562 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 Pentoses are found in the urine in rare 

 cases. 2 Some nucleins, especially those of the pancreas and thymus, yield 

 pentoses on decomposition. Subcutaneous injection of arabinosc, xylose, and 

 rhamnose results in their excretion to the extent of more than 50 per cent, 

 in the urine. 3 The rest may be burned. 



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



Mannite. Mannose Mannonic 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 duleite, whereas glucose is probably the aldose of 

 sorbite — duleite 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. 538). Of the higher saccharides only maltose and 

 milk-sugar give this reaction. 



(3) Strongly characteristic are the insoluble crystalline compounds formed 

 by all glycoses with phenvlhydrazin, called osazones (see p. 534) : 



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



Levulose. Phenvlhydrazin. Glycosazone. 



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

 azones are decomposed into osones by fuming hydrochloric acid : 



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



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. 



1 Weiske: Zeitschrift fiir physiologischi Chemie, 1895, Bd. 20, S. 489. 

 > Salkowski : Zeitschrift fiir phy&iologische Chemie, 1899, lid. 27, S. 507. 

 3 Vi.it. F. : Deutsche* Archiv fiir klinische Medizin, Bd. 58, S. 523. 



