During the nineteenth century, scientific medicine was profoundly influenced by major advances in several fields: in microbiology, by Pasteur; in the formulation of the tissue theory of disease, by Bichat; and in the cell theory of pathology, by Virchow. The roots of biological psychiatry can be traced to the early nineteenth century, when Bayle introduced the illness concept for mental disorders with his thesis on general paralysis.1 In this work he showed that several mental patients had clinical symptomatology associated with pathological lesions in the central nervous system. The criteria used for the identification of patients with general paralysis were purely medical, that is, symptomatology that was causally related to organic lesions and that followed a predictable course.2