A further important contribution is to have given his friend, the psychiatrist Emil Kraepelin (1856-1926), important ideas to the differentiation and systematisation of mental illness. Moebius had only made one, on the causes of diseases based classification of nervous and mental diseases. Its subdivision in endogenous and exogenous errors has long been preserved and was leading the way for the psychiatry and neurology of the 20th century. Endogenous errors established in the nervous system itself, manifested as degeneration. In the long term Möbius thus paved to way for eugenics and the crimes of psychiatric and neurological disease in German Nazism. Also, Möbius syndrome bears his name, which he first described in 1888; and he pointed the way to understanding the cause of the endocrinological disorder Graves' disease.