CHAPTER XX. 

 The Bacteria of Colour and Phosphorescence. 



Colour- Forming Bacteria-^Micrococcus Prodigiosus — Magenta Micrococcus 

 — Beggiotoa Roseopersicina — Bacillus of Blue Milk — Sulphur Figments 

 — Iron Pigments — Bacillus Fluorescens Putidus — Phosphorescent Bac- 

 teria — Six Species — Method of Cultivation — Conditions under which 

 they produce Light. 



Ik an organic medium, such as boiled potato, bread 

 soaked in broth, or nutrient gelatine, be exposed for some 

 time to the air of an ordinary room, it will be found that at 

 the end of a few days, in addition to the moulds of various 

 colours that develop on it, there appear minute yellow, 

 pink, or brown points, which on examination are found to 

 consist of yeasts, of sarcina, of micrococci, and of bacteria, 

 of which there are numerous species that give rise to these 

 coloured masses present in soil, air, and water. It is a well- 

 recognised fact that most putrefactive and decomposition 

 changes are associated with changes in colour of the putre- 

 fying media ; these colours being due to the activity of some 

 of the above colour-forming organisms which, in the exercise 

 of their full assimilating and colour-forming powers, decom- 

 pose nitrogenous substances, the elements of which are con- 

 verted into the protoplasm of the organism, into coloured 

 material, and into the other excretory products to which 

 these organisms give rise. In some cases the colour is 

 actually contained within the substance of the organisms ; 

 usually, however, it is accumulated in the sheath, as in 

 the case of the Micrococcus prodigiosus, the organism to 

 which the bright red colour of "bleeding bread" and 

 " bloody sweat " is due. This pigment is quite insoluble in 

 water, but by means of alcohol it may be extracted and ob- 

 tained in solution ; this and other pigment-forming organisms, 

 such as the magenta micrococcus, mentioned by Greenfield as 



