CHROMOGENIC BACTERIA . 137 



Another microbe of this nature which attacks milk and other food 

 articles is Bac. cyaneo-fluorescens. 



A blue coloration, sometimes appearing as patches, at other times 

 permeating the whole mass, is a well-known cheese malady. These 

 defects are sometimes, though not always, due to bacteria, the best 

 known of these being Bacillus cyaneofuscus. When cultivated in a 

 nutrient solution a thin pellicle is formed on the surface of the 

 liquid, which, when microscopically examined, is found to be composed 

 of colourless rods. The colour is due to the presence between the 

 rods of blue granules from 1*5 /A to 3'5/x in diameter. This microbe 

 is therefore chromoparous. As this organism is easily killed by 

 drought, it is not usually found in the atmospheric dust. 



A very well known organism belonging to the same class is Bacillus 

 pyocyaneus, which belongs to the pathogenic bacteria. This species 

 usually produces a blue pigment, but when cultivated in certain 

 nutrient media produces a green fluorescent matter, and in other 

 media no colouring matter of any kind. 



5. Bacteria producing Violet and Green Colouring Matters. 

 Although several chromoparous organisms producing violet colouring 

 matters are known, they have not been extensively studied. Among 

 these the best known are Bacillus violaceus, Bacillus membranaceus 

 amethystrius, and Micrococcus violaceus. 



A fairly large number of chromoparous bacteria producing green 

 excretions have also been described. One of these is Bac. fluorescens 

 liquefaciens, which in ordinary bouillon produces a beautiful green 

 fluorescence. If a bouillon culture of this species be placed in the 

 invisible violet end of the spectrum this part is made visible, being 

 seen as a pale yellow colour. Other green fluorescent bacteria are 

 Bac. fluorescens non-liquefaciens, Bac. butyri-fluorescens, Bac. syn- 

 cyaneus, Bac. viridans, Bac. pyocyaneus. 



3. PHOTOGENIC OR PHOSPHORESCENT BACTERIA. 



Phosphorescence may be described as the production of light without 

 heat. The term has reference to the fact that phosphorus even under 

 water is luminous, although no perceptible heat is developed such as 

 accompanies the ordinary production of light. This striking pheno- 

 menon may be produced in many mechanical ways, e.g. by heating, as 

 when certain diamonds are heated to a temperature of 300-400 C., 

 or by friction, as when two crystals of quartz are rubbed together. In 



