(1) 2C{6}H{12}O{6} + 2PO{4}HR{3} = 2CO{2} + 2C{2}H{6}O + 2H{2}O + C{6}H{10}O{4}(PO{4}R{2}){2}. According to this, two molecules of sugar are concerned in the change, the carbon dioxide and alcohol being equal in weight to one [p052] half of the sugar used, and the hexosephosphate and water representing the other half. Additional confirmation of this equation is afforded by the determination of the ratio between sugar used and carbon dioxide evolved when a known weight of sugar together with an excess of phosphate is added to yeast-juice at 25°. The phenomena then observed are precisely similar to those which occur when a phosphate is added to a fermenting mixture of yeast-juice and excess of sugar as described above. The rate of fermentation rapidly rises and then gradually falls until a rate is attained approximately equal to that of the autofermentation of the juice in presence of phosphate. At this point it is found that the extra amount of carbon dioxide evolved, beyond that which would have been given off in the absence of added sugar, bears the ratio expressed in equation (1) to the sugar added [Harden and Young, 1910, 2]. The results of four estimations made in this way were (/a/) 0·2 grams of glucose gave 26·5 and 27·9 c.c. of carbon dioxide at N.T.P.; (/b/) 0·2 grams of fructose gave 27·9 and 28·9 c.c. The carbon dioxide calculated from the sugar added in each of the four cases is 26·96 c.c. It has also been shown by Euler and Johansson [1913] that in the fermentation of a mixture of equivalent amounts of phosphate and glucose, the whole of the glucose had disappeared when the whole of the phosphate had become esterified. CYCLE OF CHANGES UNDERGONE BY PHOSPHATE IN ALCOHOLIC FERMENTATION. According to equation (1) the free phosphate present is used up in the reaction, and the question at once arises whether there is any source from which a constant supply of free phosphate can be elaborated in the juice, or whether some other change occurs which results in the formation of carbon dioxide and alcohol in the absence of free phosphate. The experimental evidence points in the direction of the former of these alternatives, but the question is a very difficult one to decide with absolute certainty. When a mixture of a phosphate with yeast-juice and sugar is examined at intervals and the amount of free phosphate estimated, the following stages are observed:-- 1. During the initial period of accelerated fermentation following the addition of the phosphate, the concentration of free phosphate rapidly diminishes. 2. At the close of this period, the amount of free phosphate [p053] present is very low, and, as long as active fermentation continues, no marked increase in it occurs.