622 NON-PATHOGENIC BACILLI. 



four hours in the course of three or four days this becomes a regular wall, 

 and then extends slowly over the surface of the gelatin, forming a layer 

 with irregular outlines. Upon the surface of agar the growth is very charac- 

 teristic ; at the room temperature an indigo-blue streak is seen at the end of 

 twenty-four hours, and in four or five days this becomes a tolerably thick 

 layer, which gradually thins out at the edges and which has a deep indigo- 

 blue color ; the surface is covered up to within two or three millimetres of 

 the margin with a thin, shining layer of pigment similar to that seen upon 

 a saturated solution of gentian violet. Upon potato, at the end of three or 

 four days, an abundant layer, thickest in the middle and with well-defined 

 margins, is formed ; this has a deep indigo-blue color, and also has a thin 

 film of pigment on the surface when the potato has an acid reaction; when 

 alkaline a thin, dirty-green layer is formed without the film of pigment on 

 the surface, 



243. BACILLUS CONSTRICTUS (Zimmermann). 



Found in water. 



Morphology. Bacilli with round ends, from 1.5 to 6.5 ju in length and 

 0.75 a thick; the rods are constricted at intervals so as to form two to six or 

 more segments, which in stained preparations are separated by an unstained 

 interval. 



Biological Characters. An aerobic and facultative anaerobic, non- 

 liquefying, motile, chromogenic bacillus. Forms a Naples-yellow pigment. 

 Spore formation not observed. Grows slowly at the room temperature in the 

 usual culture media no development at 30 C. and above. Upon gelatin 

 plates forms, in four to five days, small, shining drops of a Naples-yellow 

 color; the deep colonies under a low power are spherical, granular, and 

 yellowish-gray in color; they have well-defined outlines, but the margins 

 are irregularly dentate. In gelatin stick cultures development occurs along 

 the line of puncture, and upon the surface a layer is developed which con- 

 sists of irregular masses closely crowded together and which have a Naples- 

 yellow color. Upon the surface of agar a tolerably thick, shining, Naples- 

 yellow streak is developed along the impfstrich. Upon potato after a time 

 a thin layer of a cadmium-yellow color is developed. 



244. BACILLUS FLUORESCENS AUREUS (Zimmermann). 



Found in the Chemnitz water supply. 



Morphology. Short bacilli, about 1.9 n long and 0.74 /* broad, usually 

 in pairs and associated in longer or shorter groups; have long terminal 

 flagella. 



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

 chromogenic bacillus. Forms an ochre-yellow pigment. Spore formation 

 not observed. Grows in the usual culture media best at the room tempera- 

 ture. Upon gelatin plates the deep colonies are small, yellowish- white, and 

 spherical ; the superficial colonies are glistening, yellowish-gray, and have 

 ill-defined margins ; under the microscope they are seen to be thickest in the 

 middle and have irregular outlines, while the deep colonies are sphei'ical, 

 pale-yellow, and granular. In gelatin stick cultures a scanty development 

 occurs along the line of puncture, which after a time acquires a brownish 

 color; upon the surface a thin layer is developed, which later becomes 

 thicker at the centre and extends to the walls of the tube ; it has a yellow 

 color. Upon the surf ace of agar an abundant ochrous or golden-yellow 

 layer is developed. Upon potato the growth is similar but more scanty. 



245. BACILLUS FLUORESCENS LONGUS (Zimmermann). 



Found in the Chemnitz water supply. 



Morphology. Straight or slightly curved bacilli, about 0.83 n broad, and 

 varying greatly in length from 1.45 to 14 u and more. 



