142 BACTERIOLOGY. 



duced in the media in which they grow. Thus we 

 have pigment-forming, fermentative, putrefactive, 

 and pathogenic bacteria. 



Chromogenic or pigment-forming bacteria elabo- 

 rate during their growth definite colour stuffs. 

 Such species are exemplified by Bacillus ianthinus, 

 which produces a striking purple growth ; 

 Bacillus pyocyancus, which secretes pyocyanin, a 

 substance which has been isolated and obtained 

 in a crystalline form ; Bacterium prodigiosum, which 

 produces a pigment allied to fuchsine ; Beggiatoa 

 roseo-persicina, which is characterised by the 

 presence of bacterio - purpurin ; Sarcina lutea> 

 Bacillus cyano genus , and many others. 



Zymogenic or ferment bacteria produce their 

 changes in non-nitrogenised media. Bacterium 

 aceti y by its growth, produces the acetic fermenta- 

 tion in wine, by which alcohol taking up atmo- 

 spheric oxygen is converted into vinegar 



C 2 H 6 O + O 2 = C 2 H 4 O 2 + H 2 O. 



The fermentation of urine, by which urea is con- 

 verted into carbonate of ammonia, can be brought 

 about by several micro-organisms, but notably 

 by the Bacterium urea. The change produced is 

 represented by the following formula : 



= (NH 4 ) 2X CO 3 . 



Clostridium butyricum converts the salts of lactic 

 acid into butyric acid, producing the butyric fer- 



