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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.
safe to employ the galvanoscopic frog, because the difference of exposure, though it does not affect the electromotive force, may change the sensibility of the nerve as a galvanoscope.
The contractions of the living frog are not of long duration. But they reappear when it is killed. Sometimes they are exhibited after death, when they were not before. Generally, the current ceases ten or fifteen minutes after death ; seldom does it last half an hour. When it has gone, it
be restored again by cutting the spinal marrow. Nobili had inferred from his experiments that no current flows when two frogs are united so that nerve touches nerve and muscle touches muscle. He supposed the case the same as when two pairs of voltaic plates are combined so that copper is in contact with copper, and zinc with zinc. Matteucci found, however, that there was some differential current, unless symmetrical parts of the two frogs were in contact.
The animal-current which we have been considering differs from that of the torpedo, gymnotus, &c., chiefly in its origin. It cannot, like the other, be traced to any distinct electrical organs. Matteucci was never able to find this peculiar frog-current in any other kind of animal, not even in those most nearly related to the frog, as the salamander, eel, or tortoise. Two views have been broached in regard to its origin. 1. The first regards it as a kind of thermo-electric current, arising from a difference in the temperature of the nerve and muscle, - - a difference which is caused by the unequal evaporation from these two parts. The frog-current, however, does not resemble the thermo-electric current. It has more intensity comparatively; it shows itself to best advantage with a galvanometer which contains many turns of wire; it traverses a thick layer of liquid; it is produced also by the contact of muscle and muscle, and even when the animal parts are plunged in water. 2. The other view identifies the animal-current with the electrochemical action. It supposes the frog's legs to be cha ged with salts or alkali, while the thigh or the lumbar nerve contains acid or salt water. But no chemical analysis supports these assumptions. Nor could we explain by them the existence of the current in the leg alone, its short duration, or the influence exerted on its activity by cold, gases, and inflammation.
III. Muscular Current. — Matteucci calls that current we have been discussing the proper current of the frog, to distinguish it from the muscular current, which is derived not only from the frog, but more or less abundantly from all animals. The muscular current is one which flows from the internal part of the muscle to the surface. In general, any muscle of any animal will answer for the experiment. Matteucci tried it with frogs, fishes, eels, pigeons, sheep, cows, dead and alive, and pigeons' hearts and legs, and always with the same result. The most delicate experiments were repeated a hundred times with the same result. The muscular current is shown to advantage by arranging any of these animals, or parts of them, into the form of an intensity-battery. The duration of the muscular current after death is the more brief as the animal is more exalted in the scale of being. Matteucci observed, that for cold-blooded animals its intensity was proportioned to the temperature of the medium in which they lived. In some experiments, the subjects were iced before they were submitted to this trial. The muscular current varies with the nutrition of the muscle, and is strongest in muscles which are gorged with blood and inflamed. It is independent of the activity or integrity of the nervous systems of motion and sensation. Narcotic poisons produce but little effect upon it. Of the poisonous gases, sulphuretted hydrogen alone enfeebles it to any great extent. The muscular current is made manifest by the needle galvanometer and the galvanoscopic frog. Matteucci introduced the nerves of this frog into the wounded muscle of a living animal, and saw it contract from the current which flowed from one side of the muscle through a filament of the frog's nerve, and then back through another filament to the other side of the muscle. He then took a rabbit, and allowed its own nerves to come in contact with the cut muscle, when he observed a contraction as from an electrical stroke. But Matteucci detected no signs of electricity when he touched a drop of blood from a living pigeon at two points with the nervous nents of the galvanoscopic frog. Throughout this long series of delicate experiments, this ingenious physicist was at great pains to exclude every source of error. The two ends of the galvanometer wire were made of platinum, and were introduced at the same moment, and always into the same liquid.
In reading the history of animal electricity, it is important to distinguish between those experiments for which an arc of metal was used, and those in which animal substances exclusively were employed. In the former class of experiments any animal will answer, as the origin of the electricity is voltaic, and the animal contractions simply indicate its circulation. In the latter class, which includes every case of genuine animal electricity, few before Matteucci have had any success except with the frog. There are, however, one or two experiments of Aldini, which, u ough they may not detract at all from the originality and ingenuity of Matteucci's researches, deserve to be commemorated. Aldini grasped with one hand the ear of a recently killed ox, the head of which had been amputated, and with the other held the legs of a prepared frog, so that the lumbar nerves came in contact with the tongue of the ox. The contractions of the frog, which ceased when the circuit was broken, showed the circulation of the electrical current. At another time, Aldini brought the nerves of a prepared frog which he held by the leg in contact with his own tongue, and witnessed convulsions in tbe frog. Dr. Bird thinks that these experiments anticipate the musculo-cutaneous current discovered by Donné,* thirty-five years afterwards. In reference to Aldini's experiment on the ox's head, Dr. Bird observes, .“ The intensity of these contractions was much increased by combining two or three heads so as to form a sort of battery, just as Matteucci, forty years after, found to be the case with his pigeon
* Ann. de Ch. et de Phys., Tom. LVII.
and rabbit battery." This is the experiment. “I connected," says Aldini, " by means of one chain of moisture, the heads of two or three calves, and observed that by this combination the force of the galvanism was exerted with more energy; a frog which was not affected by touching one head experienced violent contractions when applied to a series of several heads connected together.” * The experiment of producing convulsions in cold-blooded animals through the current excited by warm-blooded animals was repeated with success by Aldini on the trunks of calves and birds; also, on the heads of decapitated horses, of criminals who had been executed, and of men who had died a natural death. Aldini states that he frequently observed that the nerves of the frog were attracted so as to complete the circuit, if the hand was held very near to them !
In the frog the proper current and the muscular current coexist, and may be made to coöperate with one another, or to interfere. The proper current runs in the frog from the foot to the head, the muscular current moves from the inside to the outside of the muscle through the connecting arc. Therefore, a frog battery made of legs alone will yield a stronger current than when the lower joint of the thigh is added. Even with the thigh and leg there is some current, the direction of which shows a difference in the strength of the muscular and proper currents in favor of the latter. If the whole of the lumbar and crural nerves are used, the current is diminished, on account of the poor conducting power of the substance. It appears that those circumstances which influence one of these currents influence the other also, but the muscular current ceases sooner after death.
Matteucci presents the following theoretical considerations in regard to the muscular current. It depends on vitality. It is affected by circulation and inflammation. It may be developed by nutrition. It is well known that the action of the oxygen of the arterial blood is carried to all points of a living body; that all parts of the organism are incessantly renewed, and that a kind of combustion attends this renovation, that is, a development of heat and carbonic acid gas. We can conceive that such chemical changes may develop electricity. The fibres of the muscles are the battery-plates ; the arterial blood is the acid solution; the nerve is the conductor. Experiment shows, that in the muscular and proper currents the direction of the nerve does not affeci that of the current. The nerve acts as a poor conductor; it conducts only one quarter as well as muscular matter; its conducting power, however, is better for crirrents which flow from the spinal marrow to the crural nerves than for those which move in the opposite direction. But the difference is less, the longer the interval after death. Still Matteucci thinks the nerves may act in a more important way by influencing nutrition. The integrity of the nerves may be destroyed without the immediate suspension of the muscular current, although it dies away the more quickly as the life of the animal is the more centralized. Matteucci proved that muscular contractions generated electricity, as Becquerel
* An Account, &c., p. 4.
and Breschet had already proved that they generated heat. Matteucci made a frog-battery, and irritated the frogs simultaneously, so as to obtain a current which deflected the galvanometer. We have recently had an account of an experiment in which metallic handles, fastened to the galvanometer-wires, were grasped in the hands, and the needle was deflected by a muscular exertion.
Since our paper on animal electricity was sent to the press, we have had an opportunity of glancing at a very complete work on the subject recently published at Berlin.* We deem it proper to state that the author has taken exceptions to some of the conclusions of Matteucci, but a more particular examination of his criticisms must be reserved for another occasion.
We shall conclude this review of animal electricity by a brief allusion to a few observations and experiments, some of which are involved in considerable obscurity. Cotugno t relates that a medical student, having killed a mouse, resolved to dissect it, and, touching with his knife the intercostal nerve, felt an electrical sensation which benumbed his hand. Molina reports that a spider, in Chili, was able to paralyze the hand of any person who touched it. Other insects have been thought to possess the power of giving shocks. Dr. Donné deflected the galvanometer-needle, by putting one end of the wire on the skin and the other in the mouth. The current flowed from the skin to the mouth. Pouillet supposed he had detected free electricity circulating in the nerves. Prevost assures us that, by transfixing a nerve with a steel needle, and irritating the animal so as to produce a contraction, the needle became magnetic. Matteucci is disposed to adopt the result of two other experimenters, who believed they obtained a current by introducing one end of the galvanometer-wire into the muscle, and the other into the brain of a living animal. The human body is always in a state of electric tension, more or less intense. Sometimes, it is said, it is so highly charged that the hair is phosphorescent. There are undoubted cases where sparks can be drawn from the hair or the lips, and a kiss is accompanied with a shock. I have known instances where the saliva from the mouth was luminous in the dark. Schilling had the extraordinary idea that the gymnotus was magnetic, and was attracted and repelled by the opposite poles of a magnet; also, that it grew more lively when placed in water sprinkled with iron filings.
Finally, in regard to the reality of animal electricity in general, may we not adopt the words of Aldini, uttered half a century ago ?. “And since I am ready to allow that the invention of the metallic pile gives Volta a title to the discovery of metallic electricity, I hope the discovery of animal electricity, properly so called, will be allowed to Galvani, as similar phenomena are exhibited by the nervous and muscular systems, independently of common electricity.” (p. 48.)
* Untersuchungen uber Thierische Electricität von Emil du Bois Reymend. Berlin, 1848. † Jour. Encyc. de Bologne, No. VIII., 1786.