Precisely the same products are given with phenylhydrazine by the hexosephosphoric acid prepared from glucose, mannose, and fructose, proving that all these sugars yield the same hexosediphosphoric acid, a point of fundamental importance. Direct measurements of the molecular weight of the acid by the freezing-point method, combined with the determination of the degree of dissociation by the rate of cane-sugar inversion, are indecisive, but indicate that the acid has a molecular weight considerably higher than that required for a triosephosphoric acid. A similar uncertainty attaches to the determination of the molecular weight from the freezing-point depression and conductivity of the acid potassium salt [Euler and Fodor, 1911]. Euler however concludes [p051] that both a hexosediphosphoric acid and a triosemonophosphoric acid are formed, but has not prepared any derivatives of the latter. As regards the constitution of the hexosephosphoric ester several suggestions have been made by Young, but no decisive evidence at present exists. The identity of the products from glucose, mannose, and fructose may be explained by regarding the acid as a derivative of the enolic form common to these three sugars (p. 97), or by supposing that portions of two sugar molecules may be concerned in its production. The formation and composition of the hydrazone and osazone are of great importance as they indicate that in all probability one of the phosphoric acid residues is united with the carbon atom adjacent to the carbonyl group of the hexose. They moreover render it certain that the original phosphoric ester is a hexosediphosphoric ester and not a triosemonophosphoric ester. Hexosediphosphoric acid has not as yet been discovered in the animal body. The action of a number of enzymes upon it has been examined [Euler, 1912, 2; Euler and Funke, 1912; Harding, 1912; Plimmer, 1913] with the following results. The lipase of castor oil seeds, a glycerol extract of the intestinal mucous membrane of the rabbit and pig, and an aqueous extract of bran have a slow hydrolytic action, whereas pepsin and trypsin are without effect. Feeding experiments with rabbits and dogs indicate that the ester is capable of hydrolysis in the animal body, a large proportion of the phosphorus being excreted as inorganic phosphate. The ester is also decomposed by /Bacillus coli communis/. It is remarkable that the hexosephosphate is not fermented nor hydrolysed by living yeast, a fact observed by Iwanoff, Harden and Young, and Euler, although, according to the experiments of Paine [1911], the yeast cell is at all events partially permeable to the sodium salt. THE EQUATION OF ALCOHOLIC FERMENTATION. An equation can readily be constructed for the reaction in which hexosephosphate is formed, the data available being the formula of the product and the relation between the phosphate added and the carbon dioxide and alcohol produced:--