NON-PATHOGENIC BACILLI. 



633 



FIG. 211. Bacillus arbores- 

 cens, from a gelatin culture. 

 X 1,000. (Frankland.) 



Biological Characters. An aerobic, liquefying, motile, chromogenic 

 bacillus. Forms a dark flesh-colored pigment. Spore formation not ob- 

 served. Grows at the room temperature in the usual culture media. Upon 

 gelatin plates, at the end of two days, circular cavities with well-defined 

 margins and filled with liquefied gelatin are seen; under a low power the 

 centre of the colonies is seen to be more opaque and is surrounded by con- 

 centric rings, alternately of lighter and darker color, while the marginal 

 zone is colorless and appears finely granular. In gelatin stick cultures 

 liquefaction occurs rapidly along the line of puncture, in funnel shape; at 

 the lower part of the funnel a deposit of a pale-pink color accumulates and 

 the liquefaction ceases to extend. Upon the surface of agar it grows rapidly 

 and forms a thick, slimy, pale-pink layer. Upon potato a layer is formed 

 which is first pale and later dark flesh-colored. 



272. BACILLUS ARBORESCENS (Frankland). 



Found in the London water supply. 



Morphology. Bacilli with round ends, about 2.5 ^ long and 0.5 /^ broad; 

 often united in pairs, or in chains of three or four ^^_ 



elements ; also form long, flexible filaments. /^^^ -^ 



Biological Characters. An aerobic, liquefy- -S. 



ing, chromogenic bacillus. Spore formation not 

 observed. Oscillating movements only. Grows 

 in the usual culture media at the room tempera- 

 ture. Upon gelatin plates the colonies, at the end 

 of twenty-four hours, consist of a thin axial trunk 

 with root-like offshoots at both ends; later the body becomes thicker and the 

 branching extremities are so strongly developed that the whole has the ap- 

 pearance of a sheaf of wheat ; the naked-eye appearance, in this stage, is also 

 peculiar, and the colony is seen as an iridescent bundle, constricted in the 

 middle and with the ends striped in- a radial direction; later the gelatin is 



liquefied slowly and the central part of the 

 colony acquires a yellow color, while the 

 periphery is beautifully iridescent. In* ge- 

 latin stick cultures, by the second day, an 

 iridescent layer is seen on the surface; in 

 the middle of this the gelatin is slightly 

 depressed and filled with a semi-fluid, yel- 

 lowish mass; along the line of puncture a 

 transparent, grayish cloudiness is seen ; 

 liquefaction progresses slowly at the sur- 

 face, and a funnel is formed, at the bottom 

 of which the yellow deposit gradually in- 

 creases; along the line of puncture no 

 further changes occur. Upon the surface 

 of agar a, rather thin, dirty orange colored 

 layer is formed, the margins of which are 

 slightly iridescent and striped in a radial direction. Upon potato a thick, 

 glistening stripe of a deep orange-red color is formed along the line of in- 

 oculation ; the surface of this is covered with irregular protuberances. 



273. BACILLUS CITREUS CAD AVERTS (Strassmann). 



Found in a cadaver fifty hours after death from accidental shooting in 

 blood from a vein. 



Morphology. Oval bacilli, 0.9 ju. long and 0.6 /^ broad, usually united in 

 chains. 



Biological Characters. An aerobic, liquefying, non-motile, chromogenic 

 bacillus. Forms a yellow pigment. Spore formation not observed. Grows 

 slowly at the room temperature. Upon gelatin plates forms small, pale- 



FIG. 212. Colony of Bacillus arbo- 

 escens. X 100. (Frankland.) 



