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, diaJyzable 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- 



