1875-1880. Metchnikoff at the age of 30--Lecturing in Odessa University, from 1873 to 1882--Internal difficulties-- Assassination of the Tsar, Alexander II.--Further troubles in the University--Resignation--Bad health: cardiac symptoms--Relapsing fever--Choroiditis--Studies on Ephemeridæ--Further studies on intracellular digestion-- The _Parenchymella_--Holidays in the country--Experiments on agricultural pests 96 CHAPTER XVII 1881-1882. Death of his father- and mother-in-law--Management of country estates--Agitation and difficulties--Departure for Messina with young brothers- and sisters-in-law 112 CHAPTER XVIII 1883. Messina--Inception of the phagocyte theory--Encouragement from Virchow and Kleinenberg--First paper on phagocytosis at a Congress at Odessa in 1883--The question of _immunity_ --Article in Virchow's _Archiv_, 1884 115 CHAPTER XIX 1884-1885. Ill-health of his wife and sister-in-law--Journey to Tangiers through Spain--Villefranche--Baumgarten criticises the phagocyte theory 123 CHAPTER XX 1886. A Bacteriological Institute in Odessa--Unsatisfactory conditions--Experiments on erysipelas and on relapsing fever 127 CHAPTER XXI 1887. Hygiene Congress in Vienna--Wiesbaden--Munich--Paris and Pasteur--Berlin and Koch--Failure of anthrax vaccination of sheep--Decision to leave Russia 131 CHAPTER XXII 1888. The Pasteur Institute--Dreams realised--Metchnikoff at 50--Growing optimism--Attenuated sensitiveness--The Sèvres villa (1898)--Daily routine 135 CHAPTER XXIII 1892. Opposition to the phagocyte theory--Scientific controversies--Experiments in support of the phagocyte theory--Behring and antitoxins--The London Congress-- _Inflammation_ 147 CHAPTER XXIV Cholera--Experiments on himself and others--Illness of M. Jupille--Death of an epileptic subject--Insufficient results 154 CHAPTER XXV 1894. Pfeiffer's experiments--The Buda-Pest Congress-- Extracellular destruction of microbes--Reaction of the organism against toxins--Dr. Besredka's researches-- Macrophages--The Moscow Congress--Bordet's experiments 158 CHAPTER XXVI 1900. Immunity--Natural immunity--Artificial immunity 168 CHAPTER XXVII