224 McKenney — On Luminous Bacteria. 



growth but a strong luminescence. It is to be noted tliat at every trans- 

 fer—every 24 hours— the bell-glass was removed a lew minutes. When 

 the bell-glass was replaced, a dish of freshly prepared 5^ ether water 

 was placed under it instead of the old dish of ether water. In this way 

 the supply of free oxygen was maintained as well as the action of the 

 ether; the amount of ether which could evaporate from a 5^ water 

 solution being a limited amount and not enough to exclude the oxygen 

 from the bell-glass and the organisms. 



This experiment was twice repeated and essentially the same results 

 were obtained. In one case the B cultures when about 4 days old also 

 emitted light, i. e., about 2 days after their daughter (C) cultures were 

 luminous. 



•From these experiments it is clear that ether, when not too concen- 

 trated, exerts a partial narcosis on the bacteria. While it inhibits light 

 production, it does not inhibit growth and multiplication and hence not 

 all of the metabolic activities. In the case of ether we find a second 

 adaptation of the organisms to environment. 



• Nutrition. 



Naturally the first culture medium used for the culture of photobac- 

 teria was fish— the substratum from which they had been first 

 isolated. Later the organisms were grown on agar and gelatine contain- 

 ing sea salt, peptone, asparagin, etc. The culture media best suited to 

 cultivation of pholobacteria are those first used by Beijerinck. These 

 are described in a previous section of this paper as normal fish bouillon, 

 fish agar and fish gelatine. 



That nutrient conditions exert some eflfect on light production, we 

 know from Beijerinck's researches. His results indicate that certain 

 substances which are plastic are not photogenic and vice versa. 



Further it seems for the six species studied by Beijerinck— which 

 include those I have examined— part of the nitrogen must be fur- 

 nished as peptone and in some cases all of the nitrogen maybe given in 

 this form. In some species (peptone forms) peptone wi'U alone cover all 

 the carbon and nitrogen requirements, while in other species (peptone- 

 carbon forms), although peptone will suffice for the nitrogen needs, an 

 additional source is needed for the carbon. Bacillus 2}ho,sp7iorescens and 

 Microsjnra Imniiwsa are peptone forms, while Bacterium phospJiorescens 

 is a peptone-carbon form. In all cases, however, peptone seems to be a 

 necessary part of the nutrient media. 



ORGANIC NEEDS. 



In order to test the conclusion of Beijerinck that peptone or a 

 related protein was absolutely essential, a large series protein-free 

 media were made up. These were inoculated with Bacillus phos- 

 pJiorescens and were kept under observation for from 4 days to one 



