ELECTRICITY, ANIMAL. —A power, or imponderable agent, possessed by and evolved from certain living animals, which enables them, independently of the operations of external agents on their structures, to pro duce several of the phenomena exhibited by common and voltaic electricity, generated in inorganic matter.
The animals so endowed, with which we are at present acquainted, are all fishes ; and the effect by which their power is most sensibly made known to us is the feeling of a shock, or momentary stunning, which is experienced in the hand that touches their surface.
It is still doubtful whether the agent which produces this effect be absolutely identical with those which produce the various pheno mena of common and voltaic electricity, ther &e.; but the most recent re searches on the subject render it probable that it is the same in its nature, although different in intensity.
When Galvani discovered the possibility of exciting muscular contraction by establishing an external communication between the nerves and muscles by means of metals, he imagined that the contraction was produced by the sti mulus of a peculiar agent (or fluid) existing in the nerves in a state of accumulation, which, being attracted by the metals, passed along them to the external surface of the muscles. The agent, which was supposed to remain latent in the nerves, was called by some " the nervous fluid," as it was imagined to he identical with that power which animates the nerves during life. Galvani seems to have entertained this notion. Other philosophers, avoiding a name derived from a theory, denominated the agent Galvanism. Afterwards it was called Animal Electricity. These views were supported by Valli, Carradori, Aldini, and Fowler. But, since Volta and others demonstrated that the contractions of the muscles in Galvani's expe riments were owing to electricity developed by the contact of the metals employed, and not to any fluid pre-existent in the nerves, the term Animal Electricity has had its meaning changed. At present, most physiologists use it in the sense which is implied in the defini tion given above.
That is not called Animal Electricity which is generated by the friction of animal sub stances one upon the other, or by the mere contact of animal tissues of dissimilar natures. The phenomena so developed have their source in common and voltaic electricity. They are phenomena exhibited by animals in common with inorganic matter. As the study of these, however, may ultimately lead to the elucidation of some points connected with the electricity of living fishes, they shall be noticed in the course of the following article.
It is in the mode of its development that the chief peculiarity of Animal Electricity consists. None of the usual excitants of elec tricity are concerned in it. There is no che mical action, no friction, no alterations of tern-. perature, no pressure, no change of form. The exercise of the animal's will, and the integrity of the nervous system, as well as of certain peculiar organs which exist in all the animals endowed with electrical power, seem to be alone sufficient for its evolution.
The following are the systematic names of the electrical fishes at present known: — 'Torpedo narke.
unimaculata. Risso. marmorata. Ditto.
Galvanii. Ditto.
Gymnottis electricus.
Trichiurus clectricus.
Malaptertirus clectricus.
Tetraodon electrieus.
The four species of Torpedo inhabit various parts of the Atlantic and Mediterranean. They were formerly regarded as constituting one species, (Haia Torpedo, of Linnmus;) and now Dr. John Davy proposes to reduce them to two ; having satisfied himself (and in this he is supported by the opinions of Cuvicr and of Rudolphi) that the T. marmorata and T. Gal
vanii are merely varieties of the same species, for which he suggests the name of T. diversi color. It is known in Italy by the name of the Tremola. The other species (the Oechiatella of the Italians) Dr. Davy thinks would be better named T. oeulata. Both pass in Malta under the term Iladdayla. The first of these species (T. vulgaris, of Fleming,) occurs on the south coast of England, where it some times attains a great size. Pennant mentions one which measured four feet in length and two and a half in breadth, and weighed fifty three pounds. And Mr. Walsh describes an other which was four feet six inches in length, and of the weight of seventy-three pounds.* Both species (Nave"; of Aristotle and Oppian) are abundant in some parts of the Mediter ranean, and are frequently brought to the market of Rome. Off the west coasts of France, in Table-bay at the Cape of Good Hope, in the Persian Gulf and in the Pacific Ocean, the same, or at least nearly similar species are plentiful. They frequently form an article of food amongst the poorer class in the coast towns between the Loire and the Ga ronne; but the electrical organs are carefully avoided, as they are supposed to possess some poisonous properties. The Gymnotus is found in several of the rivers of South America ; it was met with by Humboldt in the Guarapiche, the Oronoco, the Colorado, and the Amazon. The Malapterunis (Silurus, of Linnwus) occurs in the Niger, the Senegal, and the Nile; the Trichiurus in the Indian Seas; the Tetraodon has been met with only on the shores of Jo hanna, one of the Comoro Isles. According to Margrav* there is a kind of ray-shark on the coasts of Brazil, which possesses the power of giving shocks. He described the fish under the name of Paraque.t It is the Rhinobatus electricus of Schneider and other modern ich thyologists. But in an examination which Itudolphi made of the fish in question, he found no structure resembling that peculiar organ which exists in all the well-known elec trical fishes. No other naturalist has made the same observation as Margrav, so that the elec trical power of this fish cannot be regarded as satisfactorily ascertained. In Maxwell's Ob servations on Congo, mention is made of a large fish " like a cod," possessed of electrical powers, which was taken in the Atlantic Ocean. No such animal has yet come under the notice of any scientific observer. Certain insects seem to be possessed of some power re sembling animal electricity in its effects, but few observations have hitherto been made on these. Reduvius serratus is one of the insects so endowed ; with regard to which an intel ligent naturalist reports, that, on placing a living individual on the palm of his hand, he felt a kind of shock, which extended even to his shoulder; and that, immediately after wards, he perceived on his hand red spots at the places whereon the six feet of the insect had rested./ Margrav described a species of Mantis, a native of Brazil, which, on being touched, gave a shock felt through the whole body. According to the report of Molina§ and Vidaure,II when the Sepia hexapodia is seized with the naked hand, a degree of numb ness is felt, which continues for a few seconds. Alcyonium bursa, a native of the German Ocean, is said to have communicated to the hand a sensation like that of an electrical shock.5 It must he regarded as an extremely interest ing fact that the electric fishes belong to genera widely removed from one another in structure and habits, and yet that their own structure is not so peculiar as to prevent them from being arranged along with many other fishes posses sing no degree of the same power and no vestige of a structure analogous to their own.