Whilst engaged in these researches, we were pursuing others in relation to the converse of the proposition just discussed, that is to say, respecting the possibility of ferment becoming transformed into _mycoderma vini_ or _mycoderma cerevisiae_. Our experiments in connection with this subject chiefly consisted in various endeavours by way of exhausting the yeast and subsequent revival of its growth. This exhaustion was effected by growing the yeast in excess of sweetened water, and at other times in unsweetened yeast-water, our efforts being directed to deprive it of all power of fermenting. We afterwards caused it to develop afresh in highly aerated, nutritious liquids, in order that we might see how it reproduced itself, and if its new form were that of a mycoderma. The yeast after having lost its power as a ferment, and being no longer able to act in pure sweetened water, nevertheless reproduced itself when placed in fermentable media, holding in solution materials adapted to its nutrition; yet we never succeeded in obtaining any organism besides the ferment, and, indeed, the identical variety of ferment on which we had operated. In no case was _mycoderma vini_ or _cerevisiæ_ produced, and we concluded that we were justified in stating that whenever the _mycoderma vini_ appeared on the surface of a fermented or fermentable liquid, its germ must have been introduced by the surrounding air, or have previously existed in the liquid, and that the reason why this germ multiplied so abundantly was because the liquid in question had been peculiarly adapted to the vitality of the plant. In a laboratory where alcoholic fermentations are studied, these germs of _mycoderma vini_ exist in great abundance on the surfaces of different objects. This fact admits of easy proof; we have merely to open in such a laboratory some flasks containing yeast-water deprived of air, or yeast-water sweetened, or any natural saccharine medium, or any fermented liquid, which till the moment when our flasks were closed had been kept boiling (Chap. IV.); it would be a very rare thing, indeed, if _mycoderma vini_ did not develop in most of these flasks after the air was readmitted, especially if, shortly before this operation, the dust lying on the surface of the tables or floor of the laboratory had been stirred up by dusting or sweeping. This series of experiments, the salient points of which we have just given, conducted with a view to ascertain whether yeast could be transformed into mycoderma, has led the way to certain results of special interest, results which concern all alcoholic ferments, and which in all probability will be found in the long run to apply to all aërobian ferments.