Sugar. Relative Rates. Relative Totals. Glucose 1 1 Fructose 1·29 1·15 Mannose 1·04 0·67 Among the disaccharides, cane sugar and maltose are freely fermented, and the juice can be shown like living yeast to contain invertase and maltase. The extent of fermentation does not differ materially from that attained with glucose. Lactose is not fermented. Of the higher sugars raffinose is fermented by juice from bottom yeast, but more slowly than cane sugar or maltose. No experiments seem to have been made with juice from top yeast. [p033] As regards the fermentation of the higher carbohydrates, very little experimental work has been carried out. Buchner and Rapp found that the fermentation of starch paste was doubtful, but that soluble starch and commercial dextrin were fermented with some freedom. No special study has been made of the diastatic enzymes which bring about the hydrolysis of these substances. The fermentation of glycogen by yeast-juice is of considerable interest, since it is known that the characteristic reserve carbohydrate of the yeast cell is glycogen [see Harden and Young, 1902, where the literature is cited], and moreover that in living yeast the intracellular fermentation of glycogen proceeds readily, whereas glycogen added to a solution in which yeast is suspended is not affected. Yeast-juice contains a diastatic enzyme which hydrolyses glycogen to a reducing and fermentable sugar, so that in a juice poor in zymase to which glycogen has been added, the amount of sugar is found to increase, the hydrolysis of the glycogen proceeding more quickly than the fermentation of the resulting sugar [Harden and Young, 1904], but the course of this enzymic hydrolysis of glycogen by yeast-juice has not yet been studied. As a rule, it is found both with juices from top and bottom yeast that the evolution of carbon dioxide from glycogen proceeds less rapidly and reaches a lower total than from an equivalent amount of glucose. Since nearly all samples of yeast contain glycogen, yeast-juice and also zymin usually contain this substance as well as the products of its hydrolysis. These provide a source of sugar which enters into alcoholic fermentation, so that a slow spontaneous production of carbon dioxide and alcohol proceeds when yeast-juice is preserved without any addition of sugar. The extent of this autofermentation varies considerably, as might be expected, with the nature of the yeast employed or the preparation of the material, but is generally confined within the limits of 0·06 to 0·5 gram of carbon dioxide for 25 c.c. of juice.