(From Galvani, one of its earliest cultivators). Though the phenomena which Galvanism offers are by no means wholly new, yet the discovery of their nature and source, as well as their application, are among the most brilliant improvements of an inventive age. It was long since observed that the electric torpedo, and electric eel, as they were styled, could give, with powers scarcely impaired, many repeated shocks; and philosophers contemplated with astonishment batteries which required no new charge; an efficacy scarcely diminished by exertion. This effect was probably not produced by muscular exertion, for in that system there was no provision for the exercise of such powers. The discriminating organs were cellular, to which a large proportion of nerves could be traced, and anatomical investigation gave no further assistance.
Cotugno, a student of medicine, in 1788, on dissecting a mouse, punctured the intercostal nerve with his scalpel, probably while he touched the other part with his probe, and he felt a shock. The experiment, with some others, was repeated by Vassali; but the only conclusion drawn was, that nature had a power of preserving some portion of the electricity after death. Galvani added to our knowledge by showing us, that the contact of two metals was necessary for the production of this new power, which greatly resembled the electrical; and it was conjectured very early, that these metals acted as doublers of electricity. In the Annales de Chimie, we find a very ingenious calculation of their effects, on the principle of the two metals acting in this way (vol. xli. p. 3), in a report made by La Place, Fourcroy, Biot,& c. to the academy respecting the Voltaic pile. But we shall not enlarge on this part of the subject, because it is scarcely medical, and because the Galvanic phenomena are more nearly connected with the oxidation of the metals. Before, however, we leave this early stage of the history, we may remark, that Sulzer, in 1769, and Fabroni soon afterwards, found that if a piece of silver was placed on the tongue, and a plate of zinc under it, on these metals touching each other a pungent taste was perceived.
Galvani seems rather to have retarded than promoted the knowledge of this science, by connecting it too closely with the fashionable system of electricity, and attempting to find, in the muscular fibre, the two sides of the Leyden phial. The theory of Volta is still different; yet the peculiar action of this singular fluid is not yet well understood. It is shown to exist, by coating, as it is styled, a nerve and a muscle with a different metallic substance, and then joining the distant coatings by some conductor. The muscle is thus powerfully agitated; and even long after life is at end, these motions may be excited. The heart, alone, is most disobedient to this power; and for a reason easily assigned. As an organ of peculiar importance, its nerves are derived from many different sources, communicating with numerous fibres of a very distant origin, in plexuses and ganglia. If then any particular nerve is coated, but a very small portion of the nervous power which regulates that organ is affected.
In the manner, however, described, the influence of Galvanism is very inconsiderable; the Voltaic pile, called from Volta, was contrived to augment its power. This pile consists of plates of zinc and copper, placed alternately, interposing woollen cloths, wetted with a solution of muriated ammonia, between each. It is improved in its powers, and the continuance of its effects, by fixing these plates in a wooden frame, and pouring in the interstices a dilute muriatic acid. It is varied often by using one metal, and different fluids, or supplying the place of metals with other substances, as charcoal and plumbago. These varieties, however, belong rather to the general view of the science than to the present article. For medical purposes, the trough, as it is called, is very generally employed; and the plates are squares, whose sides seldom exceed three inches. Larger ones have been tried; but though they seem to possess a greater Galvanic power, they do not communicate more: after their action they are less completely discharged. The shape is of no consequence; for they are often round, and then called discs.
The action of Galvanism on the human body is nearly that of electricity; but as a stimulant, it is less intense, and more steady. The cuticle in animals, and the epidermis in plants and seeds, resist it more powerfully than the electrical influence; and it is necessary often, for the purpose of increasing its power, to puncture the skin, so as to draw some blood. The coats of the nerves have apparently a similar effect; for the influence is greater, the nearer the coating is placed to the part on which the nerves are dispersed, where the coats are thinner, or wholly lost. In general, however, Galvanism does not seem to resemble accumulated electricity; but a weaker charge diffused over a larger surface. In the operation, the metals are oxidated, and the water between them is decomposed, the zinc apparently yielding the oxygen, and the copper the hydrogen. As the water is seemingly decomposed on each side, it has become a problem to account for the disappearance of the oxygen on the side of the copper, and the contrary. Philosophers have not yet dared to face this difficulty, as it so strongly militates against the modern chemical doctrines. This decomposition of a watery fluid was, however, introduced very early into its medical system; and Galvani, resting on the hypothesis of Cotunnio de Ischiade Nervosa, that sciatica, and many other complaints, arose from the accumulation of a fluid within the nervous sheaths, supposed that it was of service from its influence on the morbid causes. We have no reason, however, to think that it has any effect in this way, though it has been supposed also from this circumstance to change the positive electricity of the healthy body to the negative state.