S40 



MICROBIOLOGY OF SPECIAL INDUSTRIES 



Bacterium hiitzingianum, Hansen. — The cells resemble those of Bact. aceti, but 

 are usually free or in pairs. The film resembles that of Bact. aceti but has a tend- 

 ency to climb up the sides of the flask above the liquid. The colonies on wort gelatin 

 are smooth and shiny. The mucilage stains blue' with the iodine solution. 



Bacterium xylinum, A. J. Brown. — This species forms a thick tough, leathery film, 

 the gelatinous substance of which stains blue with iodine and sulphuric acid. 



B. acetigenus, B. oxydans, and B. industrius axe motile species. 



All species are strictly aerobic and grow quickly only when freely 

 supplied with oxygen. This oxygen is necessary for the acetification 

 of the alcohol. Duclaux has calculated that one centigram of the 

 bacterial film is Capable of uniting 1.3 g. of oxygen to alcohol, 130 times 

 its own weight. The optimum temperature for most, species is about 





?^«ga^'=.1:?*c=o=» 







Fig. 141.— Vinegar bacteria. A, Bact. aceti; B, Bact. pasteurianum; C, Bact. 

 hiitzingiamim; D, Bact. pasteurianum, showing mucilaginous sheath. (After 

 Hansen.) 



34° and the range of temperature at which they grow is between 4° 

 and 7° to 42°. They all form acetic acid from ethyl alcohol, propionic 

 acid from propyl alcohol and most of them gluconic acid from dextrose. 

 B. industrius and B. oxydans, according to Henneberg, can form acids 

 from a large number of sugars and related substances, including 

 saccharose, maltose, starch, dextrin, glycerin and mannit. 



The presence of too much alcohol prevents the growth of acetic 

 bacteria, the limit being about 14 per cent under manufacturing con- 

 ditions. At 14 per cent and above, the film forms with difficulty, and 

 the oxidation of the alcohol is incomplete, aldehyde and irritating 

 products being formed. Acetic acid in amounts above 10 to 12 per 

 cent is moreover antiseptic to the bacteria. Below 14 per cent of 



