ACETIC ACID BACTERIA. 97 



film, on " double beer " at 34 C., which creeps up the side of 

 the flask. The slime is coloured blue under the same conditions 

 as Bad. Pasteur "ianum. The film consists of small rod-bacteria, 

 which are most frequently single or connected in pairs, and 

 seldom form chains. The thread form at 40-40-5 C. presents 

 almost the same appearance as that of Bact. Pasteurianum. 

 In plate-cultures with wort-gelatine at 25 C. the colonies are 

 analogous to those of the previous species. They consist 

 almost exclusively of small, single rod-bacteria. In peptone- 

 gelatine broth the colonies resemble those of the two previous 

 species. On sowing drops on wort-gelatine at 25 C., colonies 

 develop in the course of 18 days resembling those of Bact. Pas- 

 teurianum, but with a smooth surface without wrinkles. On 

 " double beer " gelatine these colonies are slimy, whilst in the 

 two previous species they have a dry surface. 



In " double beer " the temperature maximum of the growth 

 is 42 C., minimum 6-7 C. 



This species was discovered in " double beer." 



Hansen's thorough investigation of acetic acid bacteria has 

 assumed great importance in the general biology and mor- 

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

 factors causing multiplicity of bacterial forms. 



Each single species of the acetic bacteria examined by 

 Hansen occurs in three essentially different forms dependent 

 on temperature chains, consisting of short rods, longs threads, 

 and swollen forms. If sown on " double beer/' which is very 

 favourable to their growth, the various species give a growth 

 consisting of chains at all temperatures from 5-34 C., 

 which develops well, notably at 34 C. If a bit of this young 

 film is transferred to fresh nutritive liquid at 40-4O5 C., 

 the cells grow into long threads in a few hours (Fig. 20). In 

 some species these threads can attain a length of 500 /m* and 

 more, whilst the links of the chain measure only 2 to 3 /JL. 

 If this growth of long threads is then placed at a temperature 

 of 34 C. a transformation into the chain form again takes 

 place. Whilst developing at this temperature, the long 

 threads increase, not only in length, but also in thickness, and 



* 1 ft - O'OOl millimetre. 



