124 PHOTOGENIC BACTERIA 



he called respectively Bacterium phosphorescens and "native phosphorescent 

 bacillus." 



In 1890 BEYERINCK (XI.) proposed the generic name of Photobacterium for 

 the entire group of phosphorescent bacteria, and more closely investigated the 

 six undermentioned species : 



1. Photobacterium Pflugeri. 



2. Ph. phosphorescens. 



3. Ph. balticum = Fischer's "native phosphorescent bacillus." 



4. Ph. Fischeri = Bact. phosphorescens, F. 



5. Ph. indicum = Bacillus phosphorescens, F. 



6. Ph. luminosum. 



With these six (motile) species Katz in his above-mentioned treatise 

 associated a second half-dozen species collected on the coast of Australia, and 

 EIJKMANN (I.) added a thirteenth (Photobacterium jacanense), repeatedly found 

 by him on phosphorescent sea-fish in the market at Batavia 



100. The Food Requirements of Phosphorescent Bacteria 



formed the subject of comprehensive investigations by Beyerinck, a few of whose 

 multifarious results obtained therefrom may be given here. 



A remarkable difference exists between the first four and the last two of the 

 six species named in the foregoing list. The former require at least two organic 

 nutrient materia's, the one (supplying nitrogen) being a substance resembling 

 peptone, and the second a compound supplying the carbon : peptones alone, or 

 amides and the like, by themselves producing neither growth nor phosphorescence. 

 Ph. indicum and Ph. luminosum behave differently, peptone (or any other 

 albuminoid substance) being of itself sufficient as an organic food-stuff therefor. 



A slight addition of sugar to the medium increases the luminosity, but a 

 higher percentage arrests both growth and phosphorescence, a circumstance due 

 not to any injurious effect of the carbohydrate itself, but to the acids produced 

 therefrom by the vital activity of the organism, the luminous bacteria thriving 

 solely on neutral or faintly alkaline media. Concerning the extent of the 

 injurious content of sugar, and also the varying influence exerted by the different 

 eaccharides, Beyerinck arrived at noteworthy conclusions in respect of his six 

 species. Thus, for example, maltose is taken up by Ph. phosphorescens, but is 

 discarded by Ph. Pfluyeri ; Ph. Fischeri is very susceptible to cane sugar, a 

 content of 0.5 per cent, sufficing to retard growth and suppress phosphorescence, 

 whereas, on the other hand, Ph. balticum will stand 5 o per cent, without injury. 

 A similar relation in respect of glucose obtains between Ph. luminosum and 

 Ph. indicum, the luminosity of the former ceasing when the medium contains 

 i per cent, of this sugar, whilst the latter produces light even in presence of 

 4 per cent. 



The six species of photobacteria examined by Beyerinck are halophil, i.e., 

 absolutely require sodium chloride, of which the medium must contain at least 

 3.5 per cent. Consequently it follows that none of these species is able to thrive 

 on the flesh of land animals slaughtered for human food. The luminosity 

 appearing on this latter substance is caused by other species, among them being 

 the above-named Micrococcus Pfliigeri discovered by Ludwig. The presence of 

 oxygen is essential to the production of phosphorescence, but is not requisite for 

 mere growth. For preparing pure cultures a nutrient gelatin made from fish 

 bouillon is employed, and, for cultivation on a large scale, boiled salt-water fish 

 forms an advantageous medium. 



