ATMOSPHERIC SPIRILLA 121 



Atmospheric spirilla. — The spirilla occurring in the air 

 have been described by "\Yeibel. They usually generate 

 yellow pigment, according to the degree of intensity of 

 which there have been distinguished a Vibrio aureus with a 

 colour varying from golden to orange-yellow, a Vibrio flavus 

 of an ochre-yellow tint, and a yellowish-green Vibrio flaves- 

 cens. The individual spirilla frequently appear remarkably 

 thin, generally S-shaped, and without power of automatic 

 movement. Islets of an oval or whetstone form, or some- 

 times circular, develop on the gelatine plate; they are 

 sharp-edged and granular, and generate pigment in a few 

 days. There is no liquefaction. Thrust-cultures in gelatine 

 and superficial cultures on agar display also a copious 

 development of colour, which takes place only on the surface 

 of the former ; while on discs of potato there appears 

 a luxuriant pap-like deposit of a very pronounced tint. 

 Spirilla are decolorised by Gram's method. 



