578 PATHOGENIC MICROORGANISMS 



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

 agar being covered by a moist, grayish or yellowish, glistening, evenlayer. 

 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 appearance, 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 fluidi- 

 fied 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 flocculent precipitate. 

 In fluid media containing albuminous material, strong alkaUnity is 

 produced. 



On potato, growth develops readily and a deep brownish pigment ap- 

 pears, which is not unUke that produced by B. mallei upon the same 

 medium. 



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

 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 ' and others that this pigment 

 had no relation to the pathogenic properties of the bacillus. It is found 

 in cultures as a colorless leukobase which assumes a green color on the 

 addition of oxygen. Conversely, the tjrpical green "pyocyanin," as 

 the pigment is called, may be decolorized by reducing substances. This 

 explains the fact that it is not found in cultures sealed from the air. Pyo- 

 cyanin may be extracted from cultures with chloroform and crystallized 

 out of such solution in the form of blue stellate crystals. These, on 

 chemical analysis, have been found to belong to the group of aromatic 

 compounds, with a formula, according to Ledderhose,^ of C14II14N2O. 



Besides pyocyanin, Bacillus pyocyaneus produces another pig- 



' Charrin, loc. cit. 



i Ledderhose, quoted from Boland, Cent. f. Bakt., xxv, 1889. 



