9(5 



MICRO-ORGANISMS AND FERMENTATION. 



clear zones ; they may later become iridescent. On sowing 

 drops on wort-gelatine, flat, spreading, rosette-shaped colonies 

 are formed at 25 C. in the course of 18 days. In " double 

 beer " the temperature maximum for growth is 42 C., the 

 minimum 4-5 C. 



This species is of common occurrence both in high- and 

 low-fermentation beers. 



Bacterium Pasteurianum (Hansen) (Fig. 18) forms a dry film 

 on " double beer " at 34 C., which soon becomes wrinkled 

 and pleated. In young, vigorous films on beer or wort, at 

 favourable temperatures, the slime surrounding the cells is 

 coloured blue by iodine. The cells of the film form long 

 chains, and are, on the average, larger, especially thicker, 



Fig. 18. Bacterium Pasteurianum 

 (after Hansen). 



Fig. 19. Bacterium Kiitzingianum 

 (after Hanson). 



than in the previous species. The thread-like form at 40- 

 40-5 C. is also a little thicker than that of Bact. aceti. In 

 plate-cultures, with wort-gelatine at 25 C., the colonies re- 

 semble those of the previous species, but are a little smaller, 

 and consist chiefly of chains. In peptone-gelatine broth the 

 colonies are similar to the previous species. On sowing drops 

 on wort-gelatine wrinkled colonies develop at 25 C. in the 

 course of 18 days, which are slightly raised, and present 

 a sharp outline or one slightly jagged. In " double beer " 

 the maximum temperature for growth is 42 C., minimum 

 5-6 C. 



This species is more frequently met with in high- than in 

 low-fermentation breweries. 



Bacterium Kutzingianum (Hansen) (Fig. 19) forms a dry 



