THE BACTERIA OF COLOUR AND PHOSPHORESCENCE. 351 



been objected that such lactic acid formation can only take 

 place in the presence of sugar. 1 



In place of colour a certain amount of the energy of the 

 organism may be diverted to the production of light. 

 Although phosphorescent micro-organisms have for some 

 little time been known to exist, and special organisms have 

 been described as giving rise to phosphorescence in different 

 regions, they have not been very carefully studied until com- 

 paratively recently, when Forster, Tilanus, B. Fischer, Kunz, 

 Beyerinck, Lehmann, and Tollhausen have added very con- 

 siderably to our knowledge, not only of the morphology, but 

 of the biology of these special bacteria. In certain seas, and 

 especially on clear dark nights at the mouths of rivers, 

 any one who has rowed over them or steamed through them 

 may have observed a beautiful phosphorescence or fluorescent 

 glow at the bows or at the stern of the boat. As the oars 

 dip into and leave the water, they seem to shine with a pale 

 phosphorescent light. All kinds of explanations have been 

 given of this beautiful phenomenon, but it is now known 

 to be due in part or entirely to the presence of certain low 

 foims of life amongst which the bacteria take an impor- 

 tant place. First of all there was described the phos- 

 phorescent bacillus, then another was added, after this a 

 third, and now there are described no fewer than six of these 

 light-producing bacteria, arranged in three groups of two each. 

 The biological characters of these groups have been very 

 carefully studied by Beyerinck, who gave the result of his 

 observations in a most admirable paper presented to the 

 Royal Academy of Sciences, Amsterdam, 1890. 



We may mention briefly some of the characteristic forms 

 and features of these light bacilli. Photo-bacterium phos- 

 phor escens, which is 1.3 to 1.9/4 long, and 1.5 to i.y/i broad 

 is motile and is surrounded by a gelatinous membrane ; it is 

 readily cultivated on fish broth containing a small quantity of 

 peptone, or in sea-water ; it also grows (though slowly) on ordi- 

 nary nutrient gelatine or on nutrient gelatine to which herring 

 brine or 8 per cent, common salt has been added ; it brings 

 about the fermentation of glucose and maltose, its power of 

 producing light being apparently closely associated with these 

 fermentations, as when oxygen is cut off both the light and 



1 A number of the more important colour-producing organisms will be 

 found described in the Appendix. 



