1004 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



THE GLYCOSES. 



The triose called glycerose has already been described. 



A tetrose called erythrose, which is the aldose of erythrite, C 4 H 6 (OH) 4 , a 

 tetratomic alcohol, is known. 



Of the possible pentoses, arabinose, xylose, and rhamnose (methyl-arabinose) 

 occur in the vegetable kingdoms in considerable quantity. They may be 

 absorbed by the intestinal canal. 1 



Hexoses, or Glucoses. Through the oxidation of hexatomic alcohols 

 there may be obtained, first, glucoses, then monocarbonic acids, and lastly 

 saccharic acid, or its isomer mucic acid : 



C 6 H 6 (OH) 5 CH 2 OH. C 5 H 6 (OH) 5 CHO. C 6 H 6 (OH) 5 COOH. 



Mannite. Mannose Maiinonic acid, 



(and levulose). 



C 5 H 6 (OH) 4 (COOH) 2 . 



Saccharic acid. 



Mannose and levulose are respectively the aldose and ketose of mannite, 

 galactose is the aldose of dulcite, whereas glucose is probably the aldose of 

 sorbite dulcite and sorbite being, like mannite, hexatomic alcohols. 



Properties. (1) The hexoses are converted into their respective alcohols on 

 reduction with sodium amalgam. 



(2) The hexoses act as reducing agents, converting alkaline solutions of 

 cuprous oxide salts (obtained through presence of tartrate) into red cuprous 

 oxide, which precipitates out (Trommer's test). Levulic acid is among the 

 products formed (see p. 982). Of the higher saccharides only maltose and 

 milk-sugar give this reaction. 



(3) Strongly characteristic are the insoluble crystalline compounds formed 

 by all gly coses with phenylhydrazin, called osazones (see p. 977) : 



C 6 H 12 6 + 2H 2 N.NH(C 6 H 5 ) = C 6 H 10 O 4 (:N.NH.C 6 H 6 ) 2 + 2H 2 O + H 2 . 



Levulose. Phenylhydrazin. Glycosazone. 



Levulose, dextrose, and mannose give the same glycosazone. The glycos- 

 azones are decomposed into osones by fuming hydrochloric acid : 



C 6 H 10 4 (:N.NH.C 6 H 5 ) 2 + 2H 2 O = C 6 H 10 O 6 + 2H 2 N.NH.C 6 H 6 . 



Glycosone. 



Osones are converted into sugar by nascent hydrogen. The osone de- 

 rived from levulose, dextrose, and mannose yields levulose by this treatment, 

 and the transformation of dextrose and mannose into levulose is therefore 

 demonstrated. 



(4) Only trioses, hexoses, and nonoses are capable of alcoholic fermenta- 

 tion. 



Synthesis of the Glucoses. Formose may be ptirified by means of phenyl- 

 hydrazin as above, so that pure t-fructose is obtained ; this treated with sodium 

 amalgam yields i-mannite, which on oxidation is converted into 2-mannonic 

 acid ; this last is separated by a strychnin salt into its two components ; the 

 1 Weiske: Zeitschrift fur physioloyiseke Chemie, 1895, Bd. 20, p. 489. 



