Chap. IV The Method of Performing Galvanic Experiments With Frogs; With Some Conclusions Drawn From Them
Every sensible heart must be shocked with the idea of torturing defenceless animals, merely to gratify an idle curiosity. The chapter which we shall now lay before the reader is founded entirely on the assertions of other writers upon this subject; to which, however, we have not the least doubt that the fullest credit is due. But we have not chosen to prove the veracity of their statements by our own experiments, believing that any small additional knowledge we might possibly have obtained in this way, would have been purchased at too great a price—the sacrifice of feeling and humanity.
Take a living frog, and after amputating the hind legs, (for they are the best, on account of the number of joints) let the largest nerve, called the crural nerve, be laid bare, and surrounded with a slip of tin-foil, or a piece of sheet lead—then lay a piece of zinc, or other metal different from that on the nerve, in contact with the neighbouring muscles; form a communication by another piece of zinc, or other good conductor, between the metal in contact with the muscle and the armed part of the nerve, and violent contractions will be produced in the limb.
There is another method of producing these convulsions, which has been preferred on account of its simplicity.—It is by forming a communication between a nerve, armed as above, and an adjoining muscle, by a piece of zinc, without the assistance of a communicator.—This was one of the first methods of Galvanizing frogs, before the invention of the pile and trough. But since these discoveries, frogs have been made to show more violent convulsions.
We now proceed to relate some of the conclusions which have been drawn from the experiments on frogs.
1. The contractions produced in the limb of a frog are stronger the farther the metal is placed from the origin of the nerve.
2. When the metal has remained for some time on a particular part of the nerve the motion will cease; but it may be renewed by changing the position of the metal, and carrying it lower on the nerve.
3. Contractions may be produced in the prepared limb of a frog, by putting it in water, and then bringing two metals in contact with each other, at a short distance from the limb.
4. Only those muscles to which the nerves lead suffer contraction from the Galvanic influence.
5. When a contraction has taken place in any muscle, no other will follow while the metals remain in contact.—In order to renew the motions, therefore, the metals must be separated and joined again.
6. Galvanic excitement, instead of destroying the irritability of a muscle, gives it an additional support. Dr. Valli, an Italian physician, has fully confirmed this principle by the following experiment. “Having prepared the wing of a fowl, or the paw of a cat or dog, I subjected it to the customary trial. At the expiration of half an hour, I armed the other wing of the fowl, or the other paw of the cat or dog, and had recourse to my exciting arc.—The latter wing or paw, however, did not give any sign of electricity, (for he conceived the motion to be occasioned by electricity,) while the parts which had been subjected in the first instance to the experiment, still continued in a convulsed and agitated state.”
7. Galvanic experiments do not succeed so well in a room crowded with persons, as when only two or three individuals are present.
8. Galvanic contractions are more powerful the instant the animal is deprived of life, than some time after; and therefore more violent agitations can be produced in the living animal.
9. Volta concluded that Galvanism was generated by the metal, and not by the animal upon which he operated.
These are the principal remarks which we think worth noticing. If they do not content the reader, we must refer him to Wilkinson on Galvanism; where he will find a detail of almost every thing that happened in the Galvanic world till the time he wrote.