SUGARS SUSCEPTIBLE OF FERMENTATION. 513 



of yeast, and secondly (where pure yeast was used), the neglect 

 to consider the fact that yeast is also able to assimilate such 

 sugars and utilise them in the construction of new cells which are 

 unable to ferment them. Lactose forms a well-known example 

 of this kind. It seems by no means impossible that, given a 

 sufficiently large sowing of yeast and small amount of sugar, the 

 whole or a portion of the sugar present may be eliminated with- 

 out any true fermentating taking place. Of course, where impure 

 yeast or unsterilised nutrient solutions are used, the action of 

 bacteria may come into play, a number of which are known to be 

 capable of producing alcohol from pentoses. The proof that alco- 

 holic fermentation cannot be set up in the pentoses by yeasts has 

 been given by a number of workers, including TOLLENS and GLAU- 

 BTTZ (I.), SCHEIBLER, CROSS and BEVAN (I), STONE and TOLLENS 

 (I.), SMITH, E. 0. von LIPMANN (III.)i E. FISCHER (XVI.), and 

 P LINDNER (XXXV.). According to BUCHNER and RAPP (III.)? 

 expressed yeast juice is also inactive toward pentoses. 



The real directly fermentable sugars are the hexoses, which 

 have the general formula C 6 H 12 O 6 ; and indeed, only such 

 members of this group as belong to the dl-series, the ^-compounds 

 being unfermentable. Here also, as in the other kinds of sugars 

 mentioned, a distinction is drawn between the aldoses and ke- 

 toses. 



The most widely occurring and best known of the aldo-hexose 

 sugars is d- glucose, also known as dextrose, grape sugar, starch 

 sugar, and diabetic sugar. It is fermented by all organisms capable 

 of inciting alcoholic fermentation, and therefore by all culture 

 yeasts of which, according to LANGE (IV.), about 700 races are 

 already known and all wine yeasts. (See also pp. 207 et seq., 

 and p. 397, vol. ii.) 



The sugar, d-mannose, also known as isomannose, seminose and 

 carubinose, is only occasionally met with in nature, for example 

 according to TSUKAMTO (I.) in the Japanese Amvrphophallus 

 Konjaku, and according to PRINSEN-GEERLIGS (V.), PELLETT (I.) 

 and others, in various kinds of colonial molasses, in orange rind ; 

 and also, according to GRUSS (III.), temporarily in germinating 

 dates. On the other hand, it forms a regular constituent of the 

 mannanes, which are of widespread occurrence throughout the 

 vegetable kingdom and represent, to some extent, condensation 

 products of mannose, either by itself or in association with other 

 sugars. In the latter case the products are classed as conjugate 

 mannanes. This sugar is fermented by all LINDNER'S yeasts 

 (XXXV.) which also ferment d-glucose, except Saccharomyces 

 membrancefaciens, S. farinosus, S. Bailii, a 8. apiculatus from 

 Leipzig mead and one from raspberry juice, 8. exiguus, Endo- 

 blasterma amycoides /., E. liquefaciens, a film yeast from marsh- 

 mallow sap, a fruit-ether yeast from gall fermentation, and Schizo- 

 saccharomyces Fombe. 



