B.—CHEMISTRY 35 
molecules united through the hydroxyl positions at x and 6, which is 
found to occur in gentiobiose. Still another mode of union is exemplified 
Maltose skeleton. Cellobiose skeleton. 
nO-cH 
fo no AN 
aN CHO 
on 4 
Gentiobiose skeleton. Sucrose. 
by the formula which applies to sucrose. Here two different hexose units 
are involved, namely, glucose and fructose which are assembled as a pair 
through sharing a common oxygen atom or glucosidic link situated at 
the first carbon atom in each hexose, and it will be observed that whilst 
«-glucose is present as the pyranose form the @-fructose on the other hand 
occurs in sucrose as the furanose. It may here be added that this struc- 
tural type established for the occurrence of the fructose residue in sucrose 
occurs also in the polysaccharides inulin and the levan from grass. It 
may well be the case that other furanose sugars occur more widely than 
we have suspected in complex polysaccharides. Recently one such 
residue has been found to be present as a terminal group in xylan, or 
wood gum. It appears to be the case that the arabofuranose we have 
found in xylan constitutes also a large part of the molecule of arabic 
acid, which is the modified polysaccharide in gum arabic. 
Returning from this rapid review of these structural forms, and of the 
modes of assembly of pairs of sugar units in a biose, let me now present 
