The Chemistry of Light-Production in Luminous Organisms. 215 



prepared with acetone instead of alcohol gave no light with firefly 

 photogenin. In order to obtain a bacterial powder which will give 

 light with firefly photogenin it is necessary to remove the alcohol and 

 dry as quickly as possible; otherwise the photophelein is destroyed. 



Addition of ether to a mass of luminous bacteria causes the light to 

 disappear rapidly and it is possible that the photogenin is destroyed 

 by ether and not the photophelein; but bacteria so treated, after the 

 ether had been evaporated by a current of air, gave no light with 

 firefly photogenin. Negative results were obtained also with an alka- 

 line (m/12 KOH) extract of luminous bacteria neutralized with HC1. 

 A precipitate of nucleoprotein (?) is produced on neutralization. 

 Apparently the bacterial photophelein is formed in such small quan- 

 tities from its precursor or is so unstable that all methods of obtaining 

 it have failed, with the exception of the rapid precipitation by alcohol. 



TABLE 14. 



TEMPERATURE. 



The temperatures shown in table 14 have been recorded for the 

 extinction of the light of luminous bacteria (28). The variations in 

 the results suggest that further observations were desirable. Accord- 

 ingly luminous bacteria, isolated from fish, were grown on absorbent 

 cotton saturated with beef-broth-peptone-glycerol culture medium. 

 Free access of air between the cotton fibers supplies the conditions for 

 a brilliant light and at the same time an excellent means of handling 

 the bacteria. A wisp of cotton strongly phosphorescent with bacteria 

 was placed in a very thin-walled glass tube about 2 mm. in diameter 

 and attached to a thermometer bulb as for melting-point determina- 

 tions. On slowly raising the temperature, the light (to a dark-accus- 

 tomed eye) becomes dim at 30, very dim at 34, and disappears at 38. 

 On slowly lowering the temperature the light weakens at 0, is very 

 dim at --7, and disappears at --11.5. These values agree best with 

 those given by Lehmann for Bacterium phosphorescens and do not 

 greatly exceed the usual temperature limits of activity of organisms. 



Bacteria raised to 38, and then cooled, phosphoresce only very 

 dimly, but, as first observed by MacFadyen (27), again glow brilliantly 

 at room temperature even after an exposure to liquid air. 



