348 SUGAR DESTRUCTION IN THE ECONOMY 



of the aldehyde then condensing into aldol and this finally 

 becoming converted into its isomer, butyric acid : 



SUGAR 



The equation for butyric acid fermentation is usually 

 written: C 6 H 12 6 = C 4 H 8 2 + 2C0 2 + 2H 2 . 



Citric Acid Fermentation. In conclusion, observations 

 upon citric acid fermentation seem to be not without some 

 interest in connection with the question of sugar catabolism 

 in the body, particularly because citric acid is present in the 

 animal body as a constituent of milk. In culture of certain 

 forms of citromycetes on appropriate media which are poor 

 in nitrogen and contain an addiment of carbonate of lime 

 to fix the citric acid as the relatively insoluble citrate of 

 calcium and thus prevent its further decomposition, the 

 fermentation of the sugar may be governed so that actually 

 only citric acid and carbonic acid, but neither alcohol, acetic, 

 lactic or succinic acid, will appear. 55 Obviously the branched 

 chain of citric acid can be explained only on the supposition 

 of a synthesis. It is thought that it can be explained, for 

 example, by the combination of three molecules of glycolic 



., CH 2 .OH ,v 

 acid, I > with separation of water : 



CITRIC ACID 



IOJpCH 2 .COOH CH 2 .COOH 



OH.C-COOH > OH.C.COOH 



in: 



CH 2 .( 



2 .COOH- 

 ;OHJCH 2 .COOH 



But it must be said that there is as little proof that the 

 synthesis of citric acid actually takes place in this way, as 



" E. Buchner and H. Wiistenfeld, Zeitschr. f . Biochem., 17, 395, 1909. 



