OXALIC AND CITRIC TEEMENTATION 219 



Formation of Other Volatile Acids.— Certain bacteria 

 are capable of producing formic, propionic and valerianic 

 acids from carbohydrates. These are less frequently met 

 with and are not as important, therefore, as those bringing 

 about acetic and butyric fermentations. 



Oxalic Fermentation 



Certain species of molds are known which are capable of 

 producing oxalic acid from sugars. The most important of 

 these belong to the genera Aspergillus and Pemcillium. 

 The process is essentially aerobic. The presence of the 

 oxalic acid is easily demonstrated by growing the organisms 

 in a medium containing some soluble salts of calcium. The 

 insoluble calcium oxalate is precipitated. The crystals of 

 this salt usually may be readily observed in an agar plate 

 culture of such a mold. 



Citric Acid Fermentation 



Certain species of molds belonging to the genera Citro- 

 niyces and the closely related genus PenicilUum have been 

 found to possess the power of transforming sugar into citric 

 acid. The acid is produced in sufScient quantities so that 

 patents upon this method of preparation have been taken 

 out by commercial firms in Europe. Most of the citric acid 

 on the market, however, comes from native fruits such as 

 the orange and lemon and not from citric fermentation. 



