Euler's other results on this subject may be briefly summarised as follows:-- (1) In presence of excess of sugar the esterification of the phosphoric acid proceeds by a monomolecular reaction and is most rapid in faintly alkaline reaction [Euler and Kullberg, 1911, 3]. (2) When yeast extract has been heated for 30 minutes to 40° it effects the esterification of phosphoric acid at a much greater rate than the unheated extract (2-10 times). Heating at 50° for 30 minutes however completely inactivates the extract. The cause of the activation is as yet unknown. The temperature coefficient for the unheated extract (17·5°-30°) is 1·4-1·5 for 10° rise of temperature [Euler and Ohlsén, 1911]. (3) Yeasts which in the dried state all produce rapid esterification of phosphoric acid, yield extracts of very unequal powers in this respect [Euler, 1912, 1]. [p059] CHAPTER IV. THE CO-ENZYME OF YEAST-JUICE. In the previous chapter reference was made to the fact that the addition of boiled yeast-juice greatly increases the amounts of carbon dioxide and alcohol formed from sugar by the action of a given volume of yeast-juice. When the boiled juice is dialysed the substance or substances to which this effect is due pass into the dialysate, the residue being quite inactive. In order to ascertain the effect on the process of alcoholic fermentation of the complete removal of these unknown substances from yeast-juice itself, dialysis experiments were instituted with fresh yeast-juice, capable of bringing about an active production of carbon dioxide and alcohol from sugar. It was already known from the experiments of Buchner and Rapp [1898, 1] that dialysis in parchment paper for seventeen hours at 0° against water or physiological salt solution only produced a diminution of about 20 per cent. in the total amount of fermentation obtainable, and in view of the less permanent character of the juice from top yeasts a more rapid method of dialysis was sought. This was found in the process of filtration under pressure through a film of gelatin, supported in the pores of a Chamberland filter candle, which had been introduced by Martin [1896]. In this way it was found possible to divide the juice into a residue and a filtrate, each of which was itself incapable of setting up the alcoholic fermentation of glucose, whereas, when they were reunited, the mixture produced almost as active a fermentation as the original juice [Harden and Young, 1905, 1; 1906, 2].