upward. The mechanism whereby the electric plates become temporarily charged with electricity is not known. Bini.ior.RAPiiv. AlthouLdi the peculiar powers of the torpedo and of I lie gymnotus were well known to the ancients, the first scientific deter- mination of the electrical character of the shock of the torpedo was by Walsh, in 1772 — Of the