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actively in the fluid. Gas is passing off in large quantities. Under the action of the minute living vegetable cells that constitute yeast, the sugar is being split up into alcohol and carbonic acid. The alcohol remains in the fluid and the carbonic acid escapes into the air. Observe when I put this lighted taper into the vessel that the flame is at once extinguished Fig. 1.—Yeast cells. The cells of Saccharomyctes cerevisiæ, multiplying by budding. Magnified 300 diameters. by the carbonic acid gas. Here we have an example of molecular movements brought about by the action of living organisms—the yeast cells. Each little yeast cell acts directly or indirectly on the sugar, effects a decomposition, as I have said, into alcohol and carbonic acid, while other substances, such as glycerine and succinic acid, are formed in smaller quantity. During the fermentative process