At the outbreak of the Franco-Prussian War in 1870, he joined the French Army. At the age of 29 he became Chair of Military Diseases and Epidemics at the École de Val-de-Grâce. At the end of his tenure in 1878 he worked in Algeria, where he made his major achievements. He discovered that the protozoan parasite "Plasmodium" was responsible for malaria, and that "Trypanosoma" caused trypanosomiasis or African sleeping sickness. In 1894 he returned to France to serve in various military health services. In 1896 he joined Pasteur Institute as Chief of the Honorary Service, from where he received the Nobel Prize. He donated half of his Nobel prize money to establish the Laboratory of Tropical Medicine at the Pasteur Institute. In 1908, he founded the Société de Pathologie Exotique.