702 NON-PATHOGENIC SPIRILLA. 



nies are not crowded, they may have a diameter of 0.3 to 0.5 millimetre, 

 and at the end of several days appear to be made up of concentric zones ; at 

 the end of several weeks they have the appearance of the end of a tree trunk 

 which has been sawed off and shows many concentric rings of growth, 

 which are not very clearly defined. Under certain circumstances outgrowths 

 occur around some of the deep colonies, which give them the appearance of 

 a raspberry. The superficial colonies may attain a diameter of three to five 

 millimetres ; they remain flat and circular in outline and acquire a slight 

 yellowish color. Upon agar plates the deep colonies have a diameter of 0.5 

 to 0.7 millimetre ; those upon the surface are flat, round discs of a gray color 

 and smooth appearance ; they may attain a diameter of five millimetres. 

 In neutral bouillon containing one-fourth to one per cent of peptone, at 

 36 C., development is abundant, and the culture liquid in a few days is 

 densely clouded ; examined in a hanging-drop culture, they appear a little 

 larger than the spirillum of cholera and exhibit very active movements. 

 They grow in milk without producing any perceptible change in this fluid. 

 The cultures acquire a slightly alkaline reaction. Upon potato, at 37 C., a 

 thin, yellow layer is developed in the course of a few days. 

 Not pathogenic for guinea-pigs or pigeons. 



431. SPIRILLUM OP MILLER. 



Synonym. Miller's bacillus. 



Obtained by Miller (1884) from carious teeth. 



Morphology. Straight or slightly curved rods, frequently in pairs in 

 form of a letter S or of an O ; also in homogeneous or segmental spiral 

 filaments. 



Biological Characters. An aerobic and facultative anaerobic, liquefy- 

 ing, motile spirillum. Spore formation not observed. Grows at the room 

 temperature in the usual culture media. No growth upon the surface of 

 gelatin cultures, which are liquefied. Upon agar the growth is similar to 

 that of the SDirillum of Finkler and Prior. Growth upon potato not charac- 

 teristic. 



