“This view has been entirely confirmed by an inquiry into the mode of brewing _saké_ by the Japanese, by the aid of the Aspergillus fungus. Further researches established the fact that other forms of fungi, _e.g._, those on the surface of fruits, developed endogenous spores, which cause alcoholic fermentation. More recently, and by further experimental inquiry, partly by pure cultures of separate forms, and partly by well-devised cultures on ripening fruits still attached to the plant but imprisoned in sterilised glass vessels, it has been found that yeast and moulds are separate forms, not genetically connected, but merely associated in nature, as are so many other forms of yeasts, bacteria, and moulds. Further, Hansen has discovered that several yeasts furnish quite distinct races or varieties in different breweries in various parts of the world, so that we cannot avoid the conclusion that their race characteristics have been impressed on the cells by the continued action of the conditions of culture to which they have so long been exposed--they are, in fact, domesticated races.” The environments of yeasts are peculiar. Sauer found that a given variety of yeast, whose activity is normally inhibited when the alcohol attains a certain degree of concentration in the liquid, can be induced to go on fermenting until a higher degree is attained by the addition of a certain lactic acid bacterium. The latter, indeed, appears to prepare the way for the yeast. It has been shown, also, that damage may be done to beers and wines by allowing plant germs to gain access with the yeast; there are, too, several forms of yeast that are inimical to the action of the required fermentation. Other researches show that associated yeasts may ferment better than any single yeast, and such symbiotic action of two yeasts of high fermenting power has given better results than either alone. English ginger-beer furnishes a curious symbiotic association of two organisms--a true yeast and a true bacterium--so closely united that the yeast cells become imprisoned in the gelatinous meshes of the bacterium; and it is a curious fact that this symbiotic union of yeast and bacterium ferments is far more energetic than either when used alone, and the product is different, large quantities of lactic and carbonic acids being formed, and little or no alcohol. Many years ago I gave an account of similar curious symbiotic results obtained by introducing into a wort-infusion a small proportion of _German yeast_, an artificial product composed of honey, malt, and a certain proportion of spontaneously-fermented wheat flour. This, to my astonishment, produced ten per cent. more alcohol than any of its congeners, and did not so soon exhaust itself as brewer’s yeast.[54]