THE BIOLOGY OF MICROBES, ETC. 159 



Bacillus ianthinus. This motile microbe was first 

 found in water, and differs from B. violaceus (also 

 found in water) by not liquefying gelatine. It 

 occurs singly, and in threads. On nutrient gelatine, 

 agar-agar, and potatoes it produces white spots, 

 which rapidly become violet. The pigment, which 

 is soluble in alcohol, is only developed in the pre- 

 sence of air. 



Bacillus violaceus. This bacillus is also found in 

 water. It grows as small round colonies on gelatine 

 plates. These are first white, but rapidly assume a 

 violet colour. It also grows on agar-agar, blood 

 serum, and potatoes ; giving rise, on each of these 

 media, to the same pigment. The microbe is a 

 motile rod about four times as long as broad, with 

 rounded ends, and often contains spores. 



Bacillus cyanogenus. This microbe measures 2'5 

 to 3'5 p x 0'4 IJL ; and occurs in chains and zooglcea. 

 Spore-formation is also present. In test-tube culti- 

 vations, it gives rise to a white head, while the 

 surrounding gelatine becomes blue or dark brown. 

 In alkaline milk, it gives rise to a slate-coloured 

 pigment; while in acid or sour milk, a beautiful 

 blue pigment is developed (in fact, it is called ' the 

 microbe of blue milk'). On agar-agar, it forms a 

 brown pigment. It also grows on potatoes, boiled 

 rice, starch-paste, etc. ; and the colouring matter 

 which is formed varies with the nourishing 

 medium. These pigments are freely developed at 

 from 15 to 18 C., but at 37 C. no colour is formed 

 at all. 



Bacillus erythrospwus. This bacillus was found 



