Schwann, Theodor (1810–1882)

German physiologist who, with Matthias Schleiden, is credited with formulating the cell theory, one of the most fundamental concepts in biology. Schwann also did important work on digestion, fermentation, and the study of tissues.

Schwann was born in Neuss and studied at Bonn, Würzburg, and Berlin. He spent 1834–38 working as an assistant to German physiologist Johannes Peter Müller at the Museum of Anatomy in Berlin. In 1839, however, Schwann's work on fermentation attracted so much adverse criticism that he left Germany for Belgium, where he was professor at Louvain 1839–48 and then at Liège.

In 1836, Schwann isolated from the lining of the stomach a chemical responsible for protein digestion, which he called pepsin. This was the first enzyme to be isolated from animal tissue.

Schwann showed 1836–37 that the fermentation of sugar is a result of the life processes of living yeast cells (he later coined the term ‘metabolism’ to denote the chemical changes that occur in living tissue).

In Mikroskopische Untersuchungen über die Übereinstimmung in der Struktur und dem Wachstum der Tiere und Pflanzen/Microscopical Researches on the Similarity in the Structure and Growth of Animals and Plants 1839, he concluded that all organisms consist entirely of cells or of products of cells and that the life of each individual cell is subordinated to that of the whole organism. In addition, he noted that an egg is a single cell that eventually develops into a complex organism.