E. NEWTON HARVEY 137 



I have considered the thermostabile, dialyzing substance as simi- 

 lar to the luciferin of Pholas despite the fact that Dubois reports 

 Pholas luciferin destroyed at 70°C., whereas Cypridina luciferin is only 

 destroyed by several minutes boiling in an open beaker. I find that 

 this destruction of Cypridina luciferin on short boiling is due to the 

 increased rate of oxidation at the boiling point and that no destruction 

 of Cypridina luciferin will occur if boiled in an atmosphere of hydro- 

 gen.'* Cypridina luciferin is truly thermostabile but is oxidized to 

 oxyluciferin on boiling in the air. We may say that Pholas luciferin 

 is similar but certainly not identical with Cypridina luciferin. If so, 

 we should expect to obtain light on mixing Pholas luciferin and 

 Cypridina luciferase, yet no light appears. Neither is there light on 

 mixing Cypridina luciferin and Pholas luciferase, although the Pholas 

 luciferase prepared from the material which Dubois sent me gave a 

 rather faint light with Pholas luciferin.^ 



We have, therefore, at least three substances concerned in light pro- 

 duction: luciferin, luciferase, and photophelein. Luciferin is a body 

 oxidizing with light production, dialyzable, and relatively resistant to 

 heat. Luciferase is destroyed by boiling, non-dialyzable, and acceler- 

 ates the oxidation of luciferin. While it may be used up in the re- 

 action if mixed with a sufficient quantity of luciferin, luciferase has 



^ I have endeavored to repeat this experiment with the luciferin of Pholas 

 sent me by Professor Dubois, but without success. Pholas luciferin boiled in a 

 current of hydrogen for 15 minutes would give no light when a crystal of KMn04 

 was added. The hydrogen was produced in a Kipp generator and may have con- 

 tained a little air. In my experience short (20 to 40 seconds) boiling of Pholas 

 luciferin does not completely destroy its power of producing light when a crystal 

 of KMn04 is added. 



^ I believe the faint light obtained on mixing Cypridina luciferin and fire-fly 

 or Noctiluca luciferase and vice versa, recorded in my former paper (Am. J. Phys- 

 iol., 1917, xlii, 328) where luciferin is called photophelein and luciferase is called 

 photogenin, is not due to the oxidation of luciferin by luciferase of the second 

 species but is due to the presence of photophelein. I am led to this conclusion 

 because the light is so faint, but cannot be sure until the cases are reinvestigated. 

 The mixing of luciferin and luciferase of different species or genera of luminous 

 ostracods, especially if the colors of their luminescence differed, would shed con- 

 siderable light on this interesting question of specificity. A non-luminous Japa- 

 nese species of Cypridina does not contain either luciferin or luciferase but it does 

 contain photophelein. 



