NON-PATHOGENIC BACTERIA. 225 



a large bacillus somewhat resembling the anthrax bacillus in 

 form, with rounded ends, qften forming chains or long fila- 

 ments; motile; possessing flagella; hquefies gelatin; aerobic; 

 it is stained by Gram's method. It may have large, centrally 

 located spores, which form best on potato at about 30° C. 

 The spores are extremely resistant to heat and to chemical 

 germicides. It grows best at about 30° C. upon the ordin- 

 ary culture-media; milk is peptonized. Bacillus subtilis may 

 easily be isolated in pure culture by adding finely cut hay to 

 tubes of bouillon; placing these in the steam steriHzer for five 

 or ten minutes; then letting the tubes develop in the incubator. 

 Plates made from the bouillon will probably show colonies of the 

 Bacillus subtilis only, as the steam may be expected to have 

 destroyed all organisms except its very resistant spores. The 

 hay bacillus is entirely without pathogenic properties. 



Bacillus erythrosporus. — Found in decomposing fluids and 

 water; a slim bacillus with rounded ends; motile; does not 

 liquefy gelatin; facultative anaerobic; forms oval, red-colored 

 spores, two to eight in each filament; grows rapidly, only at 

 ordinary temperatures; produces a greenish-yellow, fluorescent 

 pigment. On potato it forms a limited, reddish growth, be- 

 coming nut-brown. 



Bacillus cyanogenus (Bacterium syncyanum; Bacillus lactis 

 cyanogenus; Bacillus of blue milk). — ^A bacillus of variable 

 size, with rounded ends; motile; spore formation doubtful; 

 is aerobic; not stained by Gram's method; grows rapidly at 

 ordinary but not so well at incubator temperatures on the 

 usual culture-media; does not liquefy gelatin; produces a 

 grayish-blue pigment, brighter in acid media, at ordinary tem- 

 peratures; milk is not coagulated or rendered acid. 



Bacillus acidi lactici (Hueppe). — Found in sour milk; a 

 short, plump rod; not motile; does not Hquefy gelatin; facul- 

 tative anaerobic; grows on the ordinary media; in milk causes 

 development of lactic acid with precipitation of casein and 



