VOL. LXXXV.] PHILOSOPHICAL TKANSACTIONS. 553 



of the same metal were to possess precisely the same degree of purity, they 

 would if used together be entirely inert, in regard to the excitement of mus- 

 cular contractions; in confirmation of which, many persons have asserted, that 

 they have never observed muscles to move by the employment of 1 such pieces 

 of metal, or of 1 piece of metal having the same fineness through its whole 

 extent. Others however, on the authority of their observations, have maintained 

 the contrary; and to the testimony of these I must add my own, as I have fre- 

 quently seen muscular motions produced not only by a single metal, but likewise 

 by charcoal alone. Nor will credit be denied me on this head, after I have 

 pointed out certain practices, by which any one of those substances may at plea- 

 sure be made to produce contraction. The most proper way of mentioning 

 these practices, will perhaps be, to relate in what manner they came to my 

 knowledge. 



I one day placed a piece of silver, and another of tin-foil, at a small distance 

 from each other on the crural nerve of a frog, and then applied a bent silver 

 probe between them, with the view of ascertaining, whether contractions would 

 arise, agreeably to Mr. Volta's declaration, from the influence passing through a 

 portion of the nerve without entering the muscles. Having finished this experi- 

 ment, I immediately after applied the same probe between the silver coating of 

 the nerve and the naked muscles, and was surprized to see these contract. A 

 2d and 3d application were followed by the same effects, but further applications 

 were of no avail. It then occurred, that motions might re-appear, if I again 

 touched the 2 coatings with the probe, and the event proved the conjecture to 

 have been fortunate; for after ever}' application of the probe to the 2 coatings, 

 contractions were several times excited by it. The fact being thus established, 

 that under certain circumstances contractions could be produced by silver alone, 

 it next became a subject of inquiry, whether this was owing to any disposition of 

 the muscles and nerve, which had been induced on them by Mr. Volta's experi- 

 ment, or whether, the condition of the muscles and nerve being unaltered by 

 that experiment, the silver had gained some new property by coming into contact 

 with the tin-foil. The point in doubt was soon determined, by applying the 

 probe to a piece of tin-foil, which had no connection with any part of the ani- 

 mal; for when this was done, it was again enabled to produce contractions. As 

 these experiments however frequently did not succeed when made on other frogs, 

 I afterwards varied the metals, and found in consequence, that zinc, particularly 

 if moistened, communicated an exciting power pretty constantly to silver, gold, 

 and iron. If any of these metals were slightly rubbed on the zinc, they almost 

 always acquired such a power. 



It will perhaps be thought, from the last-mentioned circumstance, that in 



VOL. XVII. 4 B 



