218 



Biological Chemistry. 



constant rotatory power when freshly prepared, and a 

 definite rotation is only obtained when the solutions have 

 been kept for some time. Dextrose exhibits the pheno- 

 menon of " mutarotation," and this can be explained on 

 the hypothesis of the existence of two isomerides of the 

 forms indicated above. When the rotation of the solution 

 becomes constant it contains an equilibrated mixture of 

 the a- and /3-isomerides. 



The glucosides undergo hydrolysis yielding methyl 

 alcohol and dextrose when treated with acids or ferments. 

 Some ferments will hydrolyze only the a-form, whereas 

 others will hydrolyze only the /3-forrn, an -important fact 

 which will be considered later when discussing the nature 

 of ferment action. 



Glucosides exist which yield products other than 

 methyl alcohol on hydrolysis, and also sugars other than 

 dextrose. Many of these can also be hydrolyzed bj 

 ferments, which exhibit characteristic specific actions. 

 The following are some examples of glucosides and their 

 hydrolysis products : 



Glucosides. Products of Hydrolysis. 



Arbutin . . . Dextrose + hydroquinone. 



Phloridzin . . . Dextrose + phloretin. 



Strophanthin . . Rhamnose + mannose + strophanthidin. 



Amygdalin. . . 2 molecules of dextrose + benzaldehyde + 



hydrocyanic acid. 



. . Dextrose + salicylaldehyde. 



. . Dextrose -f allyl mustard oil + KHS0 4 . 



Helicin . . . 

 Sinigrin . . 



A large number of other glucosides are known. 



SUMMARY. The carbohydrates may be subdivided 

 into the classes of the monosaccharoses, disaccharoses, and \ 

 poly saccharoses, the two latter classes being derived from! 

 the first-named by condensation of two or more molecules 

 with the withdrawal of the elements of water. Mono- , 



