Born in what is now Ukraine, he was convinced by his mother to study natural sciences instead of medicine, and enrolled at Kharkov University for natural sciences, completing his four-year degree in two years. In particular, he is credited with the discovery of phagocytes (macrophages) in 1882, and his discovery turned out to be the major defence mechanism in innate immunity. He won the 1908 Nobel Prize in Physiology or Medicine.