Moreover, the results of our labours in connection with _spontaneous_ generation, in 1862, teach us that in Gay-Lussac’s experiment the germ of the ferment might also have had its origin either in certain particles of dust adhering to the sides of the glass bell, or upon the mercury; and, in a laboratory where alcoholic fermentation is studied, dust invariably contains dry cells of ferment. The necessity of oxygen for the success of the experiment is surprising, when we reflect that alcoholic fermentation often takes place in liquids that are not exposed to contact with air; but we shall prove by experiment that, notwithstanding what may happen during fermentation, oxygen has the greatest influence on the readiness with which ferment develops itself, and that this gas is indispensable to the revival of withered cells, and still more so to the germination of special cells, which we may consider to be the true germs of the little plant. The advocates of the doctrine of _spontaneous_ generation have based most of the objections which they vainly urge against their opponents upon erroneous interpretations of certain facts relating to the spontaneous impregnation of organic infusions. Taking a very wrong view of the essential conditions of the phenomena, they require that the assertors of the diffusion of the germs of microscopic organisms should be compelled to place at any one point of space, so to say, all the germs of the products of infusions; a demand which really borders on absurdity. They believe, or feign to believe, that we are bound to admit the existence of germs of must in all places and at all times, on the banks of rivers and on the loftiest mountains, and so on. “Fermentations,” said one of these gentlemen one day, before the Academy, “cannot depend upon chance particles of atmospheric dust. How is it possible that germs of yeast can be present everywhere throughout the universe, ever ready to fall upon must?” It is an established fact that grapes crushed in any part of the globe whatsoever, even on a glacier or at the highest elevations, can set up a fermentation. The explanation of this pretended impossibility is most simple, for we know, from the facts related in the preceding paragraph, that grapes carry on their skins the germs of their own ferments. In experiments relating to the kind of organisms which we are discussing we must never fail to take into account the action of the particles of dust spread over the articles that are used. Very often an effect that should be attributed to germs adhering to the vessels and utensils used in experiments, the origin of which may be altogether special, is erroneously imputed to the dust-forming germs—that is to say, to those germs which exist in a state of suspension in the air.