CARBOHYDRATES III 



Glucose, dextrose or grape sugar, 

 Fructose, levulose or fruit sugar, 

 Galactose. 



These hexose monosaccharoses all have the formula CeHisCe. 

 They differ in constitution in ways that need not be entered 

 into here, but we shall consider in detail their relation to the 

 polysaccharose carbohydrates. 



We have given to the whole class of simple sugars the name 

 of monosaccharoses. This name is given in distinction to those 

 of disaccharoses, trisaccharoses and polysaccharoses, and be- 

 cause they are the simplest of the entire group of carbohydrates. 

 This simple nature is shown by the fact that they do not split up 

 by hydrolysis into any simpler carbohydrate compounds. The 

 disaccharoses and all polysaccharoses are known as such be- 

 cause on hydrolysis they do split up and yield two or more mole- 

 cules of these monosaccharoses. 



Glucose or Dextrose, CeHioOe 



Occurrence and Properties. — The most important and most 

 common of the hexose sugars is glucose, also known as dextrose 

 and grape sugar because it occurs naturally in ripe grapes. It 

 is found also in all other ripe fruits and in honey. It is present 

 in small amounts in many plants. It occurs in the blood of 

 all animals and in urine in the disease known as Diabetes. As 

 we shall find when we study animal nutrition, it is the final form 

 into which most of the carbohydrate food is changed in the 

 process of digestion, and the form in which it is burned in the 

 blood to furnish heat to the animal body. It occurs also in 

 combination in plants in the form of complex compounds known 

 as glucosides. These glucosides upon hydrolytic decomposition 

 yield glucose. An example may be mentioned, viz. amygdalin, 

 a glucoside found in bitter almonds and in cherry kernels, which 

 by fermentation yields glucose, hydrogen cyanide, and a sub- 

 stance known as benzaldehyde, or oil of bitter almonds. 



Determination. — Glucose possesses optical activity as ex- 

 plained in connection with lactic acid. It turns the plane of 



