20O MICRO-ORGANISMS AND DISEASE [CHAP. 



7. Of less common occurrence is the Bacillus prodigiosus, 

 forming a characteristic bright-red or bright-pink growth. 

 This microbe occurs occasionally in air, in water, and in 

 soil. On Agar plates and Agar surface it forms round 

 colonies which have a bright pink colour ; on gelatine the 

 colonies appear round, at first faintly red and rapidly 

 liquefying, making the liquefied gelatine turbid and of a 

 pale-red tint. On potato it grows rapidly, forming a bright 

 pink expansion. The microbe grows best at 20° C. ; it does 

 not grow at 37° C. The growth is composed of non-motile, 

 oval, or even spherical or cylindrical rods, singly or in 

 dumb-bells, or in short chains. The pink colour is noticed 

 only in aggregations of the microbe. I have seen a whole- 

 sale infection of food-stuffs (beef, mutton, fish) occurring in 

 a City establishment next to which an old churchyard had 

 been disturbed, owing to old graves having been dug up 

 previously ; the larder in which the infection occurred was 

 overlooking the said churchyard. By means of alcohol or 

 chloroform the pigment can be easily extracted. 



8. Bacillus pyocyaneus is the microbe found in blue-green 

 pus — in fact, it is the organism which produces the blue- 

 green colour. Gessard and Charrin (Gessard : These de 

 Paris, 1882. Charrin: Communication k la Soci^td Ana- 

 tomique, December 1884) first described the microbe. 

 Gessard particularly isolated the blue pigment produced by 

 it, pyocyanin. When isolated by gelatine plates the microbe 

 grows as translucent colonies irregular in outline and show- 

 ing a fine radial striation, the gelatine gradually assuming a 

 greenish colour. The gelatine is liquefied and of a uni- 

 formly greenish colour ; on Agar it forms a white film, while 

 the Agar becomes tinted greenish ; on potato it forms a 

 brownish film, while the substance of the potato underneath 

 assumes a greenish colour. It has pathogenic action on 



