 He returned to Bordeaux in 1886 and the following year he received his medical doctorate with a prize-winning thesis on leprosy.In 1895 he began work at the Pasteur Institute in Paris and while working in the laboratory of Elie Metchnikoff, he was the first to provide a comprehensive description of the sexual reproductive processes of Coccidia.This work provided experimental support for the theory of evolutionary dimorphism which had been put forward by R. Pfeiffer.