Our experiments were conducted in the following manner:—In some flat porcelain basins, we grew some pure _mycoderma vini_[70] on fermented liquids, such as wine or beer, or on artificially vinous liquids, such as alcoholized yeast-water, taking care to boil these liquids previously to kill any germs of yeast or other organism that they might contain. The basins themselves, as well as the plates of glass with which they were to be covered, were plunged into boiling water just before they were wanted for use. As soon as the film of mycoderma had become well developed and thick, and even wrinkled—a process requiring not more than two or three days during summer heat—we decanted the subjacent liquid, by means of a siphon, so as to leave the film on the bottom of the basin. We then diffused the whole mass of efflorescence in a saccharine liquid that had been boiled and afterwards cooled down in a closed vessel; generally, we used wort or must preserved by Appert’s process. After that, we emptied the mixture of saccharine liquid and efflorescence into long-necked flasks that had likewise been previously heated, as also had the funnels used in the process of transference. It seemed to us that experiments conducted with all these precautions must be free from causes of error. It was true that we were working more or less in contact with atmospheric air, but all that we had to fear for the soundness of the conclusions which we might draw was the presence of germs of alcoholic ferment, and we considered how few of these there are amongst floating particles of dust. Consequently, if we succeeded in observing the advent of yeast in each of the long-necked flasks, accompanied by an active alcoholic fermentation, we thought that we might, without danger of error, admit as a fact the transformation of cells of mycoderma into cells of yeast. Again, we thought that we should probably find in the forms of the cells of yeast which were directly derived from the cells of mycoderma, a more or less elongated structure, which would be a convincing proof of the transformation that we were seeking, if, indeed, such transformation were possible. Strange to say, everything happened in a manner that seemed to realize our expectations. The saccharine worts in the flasks in which we had mixed and submerged the mycoderma, fermented in the course of a few days; the yeast first appeared in elongated shapes; lastly, we could see under the microscope that many of the cells or jointed filaments of mycoderma were inflated and presented the appearance of undoubted gradations between their natural state and that of the cells of yeast which soon formed part of the deposit in the vessels. In spite of all this, however, we were the victims of an illusion.