_Saccharomyces Cerevisiæ._ Oval or ellipsoidal cells; reproduction by budding; ascospores, rapidly at 30° C., slowly at 12° C., not formed at all at lower temperatures; film formation, seven to ten days at 22° C.; an active alcoholic ferment, producing in a fortnight in beer wort from 4 to 6 per cent. by volume of alcohol (Jörgensen). This species is a typical English "high" yeast, possessing the power of "inverting" cane-sugar previous to producing alcohol and carbonic acid. It is said to have no action on milk-sugar. [Illustration: S. ELLIPSOIDEUS] [Illustration: S. PASTORIANUS] _Saccharomyces Ellipsoideus I._ Round, oval, or sausage-shaped cells, single or in chains; ascospores in twenty-four hours at 25° C. (not above 30° C., not below 4° C.). Grown on the surface of wort-gelatine, a network is produced by which they can be recognised (in eight to twelve days at 33° C.). At 13-15° C. a characteristic branching mass is produced. It is an alcoholic ferment as active as _S. cerevisiæ_. _S. Ellipsoideus II._ Round and oval, rarely elongated, a widely distributed yeast, causing "muddiness" in beer and a bitter taste. It is essentially a "low" yeast. _Saccharomyces Conglomeratus_ is a round cell, often united in clusters, and occurring in rotting grapes, and at the commencement of fermentation. _Saccharomyces Pastorianus I._ Oval or club-shaped cells, occurring in after-fermentation of wine, etc., and producing a bitter taste, unpleasant odour, and turbidity. The spores frequently occur in the air of breweries. _S. Pastor. II._ Elongated cells, possessing an invertose ferment. They do not, like _S. pastor I._, produce disease in beer. _S. Pastor. III._ Oval or elongated cells, producing turbidity in beer. Grown on yeast-water gelatine, the colonies show after sixteen days crenated hairy edges. _Saccharomyces Apiculatus._ Lemon-shaped cells. They give rise to a feeble alcoholic fermentation, and produce two kinds of spores--round and oval; they appear at the onset of vinous fermentation, but give way later on to _S. cerevisiæ_. _Saccharomyces Mycoderma._ Oval or elliptical cells, often in branching chains. They form the so-called "mould" on fermented liquids, and develop on the surface without exciting fermentation. When forced to grow submerged they produce a little alcohol. _Saccharomyces Exiguus._ Conical cells, appearing in the after-fermentation of beer. _Saccharomyces Pyriformis._ Oval cells, converting sugary solutions containing ginger into ginger-beer. _Saccharomyces Illicis_, _Hansenii_, _et Aquifolii_ produce a small percentage of alcohol. 2. _Acetous Fermentation._ Cause, Mycoderma aceti; medium, wine and other alcoholic liquids; result, the formation of vinegar.