ACETIC FERMENTATION 211 



motile and do not produce spores. For the most part, they 

 grow readily upon suitable culture media and are obligate 

 aerobes. Some produce such small quantities of acid that 

 they are of no economic significance. Others produce the 

 acid rapidly and in large quantities. Different species have 

 been described from wines, from cider, from beer and from 

 the so-called quick process of vinegar manufacture. The 

 cells for the most part produce considerable amounts of 

 slime and tend to form films on the surface of the medium. 

 Involution forms, that is, cells showing unusual shapes such 



Pis. 51. ACTETOBACTER. Normal rods and involution forms. 



as clubs, branched forms, spheres, etc., are very common, 

 particularly in the older films. 



Acetobacter aceti. This organism may usually be dif- 

 ferentiated from related acetic bacteria by the fact that it 

 produces a surface pellicle upon the alcoholic solution which 

 can be easily broken up ; that is, the development of slime 

 is not so evident as in some other species. The slime from 

 this organism is not stained by the use of a solution of 

 iodine or of potassium iodide. The organism has usually 

 been isolated from the surface of souring beer. 



Another organism which has been described from beer 

 vinegar is the Acetobacter pasteurianum. Some authors 

 have also described it as one of the important agencies in 

 the production of wine and cider vinegar. It develops as a 

 membrane on the surface of the liquid, at first appearing 



