The French physician Pierre Charles Alexandre Louis (1787-1872) was the founder of the "numerical method" in medicine—that is, medical statistics— and the champion of exact observation and conservative deduction in medical studies.
The son of a rich wine merchant, P. C. A. Louis was born in the small town of Ai (Marne). He began his studies in Reims in 1807 and received his medical degree in Paris in 1813. He spent the next 6 years practicing in Russia. He had witnessed the havoc wrought by a diphtheria epidemic in Odessa in 1820, and on his return to Paris he hoped that further study might enable him to deal with such a calamity.
In Paris Louis saw that medicine had not progressed. Medical theory was not based on reliable data; physicians relied on their memory of striking cases in the discussion of diagnosis and justified their treatment on theoretical grounds. Louis thought that medicine could become a science only if it was based on large numbers of detailed observations which lent themselves to numerical analysis. He spent the years 1820-1826 making daily observations of all patients on two wards of the Charité Hospital. He did not treat them but obtained complete family and personal histories, detailed accounts of the onset and progression of their illness, and a complete autopsy report of those who died. He relied exclusively on his own observations, including negative findings and the results of treatment. All data were carefully recorded and whenever possible presented in statistical tables, which gave the actual number of cases. This work led to several publications, including a book on consumption (1825) and a book on typhoid fever (1829), which were translated into English. His Researches on the Effects of Bloodletting (1835) demonstrated that the benefits claimed for this popular mode of treatment were unsubstantiated.
Louis's influence spread through the foreign students who flocked to Paris, attracted by his approach. His American students propagated Louis's numerical method in the United States, where the emphasis on the collection of observable, detailed data and their statistical analysis was readily appreciated and became a guideline for medical research.
Although Louis's work had been largely responsible for overthrowing the old theory, recognition of his importance in Paris was not unanimous. He was not elected to the faculty. He continued his teaching at the hospitals and became a member of the Academy of Medicine and, in 1832, president of the Society for Medical Observation in Paris, founded by his admirers and students. Out of a similar society founded in Boston grew the concept of the clinical-case conference.
Louis lived to see the rising importance of laboratory research for medicine. Medical science could not rest completely on the statistical analysis of bedside observations and autopsy findings, as he had proposed. But his demand for reliable quantifiable data in clinical medicine and for the statistical determination of the efficacy of treatment became one important basis of modern medicine.
There is little biographical material on Louis in English. Henry I. Bowditch eulogized him in Brief Memories of Louis (1872). His place in the development of medical statistics is defined in Charles Singer, A Short History of Medicine (1928; 2d ed. with E. Ashworth Underwood, 1962). An excellent description of contemporary medicine and of the context in which the work of Louis developed is in Erwin H. Ackerknecht, Medicine at the Paris Hospital, 1794-1848 (1967).