Euler and Bäckström [1912], however, have made the important observation that sodium hexosephosphate causes a considerable acceleration although it is itself neither fermented nor hydrolysed under these conditions. The extent of this is evident from the following numbers:-- ──────────────────────────────────────────────────── 20 c.c. of 20 per cent. glucose solution. 0·25 g. yeast [Yeast H of St. Erik's brewery]. ────────────────────┬─────────────────────────────── Without addition. │ + 0·5 g. Na hexosephosphate. ────────┬───────────┼───────────┬─────────────────── Time. │ CO{2}. │ Time. │ CO{2}. Min. │ │ Min. │ ────────┼───────────┴───────────┴─────────────────── 46 │ 10·5 37 8 76 │ 17·5 73 19 197 │ 45 188 52·5 347 │ 74·5 321 123 488 │ 95 450 193·5 ──────────────────────────────────────────────────── The observation has been confirmed with English top yeast (Harden and Young, unpublished experiments), but no explanation of the phenomenon is at present forthcoming. Euler has also found [Euler and Cassel, 1913; Euler and Berggren, 1912] that yeast extract, sodium nucleinate and ammonium formate also increase the rate of fermentation of glucose by yeast, but these results have been criticised by Harden and Young [1913] on the ground that the possibility of growth of the yeast during the experiment has not been excluded. FERMENTATION OF DIFFERENT SUGARS BY YEAST. Many valuable ideas as to the nature of fermentation have been obtained by a consideration of the phenomena presented by the action of yeast on the different hexoses. Of these only glucose, fructose, mannose, and galactose are susceptible of alcoholic fermentation by yeast, the stereoisomeric hexoses prepared in the laboratory being unfermentable, as are also the pentoses, tetroses, and the alcohols corresponding to all the sugars. The yeast-cell is therefore much more limited in its power of producing fermentation than such an organism as, for example, /Bacillus coli communis/, which attacks substances as [p131] diverse as arabinose, glucose, glycerol and mannitol, and yields with all of them products of the same chemical character, although in varying proportions.