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lobe not only produces the discharge, but sometimes alters its direction; 10. that an electrical current acts upon the nerves of the organ to make it discharge according to particular laws; we must conclude, – 1. that the electrical discharge of the torpedo and its direction depend on the will of the torpedo, which, for this function, has its seat in the electrical lobe of the brain; 2. that it comes from the electrical organs so called at the bid of the will; 3. that every foreign disturbance which influences the discharge is transmitted by the nerves from the point influenced to the electrical lobe of the brain ; 4. that every irritation of the fourth or electrical lobe produces no other phenomena than the electric discharge ; 5. that the electrical current acting upon this electrical lobe produces only electrical discharge, and its action continues longer than that of any other stimulant; 6. that all the circumstances which act upon the function of the electrical organs act upon the function of the muscles, that is, upon the contractions."
Some philosophers suppose that there are four species of the torpedo in the Mediterranean. Dr. Davy, however, thinks there are but two; – 1. the spotted ; 2. the unspotted. He further states, that the torpedo is irrégular in its visits to shallow waters. Still, a fisherman can generally furnish the experimenter in the course of two or three weeks. Dr. Storer published, in 1843,* an interesting account of a torpedo, four feet two inches in length, which was captured the year before, near Wellfleet. In 1839, in his Report on the Fishes of Massachusetts, he mentions the fact, that a fish called the cramp-fish, or numb-fish, was sometimes found in the neighbourhood of Cape Cod. Mitchell, also, in his description of the fishes of New York, † alludes to a torpedo as known to the fishermen in the neighbourhood, and belonging, as he thought, to the European species. But neither Mitchell nor Storer had yet seen one, nor is it known that the American torpedo had been examined by any scientific man previous to 1842. Dr. Storer compares his specimen with one caught on the Irish coast, and described by William Thompson, of Belfast, in the Annals of Natural History, under the name of Torpedo nobiliana. He concludes from this comparison, that the American species is new, and proposes to call it Torpedo occidentalis. The electrical organs of the Wellfleet torpedo were dissected by Professor J. Wyman, and an accurate delineation of them accom
panies the communication of Dr. Storer. The masses of nerves which are I connected on each side with the electrical organs are very large, larger even
than the spinal marrow. Dr. Storer has published part of a letter from a fisherman in Provincetown, who has been familiar with these waters for twenty-five years. He says, that when he first came there, in 1819, the electrical fish was not uncommon, from sixty to eighty being found every year. But of late they have been very scarce, and not more than thirty have been captured for the last ten years. The smallest never weigh less than 20 pounds, and the largest weigh 200 pounds. From a pint to three gallons of oil is taken from the liver. Sometimes the shock has been felt
* Silliman's Journal, XLV.
at the distance of eight or ten feet from the fish along the harpoon to the hand that held it; at other times, it has been sufficient if the hand touched the rope only. The shock is described as producing the sensation of being struck upon the head with an axe.
The gymnotus was first described in 1677, by Richer, who went with a scientific commission from the French government to Cayenne. This fish is a native of the warm parts of America and Africa. It is found in the large fresh-water rivers. In Africa it is confined chiefly to the branches of the Senegal. In America it is taken in Surinam, and in all the small rivers which flow into the Orinoco in Guiana. It is often four or five feet long. In 1775, Mr. Hugh Williamson published an account of one of these fishes, which had been brought from Guiana to Philadelphia by a seafaring man.* It was three feet long; killed small fish by its shock, and then eat them. The shock was easily given to eight or ten persons at a time, holding each other by the hand. In the same year, Alexander Gordon,t of Charleston, S. C., described some experiments made on another specimen which was brought from Surinam, and measured three feet eight inches. Also in the same year, Hunter # gave the anatomy of the gymnotus from specimens furnished by Walsh. This fish, from its rude resemblance to the common eel, is popularly called the electrical eel; ichthyologists, however, do not place it even in the same genus of fishes. The electrical organs of the gymnotus are double, and extend on each side from the head to the tail. They are supplied with 224 pairs of intercostal nerves.
These organs are divided by horizontal membranes, and then again by transverse ones. The included spaces are filled with a fluid. Humboldt, in one of his works, § gives an interesting description of the gymnotus as found in the rivers and lakes of Venezuela and Caraccas. He says,|| that an old road near Uritucu has been abandoned on account of the danger of fording. The mules even, are paralyzed by the shock, and are drowned. Anglers sometimes receive a stroke along their rod and line, though the former is six feet long. The Indians have such a dread of these shocks, that Humboldt found it difficult to procure specimens enough for experiment. He gives the following lively description of the manner of capturing the gymnotus at Calobozo, by first sending horses and mules into the water to take the edge off from the electrical weapons of the fish :
6 About thirty horses and mules were quickly collected from the adjacent savannas, where they run wild, being only valued at seven shillings a head, when their owner happens to be known. These the Indians hem on all sides, and drive into the marsh; then, pressing to the edge of the water, or climbing along the extended branches of the trees, armed with long bamboos or harpoons, they, with loud cries, push the animals forward, and prevent their retreat. The gymnoti, roused from their slumbers by this noise and tumult, mount near the surface, and swimming like so many
* Phil. Trans., 1775.
1 Phil. Trans., 1775. Tableau Physique des Reg. Equat., II. 175. || Personal Narrative, Ch. XVII.
livid water serpents, briskly pursue the intruders, and, gliding under their bellies, discharge through them the most violent and repeated shocks. The horses, convulsed and terrified, their mane erect, and their eyes staring with pain and anguish, make unavailing struggles to escape. In less than five minutes, two of them sunk under the water and were drowned. Victory seemed to declare for the electric eels. But their activity now began to relax. Fatigued by such expense of nervous energy, they shot their electric discharges with less frequency and effect. The surviving horses gradually recovered from the shocks, and became more composed and vigorous. In a quarter of an hour, the gymnoti finally retired from the contest, and in such a state of languor and complete exhaustion, that they were easily dragged on shore, by help of small harpoons fastened to cords. This very singular plan of obtaining the electric eel is, in allusion to the mode of catching fish by means of the infusion of narcotic plants, termed embarbascar con cavallos, or poisoning with horses."
Humboldt discovered that the gymnotus suffered from too free an exertion of its electrical powers, but that it recovered its strength by repose and abundant nourishment. He infers that the electrical function is proportional to the activity of respiration and nutrition, inasmuch as the animal is more vigorous when the water in which it is kept is frequently changed. The strongest shocks are obtained when the animal is irritated in the lips, eyes, or the skin near the gills. The same is true of the torpedo. The discharge is sometimes accompanied by very strong muscular movement; at other times, the fish gives no such warning. Humboldt states, that he often knew it to produce its shocks while wholly at rest, while at other times it has beat against him, winding its body around his own like a serpent, without making any electrical discharge. He believes that the electrical power is under the control of the fish, both as to when it will discharge, and from what parts of its body, the shock being given from those places which are irritated. Matteucci maintains, on the contrary, that the latter phenomenon is only apparent. When the brain is taken out of the animal, the irritation of the spinal marrow does not provoke a discharge.
In 1838, a young gymnotus was brought from one of the tributaries of the Amazon to Paris, and afterwards exhibited in London. It was said at the time to be the only one of its kind in Europe. Faraday subjected it to experiment, and showed that the anterior parts are positive, and the posterior parts are negative; and that any part is positive with respect to another part nearer the tail. With this fish Faraday was able to repeat Linari's experiment, and obtain the spark. For this purpose it was necessary to make it discharge through an electro-magnetic coil. With it Faraday performed a beautiful experiment of deflagration upon silver paper. Notwithstanding this success with the secondary current, the old doubt still lingers over the statement of Humboldt and Leslie, both of whom assert that Walsh and Ingenhouz obtained a spark by the direct current. The authority for this assertion is wanting. The gymnotus of which we have been
speaking was able by its shock to stupefy small fish at a distance of two feet. It always prepared its food in this way. Faraday thought that it could adapt the strength of the shock to the emergency, by curving more or less round the body it wished to attack. Once, when a live fish, five inches long, was thrown in to it, it bent its body into a semicircle of which its prey was the diameter. This gymnotus could give a shock equal to that of fifteen Leyden bottles, which contained 3500 square inches of charged surface. It could repeat its electrical blows with great rapidity. But it must be irritated before it would exert itself. When it was touched by good conductors, it would give frequent discharges; otherwise, but few. When, by mistake, it discharged through a poor conductor, its own body we may suppose carried most of the current, and was the greatest sufferer. Like other doctors, it did not appear to be fond of its own medicine. It is not by chance, therefore, that all animals with distinct electrical organs are fishes. They can easily send their discharge by water, but if they attempt to send it through the air, the shock recoils on themselves. Daniells gives an account of a gymnotus which perished ignobly under the attacks of a water
The fur of the rat resisted the moisture, and thus covered the animal with a non-conducting panoply, which effectually shielded it from the electrical blows of its antagonist.
II. Animal Electricity of the Frog.– The history of this department of animal electricity is intimately associated with that of galvanism. Matteucci assures us that the recent publication, by the Institute of Bologna, of the memoirs and manuscripts of Galvani, presents his scientific character in a new light. All are familiar with the story of the frogs which Galvani had prepared for a broth to be administered to his sick Lucia, and the contractions which he observed in them when a spark was drawn from an electrical machine in the neighbourhood. And who has not heard the other story of the frogs hanging from the balcony, and exhibiting contractions from the accidental contact of two metals. Those who delight to be surprised in science will believe that one of these observations suggested the irritability of the frog, and the other its power of developing an animal current of electricity. However this may be, it is common to refer the date of Galvani’s discovery to the publication of “De Viribus Electricitatis," in 1791. The records of the Academy of Bologna, signed by the celebrated Secretary Cantezzani, show that Galvani had been engaged for twenty years before this publication in experiments on the muscular contractions of frogs, and on the effect of opium upon their nerves. For five years he had been acquainted experimentally with the voltaic arc of metals.
All know the conclusions which Galvani drew from his experiments and observations, and his clear announcement of an independent source of electricity in animals, particularly frogs. It is with surprise that we hear bim declare that the current flows in the frog from the muscle to the nerve. For in the absence of the galvanometers, so common now, it is not possible to see how he was able to determine the direction of the current, unless he reasoned from some peculiarity in the animal contractions, according as
the current flows in the direction of the ramification of the nerves, or opposite to it. We have the authority of Matteucci for declaring that the researches of Galvani were made with great skill, and that his conclusions in regard to the animal electricity of the frog have been confirmed and extended by recent investigations. The scientific world, however, were absorbed at the time in the pursuit of voltaic electricity, and concluded with too great haste, that, because Volta's view was proved, that of Galvani had been disproved. Half a century passed away before men were recalled from this brilliant chase, and were able to understand that two new and independent sources of electricity had been discovered simultaneously, the adoption of one of which did not require or justify the rejection of the other. For a few years Galvani did not stand wholly alone. In 1799, A. de Humboldt * published his experiments on various animals and his own body, among which was that most remarkable one of convulsing one frog by the current of another frog. This experiment, as well as that of Galvani, in which, without any metal, the same frog developed and indicated the current, was sufficient to prove the reality of an animal or nervous current. In 1792, Valli wrote his letters on animal electricity. Aldini, the nephew of Galvani, espoused with zeal the cause of his uncle, and lectured and experimented on animal electricity, not without success, before the commissioners of the French Institute, and in the anatomical theatres of London. An account of these demonstrations was published in London, in 1803.t Still, no permanent and general impression was produced, and for many years animal electricity was not mentioned, except to illustrate the failure of Galvani and the triumph of Volta. In 1827, Nobili, # who had imparted increased delicacy to the galvanometer by his suggestion of an astatic needle, joined one end of the wire to the lumbar nerves of the frog, and the other end to the legs, and obtained from the animal current a deflection amounting sometimes to 30°. This experiment showed conclusively that the current flowed in the animal from the feet to the head, that is, from the legs or muscle to the nerve. Nobili found that the power lasted some hours, and might be increased by connecting several frogs together in the same order as the zinc and copper plates of a voltaic battery. When the needle moves, the frog contracts; by which it is proved that the frog both generates and indicates a current. Moreover, the electro-magnetic effect furnishes convincing proof that the force which originates in the frog is electrical, and that the muscular contraction of the frog is the effect of an electrical current. Wilkinson s mentions an experiment of Valli, who united fourteen frogs on the plan of a quantity battery, and thus succeeded in showing the electrical tension by means of a strawleaf electrometer. A result so disproportioned to the agency which produced it requires the confirmation of oft-repeated experiment.
* Experiments on Galvanism, and in General on the Irritation of the Muscular and Nervous Fibres.
† An Account of the late Improvements in Galvanism.