In 1897 an International Congress took place in Moscow. Metchnikoff read a paper on the phagocytic reaction against toxins and another dealing with the whole of the knowledge acquired concerning human plague. He ended this by a plea in favour of Science, so often accused of having contributed nothing to the solution of the most important human problems, particularly ethical ones, and of having, on the contrary, sanctioned the law of Might by tabulating the laws of the struggle for existence. Metchnikoff objected that, far from doing so, Science, by revealing the laws of Nature, applied to humanity the benefits derived from them, whilst striving to counterbalance their cruel or harmful effects. The struggle against plague and other diseases was a concrete example of this, for here medical science opposed itself to the cruelty of "natural selection." He wound up his speech by the following words, "Just as, in order to satisfy his æsthetic tastes, Man revolts against the laws of Nature which creates races of sterile and fragile flowers, he does not hesitate to defend the weak against the laws of natural selection. Science has been faithful to her mission and to her generous traditions. Let her, then, progress unhindered." Metchnikoff's friend and companion, M. Nocard, wrote to me concerning Metchnikoff's paper: Do not believe a word that Metchnikoff tells you. He had tremendous success. The somewhat free form of his paper contributed to its success, as it only made his conviction and enthusiasm more apparent. Thus the Sibyl on her tripod. Metchnikoff had at this period a very talented disciple, M. I. Bordet, who opened a new path by a series of researches of the greatest importance. He found, among other things, that "the figured elements" can be destroyed outside the cells, in the humors. Thus, if red blood corpuscles from one animal are injected into an animal of a different kind, these globules are destroyed, not within the phagocytes, but outside them, in the ambient humors. Metchnikoff studied this phenomenon and proved that the explanation was the same that he had previously given of Pfeiffer's phenomenon in the case of cholera vibrions. In Bordet's experiments, the leucocytes which were already existing in the humors were also damaged by the experimental shock; but, if this was carefully avoided, the phagocytes, remaining intact, englobed and digested the injected red corpuscles and no phenomenon similar to Pfeiffer's took place.