SUGAR 417 



resembles glucose in many properties, differing from it in its 

 action on polarised light. Glucose rotates the polarised ray to 

 the right and is, hence, frequently called dextrose, while fructose 

 rotates to the left and is sometimes called laevulose in reference 

 to this fact. For reasons to be explained later these terms are 

 liable to confusion. Fructose behaves in many respects as if 

 possessed of the constitution known as ketonic. 



As the result of recent researches, especially by E. F. Arm- 

 strong, chemical opinion as to the constitution of glucose has 

 undergone a serious modification. It is now believed that there 

 are two varieties of glucose containing the same constituents 

 attached to the fundamental carbon atoms in the same order, 

 but disposed differently in space so that in the main their 

 properties are very close together, and they are mutually con- 

 vertible the one into the other. The formulae by which these 

 sugars are now represented are shown below. 



CH 2 -OH CH 2 -OH 



I I 



CH-OH CH-OH 



HC-OH HOCH 



a. Glucose. . Glucose. 



Here it will be observed an attempt is made to indicate the 

 nature of this difference, though it must be understood that such 

 formulae pretend not in the slightest degree to afford a pictorial 

 representation of the molecules (see Chapter XII). 



The number of distinct saccharoses now known is very large. 

 Some of the more important sugars of this class occurring in 

 nature have been mentioned as derived from vegetable sources. 

 Perhaps it ought also to be stated that glucose occurs in small 

 quantity in the blood and tissues of the higher animals, where it 

 is found as the result of changes in a peculiar compound known 

 as glycogen which occurs in the liver. In books on physiology 



2 E 



