212 STUDIES ON BIOLUMrNTESCENCE. XH 



tion oxygen in alkaline medium has a higher oxidation potential than 

 in neutral or acid media. I believe this is the explanation of the 

 action of acid in the formation of luciferin from oxyluciferin. 



Addition of acid is not the only means of favoring the formation 

 of luciferin from oxyluciferin. Any reaction which proceeds in one 

 direction with evolution of light should, theoretically, proceed in 

 the opposite direction under the influence of Kght. As far as I know 

 the case of a reaction, photogenic in one direction and photochemical 

 in the other direction, has never been described, unless we are to 

 accept the cases of phosphorescence; for instance, the absorption of 

 light by CaS and its emission in the dark. However, the reaction 

 which occurs during phosphorescence cannot be stated. 



It is a fact that hght will cause the reduction of oxyluciferin. A 

 tube of oxyluciferin exposed to sunKght for 6 hours or the mercury 

 arc for 2 hours will be partially converted into luciferin. It will 

 luminesce when luciferase is added while a control tube kept in dark- 

 ness shows no trace of luciferin. The action is more marked with the 

 ultra-violet, as a solution of oxyluciferin in a quartz tube showed 

 more reduction than one in a glass tube when exposed for the same 

 length of time to the quartz mercury arc. The reduction is not 

 dependent on the formation of acid under the influence of light since 

 two tubes of oxyluciferin, one kept in darkness and the other exposed 

 to sunlight for 6 hours, had the same reaction, pH = 9.3. Of course 

 some reducing substance might be formed under the influence of 

 hght but this is not very probable. 



We may therefore write the reaction for luminescence in the fol- 

 lowing way. 



Darkness. 

 Alkali. 

 Luciferase. 

 Luciferin (LH2) + O ?=i oxyluciferin (L)* + H2O (luminescence) 

 Perhydridase. 

 Acid. 

 Light. 



* It is unfortunate that Dubois (1918) has used the word oxyluciferin in quite 

 a different sense from my own. His idea of the processes involved is as follows 

 (p. 319): 



