[Illustration: M. ÉLIE METCHNIKOFF ] THE NATURE OF MAN STUDIES IN OPTIMISTIC PHILOSOPHY BY ÉLIE METCHNIKOFF PROFESSOR AT THE PASTEUR INSTITUTE THE ENGLISH TRANSLATION EDITED BY P. CHALMERS MITCHELL M.A., D.SC. OXON. SECRETARY OF THE ZOOLOGICAL SOCIETY OF LONDON G. P. PUTNAM’S SONS NEW YORK AND LONDON =The Knickerbocker Press= COPYRIGHT, 1903 BY G. P. PUTNAM’S SONS Eleventh Printing EDITOR’S INTRODUCTION When Pasteur died a remarkable article appeared in one of the Paris newspapers. The writer described the intimate routine of the life at the Pasteur Institute, and compared it with that of a mediæval religious community. A little body of men, forsaking the world and the things of the world, had gathered together under the compulsion of a great idea. They had given up the rivalries and personal interests of ordinary men, and, sharing their goods and their work, they lived in austere devotion to science, finding no sacrifice of health or money, or of what men call pleasure, too great for the common object. Rumours of war and peace, echoes of the turmoil of politics and religion, passed unheeded over their monastic seclusion; but if there came news of a strange disease in China or Peru, a scientific emissary was ready with his microscope and his tubes to serve as a missionary of the new knowledge and the new hope that Pasteur had brought to suffering humanity. The adventurous exploits and the patient vigils of this new Order have brought about a revolution in our knowledge of disease, and there seems no limit to the triumphs that will come from the parent Institute in Paris and from its many daughters in other cities.