Traube’s conceptions were governed by a theory of fermentation entirely his own, a hypothetical one, as he admits, of which the following is a brief summary: “We have no reason to doubt,” Traube says, “that the protoplasm of vegetable cells is itself, or contains within it, a chemical ferment which causes the alcoholic fermentation of sugar; its efficacy seems closely connected with the presence of the cell, inasmuch as, up to the present time, we have discovered no means of isolating it from the cells with success. In the presence of air, this ferment oxidizes sugar, by bringing oxygen to bear upon it; in the absence of air it decomposes the sugar by taking away oxygen from one group of atoms of the molecule of sugar and bringing it to act upon other atoms; on the one hand yielding a product of alcohol by reduction, on the other hand a product of carbonic acid by oxidation.” Traube supposes that this chemical ferment exists in yeast and in all sweet fruits, but only when the cells are intact, for he has proved for himself that thoroughly crushed fruits give rise to no fermentation whatever in carbonic acid gas. In this respect this imaginary chemical ferment would differ entirely from those which we call _soluble ferments_, since diastase, emulsine, &c., may be easily isolated. For a full account of the views of Brefeld and Traube, and the discussion which they carried on on the subject of the results of our experiments, our readers may consult the _Journal of the Chemical Society of Berlin_, vii. p. 872. The numbers for September and December, 1874, in the same volume, contain the replies of the two authors. Footnote 135: See PASTEUR, _Comptes rendus de l’Académie des Sciences_, t. lvi. p. 416. Footnote 136: [Carbonic acid being considerably more soluble than other gases possible under the circumstances.—ED.] Footnote 137: We had to avoid filling the small flask completely, for fear of causing some of the liquid to pass on to the surface of the mercury in the measuring tube. The liquid condensed by boiling forms pure water, the solvent affinity of which for carbonic acid, at the temperature we employ, is well known. Footnote 138: