138 BACTERIOLOGY 



by Claessen in the water of the Spree, has slender rods with 

 rounded ends and showing vigorous motility, but which 

 often adhere together and form entire clumps, and seem to 

 possess a jelly-like envelope. The colonies, which do not 

 develop on the gelatine plate until the third day, contain 

 an indigo-blue pigment as early as the day following. In 

 thrust-cultures a punctiform mass of a deep indigo blue 

 appears round the site of inoculation even in twenty-four 

 hours, and the gelatine is not liquefied. On agar an indigo- 

 blue layer develops over the extent of the line of inocula- 

 tion, its surface being covered with a shining pellicle. On 

 potato an intensely deep indigo blue develops in three or four 

 days, but only when the reaction is acid. The formation of 

 pigment does not seem to depend on the presence of light. 



Bacillus ianthinus was found by Zopf in the Chemnitz 

 water-supply. It consists of short rods with active motile 

 power, which liquefy gelatine, and form a bluish-violet 

 pigment. 



Bacillus ochraceus. Zimmermann obtained from the 

 same source as the foregoing a bacillus with ochre-yellow 

 pigment, which has been described as the Bacillus ochraceus. 

 Gelatine is slowly liquefied. The rods show little motility. 



Bacillus gracilis, Zimmermann described a micro-or- 

 ganism to which this name has been given on account of 

 the form of the rods, which are slender and fine and 

 possess an oscillating rotatory motion. Gelatine is liquefied. 

 On agar a bluish-white pigment appears. There is but little 

 growth on potato. It has the property of thriving better 

 in the substance of the solid media than on the surface ; 

 hence it will also develop under the mica plate (see p. 61). 



Bacillus sulphydrogenus. Miquel found not only in 

 drinking-water, but in rain and canal water, an anaerobic 

 bacillus possessing the peculiar property of decomposing 

 albumen with the formation of sulphuretted hydrogen. Its 



