John Walsh's research on electric fish, carried out between 1772 and 1775, proved fundamental for demonstrating that electricity might be involved in animal physiology, and, moreover, in favouring a period of great progress in both the physiology and physics of electrical phenomena. However, Walsh is hardly known to modern neuroscientists and is largely neglected by science historians also. One of the reasons for this neglect is that he never published his 'crucial experiment', that is the production of a spark from a discharge of the electric eel.