Siegal investigates amnesia and the various forms of memory impairment in order to clarify the differential diagnosis and therefore the treatment of these conditions. Characteristics are given of the disturbances in this sphere as they occur in both the psychogenic and organic disorders of retentivity. Among the psychogenic situations which may bring about such impairment, Siegal discusses various degrees of hysterical dissociation, somnambulism, and malingering. Among the organic disorders he discusses the symptoms and pathologic physiology of head trauma, dementia paralytica, Korsakoff's psychosis (which may be simulated by brain tumor), arteriosclerosis, senile psychosis, epilepsy, and the encephalopathies of pugilists.