426 LIFE : OUTLINES OF GENERAL BIOLOGY 



Photoblepharon), from the East Indian Archipelago, where the 

 luminous organs can be turned inwards, obscuring their constant 

 luminescence. This corresponds, in a way, to shutting the eye, 

 which, however, in the absence of lids, no fish can do! 



Theory of Bio-Luminescenxe. — About 1887, Prof. Raphael 

 Dubois of Lyons University showed that a hot-water extract of 

 the luminous tissue of the rock-boring Pholas very rapidly loses 

 all trace of luminescence. A cold-water extract of the same remains 

 luminescent for a longer time. But when the two extracts, which 

 have both ceased to show any light, are mixed together, there 

 is luminescence once more. These facts led Dubois to the theory 

 that the hot water rapidly destroys a ferment or enzyme, lucif erase, 

 which acts on a photogenic substance, luciferin. In the hot-water 

 extract the ferment had disappeared, and without the ferment the 

 luciferin, unaffected by heating, could not produce light. In the 

 cold-water extract the luciferase had acted on the luciferin and 

 eventually oxidised it all. In short, the hot-water extract had 

 luciferin without luciferase; the cold-water extract had luciferase 

 which had used up all the luciferin in solution ; a mingling of the two 

 naturally produced light — naturally, if this theory is sound. 



For many years Newton Harvey has been following the clue 

 which Dubois discovered; and his general result is a confirmation 

 of the view that bio-luminescence is the result of an energetic 

 interaction between protein-like fermenting substances [luciferases) 

 and photogenic substances {lucif erins), which have much in common 

 with peptones — the results of digesting proteins. 



The three cases which have been most intimately studied are 

 the fire-flies, the boring shell, and a small marine crustacean called 

 Cypridina; and in these there is strong evidence in support of the 

 conclusion that bio-luminescence is due to the interaction of luci- 

 ferase and luciferin. It must be admitted that there remains 

 considerable vagueness in regard to these two substances, which 

 appear to differ in different animals, as is the way with proteins. 

 The luciferase is gradually used up when it oxidises large quantities 

 of luciferin, which would not be true of a typical enzyme or ferment, 

 but its behaviour indicates something enzyme-like. One part of 

 luciferase in i.yoo million parts of water will give light when some 

 luciferin is added, and a similar dilution of luciferin will give visible 

 light when luciferase is added. The probability is that luciferase 

 is an organic enzyme or catalyst which oxidises luciferin, or 

 accelerates the oxidation of luciferin, with the result that light is 

 produced. 



The Bacterial Theory of Bio-Luminescence.— Of recent 

 years there has developed a very different theory of bio-luminescence, 

 that it is due to partner-bacteria, and it is possible that both theories 

 are correct. Certain cases of bio-luminescence may be intrinsic and 



