116 THE NATURE OF ANIMAL LIGHT 



all cells are responsible for the coloration of these re- 

 agents. Dubois has found lucif erases or substances cap- 

 able of giving light with Pholas luciferin in the blood of 

 many non-luminous Crustacea and moUusks (in Barnea 

 Candida, Solen, Cardium edulis, Ostrcea and Mytilus). 



Cypbidina luciferin. — Despite the large amount that 

 has been written on luminous animals, Dubois' work on 

 Pholas and my own on Cypridina and the firefly are the 

 only truly chemical studies that give us any idea of the 

 nature of the photogenic substances in any luminous ani- 

 mal. In many ways Cypridina luciferin is similar to 

 Pholas luciferin, but the two differ in a sufficient number 

 of points to make certain that they are not identical sub- 

 stances. As I have emphasized above, we should speak 

 not of luciferin and lucif erase but of the lucif erins and 

 the lucif erases. The luciferins, as the oxidizible sub- 

 stances, must claim first attention. They are more simple 

 substances than the luciferases. If we are to produce 

 light artificially in the same way that animals do, the 

 luciferins must be synthesized. The luciferin of Pholas 

 will luminesce with KMnO^ and other oxidizing agents, 

 and, although I have not yet succeeded in oxidizing Cypri- 

 dina luciferin with oxidizing agents, I have no doubt 

 but that some inorganic catalyzer will be found to taKe 

 the place of lucif erase and accelerate oxidation of Cypri- 

 dina luciferin with light production. 



The most remarkable peculiarity of Cypridina luciferin 

 is its stability. In my first paper on Cypridina I stated 

 that luciferin was not destroyed by momentary boiling but 

 would be destroyed if boiled four or five minutes; also, 

 that it was unstable at room temperatures and would dis- 

 appear from solution in the course or a day or so. The 



