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...