In order that the argument may be sufficiently clear in every part, Lapponi deemed it advisable to begin with the narration of certain historical facts bearing on hypnotism as well as on spiritism. He speaks of the facts peculiar to hypnotism and spiritism, indicating when necessary the authorities which prove, at least in part, their objective existence. He then examines the analogy and the difference between the two kinds of facts so far placed on record. Contents: hypnotism; spiritism; details about hypnotism; phenomena proper to spiritism; analogy and difference between hypnotic and spiritistic phenomena; on the nature of hypnotism and its manifestations; on the nature of spiritism and its relative manifestations; effects of hypnotic and spiritistic practices; conclusions.