748 THE EYE IN EVOLUTION 



compounds in solution. That bioluminescence is also a simple chemical 

 reaction not associated with the metabolic integrity of living cells has also 

 been appreciated for a long time, for on desiccation of the cells or their 

 products, luminescence ceases but recommences on the addition of water in 

 the presence of oxygen. The role of the cells is to produce and store the 

 reacting substances and bring them together at the appropriate time. 

 Luminous cells are always granular and their production of light is associated 

 with the dissolution of the granules, either on their extrusion into sea-water 

 or on the complete breakdown of the organization of the cell in the act of 

 secretion (Hickling, 1925-26). 



For Kiminescence to occur, water is always necessary, and in most cases oxygen 

 either in the air or dissolved in water, a fact first discovered by the great English 

 natural philosopher, Robert Boyle (1667).^ Sometimes, as in the case of certain 

 radiolarian Protozoa and some Coelentefates such as the jellyfish, Pelagia, and the 

 comb-jelly, Mnemiopsis, luminescence occurs in the absence of free oxygen : the fact 

 that Harvey and Korr (1938) found that the extract of the last organism became 

 luminous in the presence of nascent hydrogen suggests that in such cases bound O^ is 

 made available by the appropriate stimulus. 



It was first shown by Dubois (1885-87), studying the luminescence of 

 the beetle, Pyroi)horus, and the clam, Pholas, that the reaction involved 

 two substances, the one, luciferase, a heat-labile, non-dialysable, protein- 

 like substance with the characteristics of an enzyme, the other, luciferin, 

 a readily oxidizable, diffusible substance of low molecular weight and 

 undetermined chemical composition. ^ These two substances have beeii 

 identified in some polychsete worms, crustaceans and beetles, and although 

 they are apparently absent in most luminous species, it has been assumed 

 that a system resembling luciferase-luciferin is the basis of most reactions. 

 Luciferin is readily oxidized in many ways but luminescence appears only 

 when the reaction is catalyzed by luciferase. It used to be generally 

 accepted that in the reaction the light was emitted by molecules of activated 

 luciferase (Harvey, 1917), but further study has shown that the matter is 

 probably not so simple. CJlucose and phosphates appear to be important in 

 the reaction, suggesting a relation with the carbohydrate metabolism 

 (McElroy and Ballentine, 1944), but the intimate nature of the process, 

 whether the emitting molecule is luciferase or luciferin or even another 

 unidentified substance, or how far the reactions occurring in different 

 species are alike, are all matters which must await further research (see 

 Chance et al, 1940 ; Chase, 1940 ; Harvey, 1940 ; Kluyver et al., 1942 ; 



1 New Experiments Physico-mechanical touching the Spring of Air and its Effects, London, 

 1660-82. 



2 Anderson (193.3-36), who first purified luciferin, considered it a polyhydroxy benzene 

 derivative; Chakravorty and Ballentine (1941) identified a ketohydroxy side-chain and a 

 hydroquinone ring ; and Eymers and van Schoxiwenburg (1936) suggested a derivation from 

 flavine. Using chromatography, however, McElroy and Strehler (1949) found that the com- 

 pound generally described as luciferin had at least three constituents — a bivalent metallic ion 

 (Mg, Mn, Co), adenosine trijihosphate, and a further iniidentified compound. 



