It has been a great satisfaction to me to carry out the wish of my dear friend Elie Metchniknoff, and arrange for the production of an English translation of his biography. The account of his life and work written by Olga Metchnikoff is a remarkable and beautiful record of the development and activities of a great discoverer. It is remarkable because it is seldom that one who undertakes such a task has had so constant a share in, and so complete a knowledge and understanding of, the life portrayed as in the present case: seldom that the intimate thought and metal "adventure" of a discoverer presents so clear and consistent a history. It is beautiful because it is put before us with perfect candour and simplicity guided by rare intelligence and inspire by deep affection. Madame Metchnikoff has drawn the picture of the development of a single-minded character absolutely and tenaciously devoted to a high purpose - the improvement of human life. It is a story of "struggles and adventures," but they are wholly in the field of the investigation of Nature. We read here little or nothing of the quest for personal advancement, for fortune or official position. These things had no attraction for Metchnikoff.