It would have been an act of graceful welcome to Pasteur, and a fitting homage to the memory of the celebrated Trousseau, who had died five years before, in 1867, if any member present had then quoted one of the great practitioner’s last lectures at the Hôtel Dieu, wherein he predicted a future for Pasteur’s works: “The great theory of ferments is therefore now connected with an organic function; every ferment is a germ, the life of which is manifested by a special secretion. It may be that it is so for morbid viruses; they may be ferments, which, deposited within the organism at a given moment and under determined circumstances, manifest themselves by divers products. So will the variolous ferment produce variolic fermentation, giving birth to thousands of pustules, and likewise the virus of glanders, that of sheep pox, etc.... “Other viruses appear to act locally, but, nevertheless, they ultimately modify the whole organism, as do gangrene, malignant pustula, contagious erysipelas, etc. May it not be supposed, under such circumstances, that the ferment or organized matter of those viruses can be carried about by the lancet, the atmosphere or the linen bandages?” But it occurred to no one in the Academy to quote those forgotten words. Pasteur, answering Bouillaud, recalled his own researches on lactic and butyric fermentations and spoke of his studies on beer. He stated that the alteration of beer was due to the presence of filiform organisms; if beer becomes altered, it is because it contains germs of organized ferments. “The correlation is certain, indisputable, between the disease and the presence of organisms.” He spoke those last words with so much emphasis that the stenographer who was taking down the extempore speeches underlined them. A few months later, on November 17, 1873, he read to the Academy a paper containing further developments of his principles. “In order that beer should become altered and become sour, putrid, slimy, ‘ropy,’ acid or lactic, it is necessary that foreign organisms should develop within it, and those organisms only appear and multiply when those germs are already extant in the liquid mass.” It is possible to oppose the introduction of those germs; Pasteur drew on the blackboard the diagram of an apparatus which only communicated with the outer air by means of tubes fulfilling the office of the sinuous necks of the glass vessels he had used for his experiments on so-called spontaneous generation. He entered into every detail, demonstrating that as long as pure yeast alone had been sown, the security was absolute. “That which has been put forward on the subject of a possible transformation of yeast into bacteria, vibriones, _mycoderma aceti_ and vulgar mucors, or vice versa, is mistaken.” He wrote in a private letter on the subject: “These simple and clear results have cost me many sleepless nights before presenting themselves before me in the precise form I have now given them.”