The public at large and many critics did not understand the deep and general meaning of Metchnikoff's thoughts. They reproached him with having an insufficiently exalted ideal, for they only saw in his doctrine the desire of postponing senility and living longer. They did not understand that to revolt against the lack of harmony in nature, through which all humanity has to suffer, not only physically but morally, was to aspire to perfection. They did not consider that, in order to attain that end, all human culture and the whole social state would have to be modified; that this could only be done through many virtues, intense energy, and great self-control. They had not understood the elevation and power of an ideal which aspired to perfect not only the direction of life but human nature itself. They had not understood the audacious beauty of such a struggle, the benefit conferred by the belief that the human will and the human mind are capable of transforming Evil into Good according to a conceived ideal!... In the meanwhile Metchnikoff, convinced that Knowledge is Power and that "Science alone can lead suffering Humanity into the right path," quietly continued his task. * * * * * One of the most characteristic symptoms of old age is the hardening of the arteries--arterio-sclerosis. He therefore especially wished to elucidate the mechanism of that phenomenon. Whilst many, yet unknown, factors come into play in senility, one disease, syphilis, often provokes arterio-sclerosis, indisputably due to a morbid agent. Metchnikoff therefore began to study this disease, of which the origin is infectious--especially as he thought he could do so experimentally. Long before this, he had conceived the idea that the study of those human diseases which cannot be transmitted to ordinary laboratory animals might be carried out on anthropoid apes, of all animals the nearest to man. He had spoken of it to M. Pasteur, but, at that time, the Institute could not afford to acquire these costly animals. In 1903, at the Madrid Congress, Metchnikoff received a 5000 fr. prize and utilised this money in the acquisition of two anthropoid apes. The same year M. Roux won the Osiris prize of 100,000 fr. which he devoted to the same object, and it was decided that the two together would undertake researches on syphilis. Other donations, 30,000 fr. from the Morosoffs of Moscow and 250 roubles from the Society of Dermatology and Syphilography of the same city, completed the capital required to execute the projected plan. The following is a short sketch of the researches that were undertaken and the results that were obtained.