203

ESTRATTO
DELLA LETTERA A TIBERIO CAVALLO

22 Maggio 1793

Extract of a letter from Mr. Alexander Volta, F. R. S., Professor of Natural
Philosophy in the University of Pavia, to Mr. Tiberius Cavallo, F. R. S.,
containing some further remarks on the Influence discovered by
Mr. Galvani.

Read December 5, 1793.

I have varied, in many ways, the experiments respecting the taste excited
upon the tongue, by the application of the two metals, Tin and Silver, and of
other metals dissimilar in themselves; for this dissimilarity is a most essential
condition. And one of the most remarkable circumstances I have observed is,
that if, instead of applying the tin to the tip of the tongue, and thesilver to the
back part of it, you apply contrariwise, the tin upon the back part of it, and the
silver upon the tip, as soon as you make a communication between these me-
tallic coatings, the tip of the tongue will not, as before, perceive an acid taste,
but an acrid burning taste, which may be called alkaline. Yet all the combi-
nations of metals capable of exciting the acid taste are not capable of exciting
the alkaline one, by inverting the experiment in the manner described, but
only those which excite a very strong acid taste, such as Zinc or Tin or Lead,
opposed to Silver, Gold, Platina, or Mercury. All the other combinations, by
means of which the acid taste is obtained only in a weak or moderate degree,
as by placing Iron or Copper in opposition either to Silver or Gold, or to lead,
or Tin, are inactive with respect to the alkaline taste. Omitting for the present
all enquiries into the reasons why it is so much more difficult to excite the
alkaline taste than the acid one, by means of the forementioned expedient
of metallic coatings; I shall lead you to reflect upon the inferences which must
necessarily be drawn from this diversity of sensation. The nerves of taste are
differently affected by the current of Electric fluid drawn into circulation by
the virtue and power of two different metals applied to the tongue; the nervous
papillae, which are numerous and almost naked, at, and about the tip of the