The article deals with the course of life and scientific activity of founder of conception of quantitative approach in clinical medicine of Pierre-Charles-Alexandre Louis. The period of his life and work in Russian Empire was investigated for the first time. The name of Louis’s follower in the Russian state was found — Ivan Andreevich Petrovskiy (1829–1903). It was highlighted the biography of Petrovsky and information about his book (1865) was introduced into the scientific circle for the first time. The book deals with elaboration of the Louis’s concept on application of quantitative approach in clinical medicine.
