The 18th century was an age of transition. The time-honored neuropsychology of classical and medieval times, mechanized in Descartes' hydraulic neurophysiology, was undermined by microscopical observations and careful physiological experimentation. Yet it was not until the very end of the century, when work on electric fish and amphibia began to suggest an acceptable successor to "animal spirit," that the old understanding of human neurophysiology began to fade. This chapter traces this slow retreat from the iatrophysics of the early part of the century, with its hollow nerves and animal spirits, through a number of stop-gap explanations involving mysterious subtle fluids or forces described variously as irritability, élan vital, vis viva, vis insita, the spirit of animation etc., or perhaps involving vibrations and vibratiuncles and mysterious magnetic effluvia, to the dawning electrophysiology of the end of the century and the beginning of the next. This developing understanding filtered slowly through to affect medical education, and the 18th century saw the development of strong medical schools at Leiden, Edinburgh, Paris, Bologna and London. Associated with these developments there was a great increase, as a well-known physician looking back at the beginning of the following century noted, in a class of diseases that had little concerned physicians in the preceding century - "nervous disorders.".