and enriched with new observations by the celebrated Volta[5].
XVII. That the phænomena already mentioned arise from an interior arc, will be proved, in my opinion, by the following experiment: If an insulated metallic arc, or a piece of charcoal, be applied to the tip of the tongue with the moistened hand, no taste will be produced; but if the same hand be applied to the same metallic arc or charcoal, a taste will be experienced. In both cases of this experiment dissimilar armatures were brought into contact, and reduced to that state of equilibrium to which they tended. Why then should the result
of the experiment be so different? When the metals or charcoal touch the moistened hand, a speedy and uninterrupted communication is formed even between the remote muscles and the nerves of the tongue, which when intercepted by the non-conducting body prevents all sensation of taste. It may therefore be established as a principle, that to excite a sensation of taste, it is necessary besides the application of external armatures to have an internal arc, which may bring the internal electricity to a state of equilibrium. This observation is confirmed by Carradori, who, while endeavouring to excite a sensation of taste in two persons at the same time, found that it was necessary to establish an arc between them, either by making them join hands, or by moistening the plane on which they stood[6].
XVIII. I shall conclude this dissertation with an account of some later experiments on this subject. Volta, in a letter which I received from him, requested I would try to produce contractions without any metallic application, and recommended
charcoal, which in his first experiments he had found to be the best armature for animal electricity. I therefore took the earliest opportunity of attempting to produce contractions in the beforementioned manner without the aid of metals. I was encouraged in this design by Aloysius Laghi, professor of chemistry; who having analysed our fossil coal in consequence of a public decree for that purpose, was desirous that chemical processes might be made subservient to my researches. It was well known, that every kind of vegetable charcoal formed the best armature, so that when this coal was used there was no need for metallic armatures. Hence, in that Galvanic experiment called the animal alarum, a charcoal plane substituted for one of silver produced the same effect: charcoal arcs also were used instead of metallic. The coal employed in this manner was vegetable coal: but the English fossil coal, and that dug up in our territories, did not produce the same effect. I employed the different principles extracted from our fossil coal, namely, calcareous earth saturated with the acetous acid, siliceous earth semi-vitrified by fixed alkali, and argillaceous earth. All these, however, formed bad armatures for animal electricity; and the case was the same with the ashes of our fossil coal, and of the English coal.
XIX. None of these phænomena, however, afforded any grounds for objecting against the theory of electricity in general; as that bituminous substance which is always found combined with fossil coal, deprives it of the power of being a conductor
of animal electricity. This conjecture was confirmed by experience; for, having employed our own fossil coal and the English in the state of coke, they formed excellent armatures, as by the action of the fire they had been freed from those idio-electric principles which opposed the development of animal electricity, A phænomenon in the mean time occurred, which tended to throw great light on the nature of this electricity. Having placed the spinal marrow upon a piece of coke, and formed an arc from the muscles to the coke, contractions always took place in certain parts, while in others there was no appearance of them. The reason of this seemed to be, that the action of the fire had made some parts of the same coal conductors, and left others idio-electric, in consequence of the large quantity of the bituminous principle which they contained. But though torrified fossil coal acquired a conducting property, vegetable charcoal was still found to be much fitter for conveying animal electricity. Hence I conceived a hope, that I should be able to excite contractions, in the manner before described, without any metallic arc, and by the application of charcoal alone. For these new experiments, I employed the largest frogs, and I selected on purpose such pieces of charcoal as seemed the least fitted for being conductors of animal electricity. I placed the prepared muscles of a frog on the charcoal, and suspended the unarmed spinal marrow, by a silk thread, in such a manner that the marrow could be made to touch the charcoal at pleasure. When large frogs were employed, contractions always took place; and Galvani found the case to be same in
his experiments. Here then we have contractions produced without the intervention of any metallic substances: why then ascribe to the different power of metals, effects which can be produced by bodies which certainly have nothing of the metallic quality? If the spinal marrow or muscles be made to communicate separately with the charcoal, there will be no contraction; and it appears that to produce contractions, the arc and the armature must consist of homogeneous charcoal. Having given an account of my experiments, it remains that I should collect in a few words the inferences which may be deduced from them.
XX. In the first place, it is certain that to produce contractions it is not necessary to employ two different kinds of metal, and that one is sufficient. In vigorous animals this result may be obtained by silver, and particularly by gold.
2d. If any suspicion of heterogeneity should arise, in regard to the solid metals, this difficulty may be easily obviated by employing a fluid metal, that is to say, mercury purified by chemical means.