ACETIC ACID BACTERIA. 



99 



physiologically. In sterilised beer they give different fermen- 

 tation reactions. At higher temperatures Bact. Pasteurianum 

 acquires a higher acidifying power than Bact. aceti ; on the other 

 hand, Bact. aceti is able to carry on a vigorous fermentation 

 at 4-4-5 C., whilst at this temperature Bact. Pasteurianum 



Fig. 21. Bacterium Pasteurianum. Transformation of the thread-forms and chains after 

 cultivation in " double beer" at about 34 C. (after Hansen). 



forms no appreciable amount of acetic acid. At 33-34 C. 

 Bact. Pasteurianum reaches the maximum of acetic acid 

 formation 3-3 per cent, by weight in seven days after 

 which the formation slowly diminishes, and finally ceases. 

 After the maximum of acid formation has been reached, 



