So early as 1462 Pomponatus of Mantua came to the conclusion, in his work on incantation, that all the arts of sorcery and witchcraft were the result of natural operations. He conceived that it was not improbable that external means, called into action by the soul, might relieve our sufferings, and that there did, moreover, exist individuals endowed with salutary properties; so it might, therefore, be easily conceived that marvellous effects should be produced by the imagination and by confidence, more especially when these are reciprocal between the patient and the person who assists his recovery. Two years after, the same opinion was advanced by Agrippa in Cologne. "The soul," he said, "if inflamed by a fervent imagination, could dispense health and disease, not only in the individual himself, but in other bodies." However absurd these opinions may have been considered, or looked on as enthusiastic, the time has come when they will be gravely examined. That medical professors have at all times believed the imagination to possess a strange and powerful influence over mind and body is proved by their writings, by some of their prescriptions, and by their oft-repeated direction in the sick-chamber to divert the patient's mind from dwelling on his own state and from attending to the symptoms of his complaint. They consider the reading of medical books which accurately describe the symptoms of various complaints as likely to have an injurious effect, not only on the delicate but on persons in full health; and they are conscious how many died during the time of the plague and the cholera, not only of these diseases but from the dread of them, which brought on all the fatal symptoms. So evident was the effect produced by the detailed accounts of the cholera in the public papers in the year 1849, that it was found absolutely necessary to restrain the publications on the subject. The illusions under which vast numbers acted and suffered have gone, indeed, to the most extravagant extent; individuals, not merely single but in communities, have actually believed in their own transformation. A nobleman of the court of Louis XIV. fancied himself a dog, and would pop his head out of the window to bark at the passengers; while the barking disease at the camp-meetings of the Methodists of North America has been described as "extravagant beyond belief." Rollin and Hecquet have recorded a malady by which the inmates of an extensive convent near Paris were attacked simultaneously every day at the same hour, when they believed themselves transformed into cats, and a universal mewing was kept up throughout the convent for some hours. But of all dreadful forms which this strange hallucination took, none was so terrible as that of the lycanthropy, which at one period spread through Europe; in which the unhappy sufferers, believing themselves wolves, went prowling round the forests uttering the most terrific howlings, carrying off lambs from