We have frequently, but without success, endeavoured to bring about the conversion of these unsubmerged _torulæ_ and _mycoderma vini_ into alcoholic ferments; in other words, we have never succeeded in imparting to these _torulæ_ or to _mycoderma vini_, which bear so striking a resemblance to alcoholic ferments, the permanent fermentative character peculiar to the latter. At one period of our researches, in 1862, and more recently, in 1872, we thought that we had discovered the conditions under which such conversion might be possible, but, as we shall explain in a subsequent chapter, our experiments were affected by certain errors that had escaped our notice. § VI.—Yeast may become Dry and be Reduced to Dust without losing its Faculty of Reproduction. In the preceding paragraphs we have given examples of liquids becoming impregnated with self-sown alcoholic ferments. We shall proceed to show that this little cellular plant may actually exist in the form of dust, floating in the air, after the manner of spores of fungoid growth and the encysted forms of certain infusoria, without losing its powers of reproduction. On December 16th, 1872, we collected and pressed all the yeast resulting from a brewing of about one hectolitre (about 22 gallons). From the centre of the cake we took a few grammes (50 or 60 grains) of yeast, which we mixed in a porcelain mortar with five times its weight of plaster—both mortar and plaster having been heated, just before, in an oil bath, to a temperature of about 200° C. (392° F.), and then cooled rapidly. The powder thus prepared was immediately done up in a twist of paper, which had been passed through the flame of a spirit lamp, and the twist and its contents were then placed in an oven at a temperature of from 20° C. to 25° C. (about 75° F.). The object of these several precautions was to free the powder composed of the yeast and plaster, if not from the germs contained in floating particles of dust, at all events from those contained in the dust existing on the surface of the articles we used—the mortar, plaster, and paper. [Illustration: Fig. 14.] On December 18th, we took up with a platinum spatula, previously passed through the flame, a pinch of the yeast-and-plaster powder, and sowed it in a two-necked flask (Fig. 14) containing some pure wort. We then placed the flask in an oven, at 20° C. On December 21st, three days after we had sown the powder, fermentation began to manifest itself by the appearance of patches of froth on the surface of the wort. On December 19th and 20th the yeast was sensibly developing, although there was no liberation of gas to denote the presence of actual fermentation. The yeast, examined under the microscope, appeared very pure. On March 5th, 1873, we took another pinch of the yeast-and-plaster powder from the twist of paper, and placed it in a flask of pure wort, as in the foregoing experiment.