ANIMAL ELECTRICITY. By Professor Joseph Lovering. ON account of the close relations, not to say the actual identity, of electricity and magnetism, let no one confound the subject of Animal Electricity, as expounded in physical science, with that of Animal Magnetism. Of Animal Magnetism we know little, and have still less to say. Animal Electricity is a branch of inductive science to which large contributions have been made within the last twenty years. Our plan is to consider, first, that class of animals in which there are distinct electrical organs, and an electrical lobe in the brain to control them; secondly, that animal current which depends on the general organization, as in the frog; and thirdly, the muscular current. I. Animals with distinct Electrical Organs.— This peculiarity is confined exclusively to fishes. There are five different kinds of fishes which possess the remarkable power, even in their normal state, of originating electrical currents. They are known by the names of the torpedo, or electric ray, the gymnotus, or electric eel, the Silurus electricus, Tetrodon electricus, and the Trichiurus electricus. The torpedo and gymnotus have been studied with particular attention. The Silurus electricus is described and delineated by Broussonet,* under the name of trembleur, and more recently by Rudolphi and Müller. The other two are less known. The reader who desires to pursue the study of these fishes will find valuable references in the notes to the chapter on animal electricity, in [Bird's Elements of Natural Philosophy. We shall confine our remarks to the torpedo and the gymnotus. The torpedo, a member of the ray family, inhabits the Mediterranean, the North Sea, the waters which wash the coast of France, and is occasionally found on the Atlantic coast of America, in the neighbourhood of Cape Cod and Martha's Vineyard. It is common in the markets of Rome, and is eaten by the poorer classes. The numbness or shock which this fish is capable of producing in those who touch it has been long known. Aristotle and Pliny describe it in their Natural Histories. On account of this power it is vulgarly called the trembler and the magician-fish. Before the discovery of the Leyden jar, it was supposed, to account for the benumbing power of the torpedo, that it sent forth prickly particles, or that it struck like a bent spring, or like a body in very rapid vibration. Steffano Lorenzini, who, with Redi, first studied the torpedo anatomically, published his observations on it in 1678. He says, "The chief wonder of this animal, and that which gives it its name, is the benumbing faculty which is seated in the two semicircular or falcated muscles on each side of the * Hist. de l'Acad. des Sciences, 1782. † Osservazioni intorno alle Torpedini, fatte de Steffano Lorenzini Fiorentino. Firenze, 1678. An English translation was published at London, in 1705. thorax, which consists of fibres, irregular, but as large as a goose-quill, and made up of bladders filled with a kind of water; one end of these fibres being fixed to the skin of the belly, and the other to that of the back, on which may be plainly seen the vestigia of the fibres' ends. Now, when the fish contracts those fibres, there issue out corpuscles, fitted to the pores of a man's skin, so as to enter upon immediate contact, but not otherwise, and disturb the posture of the parts, and to cause pain as when one's elbow is hit or knocked, and this comes most by the fingers' ends, because these are ends of tendons. And this pain is more or less, as the contraction of the fibres have emitted more or less." Musschenbroek, who, with Cuneus and Kleist, invented the Leyden jar in 1700, at once recognized the analogy in the shocks of this electrical vial and of one of the electrical fishes. In 1773, Walsh * published a letter addressed to Franklin, which gives an account of some experiments made on the torpedo at La Rochelle and the Isle of Ré. At this time the phenomena of friction-electricity were well known, and Walsh perceived and asserted the electrical character of the powers of the torpedo. By his experiments he discovered that the shock could be given through electrical conductors, but not through nonconductors. He proved the different electrical states of the breast and back of the fish, and showed that a connection between the upper and lower surfaces of the body is necessary in order to obtain the best shock, and that the shock, when the fish was in air, was four times as strong as when it was in water. Walsh concludes his letter in these words: "I rejoice in addressing these communications to you. He who predicted and showed that electricity wings the formidable bolt of the atmosphere, will hear with attention that in the deep it speeds a humbler bolt, silent and invisible. He who analyzed the electrified phial will hear with pleasure that its laws prevail in animal phials. He who by reason became an electrician will hear with reverence of an instinctive electrician, gifted in its birth with a wonderful apparatus, and with skill to use it." In the same year, John Hunter f made, at the request of Walsh, an anatomical examination of the torpedo. Hunter found that two sets of electrical organs run along the length of the body. Each set consists of plates amounting, in one case, to 1182. These organs appear to be under the control of the will. Hunter observed that the nerves connected with these organs are larger than any except those on which the important sense of seeing depends, or which are associated with great muscular action. He found that the electrical organs were not essential to any of the purposes of life except the preservation of the electrical power. In all other respects the animal thrives as well if the electrical organ is cut out. In 1775,‡ Ingenhouz published some account of the torpedoes caught by him near Leghorn, twenty miles from the shore. He gave a Leyden shock to the sailors, who at once declared its resemblance to those with which they were more * Phil. Trans., 1773. See, also, Borelli, De Motu Animalium. † Phil. Trans., 1773. 1 Phil. Trans., 1775. familiar from the torpedo. Ingen houz remarks, that these torpedoes did no In 1815, Sir Humphrey Davy* made some experiments on the torpedo at the Bay of Naples, Rimini, and Trieste. In 1828, being at Rome, he renewed his researches. But they were directed to the anatomical structure of the animal, and not so much to the study of the electrical character of the shock. However, he made an unsuccessful attempt to produce chemical decomposition, and obtain a spark by means of animal electricity. He also failed to repeat with the animal current Oersted's experiment of magnetic deflection. Down to this late period, the science of animal electricity was confined chieflyt to the simple physiological effect, — the shock. So far as relates to the torpedo, all agree that the shock is very great. Kaempfer, in 1712, compared it to lightning. Fishermen, when they wish to describe its power, say that it kills pollards, which are very hardy and tenacious of life. After the fishermen have drawn their nets into the boat, they throw water on the contents, and, if there are any torpedoes within, they feel their shock through the stream of water. Sometimes the shock is received through the wet cordage before the net is drawn in. The shock of a vigorous torpedo, fourteen inches long, is enough for one man. Matteucci com ments. pares the shock to that received from a galvanic battery of 100 or 150 elements charged with salt water. These shocks can be repeated with great rapidity. A dying torpedo gave 316 in seven minutes. The later ones are like those which come from a smaller number of galvanic eleFor the full effect it is best to use wires soldered to plates of metal. These plates are placed like saddles on the back and belly of the animal. Linari, by employing the electro-magnetic balance of Becquerel, measured the intensity of the discharge, and found that it exceeded that of nine jars, each having ninety-four square inches of armed surface. In 1831-2, Dr. John Davy, while at Malta, made numerous experiments on the living torpedo, and obtained the most conclusive evidence of the electrical character of the discharge. 1. With a fish only six inches long he magnetized a steel needle which was placed inside a coil of wire. 2. He deflected the galvanometer. 3. He produced chemical decomposition of common salt, acetate of lead, and nitrate of silver. § By all these *Phil. Trans., 1829. † Valli, Aldini, and Humboldt connected nerve and muscle by long electrical conductors. Phil. Trans., 1832. § Aldini said, "For my part, I entertain no doubt that, after repeated trials, it may be effected by means of large animals possessing a great abundance of animal electricity." Galvanism, p. 45. experiments it appears that the upper surface corresponds to the positive end of a battery. At this time, Davy failed to obtain any sign of the spark or of electric tension. He sent the discharge through a silver wire only 1000 of an inch in diameter without sensibly heating it. Faraday,* in his third series of researches, suggested that the evolution of heat by the torpedo would probably be observed if Harris's electrometer were used. In 1834, Davy made use of an instrument similar to that described by Harris,t and succeeded in heating the wire sensibly, even with the least energetic specimens of the torpedo. He was able to warm a fine platinum wire, but could produce no ignition, even in the dark. Davy took occasion to make some interesting observations on the habits and anatomical structure of the torpedo. He says he was never able to see in the fresh fish what Hunter likens to a regular voltaic arrangement of plates or cells, though he fancied he detected some approach to it in preserved specimens, after the animal matter had been deposited. Sometimes the whole fish weighed only 410 grains, and the electrical organs 150 grains, and yet it gave shocks, made magnets, deflected the galvanometer, and decomposed water. It was Davy's opinion that the novel power of the torpedo was not given so much as a means of procuring food as of defending itself from attacks, since the young animals had the largest share of it. Davy kept a nursery of torpedoes under his own eyes, and sometimes these fishes were examined as soon as they were born, and the first act of their lives was to magnetize needles and produce the other changes due to electricity. Some were kept for five months in salt water, which was renewed every day. They eat nothing, though small fish, dead and alive, were offered to them. At death their stomachs were found empty, and yet their electrical energies had been on the increase. When old fish were tried, a few shocks exhausted them, and they soon died. Small, puny, delicate fishes were always more powerful in their electric organs than fat ones of the same age. Davy thinks the failure of his distinguished brother to anticipate him in his elucidation of the electrical character of the torpedo's peculiar gifts is attributable to his use of large specimens. Dr. Davy observes that the gastric nerves are derived from the electrical nerves, and suggests that the superfluous electricity not required for the purposes of defence goes to help the digestion. He remarks, that animal electricity, like animal heat, animal light, and animal secretions generally, appears to be a result dependent on living functions. He was able to produce no electrical excitement in the fish after death. He thinks that friction, chemical action, or changes of form and temperature, are not concerned in its production. Dr. Davy in his last paper discusses the mode of generation of the torpedo, in regard to which opinions are discordant. Aristotle makes the torpedo viviparous. Lorenzini, to whom we have referred before, does the On the contrary, Blumenbach and Cuvier rank it among oviparous animals. Analogy was in favor of the latter view, and observation was not same. Phil. Trans., 1833. † Phil. Trans., 1827; see, also, 1813. familiar from the torpedo. Ingen houz remarks, that these torpedoes did no In 1815, Sir Humphrey Davy* made some experiments on the torpedo at the Bay of Naples, Rimini, and Trieste. In 1828, being at Rome, he renewed his researches. But they were directed to the anatomical structure of the animal, and not so much to the study of the electrical character of the shock. However, he made an unsuccessful attempt to produce chemical decomposition, and obtain a spark by means of animal electricity. He also failed to repeat with the animal current Oersted's experiment of magnetic deflection. Down to this late period, the science of animal electricity was confined chieflyt to the simple physiological effect, — the shock. So far as relates to the torpedo, all agree that the shock is very great. Kaempfer, in 1712, compared it to lightning. Fishermen, when they wish to describe its power, say that it kills pollards, which are very hardy and tenacious of life. After the fishermen have drawn their nets into the boat, they throw water on the contents, and, if there are any torpedoes within, they feel their shock through the stream of water. Sometimes the shock is received through the wet cordage before the net is drawn in. The shock of a vigorous torpedo, fourteen inches long, is enough for one man. Matteucci compares the shock to that received from a galvanic battery of 100 or 150 elements charged with salt water. These shocks can be repeated with great rapidity. A dying torpedo gave 316 in seven minutes. The later ones are like those which come from a smaller number of galvanic eleFor the full effect it is best to use wires soldered to plates of metal. These plates are placed like saddles on the back and belly of the animal. Linari, by employing the electro-magnetic balance of Becquerel, measured the intensity of the discharge, and found that it exceeded that of nine jars, each having ninety-four square inches of armed surface. ments. In 1831-2, Dr. John Davy, while at Malta, made numerous experiments on the living torpedo, and obtained the most conclusive evidence of the electrical character of the discharge. 1. With a fish only six inches long he magnetized a steel needle which was placed inside a coil of wire. 2. He deflected the galvanometer. 3. He produced chemical decomposition of common salt, acetate of lead, and nitrate of silver.§ By all these *Phil. Trans., 1829. † Valli, Aldini, and Humboldt connected nerve and muscle by long electrical conductors. Phil. Trans., 1832. § Aldini said, "For my part, I entertain no doubt that, after repeated trials, it may be effected by means of large animals possessing a great abundance of animal electricity." Galvanism, p. 45. |