Johann Lukas Schonlein of Bamberg, Germany was the founder of the Natural History School of medicine, the goal of which was to see medicine studied in the same way that descriptive botany and zoology are studied. As Schonlein's career progressed from Wurzburg to Zurich to Berlin, his medical theories passed from parasitic, to nosologic, to scientific, paralleling the developmental phases of the Natural History School. Schonlein is remembered as a man of rather eccentric character. It is said that in his later years in Berlin, he would occasionally assume the character of a recluse, and deny himself to patients whenever it suited his fancy. (Medical historians have pointed out, however, that such coarseness in the treatment of patients was at the time in vogue). As a result, although Schonlein's scientific abilities have never been in dispute, some of his critics have labeled him a boor.

Inspired by Canfolle's classification of plants, Schonlein, his pupil Carl Canstatt, and Conrad Heinrich Fuchs began to make arbitrary classifications of disease based on a hazy system of fundamental divisions. Some of Schonlein's classifications now seem whimsical, such as his forcing gangrene of the uterus into the class neurophlogoses (inflammation of the nerves), and cholera into the category of catarrhs (excessive mucus discharge).

Schonlein is perhaps best remembered for being the first to lecture in German instead of Latin (1840) at the clinic at the Charité in Berlin, and for his introduction of modern clinical teaching in Germany; the latter included examinations of the blood and urine, chemical analysis, auscultation, percussion, and microscopic investigations. Although he was not a prolific writer, he nevertheless left notable contributions to the field of medicine; these included his observation of triple phosphates in the excreta of typhoid fever (1836), his description of peliosis rheumatica (Schonlein's disease, 1837), his discovery of the parasitic origin of favus (Achrorion Schonleinii, 1839); his differentiation of two types of typhus (typhus abdominalis and typhus exanthematicus, 1839); and his coining of the phrase hemophilia for hemorrhagic diathesis.