The Chemistry of Light-Production in Luminous Organisms. 177 



it to appear again. If we add to this natural secretion an extract of 

 Cypridina heated to boiling, a brilliant light again results; or if we mix 

 a water extract of Cypridina whose light has disappeared on standing 

 with a similar extract whose light has been destroyed by boiling, light 

 again results. As already mentioned, Dubois first demonstrated this 

 for Pyrophorus and a year later for Pholas dactylus. In Dubois's 

 phraseology we have mixed two substances luciferin (in the boiled 

 tube) and lucif erase (in the tube allowed to stand) necessary for light- 

 production. According to Dubois (10), one of these, luciferase, is an 

 oxidizing enzyme and is destroyed by heat; the other, luciferin, a sub- 

 stance not destroyed by heat, is capable of oxidation with light-produc- 

 tion by means of luciferase. When the natural secretion of Cypridina 

 is allowed to stand all the lucif erin is oxidized and the luciferase is left ; 

 when a luminous extract of Cypridina is boiled the luciferase is de- 

 stroyed before all the luciferin is oxidized. The two substances alone 

 in solution are non-luminous. 



At one time I believed Dubois's interpretation of this experiment 

 to be correct, but results on Cypridina have led me to wholly different 

 conclusions regarding the existence of luciferin and luciferase. Dubois's 

 interpretation is indeed attractive. We know that the light-produc- 

 tion is an oxidation; that two substances are concerned; that these 

 substances give light in very small concentration comparable with 

 enzyme activity (see p. 188); that one of them can use up a large 

 amount of the other (see p. 189) and possesses certain properties 

 (destruction by heat, phosphotungstic and tannic acid) characteristic 

 of enzymes. Further, we actually know of oxidative reactions taking 

 place with the production of light under the action of oxidizing enzymes 

 from plants and animals (see p. 225). 



It is quite possible that light-production in Pholas dactylus is of this 

 nature, as it differs radically in very essential points from the mech- 

 anism in Cypridina and in the firefly. Thus, Dubois finds that Pholas 

 luciferin (the substance not readily destroyed by heat and giving light 

 with luciferase) can be oxidized with light-production by many oxi- 

 dizing agents blood, H 2 O 2 , KMnO 4 , Ba0 2 , PbO 2 , etc. and that it 

 occurs only in the luminous organs of Pholas dactylus (10). I find that 

 Cypridina luciferin (a substance not readily destroyed by heat and 

 giving light with luciferase) will not give light with the above-men- 

 tioned oxidizing agents and is found in many other non-luminous 

 animals and in the non-luminous parts of Cypridina hilgendorfii. 



Dubois finds that Pholas luciferase (a substance destroyed easily 

 by heat and using up Pholas luciferin with light-production) occurs in 

 many other non-luminous animals (10), whereas I find a body with the 

 same properties only in the luminous organs of Cypridina. This sub- 

 tance, which we may temporarily call Cypridina luciferase, in concen- 

 trated solutions, will give light (as before mentioned) with extracts of 



