Rudolf Ludwig Karl Virchow (1821-1902) was one of the most prominent physicians of the 19^th century. He was a pioneer in introducing the concept of the pathological processes of disease, and emphasized that disease originated from individual cells rather than generally from organs or tissues as previously thought. In the 1840s he described one of the earliest cases of leukemia and went on to make many more pathologically based observations of tumorigenesis. Virchow trained many young scientists in pathology and medicine at the time, and in many ways could be considered a "Godfather of Pathology".

Paul Langerhans (1847-1888) published his doctoral thesis in 1869 describing a subset of pancreatic cells, now named the islets of Langerhans. Islets of Langerhans contain insulin producing beta cells which are of fundamental importance to diabetes research today. Also while still a medical student working in Virchow"s laboratory in Berlin, in 1868 he published a description of structures in human skin, now called Langerhans' granular layer and Langerhans' stellate corpuscles. The former of these structures contains the "Langerhans' cells" now found to be antigen presenting cells in tumor immunology.