Pouchet, the most celebrated of them, who considered that part of a scientist’s duty consists in vulgarizing his discoveries, was preparing for the New Year, 1872, a book called _The Universe: the Infinitely Great and the Infinitely Small_. He enthusiastically recalled the spectacle revealed at the end of the seventeenth century by the microscope, which he compared to a sixth sense. He praised the discoveries made in 1838 by Ehrenberg on the prodigious activity of infusories, but he never mentioned Pasteur’s name, leaving entirely on one side the immense work accomplished by the infinitely small and ever active agents of putrefaction and fermentation. He owned that “a few microzoa did fly about here and there,” but he called the theory of germs a “ridiculous fiction.” At the same time Liebig, who, since the interview in July, 1870, had had time to recover his health, published a long treatise disputing certain facts put forward by Pasteur. Pasteur had declared that, in the process of vinegar-making known as the German process, the chips of beech-wood placed in the barrels were but supports for the _mycoderma aceti_. Liebig, after having, he said, consulted at Munich the chief of one of the largest vinegar factories, who did not believe in the presence of the mycoderma, affirmed that he himself had not seen a trace of the fungus on chips which had been used in that factory for twenty-five years. In order to bring this debate to a conclusion Pasteur suggested a very simple experiment, which was to dry some of those chips rapidly in a stove and to send them to Paris, where a commission, selected from the members of the Académie des Sciences, would decide on this conflict. Pasteur undertook to demonstrate to the Commission the presence of the mycoderma on the surface of the chips. Or another means might be used: the Munich vinegar maker would be asked to scald one of his barrels with boiling water and then to make use of it again. “According to Liebig’s theory,” said Pasteur, “that barrel should work as before, but I affirm that no vinegar will form in it for a long time, not until new mycoderma have grown on the surface of the chips.” In effect, the boiling water would destroy the little fungus. With the usual clear directness which increased the interest of the public in this scientific discussion, Pasteur formulated once more his complete theory of acetification: “The principle is very simple: whenever wine is transformed into vinegar, it is by the action of the layer of _mycoderma aceti_ developed on its surface.” Liebig, however, refused the suggested test.