Schwann, Theodor 1810-82
German physiologist

Born in Neuss, he was educated in Cologne and studied medicine, graduating in Berlin in 1834. He remained in Berlin for four years as assistant to Johannes M�ller, studying digestion, and isolating the enzyme pepsin from the stomach lining. He later showed the role of yeast cells in producing fermentation. Schwann also discovered the 'Schwann cells' which compose the sheath around peripheral nerve axons, and he showed an egg to be a single cell which, once fertilized, evolves into a complex organism. His most renowned work, however, was on cell theory. In a major book of 1839 he contended that the entire plant or animal was comprised of cells, that cells have in some measure a life of their own, but that the life of the cells is also subordinated to that of the whole organism. The cell theory became pivotal to 19th-century biomedicine. In 1838 he emigrated to Belgium, where he became professor at the University of Leuven, and in 1848 at the University of Li�ge.