Before returning to France he went to Vienna and then to Munich: he desired to talk with the German chemist, Liebig, the most determined of his adversaries. He thought it impossible that Liebig’s ideas on fermentation should not have been shaken and altered in the last thirteen years. Liebig could not still be affirming that the presence of decomposing animal or vegetable matter should be necessary to fermentation! That theory had been destroyed by a simple and decisive experiment of Pasteur’s: he had sown a trace of yeast in water containing but sugar and mineral crystallized salts, and had seen this yeast multiply itself and produce a regular alcoholic fermentation. Since all nitrogenized organic matter (constituting the ferment, according to Liebig) was absent, Pasteur considered that he thus proved the life of the ferment and the absence of any action from albuminoid matter in a stage of decomposition. The death phenomenon now appeared as a life phenomenon. How could Liebig deny the independent existence of ferments in their infinite littleness and their power of destroying and transforming everything? What did he think of all these new ideas? would he still write, as in 1845: “As to the opinion which explains putrefaction of animal substances by the presence of microscopic animalculæ, it may be compared to that of a child who would explain the rapidity of the Rhine current by attributing it to the violent movement of the numerous mill wheels of Mayence?” Since that ingeniously fallacious paragraph, many results had come to light. Perhaps Liebig, who in 1851 hailed J. B. Dumas as a master, had now come to Dumas’ point of view respecting the fruitfulness of the Pastorian theory. That theory was extended to diseases; the infinitely small appeared as disorganizers of living tissues. The part played by the corpuscles in the contagious and hereditary pébrine led to many reflections on the contagious and hereditary element of human diseases. Even the long-postponed transmission of certain diseases was becoming clearer now that, within the vibrio of flachery, other corpuscles were found, germs of the flachery disease, ready to break out from one year to another. To convince Liebig, to bring him to acknowledge the triumph of those ideas with the pleasure of a true _savant_, such was Pasteur’s desire when he entered Liebig’s laboratory. The tall old man, in a long frock coat, received him with kindly courtesy; but when Pasteur, who was eager to come to the object of his visit, tried to approach the delicate subject, Liebig, without losing his amenity, refused all discussion, alleging indisposition. Pasteur did not insist, but promised himself that he would return to the charge. CHAPTER VII 1870--1872