[AS.] The froth that rises on the top of liquors in the process of fermentation; or the substance used for raising dough to be baked into bread (q. v.). Although yeast looks like a liquid to the naked eye, yet under the microscope a drop of yeast is found to contain thousands of extremely small rounded bodies, which are tiny plants of the Fungus kind. The yeast-plant feeds on part of the starch in the flour, and the result is that this starch is changed into grape-sugar. Leaven is only a little flour and water which has been left exposed to the air until some of the "spores" 0r "seeds" of the yeast-plant (which are always floating about in the air) have settled in it and begun to grow, which they do with wonderful rapidity.

YEAST FUNGUS, MAGNIFIED 4OO TIMES.

YEAST FUNGUS, MAGNIFIED 4OO TIMES.