286 



AGRICULTURAL BACTERIOLOGY. 



slight differences in structure but also by some more promi- 

 nent and important differences in relation to conditions, and in 

 their power of forming acetic acid. 



The differences in the physiological characters of these varie- 

 ties are considerable and are factors of much importance in the 

 actual processes of vinegar-making. They have varying powers 

 of fermenting different organic bodies, and differ very much in 

 the amount of acetic acid they will produce under similar con- 

 ditions. For example B. accti produces 1.27 per cent, of acid 

 at 59 F. while under the same condition B. pastciiriaiinui will 



FIG. 36. 



Acetic acid bacteria, showing long rods and rounded swollen centers. 



produce .08 per cent. But, more important still, is the fact 

 that the temperatures which favor the different varieties are not 

 the same. B. aceti, for example, produces a good fermentation 

 at a temperature of 42 F., whereas B. pastcurianum at 44 will 

 not even multiply, and produces no fermentation. Some of 

 the species produce their maximum effect more quickly than 

 others, and some may begin to destroy the acid produced 

 under conditions of temperature and time in which other varieties 

 are still active. With such a very wide difference in the opti- 

 mum conditions of action, it is manifest that the best results 



