Volume 2

The cyclopaedia of anatomy and physiology / edited by Robert B. Todd.

Date:
1836-1859
Catalogue details

Licence: Public Domain Mark

Credit: The cyclopaedia of anatomy and physiology / edited by Robert B. Todd. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

    96/1034 (page 82)
    Both species (Na§xii 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 Malapterurus (Silurus, of Linnreus) 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.f It is the Rhinobatus electricus of Schneider and other modern ich- thyologists. But in an examination which Rudolphi 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,|| 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. It must be regarded as an extremely interest- * Hist, rerum Nat. Brasil. 1648. t The name Puraqua is used by Condamine in reference to the Gymnotus. X Kirby and Spence's Entomol. vol. i. 110. 6 Naturgesch. von Chili. S. 175. jj Gesch. des Kbnigr. Chili. S. 63. f Treviranus, Biologie. V. 144. 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. As the fishes enumerated above have not all been examined with the same degree of atten- tion, we are ignorant of the extent to which they exhibit phenomena exactly resembling one another. But it is well ascertained that they all agree in possessing the power of commu- nicating a sudden shock to the hand which touches them. This shock causes a certain degree of temporary numbness not only in the finger which immediately touches the fish, but also in the hand, and sometimes even in the arm. The sensation produced has been com- pared by different experimenters to the shock felt on the discharge of a Leyden phial, dif- fering from it only in force. Hence the shock caused by an electrical fish is said to be pro- duced by a discharge of its electricity. The numerous facts relating to the phenomena which accompany or are connected with this discharge, which have been collected by the industry of the many observers of the last and the present age, who have devoted their atten- tion to the subject,* may be conveniently ar- ranged under the following heads: 1. the circumstances under which the discharge takes place : 2. the motions of the fish in the act of discharging: 3. physiological effects of the discharge: 4. magnetical effects of the discharge: 5. chemical effects of the dis- charge : 6. results of experiments on the transmission of the discharge through various conducting bodies: 7. the production of a spark and evolution of heat: 8. results of experiments in which the nerves, electrical organs, and other parts, were mutilated : 9. descriptions of the electrical organs in the several fishes which have been anatomized. I. Circumstances under which the discharge takes place.—Electrical fishes exert their pecu- liar power only occasionally, at irregular inter- vals, and chiefly when excited by the approach of some animal, or by the irritation of their surface by some foreign body. The discharge, both with regard to time and intensity, seems to be dependent on an exertion of the will. They discharge both in water and in air. Sometimes the discharge is repeated several times in close succession ; at other times, par- ticularly when the fish is languid, only one discharge follows each irritation. The inten- sity of the torpedo's discharge is generally greater when the fish is vigorous, becomes gra- dually less as its strength fails, and is wholly imperceptible shortly before death takes place ; but Dr. Davy has met with some languid and dying fish which exerted considerable electrical * Redi, Reaumur, Walsh, Ingenhousz, John Hunter, Cavendish, Bancroft, Spallanzani, Wil- liamson, Humboldt, Gay Lussac, Geoffroy, J. T. Todd, and Dr. John Davy, have all laboured in the same field of inquiry.