This is a fascinating study of the physiological state that occurs when a person believes some outside force -- usually a god or devil -- is in possession of his soul. From his work with traumatized soldiers in World War II, Sargant came to believe that this state and its abreactive (or cathartic) cure -- produced by drug-induced ""recollection"" of an incident, either real or imaginary -- was physiologically identical to that induced by faith healers and witch doctors. This is a fascinating survey of the systems of belief that employ various ""hypnotic"" or ""suggestive"" means of invoking ""spirit"" possession to induce radical changes of behavior in their adherents -- from the followers of Wesley, to the practitioners of voodoo, to the psychiatrist who imposes his ideas upon an unduly susceptible patient. The beliefs and forms of stimulation of stress (drugs, alcohol, sex, music, dancing, prayer, reliving past traumas) prior to the ""post-hypnotic"" period may differ, and so may the subsequent imprinted content of beliefs -- but the catharsis itself is undeniable, as are the possible dangers arising from the unscrupulous use of this power -- as manifested, variously, by witchcraft trials and Hitler's influence in Germany. The author's purpose is not so much a condemnation of faith -- which he considers psychically necessary, if not rationally justifiable -- as it is a warning to better understand, and therefore control, possibly irrational forms of behavior.