The rates attained during the initial period of rapid fermentation and the subsequent period of slow fermentation are thus seen to represent the velocities of two entirely different chemical reactions. These considerations also explain why it is the /extra/ carbon dioxide evolved during the initial period, and not the total carbon dioxide, which is equivalent to the added phosphate. As the production of phosphate is proceeding throughout the whole period at a rate which is equivalent to the normal rate of fermentation, it is obviously necessary to deduct the corresponding amount of carbon dioxide from the total evolved in order to ascertain the amount equivalent to the added phosphate. An explanation is also afforded of the fact that a considerable increase in the concentration of hexosephosphate does not materially increase the normal rate of fermentation. This is probably due to the circumstance that, in accordance with the general behaviour of enzymes in presence of excess of the fermentable substance, the hexosephosphatase hydrolyses approximately equal amounts of hexosephosphate in equal times whatever the concentration of the latter may be, above a certain limit. According to the experiments of Euler and Johansson [1913] the hydrolytic activity of the hexosephosphatase is greatly diminished by the presence of toluene. EFFECT OF PHOSPHATE ON THE TOTAL FERMENTATION PRODUCED BY YEAST-JUICE. The addition of a phosphate to yeast-juice not only produces the effect already described, but also enables a given volume of yeast-juice to effect a larger total fermentation, even after allowance is made for the carbon dioxide equivalent to the quantity of phosphate added. The increase in the case of ordinary yeast-juice has been found to amount to from 10 to 150 per cent. of the original total fermentation [p055] produced by the juice in the absence of added phosphate. The numbers contained in columns 1 and 2 of the table on p. 56 illustrate this effect, the ratio of the total in the presence of phosphate to that obtained in its absence being given, as well as that of the total in presence of phosphate less the equivalent of the phosphate added, to the original fermentation. The cause of this increase in the total fermentation is probably to be sought mainly in a protective action of the excess of hexosephosphate on the various enzymes, for, as has been stated above, the rate of fermentation after the termination of the initial period, is practically the same as in the absence of added phosphate (see p. 43). Now it follows from equation (1) (p. 51) that in the total absence of phosphate no fermentation should occur, and the experimental realisation of this result would afford very strong evidence in favour of this interpretation of the phenomenon.