Theodor Schwann
Theodor Schwann (December 7, 1810 in Neuss, Prussia - January 11, 1882, in Cologne) was a German physiologist, histologist and cytologist.
Among his many contributions to biology there was the development of cell theory, the discovery of Schwann cells in the peripheral nervous system, the discovery and study of pepsin, the discovery of the organic nature of yeast and the invention of the term metabolism.
Vitalism and Germ theory
Schwann was thus the first of Müller's pupils who broke with the traditional vitalism and worked towards a physico-chemical explanation of life.
Cell theory
Once, when Schwann was dining with Schleiden (who in 1837 had viewed and stated that new plant cells formed from the nuclei of old plant cells) in 1837, the conversation turned on the nuclei of plants and animal cells. Schwann remembered seeing similar structures in the cells of the notochord (as had been shown by Müller) and instantly realized the importance of connecting the two phenomena. The resemblance was confirmed without delay by both observers, and the results soon appeared in his famous Microscopic Investigations on the Accordance in the Structure and Growth of Plants and Animals [scanned source](Berlin, 1839; trans. Sydenham Society, 1847). Thus cell theory was definitely constituted. In the course of his verification of cell theory, in which Schwann traversed the whole field of histology, he proved the cellular origin and development of the most highly differentiated tissues including nails, feathers, and tooth enamel.
His generalization became the foundation of modern histology, and he was (whose cellular pathology was an inevitable deduction from Schwann) afforded the means of placing modern pathology on a truly scientific basis.