which incites the Muscles of Animals to contract . 249 
stance of motion being produced by the mere application of 
a single metal to a muscle and its nerve. I shall, therefore, 
defer treating this case, till I speak of the conditions which 
are necessary for the- excitement of the influence. Nor will 
the present subject suffer from this delay ; for if it be shewn, 
as I expect it will, that, when two or more metals are used, the 
muscle and its nerve do not furnish any thing but what every 
other moist substance is equally capable of doing, it will, I 
think, be readily granted, that they can give nothing more, 
when only one metal is applied to them. 
In regard to the second case, Mr. Volta has affirmed, or 
has said at least, what I regard as equivalent to affirming, that, 
when two metals are employed, the influence in question is 
excited by their action upon the mere moisture of the parts 
which they touch. The proofs, however, of this assertion were 
reserved for some future communication. But as more than 
two years have now elapsed since they were promised, and 
none have been given to this Society, or have appeared, as far 
as I can learn, in any other way, I hope I shall not be thought 
precipitate, if, at this distance of time, I offer one of the same 
point, which seems to me both plain and decisive. 
It is known, that, if a muscle and its nerve be covered with 
two pieces of the same metal, no motion will take place upon 
connecting 'those pieces, by means of one or more different 
metals. After making this experiment one day, I accidentally 
applied the metal I' had used as the connector, and which I 
still held in one hand, to the coating of the muscle only, 
while with the other hand I touched the similar coating of 
the nerve, and was surprised to find that the muscle was im- 
mediately thrown into contraction. Having produced motions 
