Here Metchnikoff formulates an optimistic view of man's relationship to disease, old age, and death based on his discovery of "phagocytes," the chief function of which is to devour intruding microbes. The scientific importance of this work was so great that it was spoken of in England as the most valuable production since Darwin's Origin of Species. Elie Metchnikoff (1845-1916) was Sub-Director of the Pasteur Institute, and a Nobel Prize winner for medicine. Metchnikoff was born in Russia and lived in Paris from 1888, where many of his works were originally published in French. He worked in the fields of embryology, comparative anatomy, pathology, bacteriology and immunology. "An extremely interesting and typical book ... With a distinguished frankness, M. Metchnikoff defines his attitude to our universal prepossessions. It is his theory that the infirmities of age are to be overcome. If there be ground for this conception, humanity is to be profoundly changed and what we call life now, will be the childhood and youth of that longer and larger life." - H. G. Wells, in London Speaker "Undoubtedly a great book (in some quarters it has been hailed as the greatest since Darwin's famous message to the world) and should be read by all intelligent men and women." - The Nation "A book to be set side by side with Huxley's Essays, whose spirit it carries a step further on the long road towards its goal." - Mail and Express