In the spring of 1784 the Marquis of Puységur, a great landowner and colonel in an artillery regiment, was called to the bedside of Victor, the son of his steward, who was suffering from pneumonia. Puységur was a follower of the new holistic medicine taught in an atmosphere of intense enthusiasm and scandal by Franz-Anton Mesmer, an Austrian doctor who had been living in Paris for several years. As a disciple of Mesmer, he intended to direct his ‘vital fluid’ onto the young patient, by means of ‘magnetic passes’, to provoke ‘spasms’ which would lead to a calm state and an improvement in health. But things did not go as anticipated. Instead of displaying the anticipated spasms, the young Victor sank into a strange state of unconsciousness which, at first sight, resembled a deep sleep. Then he revived once more and came to life with a new personality. Freed from his inhibitions, he no longer spoke his habitual dialect, but the French of aristocrats, and he had no hesitation in berating his school teacher, whose secret thoughts he appeared to be able to read. Finally, he forecast the stages by which he would be cured and the remedies which would be suitable for him. Puységur wrote down all these strange facts and the following year he published a report which caused a sensation. Soon, throughout France, somnambulists appeared and observations about their subjects gathered. From that time onwards, the incomprehensible facts apparently evident in ‘provoked’ or ‘artificial somnambulism’ and also in ‘magnetic sleep’ - such expressions were used by Puységur and his followers for the state that he had just discovered - were to give rise to huge controversy. The Marquis of Puységur triggered the development nineteenth century of a movement of reflections and practices which have generally been referred to by the expression ‘animal magnetism’, invented by Mesmer. On the eve of the Revolution and throughout the nineteenth century this movement held a real fascination for philosophers, writers, and scholars. But there has been a tendency to overlook this episode in European culture, which has ultimately become a “lost continent” in our own period.