Experiments and Observations Relative to the Influence Lately Discovered by M. Galvani and Commonly Called Animal Electricity

by Richard Fowler

With respect to the single instance related by M. Cotugno, it is probable that both he himself, and all who have repeated experiments of this nature, must have been long ago convinced, that he was deceived into the belief of a shock, from the sensation produced by the struggles of the animal he dissected.

That some kind of disagreeable sensation is occasioned by it, even in frogs, independent of that which must necessarily arise from irritation, and the contractions of their muscles, is evident from their restlessness, and expressions of uneasiness. In other animals, as I shall afterwards have occasion to shew, these expressions are still less equivocal: and, in man, we can ascertain both their degree and their kind. That they differ considerably from such as are produced by electricity, will be proved when I come to speak of the effects of this influence upon our senses.

But the most important, and characteristic difference, which I have yet been able to discover, between this new influence and electricity, consists in their effects upon the contractile power of animals and of plants. The contractions of animals excited by electricity have a tendency to destroy that power upon which contractions depend. But the contractions excited, by the application of the metals, have, in all my experiments, had the directly opposite effect. The more frequently contractions have been, in this way, excited, the longer do they continue excitable: and the longer are the parts, upon which such experiments are made, preserved from putridity. An influence, capable of exciting contractions, without occasioning exhaustion, was a thing I so little expected to find, and so contrary to the character which had been given of this, both by Galvani and by Dr Valli, that I, at first, distrusted my own observation of the fact: but the number of comparative experiments, which I had afterwards occasion to make, though with views different from that of ascertaining the point in question, convinced me that this influence, so far from destroying the contractility of muscles, has a tendency to preserve it. Oxygene is, so far as I know, the only stimulus in nature, whose effects are at all analogous.

When a frog has been long dead, I have been sometimes more than a quarter of an hour without being able to excite a single contraction by the application of the metals: but after this, without at all varying the means employed, contractions have appeared, and have become gradually more and more vigorous.

It is said, (for I have never had an opportunity of making the experiment,) that a stream of electricity passed through a sensitive plant produces an almost immediate collapse of its leaves. But the influence, discovered by Galvani, produced no such effect in the following experiment. Having separated the leg of a frog from its body, I freed its crural nerve from surrounding parts, and with one hand held it supported upon the end of a probe. An assistant placed a piece of silver under its foot, and held the zinc with which it was to be touched. A sensitive plant formed the medium of communication between us. He held the bottom of its stem between his fingers, while I held the top: so that when the silver was touched by the zinc, the influence passed up the plant, and through the whole of its stem. The frog’s leg instantly contracted, and repeated its contractions every time the silver and zinc were in contact: but the leaves of the plant did not collapse; neither did they when any of its branches formed part of the circuit.

I must, however, confess that the plant, upon which this experiment was made, had been kept through the winter. With a young one the result might possibly be different; but such an one I have not yet had it in my power to procure.

The torpedo does not appear at all affected by the influence which itself produces. Animals, in which Galvani’s phenomena are produced, are strongly affected. From this circumstance, and still more from the presence of metals being absolutely requisite to their production, some may be induced to believe, that the influence, which causes them, is something external to animals; and that it arises from the mutual contact of the metals only. I must confess I was, for some time, inclined to entertain this opinion; and its probability appeared to be not a little increased by observing that its effects differed with the metals employed, and were strongest when their surfaces were extended, and applied horizontally to each other. I began, therefore, to suspect that it might be some hitherto undiscovered property of metals; for that it was not an electrical phenomenon, seemed still further proved by the circumstance above related. It has been demonstrated, by the very interesting discoveries of M. Volta, that, ‘wherever the capacity of holding electricity is greater, there the intensity of electricity is less’:—‘and that the capacity of a conductor is increased, when, instead of remaining quite insulated, the conductor is presented to another conductor not insulated; and this increase is more conspicuous, according as the surfaces of those conductors are larger, and come nearer to each other[^[10]].’

When, therefore, a plate of silver, communicating with the leg of a frog, was laid upon glass, and a plate of zinc was lowered horizontally upon it, the capacities of both, for any electricity which they might have contained, must have been so much increased, that no one will suspect the contractions of the frog’s leg, to have been occasioned by any discharge of the electrical fluid from them.

As little are we authorised to suppose, that the contractions were produced in consequence of the metals attracting the electrical fluid from the leg: for, since the leg was insulated, it is impossible that it should have received a new supply of electricity, after having been deprived by the metals of what it naturally possessed; and consequently, after once or twice contracting, no further contractions should have taken place: but this is contrary to the fact.

I have before shewn, that flakes of gold leaf, placed between the metals, were not affected by their approach to each other; and that, besides, a quantity of electricity, sufficient strongly to affect an electrometer, was far too weak to excite contractions in the muscles of a frog.