92 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



kingdom, e.g., in the roots of celery, in the sugar cane and in 

 various algae and fungoid growths ; it can be extracted from 

 manna by boiling out with dilute alcohol and recrystallising. 

 It has a pleasant sweet taste, and is sparingly soluble in cold 

 but readily in hot water. 



Dulcite or Dulcitol is isomeric with mannite ; it occurs in 

 Madagascar manna, from which it can be extracted by hot 

 water. Dulcite is not so sweet tasting as manna and is less 

 soluble in water. It is important to note that both mannite 

 and dulcite yield secondary hexyl iodide, CH 3 (CH 2 ) 3 CHICH 3 , 

 when treated with concentrated hydriodic acid. 



Glucose, also known as dextrose or grape sugar, is found in 

 large quantities in grapes. As already mentioned, it is a 

 characteristic member of the aldohexose group ; it occurs 

 frequently, together with laevulose, also called fructose or fruit 

 sugar, which is the corresponding ketohexose (see pp. 84, 85), in 

 the juice of sweet fruits and in honey. The mixture of the two, 

 dextrose and laevulose, is generally known as invert sugar. 

 Dextrose and laevulose can be obtained from invert sugar by 

 the crystallisation of the dextrose from an alcoholic solution ; 

 or by the preparation of an insoluble lime compound of laevu- 

 lose, which is decomposed by suspending it in water and 

 passing carbon dioxide through the mixture. On filtering 

 off the calcium carbonate and evaporating the filtrate the 

 laevulose is obtained as a syrup which can be crystallised 

 from alcohol. 



Inosite. This is a somewhat rare substance l obtained as 

 an extract from the heart or lungs of the ox by a complicated 

 process ; it crystallises from dilute alcohol with 2H 2 0. 



Galactose is a sugar formed along with dextrose when 

 milk sugar is boiled with dilute sulphuric acid ; it is also 

 formed when gum arabic is similarly treated. It is less soluble 



1 Formerly classed as a sugar from its empirical composition ; it is 

 however a ring compound, viz., hexa-hydroxy-cyclohexane. 



