45 



MICROBIOLOGY OF SPECIAL INDUSTRIES. 



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. acetigenum, B. oxydans, and B, industrium are 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 





FIG. 88. Vinegar bacteria. A, Bact. aceti; B, Bact. pasteurianum; C, Bact. kutz- 

 zingianum; D, Bact. pasteurianum, showing mucilaginous sheath. (After Hansen.) 



weight. The optimum temperature for most species is about 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. industrium 

 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 conditions. 

 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 alcohol, the bacteria develop readily 

 and produce in suitable solutions, besides acetic acid, agreeable ethers 

 which are more abundant when the oxidation is slow. Below i or 2 per 



