Illustration showing the various experiments conducted by Italian physicist Luigi Galvani in 1791 on frog muscle and electricity. The result was that the muscles in the frog's leg twitched, indicating the presence of electricity. Galvani believed it resided in the muscle and declared for animal electricity. Some years later, Volta showed that the electric current was in fact set up by two metal rods in contact. This engraving was taken from Galvani's De viribus electricitatis in motu musculari commentarius, 1791.