The theory that all disorders, both physical and mental, have an organic basis.Those who adhere to this point of view in psychiatry hold that all psychotic disorders, and possibly the more severe neurotic disorders as well, are due to structural brain changes or biochemical disturbances of the nervous or glandular systems. The disorders include not only brain syndromes caused by infectious diseases, nutritional disorders, toxic substances, head injury, and other physical conditions, but also disorders usually classified as functional, such as schizophrenic and manic-depressive reactions.The organic viewpoint got its start in early Greek and Roman times when Hippocrates, Galen, and others ascribed mental disorders to disturbances in the brain, liver, heart, or other organs. This was a distinct advance over the prevailing view that mental illness was due to possession by demons or spirits. Little was done, however, to build on the theories of these early physicians, and demonology remained the dominant theme throughout the Middle Ages and early modern era. In 1757 Albrecht von Haller advocated the post-mortem study of brains of the insane, but the organic viewpoint was not systematically developed until Wilhelm Griesinger and Emil Kraepelin became convinced that all mental illness could be explained in terms of brain pathology. This was the prime approach in the first general period of modem psychiatry, beginning in the latter part of the nineteenth century, and it resulted in such great advances as the discovery of the effects of brain tumor, toxic conditions, syphilitic infection, arteriosclerosis, and brain injury on mental functions. It also led to the first thoroughgoing description and classification of mental illnesses and the first clear-cut triumph over a mental disorder by medical science—the successful treatment of general paresis, first by malaria therapy and later by penicillin.As a result of these discoveries, the great majority of medical men in the early part of the twentieth century accepted the organic viewpoint, and strong impetus was given to research in the fields of physiology, anatomy, neurology, and biochemistry to discover the underlying causes of all types of mental disorder. These investigations were continued throughout the period when the psychological and holistic points of view were being developed, and have contributed heavily to three types of advance. First, the discovery and tion of many organic psychoses and conditions causing mental retardation— among them, psychoses associated with nutritional disorders, glandular disorders, and infectious diseases; and mental deficiency due to encephalitis, German measles and other infections, brain injury and anoxia at birth, chromosomal anomalies, and metabolic disorders such as phenylketonuria and galactosemia.Second, physical treatments, including insulin shock, electroconvulsive therapy, psychosurgery, tranquilizers, and energizers—all of which are applied to conditions usually believed to be functional, such as schizophrenic and depressive reactions—as well as vitamins and special diets for nutritional disorders (pellagra, phenylketonuria), replacement therapy for endocrine disorders (hypothyroidism, for example), and sedatives for convulsive disorders. Third, the fuller recognition of the collaboration between physical and psychological factors in reactions to stress and in such psychophysi- ologic (psychosomatic) reactions as asthma and migraine; and the possibility that organic conditions and hereditary tendencies may be involved in the etiology of schizophrenia and manic- depressive reactions. See ETIOLOGY, GRIESINGER, KRAEPELIN, HIPPOCRATES, GALEN.