This article examines the science of electrophysiology developed by Emil du Bois-Reymond in Berlin in the 1840s. In it I recount his major findings, the most significant being his proof of the electrical nature of nerve signals. Du Bois-Reymond also went on to detect this same ‘negative variation’, or action current, in live human subjects. In 1850 he travelled to Paris to defend this startling claim. The essay concludes with a discussion of why his demonstration failed to convince his hosts (...) at the French Academy of Sciences. (shrink)