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: —

"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. † 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 waterrat. 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 him 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.† 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 § 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.

t Bib. Univ.

§ Elements of Galvanism.

Animal electricity, in all its forms, has been a favorite branch of study with the Italian philosophers. Matteucci, whose name we have had already frequent occasion to mention, has made very elaborate researches into the most delicate parts of the subject, the results of which were published in 1844.* He experimented on frogs singly and in battery, dead and alive. His batteries were arranged as in Volta's "Crown of Cups." Some of his experiments were repeated a hundred times. Matteucci maintained a corps of assistants, whose business it was to scour the country and bring in subjects. His inquiries aimed particularly to ascertain what parts of the animal were essential to the frog-current, and what were the physiological and anatomical conditions of its activity. He finds that each half of the frog is an electromotor by itself, and that it deflects the galvanometer as much as the whole frog. Indeed, a dozen frogs produced no more deflection than half of a single one, provided all the nerves were placed in one vessel, and all the legs in the other. More electricity might circulate, but no more passed through the wires of the galvanometer, as the current evolved by each element was partially conducted away by the closed circuits it found in all the rest. The frog-current retains its direction and intensity, even after the spinal marrow, the spinal and crural nerves, and all the visible nervous filaments of the muscular matter of the thigh, have been removed. A battery of legs is as efficacious as a battery of whole frogs, and the direction of the current is the same, namely, from foot to head. A battery of the thighs alone gives a feeble current. In the leg battery the current is improved in strength, but not in duration, by removing the tendon Thus it appears that the electromotive element of the frog-current is reduced to the muscles of the leg and thigh united organically. In all these comparisons of different kinds of batteries together, Matteucci arranged the two to be compared in a single series, the order of one being opposite to that of the other, and he judged from the direction of the differential current which of the two was the strongest. To make sure that the absence of any differential current (when such was the fact) arose from the equality of the two antagonistic currents, and not from the feebleness of both, Matteucci repeated the experiment, after having added an element in excess to one of the batteries. When this was done, he always had unequivocal signs of a differential current. To measure and indicate the current, Matteucci used, in succession, the needle-galvanometer and the galvanoscopic frog.

The current is injured if the frogs are put in hydrogen, receive nux vomica, or bleed to death. If one of two equal batteries is exposed to oxygen or carbonic gas, and the other not, there is no differential current. If one is immersed in boiling water, and the other not, there is a differential current in favor of the cold battery. In these last experiments, it is not

* Traité des Phénomènes Electro-physiologique des Animaux, par C. Matteucci; suivi d'Études Anatomiques sur le System Nerveux et sur l'Organe Electrique de la Torpille, par Paul Savi. Paris, 1844. See, also, four papers on the Muscular Current, in Phil. Trans., 1846, &c.