The German doctor Rudolf Virchow proposed that all cells result from the division of previously existing cells, and this idea became a key piece of modern cell theory. Virchow also founded the discipline of cellular pathology based on the idea that diseases do not affect an entire organism but are instead localized to certain groups of cells. This made it easier to diagnose and treat diseases.
Virchow was appointed as the chair of pathological anatomy at the University of Wurzburg in 1849 and carried out a great deal of research. In 1855, he first published his idea that all cells arise from other cells. Rather than being formed by the action of a life force or spontaneously crystallizing from other matter, Virchow argued that cells only formed from the division of other cells. This idea is one of the key principles of cell theory, along with the idea that the cell is the basic unit of organization for living organisms.
During this period, he also proposed the basic ideas of cellular pathology. Rather than being the result of changes in an organism as a whole, Virchow believed that diseases result from changes in specific groups of cells. By examining cells for certain changes or alterations, doctors can more precisely identify and diagnose a disease.