The results of the experiments with yeast-juice therefore indicate that what is being measured is a typical enzyme action, but afford no information as to which of the many possible actions is the controlling one, a fact which must be ascertained for each particular case in the manner indicated above. Clowes [1909], using washed zymin free from fermenting power and adding various volumes of boiled yeast extract, found that the velocity of reaction was proportional to the product of the concentrations of zymin and yeast extract up to a certain optimum concentration. He interprets these concentrations as representing the concentrations of zymase and co-enzyme, but they also represent the concentrations of hexosephosphatase (present in the zymin) and phosphate (present in the yeast extract), so that at least four factors were being altered instead of only two. It has already been mentioned that Euler and Kullberg [1911, 3] found the conversion of phosphate into hexosephosphate in presence of excess of glucose to proceed according to a monomolecular reaction (p. 58). The rate of fermentation is diminished by dilution of the yeast-juice, but less rapidly than the concentration of the juice. Herzog found that when the relation between concentration of enzyme and the velocity constant of the reaction is expressed by the formula K{1}/K{2} = (C{1}/C{2})^{/n/} where K{1} and K{2} are the velocity constants corresponding with the enzyme concentrations C{1} and C{2}, the value for /n/ is 2 for zymin, whilst Euler working with yeast-juice obtained values varying from 1·29 to 1·67 and decreasing as K increased. The temperature coefficient of fermentation by zymin was found [p123] by Herzog to be K{24·5°}/K{14·5°} = 2·88, which agrees well with the value found by Slator for yeast-cells (p. 129).