PRODUCTS OF THE LOWER FUNGI 



290 



This mechanism accounts for the high yields of oxahc 

 acid which can be obtained and also for the fact that it is 

 formed from the four-carbon dibasic acids, which can all 

 give rise to oxalacetic acid, and from acetic acid, but not 

 from the three-carbon acids. They consider that citric 

 acid is formed by the same mechanism as far as the 

 breakdown into oxalacetic and acetic acids, which then 

 recondense to give citric acid : — 



Challenger has suggested that citric acid may arise via 

 saccharic acid and [3 y-diketo-adipic acid, which undergoes 

 a benzilic acid transformation to give citric acid (a process 

 which occurs in presence of alkali in vitro) : — 



He regards citric acid as being the source of oxalic acid 

 via acetic acid, which is formed by decarboxylation of 

 malonic acid derived from acetonedicarboxylic acid : — 



