138 THE NATURE OF ANIMAL LIGHT 



tion which proceeds in one direction with evolution of 

 light should, theoretically, proceed in the opposite di- 

 rection under the influence of light. So far as I know 

 the case of a reaction, photogenic in one direction and 

 photochemical in the other direction, has never been de- 

 scribed, unless we are to accept the cases of phosphores- 

 cence, 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 light will cause the reduction of oxy- 

 luciferin. A tube of oxyluciferin exposed to sunlight for 

 six: hours, or the mercury arc for two hours, will be 

 partially converted into lucif erin. It will luminesce when 

 luciferase is added, while a control tube kept in darkness 

 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 six hours, had the same reaction, 

 Ph = 9.3. Of course some reducing substance might be 

 formed under the influence of light but this is not 

 very probable. 



We may therefore write the reaction for luminescence 

 in the following way : 



darkness 



alkali 



luciferase 



luciferin (LH2) + O ±5 oxyluciferin (L) + H2O (luminescence) 



perhydridase 

 acid 

 light 



