On the evening of April 21, 1896, Sigmund Freud presented a paper before his colleagues at the Society for Psychiatry and Neurology in Vienna, entitled "The Aetiology of Hysteria". Using a sample of 18 patients—male and female—from his practice, he concluded that all of them had been the victims of sexual assaults by various caretakers. The cause of the patient's distress lay in a trauma inflicted by an actor in the child's social environment. The source of internal psychic pain lay in an act inflicted upon the child from outside. This led to his well-known ‘seduction theory’.