In a letter written at the end of 1873, Pasteur wrote: “How I wish I had enough health and sufficient knowledge to throw myself body and soul into the experimental study of one of our infectious diseases!” He considered that his studies on fermentations would lead him in that direction; he thought that when it should be made evident that every serious alteration in beer was due to the micro-organisms which find in that liquid a medium favourable to their development, when it should be seen that--in contradiction to the old ideas by which those alterations are looked upon as spontaneous, inherent in those liquids, and depending on their nature and composition--the cause of those diseases is not interior but exterior, then would indeed be defeated the doctrine of men like Pidoux, who à propos of diseases, said: “Disease is in us, of us, by us,” and who, à propos of small-pox, even said that he was not certain that it could only proceed from inoculation and contagion. Though the majority of physicians and surgeons considered that it was waste of time to listen to “a mere chemist,” there was a small group of young men, undergraduates, who, in their thirst for knowledge, assembled at the Académie de Médecine every Tuesday, hoping that Pasteur might bring out one of his communications concerning a scientific method “which resolves each difficulty by an easily interpreted experiment, delightful to the mind, and at the same time so decisive that it is as satisfying as a geometrical demonstration, and gives an impression of security.” Those words were written by one of those who came to the Académie sittings, feeling that they were on the eve of some great revelations. He was a clinical assistant of Dr. Béhier’s, and, busy as he was with medical analysis, he was going over Pasteur’s experiments on fermentations for his own edification. He was delighted with the sureness of the Pastorian methods, and was impatient to continue the struggle now begun. Enthusiasm was evinced in his brilliant eyes, in the timbre of his voice, clear, incisive, slightly imperious perhaps, and in his implacable desire for logic. Of solitary habits, with no ambition for distinction or degrees, he worked unceasingly for sheer love of science. The greatest desire of that young man of twenty-one, quite unknown to Pasteur, was to be one day admitted, in the very humblest rank, to the Ecole Normale laboratory. His name was Roux.