110 THE NATURE OF ANIMAL LIGHT 



but later, adopting McDermott's terminology, speaks of 

 as luciferesceine. This Dubois regards as a substance 

 intensifying the light and modifying its color by chang- 

 ing invisible into visible rays. As we have seen, this 

 theory, while attractive, will not stand the test of 

 critical examination. 



Phipson's noctilucin, while the first name for the pho- 

 togen of luminous animals, is too vague a substance, chemi- 

 cally, to warrant a retention of the term. Of the names, 

 luciferin, luciferase, preluciferin or proluciferin, co- 

 luciferase, photogenin, photophelein, oxyluciferin, lucife- 

 resceine, I believe that only proluciferin, luciferin, oxylu- 

 ciferin, luciferase and photophelein stand for substances 

 which are really significant for the theory of light pro- 

 duction. Luciferin is the heat resistant, dialyzable sub- 

 stance which takes up oxygen and oxidizes with light pro- 

 duction in the presence of the heat sensitive, non-dialyzing, 

 enzyme-like luciferase. The luciferin must come from 

 some precursor, proluciferin, but I have been unable to 

 demonstrate the existence of this body in Cypridina and 

 know nothing definite of its properties. The luciferin 

 oxidizes to oxyluciferin which has the same chemical prop- 

 erties as the luciferin itself and may be reduced to luci- 

 ferin again by reducing substances in luminous and other 

 animals or by inorganic reducing agents. Photophelein 

 is a name for substances in various animal or plant 

 extracts which are capable of liberating luciferin from 

 some bound condition in solutions containing luciferase. 

 Under this term are included a number of unknown, 

 probably quite different substances, some of which are 

 thermostable and others thermolabile. 



We have seen that Bioluminescence is an oxylumines- 



