Chemical Constituents of the Animal Body. 217 



that is to say, they are stereoisomerides containing a 

 methoxyl group, but that this latter occupies different 

 positions with regard to the terminal carbon atom. 

 Dextrose itself is an aldehyde, but it is assumed that it 

 may form an addition product with water, like so many 

 other aldehydes. Now, as a substance derived in this 

 manner contains a terminal hydroxyl group which is in 

 the y position to another hydroxyl group, it should 

 readily form an anhydride analogous to a lactone (see 

 p. 202). If tetrahedra models are employed to represent 

 the formulae, it will be easy to see that the two hydroxyl 

 groups in question can be readily brought into close 

 apposition. Two possible stereoisomerides can be pro- 

 duced by this anhydride formation, and the relationship 

 can be expressed in the following formulae : 



C OH 



HC-OH\ 



I O 



OH-CH 



Hi 

 OH 



HO- ' 



i, 



)H 2 OH 

 /3-form of 

 Anhydride. Anhydride. 



There is evidence of the existence of the two forms of 

 dextrose, for Tanset has shown that by employing dif- 

 fer^nt methods of crystallization, dextroses with different 

 rotations, melting points, etc., can be employed. Solutions 

 of these forms change rotation when dissolved in water; 

 dextrose solutions, in fact, do not show as a rule a 



