THE CARBOHYDRATES AND THEIR METABOLISM. 225 



Since there are two closed ring forms for eacii aldohexose, the a and 

 P forms, there should he 'W closed chain aldehesoses, 4 with which the 16 

 already discussed make a total of 48 isomeric aldohexoses theoretically 

 possible. Alost of the carbohydrates exist in more than one form and 

 possess the power of mutarotation. 



TABLE III 

 SPECIFIC ROTATIONS OF 



a Methyl glucoside +157. Methyl glucoside 



Chemical Reactions of the Carbohydrates 



In most cases glucose will be nsed as a typical carbohydrate in dis- 

 cussing the reactions which the carbohydrates undergo. (Only those that 

 have a direct interest to the biochemist will be presented.) 



Synthesis and Degradation of Carbohydrates Most of the methods 

 of synthesizing the carbohydrates we owe to the masterly researches of 

 Emii Fischer, who devised most of the methods and synthesized a vast 

 number of them. 



1. Polymerization (aldol condensation) of simple sugars by action 

 of dilute alkali, e.g., 



2 C 3 IT 6 3 

 Glycerose 



Fructose 



This reaction is somewhat similar to one by which it is believed carbo- 

 hydrates may be formed in plants from formaldehyde. Baeyer, in 1870, 

 first advanced the theory that the plant tissues fonned formaldehyde from 

 C(X and 1I 2 O. Loew, in 1880, discovered that formaldehyde (HCOH) 

 and lime water at room temperature produced a sweet substance which was 

 unfennentable. Fischer later showed that what is fonned here is a acrose, 



4 In the closed chain formula there is an additional asymmetric carbon atom, so 

 that the number of isomers is 2 & or 32. 



