A balance-sheet of materials and products was constructed which showed that the alcohol and carbon dioxide formed amounted only to about 95 per cent. of the invert sugar fermented, the difference being made up by glycerol, succinic acid, cellulose, and other substances [1860, p. 347]. In every case of fermentation, even when a paste of yeast was added to a solution of pure cane sugar in water, the yeast was found by quantitative measurements to have taken something from the sugar. This "something" was indeterminate in character, but, including the whole of the extractives which had passed from the yeast cells into the surrounding liquid, it amounted to as much as 1·63 per cent. of the weight of the sugar fermented [1860, p. 344]. Pasteur was therefore led to consider fermentation as a physiological process accompanying the life of the yeast. His conclusions were couched in unmistakable words: "The chemical act of fermentation is essentially a phenomenon correlative with a vital act, commencing and ceasing with the latter. I am of opinion that alcoholic fermentation never occurs without simultaneous organisation, development, multiplication of cells, or the continued life of cells already formed. The results expressed in this memoir seem to me to be completely opposed to the opinions of Liebig and Berzelius. If I am asked in what consists the chemical act whereby the sugar is decomposed and what is its real cause, I reply that I am completely ignorant of it. "Ought we to say that the yeast feeds on sugar and excretes alcohol and carbonic acid? Or should we rather maintain that yeast in its development produces some substance of the nature of a pepsin, which acts upon the sugar and then disappears, for no such substance is found in fermented liquids? I have nothing to reply to these hypotheses. I neither admit them nor reject them, and wish only to restrain myself from going beyond the facts. And the facts tell me simply that all true fermentations are correlative with physiological phenomena."