Examination of contemporary medical conference papers reveal that the German clinician, Carl Wernicke, conducted a unique on-going inquiry into psychiatric nosology. Wernicke was searching for what he called the elementary symptoms of mental disorder, or, in other words, the single psychopathological feature, from which all others arose. From 1892 onwards, he postulated a variety of such elementary symptoms. Wernicke's theory makes sense in terms of such categories as anxiety-psychosis and hallucinosis. His work contrasts with that of Kraepelin and also with modern diagnostic criteria. Neither Wernicke nor his followers pursued the theory of elementary symptoms, but an examination of his work sheds light on modern ideas about diagnosis.