THE CARBOHYDRATES 71 



rotatory, reduces Fehling's solution, and gives an osazone resembling 

 that derived from glucose. 



GLYCURONIC ACID, C 6 H 10 7 , may be regarded as one of the 

 first results of oxidation of the glucose molecule. The group 

 which has undergone oxidation is not the readily oxidisable CHO 

 group, but the CH 2 OH group at the other end of the molecule. The 

 formula of this acid is therefore : 



COOH 



(CH.OH) 4 



CHO. 



In the free state it does not occur in the animal body. It is 

 constantly found in the urine after administration of certain drugs 

 such as phenol, camphor, or chloral, and then occurs as a conjugated 

 acid with these substances. These conjugated acids are Isevo- 

 rotatory, though the free acid is dextro-rotatory. In the free state 

 it reduces Fehling's solution and gives an osazone which is not 

 sufficiently characteristic to distinguish from glucosazone. It does 

 not undergo fermentation with yeast. This test is therefore the 

 best means of distinguishing the acid in urine from glucose. 



THE FORMATION OF GLUCOSIDES 



The graphic formula given on p. 66 do not explain all the 

 possible modes of arrangement of the groups of the sugar molecules. 

 Many of these sugars, when dissolved in water, present the phenomenon 

 known as multi-rotation. If their rotatory power be taken immediately 

 after solution, it is found to be greater or less than the rotatory power 

 taken some hours or days later. Glucose, for instance, immediately 

 after solution, has a high specific rotatory power, which diminishes 

 rapidly if the solution be boiled, and more slowly if it be allowed to 

 stand. Finally, the specific rotatory power becomes constant at 

 + 53 D. This change in rotatory power seems to be associated 

 with a change in the arrangement of the groups, the aldose, for example, 

 assuming, by the shifting of a mobile oxygen atom, what is known as a 

 lactone arrangement. 



Thus glucose COH(CHOH) 2 CHOH.CHOH.CH 2 OH be omes 

 CHOH . (CHOH) 2 . CH . CHOH . CH 2 OH 







This change in the arrangement of the molecule renders a further 



