We know how wine and beer are prepared. The must of grapes and the must of beer are placed in wooden vats, or in barrels of greater or less dimensions. Whether the fermentation proceeds from germs taken from the exterior surface of the grapes, or from a small quantity of ferment sown in the must under the form of yeast, as in the fermentation of beer, the life of the ferment, its multiplication, the augmentation of its weight, are so many vital actions which to a certainty cannot borrow from the free oxygen of the external air, or from that originally dissolved in the must, an appreciable quantity of this gas. All the life of the cells of the ferment which multiplies itself indefinitely appears then to take place apart from free oxygen gas. In certain breweries in England the fermenting vats have sometimes a capacity of several thousands of hectolitres; and the fermentation liberates pure carbonic acid, a gas much heavier than atmospheric air, which rests on the surface of the liquid in the vat in a layer thick enough to protect the liquid underneath from any contact with the external air. All this liquid mass, then, is inclosed between the wooden sides of the vat and a deep layer of heavy gas which contains no trace of free oxygen. In this liquid, nevertheless, the life of the cells of the ferment and the production of all its constituents go on for several days with extraordinary activity. Here certainly we have life without air, and the ferment character expresses itself in the enormous difference between the weight of the ferment formed and collected from the vats under the name of yeast, at the end of the operation, and the weight of the sugar which has fermented, transforming itself into alcohol, carbonic acid, and various other products.