Perhaps a general plan of the whole, in the shape of a comparative study, embracing the whole animal scale, would throw light over the generality of phagocytic phenomena and would make their continuity understood through normal and pathological biology. He determined to make this effort. In order to place in a fresh light the biological evolution of phagocytosis phenomena _in disease_, he chose one of the principal manifestations of pathological phagocytosis, _inflammation_, and, in 1891, gave a series of lectures on this subject which he afterwards published in a volume. According to his usual method, he began by the most primitive beings, taking as a starting-point the lower organisms which do not yet possess differentiated functions, and whose normal digestion is, if necessary, used as a means of defence against noxious agents. Then, by a comparative study in every grade of the animal kingdom, he proved that the same mode of struggle and defence persists in the mesodermic cells, the phagocytes in all animals in general. In all of them, thanks to a special sensitiveness, _Chimiotaxis_, phagocytes move towards the intruder, to englobe it and digest it if they can. This reaction for defence by the organism takes place in beings endowed with a vascular system by the migration of the blood-phagocytes which traverse the walls of the blood-vessels in order to betake themselves to the invaded point. In higher animals, all the symptoms which accompany this phenomenon of defence and which constitute the classical picture of inflammation (a heightened temperature, pain, redness, tumefaction) are due to the complexity of the organism; but the _essence_, the _primum movens_ of inflammation, with them also, is a _digestive_ action of the phagocytes upon the noxious agent, therefore a salutary reaction of the organism, essentially similar to the normal digestion of inferior beings. Metchnikoff adduced numerous examples giving evidence of the genetic link which exists between inflammation and normal intracellular digestion, and while establishing the evolution of the former on biological and experimental bases, he showed at the same time the close connection which binds normal biology and pathological biology. This series of lectures formed a volume which appeared in 1892 under the title of _Leçons sur la pathologie comparée de l'inflammation_, a book which contributed to the acceptation of the phagocyte theory and which showed the importance of Natural History applied to Medicine. CHAPTER XXIV Cholera--Experiments on himself and others--Illness of M. Jupille --Death of an epileptic subject--Insufficient results. The acute period of the struggle in defence of the phagocyte theory now seemed to have come to an end and Metchnikoff turned his thoughts towards a new field of ideas.