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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 Tood 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 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
* Phil. Trans., 1833.
† Phil. Trans., 1827; see, also, 1813.
easy. Davy waited twelve months, even at Malta, before he could procure a pregnant torpedo, though he offered the fishermen fifteen times the market price. Davy decides from his own knowledge against the opinion of Cuvier. He allows, however, that the torpedo may not be viviparous, but between that and ovoviviparous.
These valuable researches of Davy were rapidly succeeded by those of Becquerel and Breschet, in 1835. To the former we are indebted for the means of measuring exactly the force of the current, and determining its direction, and thus bringing animal electricity into the ranks of the exact sciences. In 1836, Matteucci conceived the idea of applying to the torpedo the apparatus of Faraday for induced secondary currents, in order to obtain the spark. He made this idea known to Linari, and suggested certain modifications in the experiment. In the same year, Linari caused the tor: pedo to discharge through a long coil of wire, inclosing a bar of soft iron, and thus showed the spark, if not from the animal current itself, at least from the secondary one induced by it. He repeated Davy's experiment on the calorific effect of the discharge, substituting, however, for Harris's electrometer a thermo-electric couple. Finally, indications of electrical tension were obtained by placing the torpedo between two disks of metal, each of which carried a rod with a ball at the end. When the two balls were close together, pieces of gold-leaf placed on them mutually approached, and on touching were burned. This was the first deflagration produced by the torpedo.
Still more recently, very careful investigations in regard to the electrical powers of the torpedo have been conducted by Matteucci, who has done so much to illustrate the whole subject of animal electricity. His instruments were a magnetic galvanometer, with 600 turns of wire in the multiplier; a frog prepared in the ordinary way for galvanic experiments, and also what he calls a galvanoscopic frog. This is one half of a frog placed in a glass tube, by which it can be held insulated from the hand, with the threads of the nerves, through which the electrical current to be examined is sent, hanging outside. To prevent confusion, Matteucci destroyed one of the electrical organs, and experimented on the other. Thus furnished, he succeeded in demonstrating not only that the back of the torpedo was generally positive to the belly, but also that the parts of the back above the nerves which go to the electrical organs are positive with respect to the rest of the dorsal surface, and that places corresponding to these on the ventral side are negative to each other. Long before, Humboldt* and Aldinit had stated that a shock was received from the torpedo when one surface only was touched. Professor J. Wyman made a similar observation in regard to one on exhibition at the Boston Museum, in 1845; namely, that a. shock was felt if one hand alone was dipped in the water which surrounded the fish, though both water and fish were in a glass vessel. The solution
* Ann. de Ch., XI. 430.
which Dr. Davy gave of these facts was this. When the hand touches only one side of the torpedo, the fish twists its body so as to bring the other surface also into contact. As this artifice was noticed in the fætal fish, he thought it instinctive. Matteucci's researches render this theory of Davy superfluous. According to them we should expect a shock, of greater or less violence, whether we touch both organs, or opposite sides of the same organ, or different points of the same side. Matteucci made incisions into the organ parallel to the flat sides of the fish, and, introducing his wires, he discovered that that incision was positive which was nearest the back. The extraordinary diffusion of the electric force of the torpedo appears by this experiment. Matteucci held one so as just to touch the surface of salt water which filled a vessel six feet square, when he observed that a frog in the remotest part of the vessel was affected by the shock. This result is beyond the power of a very strong galvanic battery. Matteucci maintains that the animal discharges when it wishes, but not where it wishes. When it is vigorous, a shock is felt wherever you touch it. As its electrical powers decay, they become more centralized around the electrical organs. This was proved by covering the torpedo with frogs, and seeing which were most disturbed.
Matteucci bad imagined that he detected the signal for a discharge when the fish drew back its eyes. Davy, however, was not able to perceive that the electrical fishes of the Mediterranean, at least, betrayed their intentions by any such hint. The movements in the body of the torpedo, even when it gives its shocks, though occasionally great, are often not perceptible. Matteucci put one into a vessel filled with water; be placed a cover over the top, into which was inserted a fine tube. Wires were passed into the vessel to irritate the animal, and a frog was introduced to make sure that the torpedo discharged, and yet the level of the liquid in the tube did not alter. Hence it was inferred, that it was possible for the torpedo to give its shocks without any sensible alteration of its volume.
Matteucci sums up his conclusions in regard to the nature of the torpedo's peculiar powers in the following language:“When we reflect, 1. that no trace of free electricity is found in the organ unless it discharges; 2. that we can destroy the skin, the muscles, the cartilage which surrounds the organ, and even a part of the substance of the organ, without destroying or diminishing the discharge ; 3. that narcotic poisons produce violent electrical discharges ; 4. that irritation of the electrical lobe of the brain does the same, even when the animal has seemed dead for some time ; 5. that the action of this electrical lobe continues after it is separated from all the superior lobes, and from the spinal marrow ; 6. that the irritation of the superior lobes, or of the spinal marrow, has no effect; 7. that strong muscular contractions are observed in the parts which surround the organ, without any discharge occurring ; 8. that this discharge is produced by irritating the nervous trunks which ramify into the organ, even when these trunks are separated from the brain ; 9. that the wounding of the electrical 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, t 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.