German cytologist and physiologistTheodor Schwann, a German cytologist and physiologist, was born in Neuss, Germany on December 7, 1810. At the University of Berlin, Schwann studied medicine under Johannes Mueller, who taught many 19th century German physiologists. In 1836, while at the University of Berlin, he discovered pepsin, an enzyme responsible for digestion, in extracts from the stomach lining. Pepsin was the first enzyme prepared from animal tissue. In 1837, Schwann showed conclusively that something in the air that was destroyed by heat caused putrefaction, but the air itself did not.
Schwann became professor at the Belgium Universities of Louvain, in 1838, and Liège, in 1848. While there, he found that sugar and starch fermentation were the result of life processes, investigated muscular contraction and nerve structure, and discovered the striated muscle of the upper esophagus and the myelin sheath of peripheral axons, called Schwann cells. Schwann coined the term "metabolism" to describe the chemical changes that take place in living tissue and formulated the basic principles of embryology by observing that an egg is a single cell that will eventually develop into a complete organism.
Schwann, together with Matthias Schleiden, developed the cell theory in 1839, which identified cells as the fundamental particles of plants and animals. Schwann and Schleiden recognized that some organisms are unicellular while others are multicellular. They also recognized membranes, nuclei and cell bodies to be common cell features and described them by comparison of various animal and plant tissues. These observations and the cell theory were included in Schwann’s Microscopical Researches into the Accordance in the Structure and Growth of Animals and Plants published in 1839.
Schwann’s animal cell theory stimulated a great deal of research. He is now recognized as the founder of modern histology. Theodor Schwann died in January, 1882, at the age of 71.