In 1794 Galvani proves that the frog contractions may occur either by using a monometallic arc, or by placing in direct contact the crural nerves with the muscles of the frog legs. Volta, observing that in the Galvani experiments it is necessary to humidify with saliva or blood the contacts between nerve and muscle, hypothesizes that also the second class conductors (“humid conductors”) could generate electricity. In 1796 he eliminates the necessity of using the frog as detector: by using the condenser electrometer, which he had just invented, he shows the unbalance of the electric fluid in the contact of two different metals. At the end of 1799, he invents the pile, the instrument which makes him famous.
Galvani performs a last experiment (described in a letter to Spallanzani and considered by Du Bois Reymond as the fundamental experiment of electrophysiology), in which the contact is obtained connecting the two frog legs only by the crural nerves, thus eliminating the heterogeneity of different tissues.
1) The new Galvani experiment: the frog leg contracts even connecting directly nerve and muscle, without a metallic arc.2) New comparison between the theories of Galvani and Volta. For Volta the sequence nerve-muscle-fluid has an active function as an electromotor, it moves the electric fluid and generates the contraction.
3) From Heilbron, “...reducing the frog to two separate legs each attached to its nerve, both nerves cut free from the spinal stump, he bent one into an arc and, with a stick of glass moved the other so as to cross the first in two places. The leg attached to the second nerve twitched.
