Schwann, Theodor (1810–1882), a German physiologist and anatomist. Schwann and the German botanist Matthias Schleiden established one of the basic ideas in modern biology—the theory that all living organisms are made up of cells and cell products. Schleiden developed the cell theory for plants in 1838, while Schwann extended the theory to animals and elaborated it in 1839. Schwann also discovered the digestive enzyme pepsin and made important contributions to the study of fermentation and putrefaction.
Schwann was born in Neuss. He studied under Johannes Müller at the universities of Bonn and Berlin, receiving his medical degree from Berlin in 1834, Schwann taught anatomy at the universities of Louvain and Liège, and in 1858 he became professor of physiology at Liège.