BACTERIAL FERMENTATION OF SUGARS 79 



is well to consider this factor in relation to the chemical con- 

 stitution of the sugars. These bodies are now known to be (to 

 use the definition of Holleman) aldehyde or ketoue alcohols 

 containing one or more hydroxyl groups, one of which is directly 

 linked to a carbon atom in union with car bony 1. The group 

 characteristic of a sugar is thus CHOH - CO - . The sugars 

 are divided into monosaccharides or monoses, disaccharides 

 (dioses), and polysaccharides (polyoses). The members of the 

 last two groups may be looked on as derived from the combina- 

 tion of two or more molecules of a monosaccharide with the 

 elimination of water (e.g. 2C 6 H r2 O 6 = C 1? H. 22 O U + H ? O). 



Monosaccharides. These are classified according to the 

 number of C atoms they contain. The pentoses ordinarily used 

 are arabinose (obtained from gum arabic), xylose (from wood), 

 and rhamnose (which is really a methylpentose). Among the 

 hexoses are glucose (dextrose) with dextro-rotatory properties. 

 Glucose is an aldehyde alcohol (aldose). In fruit there is also 

 a ketone alcohol (ketose) called fructose, which from its laevo- 

 rotatory properties is also known as laevulose. Other hexosee 

 are mannose (from the vegetable ivory nut) and galactose (a 

 hydrolytic derivative of lactose). 



Disaccharides (C 12 H 2 . 2 O n ). The ordinary members of this 

 group are maltose (derived from starch), lactose, and cane sugar 

 (sucrose, saccharose). 



Polysaccharides. Examples are starch, raffinose, inulin (from 

 dahlia roots), dextrin, arabin, glycogen, cellulose. 



If we consider sugars generally from the point of view of 

 the capacity of yeast to originate alcoholic fermentation in them, 

 we may say that the simpler the constitution of the sugar the 

 more easily is it fermented. Thus the monosaccharides are 

 more easily acted on by yeast than the di- or poly-saccharides. 

 Usually an independent process resulting in the splitting of the 

 higher into the lower is preliminary to the alcoholic fermentation. 

 Thus yeast first inverts cane sugar into glucose and fructose, and 

 then acts on these products. From what is known it is probable 

 that similar facts hold with regard to the action of bacteria. 



Besides sugars, other alcohols with large molecules may be 

 broken down by bacterial action, and these bodies have been 

 used for differentiating the properties of allied bacteria. Among 

 these substances may be mentioned the trihydric alcohol glycerol 

 (glycerin), the tetrahydric erythritol and the hexahydric dulcitol 

 (dulcite), mannitol (mannite), and sorbitol (sorbite). 



Similarly certain glucosides, such as salicin, coniferin, etc., 

 have been used for testing the fermentative properties of 



