NUTRITION 359 



complexity of even the simplest carbohydrates, nor of the fact that a mere differem e 



in the position of certain atoms or groups of atoms, which docs not affect the per- 

 centage composition at all, gives wholly different chemical and physical characters 

 to the substance. 



Thus, grape sugar (glucose) exists in two forms, one of which rotates a beam of 

 polarized light to the right and the other to the left; the one, d-glucose, is abundant 

 in plants; the other, /-glucose, does not occur in nature but has been made arti- 

 ficially. The difference is shown partly in the three following structural formulas, 

 which all sum upCeH^Oe: 



OH H OH OH 



I I I I 

 COH — C C C — C — CH 2 OH =rf-glucose 



I I I I 

 H OH H H 



H OH H H 



I ! I I 



COH C C C C CHoOH =/-glucose 



I I I I 

 OH H OH OH 



Further, fruit sugar (^-fructose) is abundant in plants, and its structure is quite 



different from glucose : 



H OH OH 



I I I 

 CHoOH CO C C C CH2OH =</-fructose 



I I I 

 OH H H 



Another sugar especially abundant in plants, cane sugar, C12H22O11, probably has 

 this formula: 



saccharose 



and when it breaks at the — O — bond, it takes up IT -OH and resolves itself into a 

 molecule of glucose and a molecule of fructose. These two hexose sugars, glucose 

 and fructose, and the disaccharide, cane sugar, are the only sugars which occur in 

 abundance in plants; though mannose, galactose, and maltose are formed in the 

 course of digestion. 



