104 THE CARBOHYDRATES 



subsequently found that Bacterium xylinum had the peculiar 

 power of oxidizing a — CHOH group to CO provided the 

 hydroxyl was adjacent to another hydroxyl group on the 

 same side of the molecule ; thus it could oxidize mannitol or 

 sorbitol which contain the grouping — 



H H 



— C C CH^OH 



OH OH 

 but not dulcitol which contains the grouping — 



H OH 



— C C— CHjOH 



OH H 

 Sorbose is not fermentable by yeast. 



GALACTOSE. 



OccMrrefice. 



This sugar has rarely been recorded as occurring free in 

 nature. Von Lippmann * claims to have found it on ivy 

 berries after a sudden frost, which is analogous with the in- 

 crease of the rafhnose content of sugar beet under like con- 

 ditions. In its polysaccharide form of galactan, galactose 

 forms a constituent of mucilages, such as agar and carrageen 

 obtained from sea weeds ; it also occurs in the gums of the 

 peach and plum, and is a constituent of the pectic substances 

 of carrot, turnip, and many fruits such as apple and pear. 

 In all these instances galactose is accompanied by other 

 sugars, which may be either hexoses or pentoses. Further, 

 galactose is a constituent of the glucoside digitalin, of the 

 anthocyan idaein, and forms the carbohydrate constituent of 

 the group of lipins known as cerebrosides and galactolipins. 

 In all cases it may be set free by hydrolysis with mineral 

 acid. 



Preparation. 



A convenient material for the preparation of galactose is 

 agar, which on hydrolysis yields a mixture of sugars amongst 



* Von Lippmann : " Ber. deut. chem. Gesells," 1910, 43, 361 1. 



