220 McKemiey — On Luminous Bacteria. 



It will be noticed that not only are the previous records fragmentary, 

 but as the observers have multiplied there has been a diversity of result. 

 As a result of my observations I am convinced that theoptimum temper- 

 ature for growth is the same or very nearly the same as that for lumines- 

 cence. 



Concerning the minimal temperature for luminescence the records are 

 remarkably diverse, having a range of over twenty degrees. In all of 

 my experiments the lowest temperature for luminescence coincided with 

 that for growth. This does not mean, however, that the life becomes 

 extinct below the minimal growth point. I have repeatedly kept cul- 

 tures at 10°, at 0° and at -5° between 24 and 60 hours, and while there 

 was never any growth at these temperatures, still when the cultures were 

 subsequently placed at the optimal temperature a good growth and good 

 luminescence resulted. The light, however, obtained in such cultures, 

 particularly in those which had been kept below 0°, was especially 

 brilliant, fully twice as strong as that of control cultures which had 

 been kept at the optimum from the time of inoculation. 



In neither of the three species was I able to observe light below 10° 

 and I am of the opinion that the light which Lehmann observed in 

 Bacterium yiTios-pliorescens at -12° must have been flourescence rather than 

 true luminescence. 



EFFECT OF TEMPERATURE CHANGE. 



Having established the minimal, maximal and optimal temperatures, 

 I next endeavored to determine the effect of change of temperature on light 

 production. Good luminous cultures of Bacillus phosphorescens which 

 had been grown at 26° were placed at 20°. Although these cultures were 

 kept under continuous observation fori hour, no change was observed in 

 the intensity of the light emitted. Again, luminous cultures were taken 

 from 26° and placed at 15°. In from 12 to 15 minutes light emission 

 ceased, and did not again return in 24 hours. The cultures were then 

 placed at 26° and in the course of 30 minutes they were again luminous. 

 In these changes of temperature the change as ascertained by a ther- 

 mometer kept in the culture was comparatively slow and gradual. 



Luminous cultures from 26° containing a thermometer, were plunged 

 into water of a temperature of 5°. In from 1 to 2.5 minutes (a varia- 

 tion due probably to thickness of flask), the temperature of the culture 

 had reached 15° and in 15 to 20 seconds more the culture had reached a 

 temperature of 12°. The light intensity remained bright and even until 

 between 14° and 15° was reached, when it instantly disappeared. Some 

 of the cultures were kept between 10° and 12° for an hour and through- 

 out this time no light was emitted. After a few minutes exposure at 

 12° some of the cultures were raised to a temperature of 15° in 10 

 seconds by plunging in hot water. Immediately this temperature had 

 been obtained a weak light appeared, and when the culture had reached 

 25° the light was very brilliant. Of the cultures which had been kept 

 between 10° and 12° for 24 hours some were slowly, others rapidly, raised 



