Professor von Gudden was the judge in Nissl's college-essay competition, and he was so impressed with the study that he offered Nissl an assistantship at the Furstenried castle southwest of Munich, where one of his responsibilities would be to care for the mad Prince Otto. Nissl accepted, and remained in that post from 1885 until 1888. There was a small laboratory at the castle, which enabled Nissl to continue with his neuropathological research. In 1888 Nissl moved to the Institution Blankenheim. In 1889 he went to Frankfurt as second in position under Emil Sioli (1852–1922) at the Städtische Irrenanstalt. There he met neurologist Ludwig Edinger and neuropathologist Karl Weigert, who was developing a neuroglial stain. This work motivated Nissl to study mental and nervous diseases by relating them to observable changes in glial cells, blood elements, blood vessels and brain tissue in general.