[Degeneration theory in psychiatry].

Degeneration (called "dégénérescence" in French and "Degenerationslehre" in German terminology) as a theory of human retrogression manifested by degenerative signs in individuals, was a major factor in medicine and especially in psychiatry during the second half to the 19th century and at the beginning of the 20th century. Theories of retrogression seemed to supply conclusive hypothetic explanatory models for a wide variety of deviations from so-called "standard" values of health criteria for neurological diseases, brain disorders and mental diseases. The theory of degeneration, or retrogression, was closely interlinked with the complex ideological pattern that formed the background of philosophy and natural science during the nineteenth century. The theory of degeneration experienced mutual interaction and stimulation by the interplay with various other theories that were "en vogue" at that time, such as the development of positivistic natural science and of the theory of evolution, which in turn gave birth to the theories of social Darwinism, eugenics, genetics and to the development of biological-vitalistic approaches. In contrast with the other fields of medicine, anatomic pathology was unable to uncover any aetiological linkups for the various types of mental diseases. Hence, the theories of degeneration seemed to offer a conclusive concept for the genesis of mental disorders. The concept of degeneration was based on the theory of polymorphism which in turn positioned the wide range of neurological, mental and brain diseases within the descending series of progressing degeneration.