THE CHEMISTRY OF THE SUGARS 



97 



The following are a few typical naturally occurring gluco- 

 sides, together with their products of hydrolysis :— 



^^""'^ ' yields glucose plus 1^^^^^^" 



Salicin 

 CisHigO; 



Coniferin 



I 



(salicyl alcohol 

 ICeH40HCH20H 

 /coniferyl alcohol 

 J /OCH3 



CcH4\ 



^CH=CH20H 

 I'salicylaldehyde 

 OH 



^CHO 



( indoxyl 

 jCgHjON 



allyl mustard oil 



C,H,CNS 



+ KHSO4 



Helicin 

 C13H16O7 



Indican 

 CuH^OeN 



Sinigrin 

 CioHieO.NS^K 



The naturally occurring glucosides are accompanied, in 

 most cases at any rate, by the enzyme which is capable of 

 effecting their hydrolysis. The enzyme and the glucoside 

 occur in separate cells, and they only act upon one another 

 when the cell contents are brought together by crushing, as for 

 instance, when bitter almonds are pounded in a mortar ; the 

 emulsia in this case is probably contained in the skin of the 

 almond. It is possible that glucosides form a reserve of 

 food material for the plant, their constituents being only 

 capable of assimilation after hydrolysis, that is, when brought 

 in contact with the enzyme. 



It has been possible to prepare a certain number of sub- 

 stances artificially which belong to the same class as glucosides. 

 When glucose is dissolved in water and the freshly prepared 

 solution examined in the polarimeter, the optical activity 

 observed immediately after solution is found gradually to 

 diminish, and after about six hours becomes constant at a 



