2l8 ALCOHOL, VINEGAR, SAUER KRAUT, TOBACCO, SILAGE, FLAX. 
Henneberg still later increased our knowledge of the bacteria, so 
that we now know that there are at least fifteen varieties of these 
vinegar organisms, differing from each other in various respects, 
such as their optimum temperatures, the amount of acid they will 
produce, etc. Bad. aceti, Bact. pasteurianum, Bact. kutzingianum, 
Bact. xylinoides, Bact. orleanense, and Bad. xylinum are names 
applied to the most important types. 
All of these acetic bacteria have certain very characteristic 
points which they share in common, thus forming a group by them- 
selves. They all exist in three different forms, shown in Fig. 48. 
FIG. 48. Acetic acid bacteria, showing long rods and rounded swollen centers. 
They may form chains of short rods, looking like ordinary bacilli. 
At high temperatures they grow out in long slender threads, some- 
times very long, without any traces of divisions. These threads 
may subsequently break up into short elements. At low tempera- 
tures they have a peculiar habit of forming long threads with rounded 
swollen centers. When these threads break up into short forms 
only the thick, swollen centers remain undivided. This character 
is such a peculiar one that it places these acetic bacteria in a class by 
themselves. These different varieties are distinguished not only by 
slight differences in structure, but also by some important dif- 
ferences in relation to condition, and in their power of forming 
acetic acid. They vary in the amount of acetic acid they will pro- 
duce under similar conditions. For example, B. aceti produces 
