ACETIC ACID BACTERIA. 101 



scribed by Henneberg. The writer discovered it on low- 

 fermentation beer which had been standing in vessels at 

 a temperature of 25-27 C. It forms roundish colonies 

 on gelatine, which later assume irregular shapes with curious 

 ramifications. On sterilised beer it forms a delicate film, 

 consisting of separate prominences creeping up the sides of 

 the vessel. In its younger stages the film consists of pairs 

 of ceUs ; later, of long chains. Beer is rendered turbid by 

 this species. In its younger stages, motile cells have been 

 observed. At a temperature of 36 C. the growth on beer 

 consists almost exclusively of long, uniform threads. This 

 species also shows the irregular, swollen forms, as, for instance, 

 on beer at 26 C. The cells are not coloured blue by iodine. 

 The optimum temperature for the growth lies between 18 

 and 21 C. The upper limit of temperature for the formation 

 of motile cells was found to be 37-40 C. (or 44 when 

 rapidly heated). The temperature at which the vegetation 

 is destroyed lies between 55 and 60 C. for moist heat, and 

 between 97 and 100 C. for dry heat. The oxidation of 

 alcohol into acetic acid has its optimum between 27 and 23 C. 



This species oxidises many different kinds of carbon com- 

 pounds. 



Henneberg has recently described the following species or 

 varieties : Bact. acetigenum, which occurs in the quick vinegar 

 vats, forms small rounded swarming cells, which are not 

 grouped in chains. At a later stage swollen cells may appear. 

 The species forms a thin, matted, and very tough film, which 

 finally sinks to the bottom in isolated patches, giving room 

 for a new film formation. By treatment with iodine and 

 sulphuric acid a blue coloration may take place. The acetic 

 acid produced by this species is very aromatic, owing to the 

 formation of acetic ether. The species has its optimum at 

 33 C. 



Bact. acetosum, which is found in high-fermentation beer, 

 forms long chains, and, at the same time, irregular shapes. 

 The film is solid, dry, and after a time wrinkled ; the liquid 

 is clear. The optimum for this species is about 28 C. 



Bact. industrium occurs as short swarming cells without chain 

 formation or irregular shapes. On gelatine it forms greyish- 



