He remained at Göttingen for a year before doing a tour of other universities and clinics, which included meeting Johann Lukas Schönlein. In 1825, Berthold decided to practise medicine in Berlin and began experimenting on the effects of coal gas and mercury on the body. Unsettled, he continued to tour Germany and France, attending the lectures of other contemporary luminaries Georges Cuvier, Étienne Geoffroy Saint-Hilaire and André Marie Constant Duméril.