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Schwann, Theodor

cells theory cell animal

[shvahn] (1810–82) German physiologist: the major figure in the creation of cell theory in biology.

Schwann went to school in Cologne and then studied medicine, graduating in Berlin in 1834. He stayed there as assistant to for 4 years, when most of his best work was done. Early in this period he studied digestion, and isolated from the stomach lining the proteolytic enzyme pepsin; it was the first enzyme to be isolated from an animal source. He went on to study fermentation and showed in 1836 (independently of ) that it was a result of the life processes of the yeast cells; this led him to doubt the idea of spontaneous generation, and so he repeated and improved the experiments on this done by . He confirmed that no microorganisms appeared and no putrefaction occurred in a sterile broth to which only sterile air was admitted. His results did not prevent all belief in spontaneous generation, which persisted until work a few years later.

Schwann’s work on fermentation led to quite vicious (if comical) attacks in papers by the chemists , to the extent that Schwann saw no prospect of a career in Germany, and in 1838 he emigrated to Belgium. There he became a mystic, solitary and depressed, and did little more in science.

He had in 1838 discovered the Schwann cells composing the myelin sheath around peripheral nerve axons; and he showed that an egg (whether large or small) is a single cell which when fertilized develops into a complex organism, a central idea in embryology. Schwann’s most famous work, on the cell theory, began through discussions with his friend, the botanist , who had argued that all plant structures are cells. Animal tissues are more difficult for the microscopist, being soft, of low contrast and subject to rapid decay; and even more than plant cells, those of animals show great diversity. However, Schwann became convinced that animal tissues, like plants, are based on cells and he became, with Schleiden, a principal advocate for the cell theory, whose main points are that (1) the entire plant or animal is made up of cells or of substances thrown off by cells; (2) the cells have a life that is to some extent their own; and (3) this individual life of the cells is subordinated to that of the organism as a whole. This theory, well defined in Schwann’s book in 1839, soon became dominant in biology; the cell has been seen ever since as a natural unit of form, of function and of reproduction, at the microscopic level. This last dominance is summarized in phrase of 1855, ‘all cells arise from pre-existing cells’. Virchow saw the study of affected cells as central to pathology and physiology.

In shaping much biological research, the theory was beneficial; but it was unfortunate that Schwann accepted the older Schleiden’s erroneous idea that new cells are formed by ‘budding’ from a nucleus, which was to prove a false trail for many biologists for half a century. Neither of them had any notion of the formation of cells by division; and neither regarded the cytoplasm as important.

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