+371

CHAPTER IV.

Galvanic Electricity.

THE first discovery connected with this branch of physical science is found in a German work, published in 1767, by Sultzer, entitled The General Theory of Pleasures. He observed, that if two metals be applied, one above, and the other below the tongue, and brought in contact, a peculiar taste was perceived, attended with a gentle flash of light; but that if applied separately, no such effects were produced.

It was next discovered accidentally by Galvani, a distinguished professor of anatomy at Bologna, that on touching the crural nerve of a recently killed frog, which lay on a table, near the conductor of an electrical machine in action, with the point of a scalpel, all its muscles were thrown into convulsions, as if seized with tetanus. By repeating the experiment on different animals, he found that the effect was most remarkable in those which are cold blooded, and have white muscles. He ascertained afterwards, that when the nerves and muscles of such animals were armed with small pieces of

different metals, similar phenomena were produced on bringing the metals in contact.

From these obscure results, Galvani arrived at the conclusion, that there is a peculiar species of electricity residing in all animals,-which is secreted by the brain, and conducted to different parts of the body by the nerves, causing animal motion, secretion, &c. He supposed that this fluid is conducted from nerves to muscles by the metallic arc, as the electricity of a Leyden battery is conducted from it by means of a common discharger.

In opposition to the views of Galvani, it was maintained by the celebrated Volta, professor of natural philosophy at Pavia, that the phenomena were due to the agency of common electricity, which he supposed was accumulated by the contact of different metals.

Finding that when sticks of zinc and copper, zinc and silver, &c. were made to touch at one of their extremities, and the other brought in contact with the spine and muscles of a newly killed frog, excited convulsions, it occurred to Volta, that by a repetition of circles, or series, composed of two different metals and moistened cloth, he might greatly increase the electrical effects. This led to the construction of the well known pile, and the couronne de tasses, which have been modified into different forms of the battery. In reply to the hypothesis of Volta,

that the convulsions of the frog were owing to
the agency of common electricity, and generated
by the contact of different metals, Galvani ob-
jected that he had succeeded in producing con-
vulsions by means of a single metal. And it
was further shown by Aldini, a nephew of Gal-
vani, that by bringing a portion of a warm
blooded animal in contact with a cold blooded
one, as the nerve and muscles of a frog with the
bloody flesh of a newly decapitated ox, ener-
getic contractions were produced. When he

held a prepared frog in his hand, moistened with
a solution of salt, and applied the crural nerves
of the animal to the tip of his tongue, convul-
sions were also excited*-from which he in-
ferred, with Galvani, that there is a peculiar
electricity in animal bodies which does not
require the contact of metals for its develope-
ment. It is somewhat surprising that he was
never led to suspect, from these curious experi-
ments, the identity of animal heat with the
cause of muscular contraction-and still more
remarkable, that neither Galvani nor Volta ever
suspected the connexion of the phenomena with
chemical action.

The agency of caloric in exciting convulsions

The experiments were successfully repeated before a Committee of the National Institute of France, and afterwards at the Anatomical Theatre in London, Great Windmill Street.

in recently killed fish, was strikingly demonstrated by some experiments of Mr. Clift, who found, that four hours after the head of a carp had been cut off, and its heart taken out, (the fish being considered as perfectly dead,) when put in hot water, it leaped out of the vessel with a degree of vigour equal to the struggles of a living fish. (Phil. Transactions for 1815.)

A similar fact was observed by Lord Bacon, who relates that he saw, with his own eyes, the heart of a criminal taken out of his body some time after execution, and thrown into the fire, when it leaped up several times to a considerable height. Without commenting on these facts, which belong to another portion of the present work, it may be observed that they demonstrate the agency of heat in animal motion, at least as clearly as that of electricity,-even admitting (what has never been proved,) that electricity could exist independent of caloric.

The first philosopher who referred the phenomena observed by Sultzer, Galvani, and Volta, to chemical action, was Fabroni, in a paper communicated to the Academy of Florence, in 1792. He had often observed that fluid mercury retained its lustre for a long time when alone; but that when amalgamated with other metals, it speedily tarnished by oxidation; and that similar effects were produced on some alloys of tin.

He had remarked in the Museum of

Cortona, inscriptions engraved on plates of pure lead in a perfect state of preservation; while in the Gallery of Florence, he found that medals composed of lead and tin, or lead and some other metal, were entirely reduced to a white powder, though carefully wrapped up in paper, and preserved from the atmosphere in drawers. He had further noticed, when in England, that the iron nails then employed in fastening together the copper sheathing of ships, caused so much corrosion of the copper, that the holes made by them were sometimes larger than the heads of the nails-all of which he referred to chemical action produced by the mutual contact of different metals exposed to moisture, atmospheric air, &c. That this was the case in the experiment of Sultzer, he thought was proved by the fact, that when the tongue was wiped dry, scarcely any perceptible sensation was excited.

In another set of experiments, Fabroni put different metals in vessels filled with water, two and two, in contact, when he found that the most oxidable metal was visibly oxidized at the moment of contact. A month afterwards, the connected metals had acquired so strong a degree of cohesion as to require a considerable force to separate them. Not only were the metals oxidized, but covered over with small crystals of various forms, which had been deposited from a state of solution. (Traité de