P. C. A. Louis and the birth of clinical epidemiology.

Pierre Charles Alexandre Louis (1787-1872) has been the direct or indirect mentor of influential U.S. and English scientists in public health, epidemiology, medicine, and biostatistics during the 19th and 20th century. Louis was primarily a clinician, but his name has been more closely associated with the history of epidemiology. There is an imbalance between the fame of Louis's scientific contribution and the scarcity of in depth analyses of his work. The controversy related to the usage of bloodletting for treating inflammatory diseases is one of the most famous episodes of Louis's work. A modern analysis of Louis's data confirms his original conclusions; that is, early bloodletting seems to reduce the duration of a pneumonitis disease in patients who survive from this disease but may also increase the overall short-term mortality. Some basic algebraic mistakes in computations of means tend to attenuate the verdict against bloodletting, but these are trivial relative to the rigor of the overall demonstration and to Louis's methodological contribution to clinical observation. Louis firmly belongs to the history of epidemiology. He deserves a similar place in the history of medicine.