Citing evidence from an ancient work by Zheng Xuan (127–200), Su believed that physicians of the ancient Zhou Dynasty (1046–256 BC) used realgar as a remedy for ulcers. As believed in Su's day, the "five poisons" used by Zhou era physicians for this purpose were thought to be cinnabar, realgar, chalcanthite, alum, and magnetite. Su made systematic descriptions of animals and the environmental regions they could be found, such as different species of freshwater, marine, and shore crabs. For example, he noted that the freshwater crab species "Eriocher sinensis" could be found in the Huai River running through Anhui, in waterways near the capital city, as well as reservoirs and marshes of Hebei. Su's book was preserved and copied into the "Bencao Gangmu" of the Ming Dynasty (1368–1644) physician and pharmacologist Li Shizhen (1518–1593).