CHAPTER XVI

HISTORICAL SKETCH OF OUR KNOWLEDGE OF IMMUNITY 505 Methods used by savage races for vaccination against snake venom and against bovine pleuropneumonia.—Variolisation and vaccination against small-pox.—Discovery of the attenuation of viruses and of vaccinations with attenuated micro-organisms.—Theory of the exhaustion of the medium as a cause of acquired immunity.—Theory of substances which prevent the multiplication of the micro-organisms in the refractory body.—Local theory of immunity.—Theory of the adaptation of the cells of the immunised organism. Observations on the presence of micro-organisms in the white corpuscles.—History of phagocytosis and of the theory of phagocytes.—Numerous attacks upon this theory.—Theory of the bactericidal property of the body fluids.—Theory of the antitoxic power of the body fluids.—Extracellular destruction of micro-organisms.—Analogy between bacteriolysis and haemolysis.—Theory of side-chains. Progress of the theory of phagocytes.—Attempts to reconcile it with the humoral theory.—Present phase of the question of immunity.