NUTRITION 359 



complexity of even the amplest i arbohydrates, aor of the fact that a mere difference 

 in the position of certain atoms or groups of atoms, whi< li does qoI affet I the per- 

 centage composition at all, gives « holly different < hemi< al and physic al i haracters 

 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, i-glu< ose, is abundant 

 in plants; the other, /-glucose, does not o< i ur in nature but has been made art i- 

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

 which all sum up (V,l I pj< »« : 



OH H OH OH 



! I I I 



COH — C C — C — C CH 2 OH =<*-glucose 



I I I I 

 H OH H H 



H OH H H 



I ! I I 



COH — C — C — C C CH2OH =/-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 — CHoOH =<Z-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 If •< >H and resolves itself tntoa 

 molei ule of glui ose and a mole* ule of fru< lose. 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 



( ..u isc> of digestion. 



