Illustration of Italian anatomist Luigi Galvani's (1737-1798) experiments demonstrating contractions of the muscles by electrical stimulation. The phenomenon was first noticed when his assistant touched an exposed nerve of the frog with a metal scalpel just as an electrostatic generator was emitting sparks. Volta later showed that the electricity came from the metals, not the muscles. Illustration taken from Galvani's De viribus electricitatis in motu musculari commentarius, 1792.