96 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



compound, but like cane sugar it does not ferment with 

 pure yeast. 



The Poly-saccharoses. Of these, starch and cellulose will 

 be more usefully considered separately in the chapters devoted 

 to their decomposition by enzyme or bacterial action. It 

 will be understood that their molecular structure is much 

 more complicated than that of the carbohydrates belonging to 

 the two preceding classes. 



Glucosides. A class of substance occurs in nature, 

 generally in the leaves of plants or bark of trees, which on 

 treatment with acid, or by the action of certain enzymes, 

 yields a sugar together with another organic compound. In 

 the majority of cases the sugar present is glucose, and these 

 bodies, therefore, are termed glucosides. 



One of the earliest and, at the same time, best known of 

 the glucosides is amygdalin, which occurs in bitter almonds 

 and in the kernels of apricots, peaches and plums. 



Liebig and Wohler in 1837 isolated an enzyme which they 

 termed emulsin. They found that on crushing bitter almonds 

 the amygdalin was decomposed according to the following 

 equation : 



0^0^ + 2:0,0 = C 7 H 6 + HCN+2C 6 H 12 6 



Amygdalin Benzaldehyde Hydrogen Glucose 



cyanide 



Kecent researches by Fischer, Caldwell and Courtauld and 

 others have shown that amygdalin can be split up at several 

 centres marked x y z in the formula 



NC . CHC 6 H 5 . . C 6 H 10 4 . . C 6 H n 6 

 z x y 



which are attackable only by specific enzymes ; thus an 

 infusion of yeast only splits off one molecule of grape sugar 

 at y, leaving a residue termed almond nitril glucoside which is 

 capable of being completely split up by emulsin. 



