How is knowledge about people produced? What thinking styles underpin experiments on humans? What ideas does the experimental toolkit bring with it? Building on the reflections of the Polish physician and sociologist Ludwik Fleck regarding the emergence and development of a scientific fact from 1935, the book explores how humans became the subject of research actions since the mid-18th century. The individual case studies focus not only on the methodological translation of Fleck's thinking into a historiographical sociology of knowledge but also on the connection to his work as a serologist and his experiences in the concentration camps of Auschwitz and Buchenwald. Thus, a compendium is created that unites biographical, empirical, and methodological aspects from the life and work of Ludwik Fleck into a sociology of knowledge study.