Galvanism seems chiefly to affect the nervous system, including the muscular fibres, and, indeed, in some degree, fibres of every kind, producing even some apparent contraction in the fibrin of the blood. The nerves and muscles, however, it penetrates more actively than the electrical fluid in its usual state; for it produces powerful contractions, and sensations of pricking and burning in parts insensible, from disease, to electrical sparks, and even shocks. The effects are increased by moistening the skin, and wetting it so much as even to penetrate the cuticle; still more, we have said, if the cuticle is divided: but it often happens that one person may be insensible to its influence, and occasionally the pile is a long time in producing its effects, seemingly from some obstacle, which is removed by an apparently inconsiderable change in the apparatus. It appears to penetrate the nervous system in every direction with equal facility, and probably passes through the minutest fibres, as, after a nerve has been cut and re-united by what seems a condensed cellular or ligamentous substance, the Galvanic influence is not transmitted. It apparently acts by exciting the nervous power; since, like all powerful exciters, it soon destroys irritability. Animals killed by the destruction of this principle soon become putrid; and this is also the rapid consequence of death by putrid miasmata, electricity, and Galvanism. Galvanism, in consequence of its readily permeating the nerves, has been employed, by Humboldt, to ascertain what parts are nervous, and the real use of some nerves whose office was doubtful. The tendons, probably from the compactness of their structure, are insensible of the Galvanic stimulus. By his experiments it also appears that the third branch of the fifth pair of nerves supplies the organs of taste, and the ninth pair gives activity to the muscles of the tongue, as Galen supposed.
This active principle has been employed with success in restoring persons apparently drowned; and by establishing a communication between zinc and silver wires, introduced into the mouth and anus of small birds, Humboldt has recovered them from asphixy. Except, however, in deaths from violence, Galvanism is useless; since, in the last struggles, irritability is usually destroyed. It has been recommended to distinguish a case of peculiar difficulty and importance, viz. the existence of amaurosis in cases of cataract. If the two metallic exciters, in a proper position, do not produce the usual sensations in the retina, the operation will probably be useless, as the sentient power of the nerve is apparently lost.
M. Grappengeisser, the first author who seems to have applied Galvanism to medical purposes, used it chiefly in palsies, and in various weaknesses of the sentient or moving nervous fibres; it has been certainly useful, though obviously inefficacious in diseases arising from an organic defect. Yet, in a very considerable degree of what may be styled organic defect in the structure of the nerve itself, it seems to have been beneficial where this defect occasioned epileptic symptoms (Edinburgh Medical Commentaries, vol. last); and from this we are led to expect some advantages from the remedy, where epileptic paroxysms proceed from either extremity, and rise to the head in the form of an aura. In gutta serena, practitioners have not succeeded by means of Galvanism; and it ought to be remembered, that the very sensible retina seldom recovers its powers after it has been, for even a short time, in a paralytic state.
In cases of spasmodic contraction, as cramp, contracted fingers, or limbs, Galvanism has often relieved; and in lameness from gout it has been successful. In one instance, hydrophobia is said, by Vassalli Eundi, to have been cured by it; but, in sciatica, the same author adds, that it has been occasionally injurious, though in some circumstances he supposes that it may be beneficial. Nervous headachs, and similar symptoms, have been relieved by Galvanism; and Aldini thinks, that in two instances of mental derangement it has been highly useful. In the application of Galvanism to palsies, a remark of M. Pfaff should be attended to, though we believe it has not been confirmed by other practitioners, viz. that the zinc should be applied to the muscles, and the silver to the nerves; for if the arrangement is altered, the irritability of the muscles is diminished rather than increased.
This remedy has been employed in some cases of vitiated secretion. Its effects on the secretions, like those of electricity, are the increase of the discharge; and it is not improbable that where the secreted fluids are diseased from a relaxation of the vessels, Galvanism may be useful. It has been employed also, like electricity, in discussing indolent tumours, and in cataracts, but with no very marked or decided success. A few boasted cures have raised our expectations, but the little permanency of the benefit received has again depressed our sanguine hopes. After repeated experiments about the head, inflammations of the eyes, a catarrhal inflammation of the Schneiderian membrane, an insensibility of the organ of taste, headach, or vertigo, have followed; and Galvanism has been undoubtedly injurious where there was considerable irritability.
On the whole, then, we have not yet received very encouraging accounts of the success of Galvanism in diseases; and we fear that we must resign it, with electricity, as a remedy that promises to be beneficial, but whose advantages have not yet answered the flattering expectations first raised.
We have considered Galvanism only as electricity, but it is probably not exactly the same; and we may, with some advantage, add a few observations on this part of the subject, which, though not strictly medical, may perhaps admit of some application to medicine. Galvanism will, indeed, produce all the phenomena of electricity; but it cannot be accumulated in non-conducting bodies, or excited by any operation on them. The distinction seems to depend on this, that in the electrical machine, the fluid accumulated on the non-conducters is raised from the earth, or drawn from the atmosphere around; in the Galvanic pile it is the fluid which formed a component part of the conductor, appearing in consequence of its change of capacity in this respect. In the doubler of electricity it is the same; and the electricity of the air appears to be truly Galvanic, since it is owing to the decomposition of water, and consequently a change in the capacity of air that before contained vapour. Conductors of electricity are also conductors of Galvanism, and in the same order. In the following series, viz. gold, silver, copper, iron, tin, lead, and zinc, each will become positive when connected with that which precedes, and negative with that which follows. The metal oxidated gives out the Galvanic fluid; and it may be produced by a single metal, if one part only is changed in its state. The most and least oxidable metals form the most active combinations; and after the metals, charcoal, muscular flesh, spirits, and beer, are conductors in their order. Charcoal is the most, and beer the least, powerful. Various circumstances in common life were little understood previous to the discovery of the Galvanic fluid. As it may be excited by two dissimilar fluids, and one metal, the improved taste of porter from a pewter pot, a fact generally acknowledged, may be owing to this principle; nor is it very absurd to suppose, that two persons in a different state of electricity may excite the Galvanic fluid by the medium of a single metal, as in the management of the Perkinean tractors.
We are not yet sufficiently informed of the influence of different animal substances as conductors or exciters of Galvanism. Galvanic effects probably arise from alternate strata of muscles and nerves; but it is more certain that this fluid acts particularly through the medium of the nerves. This has been denied, because leeches are sensible of this action, and in these animals no nerves have been discovered; but we shall show that they really have a nervous system. Mushrooms are also tolerably good conductors of Galvanism.
In the animal economy, the capacity of the fluids for containing electricity is constantly changing. To the facts adduced under that article, of the different states of the electricity of the fluids of the body, may be added, from the observations of Buvina, that in the shivering fit of fever the electricity is negative. In shivering from fear it is the same; and diseased cats are no longer electrical. Vigour, spirit, and activity in the human body, and probably all animals, are, therefore, connected with the positive, or as we have been willing to style it, with the excess of electricity; languor and disease with its defect. We find, too, in the electrical organs of the torpedo and gymnotus electricus, (for as the only organs in which they differ from other fish, we may presume that they are the seat and source of their peculiar powers,) that the surface is greatly increased by the numerous plates of which they consist, and that a very large proportion of nerves is sent to these plates. When we combine these facts, we shall find reason to conclude that the nerves are the probable sources of the animal, Galvanic fluid; and that these and the nervous fluids are the same, or nearly related. If in the animal process the excess of electricity disappears, we must look for some reservoir in which it is collected, some storehouse from which it may be issued; and this appears to be the brain and nerves. Such, at least, are apparently the fair conclusions from the facts before us.
Mr. Wilkinson also supposes that the cells of the lungs are really Galvanic organs; and that the electricity of the air is discharged in these cells, where the fluid loaded with carbone (a conductor so powerful as to be discovered in a small proportion, even when me-chanicallymixed with any body, by means of Galvanism) increases its activity, thus giving a stimulus to the heart. The idea is ingenious, but it must rest on its own basis. We are not aware of any argument that will support or invalidate it. See Wilkinson's Elements of Galvanism. Le Sue's History of Galvanism. Al-dini's Experiments. Annales de Chimie; and Philosophical Magazine, passim.