LUMINESCENCE IN THE SEA 227 



As we have seen, it was the French physiologist Raphael 

 Dubois who first determined the presence of luciferine and 

 luciferase in the case of the marine boring bivalve mollusc 

 Pholas dactylus, and also in the case of a terrestrial insect, 

 the luminous beetle Pyrophorus noctilucus, and showed the 

 part these proteins played in the production of light ; but 

 the discovery has since been extended to the luminous organs 

 and secretions of various other animals, especially by the 

 recent work of the American investigators, IHric Dahlgren 

 and E, Newton Harvey. The latter finds that although 

 the luciferines and luciferases of different luminous animals 

 are similar substances, they are not identical, but are abso- 

 lutely specific ; for the luciferine, for example, of animal 

 A (say a MoUusc) wiU not give fight with the luciferase of 

 animal B (a Crustacean), and the luciferine of B gives no 

 light with the luciferase of A. 



Another point, requiring fm'ther investigation into the 

 chemistry of these substances, is the relation between their 

 composition and the various very distinct colours of the 

 light produced. Observers speak of the silvery fight of 

 Noctiluca, the green glow of Ctenophores, the briUiant 

 blue of the fittle Crustacean Cypridina, the lilac flashes of 

 some sea-pens, the ruby-red of a cuttle-fish, and the dim 

 white fight produced over large areas of the ocean by 

 miuute luminous Protozoa in the case of the so-called 

 " milky sea " or " white water " in the Gulf of Aden, 

 the China Sea, the Indian Ocean, and elsewhere in the 

 tropics. 



Newton Harvey, in his most recent work (January, 1923), 

 has shown that the luminescent reaction in such a case as 

 Cypridina is probably represented by the equation — 

 Luciferine -f oxygen = oxy-luciferine + water. 



But the presence of luciferase, acting as a catalyst, is 

 also necessary for the production of fight. Moreover, the 

 action is reversible, and the oxy-luciferine formed can be 

 reduced back to luciferinCj which wiU again oxidize under 



