208 BIOLOGY OF SPECIALIZED GROUPS 



such as calcium carbonate, etc. Lactic acid inhibits the 

 growth of most all of the species of bacteria concerned in the 

 process when its concentration reaches about (0.8 per cent) 

 eight tenths to (i per cent) one per cent. 



About eighty per cent (80 per cent) of the fermentable 

 sugar is converted into lactic acid, small amounts of acetic, 

 formic, and succinic acids, carbon dioxide, hydrogen, nitrogen, 

 methane, and alcohols, under favorable conditions. A cer- 

 tain amount of lactose and other sugars always remains in 

 solution unfermented. 



Acetic Acid Fermentation. This f ermentive or enzyme 

 process, like all others of this group, is in part a distinct 

 oxidation process. The bacterial enzymes act on the car- 

 bohydrate sugars and break them down into ethyl alcohol 

 and carbon dioxide. The oxidation of the alcohol results in 

 the formation of aceticaldehyde and later acetic acid. The 

 acetic acid is still further oxidized to carbon dioxide and water. 



The following reactions on dextrose will serve to elucidate 

 the process : 



C 6 H 12 O 6 + H 2 O = 2 CH 3 CH 2 OH + 2 CO 2 + H 2 O (ethyl 



alcohol, carbon dioxide, and water). 

 CH 3 CH 2 OH + O = CH 3 COH + H 2 (ethylaldehyde or 



aceticaldehyde). 



CH 3 COH + = CH 3 - COOH (acetic acid). 

 CH 3 COOH + 40 = 2 H 2 O + 2 CO 2 (water and carbon di- 

 oxide). 



