210 AGEICULTUEAL AND INDUSTRIAL BACTEKIOLOGT 



posed largely of microorganisms which rapidly oxidize the 

 alcohol to acetic acid. The enzyme produced by the organ- 

 isms capable of bringing about this change has not been 

 isolated, but it probably may be regarded as an intracellular 

 enzyme belonging to the general group of the oxidases. 

 The reaction may be indicated as follows : 



C^H^OH + 0^ = CH3COOH + HjO 



The bacteria which bring about the change under ana- 

 erobic conditions usually produce considerable quantities 

 of butyric, lactic, succinic or other acids simultaneously 

 with the formation of acetic acid. The changes are rela- 

 tively complex and the process of the fermentation is not 

 well understood ; it cannot, therefore, readily be represented 

 by a simple chemical equation. 



Groups of Acetic Bacteria. — As previously noted, the 

 bacteria producing acetic fermentation are either aerobic 

 or facultative and anaerobic. Of the former group the 

 organism Acetohacter aceti may be taken as a type. Of the 

 latter group, organisms belonging to the genera Bacterium 

 and Clostridium are worthy of mention. 



The Genus Acetobacter. — To this genus of bacteria 

 belong most of the forms capable of oxidizing ethyl alcohol 

 to acetic acid under aerobic conditions. Many species of 

 Acetohacter have been described but all are apparently 

 closely related. They differ from each other slightly in 

 morphology, in their ability to produce large or small 

 amounts of acid and to attack various sugars. The "mother 

 of vinegar" which forms on the surface of wine, cider or 

 other alcoholic solutions when allowed to stand, consists for 

 the most part of a tangled mass of bacteria belonging to this 

 genus together with yeast cells instrumental in bringing 

 about the preliminary alcoholic fermentation. All of the 

 bacteria belonging to this genus are rod-shaped, usually 

 relatively long and occur in chains. They are usually non- 



