210 STUDIES ON BIOLUMINESCENCE. XII 



tents, and cause the solution of oxygen and the appearance of hght. 

 It is just as if we stimulated the tube to produce light and I beheve 

 the phenomenon has a deeper significance and a more fundamental 

 similarity to the phenomena of stimulation than may at first appear. 

 What more simple means of controlHng a process can we think of 

 than by admission or withdrawal of oxygen? The firefly turns on 

 its light by stimulation, through nerves, of the luminous organ. 

 Noctiluca flashes on stimulation of any kind, even the slightest agi- 

 tation causing a brilliant emission of light. If the stimulation process 

 means merely the admission of oxygen to the photogenic cells, we 

 have a mechanism in the cell itself for automatically producing the 

 light. The admission of oxygen results in aerobic conditions, and 

 luciferin in the presence of luciferase can then oxidize to oxyluciferin 

 with luminescence. When the oxygen is used up, the light ceases,^ 

 anaerobic conditions prevail, and the oxyluciferin is reduced to 

 luciferin again. Thus, luciferin is reformed during the rest period of 

 Noctiluca or between the flashes of the firefly. What more efiicient 

 type of hght than this is to be desired. 



Again, methylene blue offers an interesting parallel to oxyluciferin. 

 A Httle (NH4)2S added to a methylene blue solution will reduce 

 (decolorize) it to the leuco base. If the tube is now shaken, the blue 

 color returns. On standing reduction again occurs. The process 

 can be repeated a number of times, the reaction going in one or the 

 other direction depending on the oxygen content of the mixture. 



As methylene blue contains no oxygen its reduction consists in the 

 addition of two atoms of hydrogen. When leucomethylene blue 

 oxidizes, water is formed by the union of these two atoms of hydrogen 

 with oxygen, thus 



C16H20N3SCI + O <=^ CieHisNsSCl + H2O 

 (Leucomethylene blue) (Methylene blue) 



More briefly 



MH2 + O ^ M + H2O 



To reduce methylene blue we can add the two hydrogen atoms 

 directly from nascent hydrogen formed in the solution or we can 

 split up water by a catalyzer in the presence of some substance which 

 will take up the oxygen of water. The hydrogen of water then adds 

 to the methylene blue, thus 



