Schwann, Theodor

(born Dec. 7, 1810, Neuss, Prussia—died Jan. 11, 1882, Cologne, Ger.) German physiologist.

He founded modern histology by recognizing the cell as the basic unit of animal structure. A year after Mathias Jacob Schleiden, a colleague Schwann knew well, advanced the cell theory for plants, Schwann extended it to animals. While investigating digestive processes, he isolated a substance responsible for digestion in the stomach, the first enzyme prepared from animal tissue, and named it pepsin. He studied muscle contraction and nerve structure, discovering the striated muscle in the upper esophagus and the myelin sheath covering nerve cells. He coined the term metabolism, identified the role played by microorganisms in the decomposition of organic matter, and formulated the basic principles of embryology by observing that the egg is a single cell that eventually develops into a complete organism.