Galvanism, an appellation given to the influence of metals y mere external contact with the human body, discovered by Prof. Galvani, at Bologna, about ten years s nee, and which he called Animal Elecitricity.
Certain convulsive motions on the nerves of living and dead animals, may be excited by the application of metallic or other conductors of electricity; but these motions may also be induced, by simply touching the animal fibre with two different metals, that are brought in contact with each other at the same moment. This surprizing phenomenon has lately been resorted to, in order to ascertain whether a drowned, suffocated, or otherwise suddenly deceased person, was really or apparently dead. For this purpose, Dr. Creve, Prof. of Medicine in the University of Mayence, has contrived an instrument formed like a bow, both ends of which are furnished with two small round plates. The whole is composed of two parts made of different metals; one-half of solid zinc, the other of fine silver; or gold and zinc, or lead, tin, and gold. The proportion of the first metal should be less than the other combined with it; namely, the weight and size of the zinc-plate should be less than the opposite one of gold. Both plates are only screwed; on the bow, which chiefly consists of silver. But, where this instrument cannot be procured on the spur of the occasion, a small piece of tin or lead, and a silver coin of a moderate size (for instance a shilling, or half-a-crown piece) may be substituted. Although any part of the body may be fixed upon for making the experiment with persons apparently dead, yet the upper arm will be the most proper. The skin, however, in that part where the incision is made, ought to be sound, and not of a gangrenous appearance. The muscles must be cleared of all fat and cellular texture, as far as this be practicable; and the blood is to be taken up By a sponge dipped in water. Next, the muscle should be slightly extended, by stretching the arm ; and, in order to keep the lips of the wound se parate, the skin ought to be expanded, and the muscular fibres clearly exposed. After these preparatory steps, either the instrument above described, or two loose metallic plates, are to be applied towards the centre of the hollow place or wound made by the incision, and both flat plates brought into perfect contact with the barer muscular fibres. If any irritability exist, or remain, in the system of the subject, the muscular fibres will be contracted and twisted in a manner similar to spasms; or convulsive motions will be evident: every symptom, however, disappears on withdrawing the instrument, and again becomes manifest on re-applying it as before. But no motion whatever will be percepti ble, if all irritability be lost or destroyed, in which case the body may be considered as irrecoverably dead. - In those instances, where persons have been deprived of life by intense cold, a moderate degree of warmth should be previously applied, with a view to render the limbs flexible. Hence, this experiment cannot with propriety be. undertaken, till all other means (see Frost, p. 334) of restoring animation have been unsuccessfully employed.
Whatever two metals be chosen, they will, with a few exceptions, produce those remarkable contrac-tions, when applied in the manner before described; but the most powerful are, zinc and silver, or zinc and gold; or in general, zinc, tin, or lead, when used in com-bination with gold, silver, molyb-dena, steel, or copper.
These singular phenomena take place in consequence of a mutual
GommuCommunication between any two points of contact, whether more or less distant, in a system of muscular and nervous organs. The extent of this communication may be considered as a complete circle divided into two parts, one of which, comprising the organs of the animal under the experiment, is called the animal arc; the other, which is formed by the metals or galvanic exciters, is denominated the excitatory arc; and consists of more than one piece, of various kinds.
Beside the effects thus produced on the muscles, the impressions made on the organs of sense are equally remarkable. And as the experiments illustrating them may be easily repeated, we shall specify some of the most interesting. For instance, if a thin plate of zinc be placed on the upper surface of the tongue, and a half crown, shilling, or silver tea-spoon, be laid on the lower surface of the tongue, and both metals after a short space of time be brought into contact, a peculiar sensation similar to taste, will be perceived at the moment when the mutual touch happens. If the silver be put beneath, and the zinc upon the tongue, the same sensation will arise, butin a weaker degree, resembling diluted ammo-niac, from which it in all probability derives its origin.
If a silver probe be introduced as far as convenient into one of the nostrils, and then be brought into contact with a piece of zinc placed on the tongue, a sensation not unlike a strong flash of light will be produced in the corresponding eye, at the instant of contact. A similar perception will result, both at the moment of contact and at that of separation, if one of the metals be applied as high as possible between the gums and upper lip, and the other in a similar situation with the under-lip, or even under the tongue - Lastly, when a probe or rod of zinc, and another of silver, are, introduced as far back as possible into the roof of the mouth, the irritations produced by bringing the external ends into contact, are very powerful; and that caused by the zinc is similar in taste to the sensation arising from its applica-tion to the tongue.
No method has hitherto been discovered, of applying theGalvanic influence in such a manner as to affect the senses of smell, hearing, and touch ; though several eminent philosophers have carefully investigated the subject. Nor are the causes of these phenomena clearly ascertained; Galvani and some of his followers, supposing them to depend on the electric fluid, while others attribute them to the influence of various physical agency.
In this state was Galvanism, when in the year 1800, Signor Volta, Professor of Natural Philosophy, at Como, in the Milanese, communicated to Sir Joseph Banks, a discovery of the vast accumulation of this power: it was accordingly presented to the Royal Society, from the 2d part of whose Transactions, for 1800, we have selected the following account.
Sign. Volta's apparatus consists of a number of copper or silver plates (which last are preferable), together with an equal number of plates composed of tin, or still better of zinc, and a similar number of pieces of card, leather, or woollen cloth, the last of which substances appears to be the most suitable. These last should be well soaked in water saturated with common salt, muriat of ammonia, o , more effectually, with nitre.— The silver or copper may be pieces of money, and the plates of zinc may be cast of the same size. A pile is then to be formed, by placing a piece of silver on a corresponding one of zinc, and on them a piece of wet cloth, or card; which is to be repeated alternately, till the number required be arranged in regular succession. But, as the pieces are apt to tumble down, if their numbers be consi-derable, unless properly secured, it will be advisable to support them by means of three rods of glass, or baked wood, fixed into a flat wooden pedestal, and touching the pieces of metal at three equi-distant points. Upon these rods may be made to slide a small circular piece of wood, perforated with three holes, which will-serve to keep the top of the pile firm, and the different layers in close contact The moistened pieces should likewise be somewhat smaller than those of metal, and gently squeezed before they are applied, to prevent the superfluous moisture from insinuating itself between the pieces of metal - Thus constructed, the apparatus will afford a perpetual current of the animal-electric fluid, or Galvanic influence, through any conductor that communicates between the uppermost and lowest plate ; and, if one hand be applied to the latter, and the other to the highest metal, a shock will be perceived, which may be repeated as often. as the contact, is renewed. This shock greatly resembles that given by the torpedo, or gymnotus electricus : and, according to the larger size of the metallic plates, the shock will be proportionably stronger. The intensity of the charge, however, is so low, that it cannot penetrate the dry skin ; it will therefore be necessary to wet both hands, and to grasp a piece of metal in each, in order to Produce the desired effect: its power may be considerably increased, both by an elevation of temperature, and by augmenting the number of pieces that compose the pile. Thus 20 pieces of each will emit a shock, that is very perceptible in the arms; if 100 be employed, a very severe but tremulous and continued sensation will extend even to the shoulders; and, if the surface of the skin be broken, the action of the Galvanic influence will be uncommonly painful.
The sensation of a flash, or shock with this apparatus, does not materially differ from that produced by two simple plates ; but it may be effected in various ways, especially if one or both hands be applied in a wet state to the lowest plate of the pile; or any part of the face be brought in contact with a wire communicating with the top piece. Farther, if a wire be held between the teeth, so as to rest upon the tongue, that organ, as well as the lips, will become convulsed, the flash will appear before the eye, and a very pungent taste will be perceived in the mouth.
Many other curious facts have transpired on this interesting discovery ; but, as they have not been hitherto applied to medical purposes (though we believe that Galvanism may be safely, and perhaps successfully, resorted to, in paralytic and other cases, where the muscles require excitement), we shall content ourselves with referring the cutious reader to Dr. Fowler's "Essay on Animal Electricity," 8vo - fcr a further a count of Signor Volta's discovery, to the volume of the "Philosophi-cal Transactions" above cited ; and to the 4th vol. of Mr. Nichol-son's "Journal of Natural Philosophy :" and, for Utter discoveries, to the 1st vol. of Dr. Garnett's "Annals of Philosophy," 8cc. 8vo. Cadell and Davies, 1801, where the subject is perspicuously treated.