BACTERIA. 63 



shows the cellulose reaction, which is not the case with the slime 

 of HANSEN'S three species. 



Acetic acid bacteria have also been described by PETERS, 

 VERMISCHEFF, DUCLAUX, LINDNER, ZEIDLER, and HENNEBERG. 

 ZEIDLER found a motile form in lager beers, which he named 

 Thermobacteriiim aceti. 



A species with motile cells, Bacterium oxydans, was 

 described by HENNEBERG, who, according to ZOPF, discovered it 

 on low-fermentation beer which had been standing in vessels at 

 a temperature of 25-27 C. This species forms roundish 

 colonies in gelatine, which later assume irregular shapes with 

 curious ramifications. On sterilised beer it forms a delicate film 

 consisting of separate prominences rising to a considerable 

 height round the sides of the vessel. The film consists, when 

 young, of cells arranged in pairs, but later, of long chains. 

 Beer is rendered turbid by this species. In the earlier stage, 

 when the cells are mostly in pairs, motile cells have been 

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

 consists almost exclusively of long, uniform threads. This 

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

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

 The optimum temperature for the growth appears to lie 

 between 20 and 25C. The higher temperature limit for the 

 formation of motile cells was found to be 44 C. in the case 

 of a culture 25 hours old. The temperature at which the 

 vegetation is destroyed lies between 55 and 60C. when 

 moist, 97 and 100C. when dry. The oxidation of alcohol 

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



HANSEN'S thorough investigation of acetic acid bacteria has 

 assumed great importance in the general biology and morphology 

 of bacteria, owing to the light thrown on one of the factors 

 which cause multiplicity of bacterial forms. 



Each single species of the acetic acid bacteria examined by 

 HANSEN occur in three essentially different forms dependent 

 on temperature, namely, chains, consisting of short rods, long 

 threads, and swollen forms. If sown on " double beer," which 

 is very favourable to their growth, the various species give at 

 all temperatures between about 5 Q and 31 C. a growth consisting 

 of the chain form, which develops well, notably at 34C. If a 



