THE BACILLUS PYOCYANEUS 803 



body is common, but is always an indication of degeneration, and 

 not a normal characteristic, as, for instance, in the diphtheria group. 



Cultivation. The pyocyaneus bacillus is aerobic and faculta- 

 tively anaerobic. It can be adapted to absolutely anaerobic environ- 

 ments, but does not produce its characteristic pigment without the 

 free access of oxygen. The bacillus grows readily upon the usual 

 laboratory media and is not very sensitive to reaction, growing 

 equally well upon moderately alkaline or acid media. Development 

 takes place at temperatures as low as 18 to 20 C., more rapidly 

 and luxuriantly at 37.5 C. 



On agar slants, growth is abundant and confluent, the surface of 

 the agar being covered by a moist, grayish or yellowish, glistening, 

 even layer. The pigment which begins to become visible after about 

 eighteen hours soon penetrates the agar itself and becomes diffused 

 throughout it, giving the medium a bright green fluorescent appear- 

 ance, which grows darker as the age of the culture increases. 



In gelatin stabs, growth takes place much more rapidly upon the 

 surface than in the depths. A rapid liquefaction of the gelatin takes 

 place, causing a saucer-shaped depression. As this deepens, pigment 

 begins to form in the upper layers, often visible as a greenish pellicle. 



In gelatin plates, the colonies have a characteristic appearance. 

 They are round and are composed of a central dense zone, and a 

 peripheral, loosely granular zone, which extends outward into the 

 peripheral fluidified area in a fringe of fine filaments. When first 

 appearing, they are grayish yellow, later assuming the characteristic 

 greenish hue. 



In broth, growth is rapid and chiefly at the surface, forming a 

 thick pellicle. Below this, there is moderate clouding. The pigment 

 is formed chiefly at the top. In old cultures there is a heavy floc- 

 culent precipitate. In fluid media containing albuminous material, 

 strong alkalinity is produced. 



On potato, growth develops readily and a deep brownish pigment 

 appears, which is not unlike that produced by B. mallei upon the 

 same medium. 



Milk is coagulated by precipitation of casein and assumes a yellow- 

 ish-green hue. In older cultures the casein may again be digested 

 and liquefied. 



The pigment of Bacillus pyocyaneus has been the subject of 

 much investigation. It was shown by Charrin 24 and others that 



24 Charrin, loc. cit. 



