1. ELECTRO-GALVANISM, OF VOLTAIC ELECTRICITY, may be said to owe its origin to the discoveries of an ingenious Italian philosopher, named Galvani, who published a Latin treatise on the subject at the close of the last century.

2. In the preceding article we have examined the various phenomena resulting from the friction of dry bodies, which, by their mutual action on each other, tend to destroy their electrical equilibrium; and we now propose to furnish our readers with an outline of that branch of electricity which has led to some of the most important discoveries and splendid triumphs connected with the progress of chemical science.

3. In the year 1790 L. Galvani, professor of anatomy at Bologna, accidentally discovered that the passage of a small quantity of electricity, through the nerve of a frog that had been recently killed, had the property of exciting distinct muscular contractions. He produced the same effect with atmospherical electricity; and afterwards by the mere contact of two different metals. His discoveries were published in 1791: he proved the phenomena to be electrical, and says, 'it you lay bare the sciatic nerve of a frog, and remove the integuments, then place the nerve on a piece of zinc, and a muscle on a plate of gold, and connect these metals by any conducting substance, contractions are produced; but, if nonconductors are used to connect the metals, contractions are not excited.'. The experiments of Galvani received considerable attention; they were varied and extended with the greatest perseverance and address by professor Volta, Dr. Valli, Humboldt, Fowler, Monro, Robison, and many others.

4. The effects obtained in the experiments of these naturalists may be illustrated by very simple experiments. The most important facts they establish are, first, that the passage of a small quantity of electricity through the nerve or nerves of any animal, occasions a tremulous motion or contraction of the contiguous muscles, and sometimes an extension of the limbs. This effect takes place both n living animals and such as have been recently küled, and even in the detached limbs of these last. It is produced when the transmitted electricity is too weak to affect the most delicate electrometers, and obtains in all animals for some time after death; their susceptibility being greatest at first, and gradually diminishing as the limbs stiffen. Animals with cold blood, as frogs and fishes, retain the power of action after death longer than others, sometimes for many hours, or even days.

5. Secondly, The same effects that are produced by the passage of electricity, also result from the contact of different metals with the nerves and muscles. If a communication be formed between any nerve and muscle by a single metal, contractions are but rarely produced, and when they appear are very feeble; but if two metals are employed, in contact with each other, motion is always obtained, and the effects are most considerable when the metals are most esVOL. VIII.

sentially different; thus zinc and gold or zinc and silver, form a very active combination.

6. Thirdly, By the same means that muscular motion is excited in these trials, some of the senses are remarkably affected, as will be evident when the experiment is made on living animals. 7. The demonstration of these facts is easily effected. For the excitation of muscular motior any small animals may be employed; the most convenient are frogs and fishes. Frogs are peculiarly susceptible. If one of these animals be employed alive, a piece of tin-foil may be pasted on its back, and the frog being then placed on a plate of zinc, spasmodic convulsions will be produced whenever a communication is made by a wire between the zinc and the tin-foil. This experiment will succeed either in the open air or under water.

8. M. Valli, an Italian physician, was one of the earliest to enter on a series of Galvanic experiments, which he began by those that relate more immediately to animal electricity. The results of these experiments he communicated in 1792 to the French Academy of Sciences, by the members of which the experiments themselves were so much approved, that the greater part of them were shortly after repeated in the chemical laboratory of Fourcroy. They were as follows:

9. Experiment I.-Two metallic coatings, one of lead the other of silver, were placed on a frog fastened to a table, the former on the belly of the animal, the latter on the pelvis. These metallic coatings having been brought into union by the means of an exciting arc of copper, very powerful convulsive movements were produced in the animal.

10. Experiment II.—The small sheet of lead, employed as one of the coatings in the former experiment, having been removed, so as to leave the abdomen bare, and the exciting arc applied in the same way as before, the convulsive movements took place but were not so sensible as in the other case.

11. Experiment II1.-In employing two coatings of the same metal, silver or gold for instance, it was found that the effects produced by the exciting arc of copper were much weaker. When these coatings were not only of similar metals, such as copper, lead, tin, zinc, &c., but the exciting arc also, no effect was produced.

12. Experiment IV.-The coating placed on the abdomen having received an horizontal direction, insomuch that the points of contact were less numerous, the effects were proportionably diminished. As soon, however, as the coating was brought into full contact with the surface of the abdomen, they became as powerful as before.

13. Experiment V.-A frog having been skinned, and cut transversely through the middle, the nerves of the thighs were laid bare, united, and placed on a piece of gold, at the same time that the thighs themselves were brought in contact with a piece of silver. On the application of the exciting arc of .copper, slight movements

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were produced; as they also were when both the coatings were of silver. But when a coating of tin, lead, or copper, was substituted for the one of silver, in which the nerves were enveloped, the movements became very violent. The following gradation was, however, observed in the action of the metals: the lead produced the most powerful movements; next the tin; and, lastly, the copper. In proportion as the vitality of the frog was diminished, the metals also lost the power of governing the direction of the progress of the electric fluid in the animal. The lead, tin, and zinc preserved this property the longest.

14. Experiment VI.-Plumbers' lead, placed on each side as a coating, produced no effect when employed with an exciting arc of the same description of lead; but when different qualities of this metal were selected, such, for instance, as the lead of the assayer, and plumbers' lead, an exciting arc of either of these descriptions of metal produced very singular effects. When these two kinds of lead, in changing the different metals, were no longer productive of any effect in one of these coatings, by substituting for the lead either silver, gold, bismuth, antimony, or zinc, movements of so powerful a nature were obtained, as to enable the animal to be susceptible of slight convulsions, when the above-mentioned pieces of lead, each of them of a distinct kind, were again applied.

15. Experiment VII.-A short interval of repose having been allowed to the frog, it was found to be susceptible of convulsive movements of a forcible nature, when again subjected to the same trials.

16. Experiment VIII.-The electric power being nearly exhausted in this animal, it was found that the different metals, when they produced by their contact new convulsions, did not, on this effect ceasing, leave to the animal the faculty of displaying fresh movements with the coatings of the different kinds of lead.

17. Experiment IX.-Lastly, the electric action disappeared totally in the following order, the plumbers' lead invariably forming one of the coatings: the assayers' lead first ceased to determine the action; next the tin; next the antimony; next the zinc; next the copper; next the gold; and finally, the silver. It ought here to be noticed, that the iron had lost its exciting quality before the antimony; but it was not ascertained whether it had likewise been deprived of that quality before the lead and the tin.

18. Experiment X.-The zinc, in losing the exciting property by which convulsions had been produced on the frog, which had been subjected to the experiment for the space of an hour, was not capable of determining any farther movements when the leaden exciting arc was placed on it. It was however remarked, that movements were still produced by this metal, the moment the person engaged in the experiment removed the exciting arc, and destroyed the communication. This singular experiment was so often repeated, as not to leave any doubt respecting the result.

19. Experiment XI.-The upper part of a frog, skinned and intersected transversely, having

its crural nerves armed with a piece of lead, as in the preceding experiments, was placed in a glass filled with water, while the inferior part of the animal was placed in another glass. The different parts displayed very powerful move ments when the communication was established, by the means of a chain formed by the persons present, two of the persons present having been selected to touch, each of them, the water in one of the glasses. One of these individuals held in his hand a bit of metal, which he brought in contact with the coating of lead.

20. Experiment XII.-When one of the company withdrew himself in such a way as to interrupt the chain, the movements were no longer perceptible.

21. Experiment XIII.-The parts of the frog having been placed in the two glasses, as in Experiment XI., the operator could not excite any movement by establishing the communication with his two fingers. He was equally unsuccessful when, with one hand armed with a piece of metal, he touched the body of the frog, while he placed a finger of the other hand on the metallic coating of the crural nerves. But when, having a finger placed on the inferior part of the frog, he presented the piece of metal to the coating of the nerves, very powerful movements were excited in the animal.

22. Experiment XIV.-When the frog was touched with a metallic exciting arc, in an insulated state, no sensible effect was produced; but, when the metal ceased to be insulated, the effect was invariably very considerable.

23. Experiment XV.-One of the fore legs of a rabbit having been detached from the body, the brachial nerves were denudated, and armed with a piece of sheet-lead. A piece of silver, which was to act as an exciting arc, was afterwards laid on an adjacent muscle; and the result was, that very violent convulsive motions were produced in the animal. In this experiment on the rabbit, as it was afterwards varied, one of the coatings being of plumbers' lead, and the other of assayers' lead, the movements were no longer excited. When they consisted, the one of lead, and the other of iron, they produced as little effect; but when the lead, as one of the coatings, was tried with another coating, either of silver, gold, copper, zinc, or antimony, convulsive movements were produced. Combined with a coating of bismuth, the coating of lead produced but very slight

movements.

24. Experiment XVI. To ascertain the state of the electricity inherent in the animal subjected to the experiment, it was plunged into a vessel containing one of Coulomb's electrometers, and successively electrified both positively and negatively. In either of these cases the animal influenced the balls of the electrometer, so as not only to evince that the electricity was in a perfect state of rest, as well before as during the experiment, but also, that the system of the body on which it was made, presented in the most marked and striking manner, the phenomenon of a Leyden phial.

25. Experiment XVII.-The left crural nerve of a living frog having been bound by a strong

instituting a series of experiments by which vitality should be, as it were, subjected to a chemical analysis.

40. M. Humboldt's attention having been directed to other objects for more than two years, he did not think of publishing his experimental observations, until the work of our countryman, Fowler, on the galvanic influence, enlightened him as to the result of his experiments, which he had hitherto apprehended to be peculiar to himself, at the same time that similar ones were made by other naturalists; such, for instance, as the experiment of Mr. G. Hunter of York, which consisted in perceiving the flash of light without any contact of metals with the eyes. Humboldt now began to collect all that had appeared on this subject, from the origin of the discovery, and to compare this information with what he had himself observed. On reading the excellent production of Pfaff on animal electricity and irritability, he found, in the very considerable number of experiments it contains, and in the important observations by which they are accompanied, results exactly similar to those with which his own experiments had supplied him, notwithstanding a very different mode of investigation had been pursued by their author. He was now obliged to renew his labors, and to suppress at least one-half of his experiments.

41. By the observations of Messrs. Jurine, Pictet, Scarpa, Tralles, and Volta, in whose presence they were made, he corrected his ideas; and their reflections conducted him to new researches. After having collected all the observations on irritation, and on the incitability of the sensible and irritable fibre, he began with the history of galvanism, as it led to the other researches. Finding it unnecessary to go into any length of detail, in penning down his observations, the results alone being of importance, he has contented himself with pointing out the principal ones, in a loose way, and in the order in which they presented themselves to him. This work is divided into ten sections, which, after the introductory matter already given in substance, form a kind of table of the subjects they discuss, and of which the following is a brief, but faithful, analysis.

42. In the first section the author expatiates, in general terms, on the relation between galvanic irritation and incitability, and on the different degrees of the former, which, he observes, act exclusively on organic parts provided with sensible fibres. The indirect effects on inanimate matter, connected with incitable bodies, have not, as yet, been experimentally demonstrated. Humboldt, with great care and attention, caused the galvanic fluid to pass through colored liquors, and through other liquors saturated with salt. These experiments he repeated with great assiduity, but could never observe the smallest alteration in the color, temperature, evaporability, or crystallisation of the fluids in question, on the chemical combination of which he could not perceive any change to have been effected. It did not produce any sensible effect either on the electrometer, or on the intermediate rings of the galvanic chain, so as to indicate its strict analogy with the electric fluid.

43. In his investigation of the effects of a metallic stimulus on the irritable and sensible fibre, Humboldt was very solicitous to ascertain the degree of irritability and incitability, which has as powerful an influence on the success or failure of the experiments, as the degree of force of the stimulus itself. In experimenting, he therefore made choice of the most incitable animals, and found that the frogs best calculated for his purpose were young and vigorous females, taken immediately after their winter slumber, and fed, together with other frogs, for some days in a warm room. By the help of art he contrived to carry the incitability to a higher degree than is remarked in the natural state; and this discovery may be considered as one of the most important that he made. By bathing the nerves of animals with a solution of alkaline salts, or with the oxygenated muriatic acid, he not only obtained results which had not previously been known; but also noticed phenomena, the possibility of which had been denied.

44. A short time after the appearance of Humboldt's great work, M. Pfaff published an interesting memoir on the subject. It cannot be questioned,' says this writer, but that vital chemistry, which appears to be the favorite object of the meditations of the physiologists of the present day, has been elucidated, as well as greatly extended in its limits, by Humboldt's experiments on the excitability of the muscles and nerves. The indefatigable zeal employed by that writer, together with the sagacity and spirit of observation of which he has given so many conspicuous proofs, in a multitude of researches on physiology, must necessarily have led him to very interesting results. The inferences, however, which he draws from his experiments, as well as the explanation he gives of the phenomena he has observed, are not invariably fixed on a solid basis.'

45. The very remarkable effects produced by chemical substances on the sensible and irritable fibre, are, according to M. Pfaff, susceptible of an explanation different from the one adopted by M. Humboldt. It is for this reason that the former proposed another, which he thought more just, and, at the same time, more coincident with the different phenomena of galvanism. The following are his reasonings on this head, together with the experiments on which they are founded.

46. A very important circumstance,' he observes, to which Humboldt did not pay attention, in his experiments relative to the influence of chemical substances, as exciters of irritability, is the effect of them as members of the galvanic chain. Among these substances may be enumerated the different alkaline substances, acids in general, the oxygenated muriatic acid in particular, and liver of sulphur. I have examined them, in the above point of view, in a series of experiments, and have found several of them to be as efficacious links of the chain, and as powerful exciters of galvanism, as metallic substance themselves.

47. The table published by M. Humboldt, of the intermediate links of the chain of his boasted exciters and conductors of animal eleø