Physician and physicist Luigi Galvani, professor of anatomy at the University of Bologna, observes that the muscles of dissected frog legs contract when the nerve is touched with a metal scalpel while an electrostatic machine operates nearby, or when the frog is connected between two different metals. Galvani interprets the phenomenon as evidence of an "animal electricity" intrinsic to living tissue, publishing his findings in 1791. His proposal triggers one of the most fertile scientific disputes in the history of physics: Alessandro Volta, skeptical of the biological interpretation, repeats Galvani's experiments and concludes that the electricity comes not from animal tissue but from the contact between two different metals in a moist medium — the frog acted only as a sensitive detector, not as a source. This direct disagreement drives Volta to abandon biological specimens and build, in 1800, the voltaic pile, the first stable, continuous electric-current source in history.