66 MICRO-ORGANISMS AND FERMENTATION. 



tation reactions. At higher temperatures Bad. Pasteurianum 

 acquires a higher acidifying power than Bad. aceti ; on the 

 other hand, Bad. acdi was able to carry on a vigorous fer- 

 mentation at 4 to 4 J C., whilst at this temperature Bad. 

 Pasteurianum formed no appreciable amount of acetic acid. 

 At 33-34 & C. Bad. Pasteurianum reached the maximum of 

 acetic acid formation in seven days, namely, 3 '3 per cent, by 

 weight. After the maximum of acid formation had been 

 reached, irregularly swollen cells made their appearance in 

 the growth, which under the existing nutritive conditions may 

 probably be considered as diseased or degenerate forms (involu- 

 tion forms). More thorough investigation into this question is 

 to be desired. The forms noted by HANSEN in the cycle 

 described above have quite a different physiological significa- 

 tion, in that they are then developing freely, and thus prepar- 

 ing the growth for the formation of new cells. 



Acetic acid bacteria play an important part in the fermenta- 

 tion of beer, spirits, and wine. Especially in the last-named 

 liquor they cause much harm, and if they once attain a strong 

 development, the wine is irretrievably spoilt. 



In low-fermentation breweries they usually do less mischief, 

 as their growth requires a high temperature and an abundant 

 supply of air. Thus, they are readily suppressed in a well- 

 arranged lager beer cellar. HANSEN 's experiments have shown 

 that Bad. aceti and Bad. Pasteurianum are able to exist during 

 the whole time of storage, whether infected at the beginning 

 or end of the principal fermentation. The contamination, how- 

 ever, did not manifest itself during the whole course of the fer- 

 mentation either by the taste or by the smell of the beer. 

 When the beer was drawn off into bottles and exposed to a 

 higher temperature, the bacteria developed further; yet, when 

 the bottles were well corked, the beer did not turn sour. Just 

 the same result was arrived at when the finished beer was 

 infected. If, on the contrary, the bottles are badly corked, 

 the growth turns the beer sour. 



In high-fermentation breweries, on the other hand, where 

 fermentation is carried on at higher temperatures, these bacteria 

 are capable of doing much mischief, even before the beer leaves 

 the brewery. 



