222 McKenney On Luminous Bacteria. 



set, g. All of the / and g cultures became luminous in from 12 to 18 

 hours from time of inoculation. This experiment was twice repeated 

 and the same result obtained. 



Evidently, then, Bacillus phosphorescent is capable of so adapting itself 

 as to produce light at a higher temperature than the normal maximum 

 for light production. This new race thus obtained by adaptation to en 

 vironment was, however, rather delicate. When kept at a temperature 

 above the growth maximum for a few minutes the bacteria did not again 

 emit light, either when brought back to 35 or even to 26, until they had 

 been previously transferred to fresh media; and then it was a new 

 generation which produced light. Again, exposure to a low temperature 

 showed this new race to be quite weak. After 24 hours exposure to a 

 temperature of it was usually 48 hours after a gradual or sudden 

 change to either 26 or to 35 before light was again produced. I was 

 unable to observe any adaptation above 35. 



These experiments show that neither sudden or gradual changes of 

 temperature within the limits for light production affect the intensity of 

 light. Further, while the bacteria may adapt themselves to higher 

 temperatures and produce light above the normal luminescence maxi 

 mum, still this is not possible for low temperatures, since the minimum 

 temperatures for growth and luminescence are coincident. It is further 

 to be noted that notwithstanding the greater adaptability for light pro 

 duction at higher temperatures, exposures to temperatures but slightly 

 above the growth maximum are much more injurious than exposure 

 to temperatures much below the growth minimum. Very low tempera 

 tures appear to act as a stimulus, since subsequent luminescence is far 

 stronger than in cultures kept continuously at the optimum tempera 

 ture. This was the only stimulating effect produced by temperature 

 which was observed. 



Relations to Illumination. 



Only Dubois has noticed any effect of illumination on luminescence. 

 He observed a slight dimunition of light production as a result of con 

 tinued illumination. My observations do not show such an effect. 



Good young luminous cultures were placed at various temperatures 

 between the minimum and maximum for luminescence. These were 

 divided into three lots; one was kept in continued darkness, another in 

 alternate light of day and darkness of night, and still another exposed 

 continuously to a 16 candle power incandescent light placed 2 feet away. 

 These three sets of cultures were kept under observation for 48 hours. 

 At the end of that time all were luminescent and there was no evident 

 difference in the intensity of the light of any of the cultures. 



Apparently a certain amount of continued illumination is without 

 effect on the power of light production. It is, however, not only pos 

 sible, but also probable that very strong illumination would not only de 

 stroy luminescence, but also the organisms as well. 



