On the Chemistry of Light Production in Luminous Organisms. 81 
pare 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, is non-dialyzable, and 
accelerates the oxidation of luciferin. While it may be used up in the 
reaction if mixed with a sufficient quantity of luciferin, luciferase has 
many of the characteristics of an enzyme and certainly as much right 
to be called an enzyme as the peroxidases of plants,which are also used 
up in the oxidation process. The Cypridina luciferase reaction appears 
to be specific to an extraordinary degree. Of many tried I have found 
no substances or plant or animal extracts which can take the place of 
luciferase? nor any substances? or plant or animal extracts* which can 
be oxidized with light production by luciferase. The light recorded 
with various extracts of luminous and non-luminous animals in my 
former paper is to be referred to the presence of photophelein, the third 
substance concerned in light production, which probably acts by assist- 
ing the luciferin-luciferase reaction in the manner already suggest d. 
Let us now turn to the oxidation product or products of luciferin. 
When luciferin is oxidized it must be converted into some substance 
or substances, and I believe this change involves no fundamental de- 
struction of the luciferin molecule, as it isa reversible process. I shall 
speak of the principal if not the only product formed as oxyluciferin. 
Most observers believe that a rather fundamental change occurs 
1T believe the faint light obtained on mixing Cypridina luciferin and firefly or Noctiluca luciferase 
and vice versa, recorded in my former paper (Am. J. Physiol., 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 con- 
clusion because the light is so faint, but can not be sure until the cases are reinvestigated. The 
mixing of luciferin and luciferase of different species or genera of luminous ostracods, especially 
if the color of their luminescence differed, would shed considerable light on this interesting 
question of specificity. A non-luminous Japanese species of Cypridina does not contain either 
luciferin or luciferase, but it does contain photophelein. 
2T have tried the blood or extracts of many species of animals or plants, including those con- 
taining strong oxidizing enzymes both with and without H2O, and have always failed to obtain 
light with Cypridina luciferin. Among others the juice of Indian pipe (Monotropa), potatoes 
and turnips (containing strong oxidases and peroxidases), the blood of the ox anda worm (Areni- 
cola) (containing hemoglobin), the blood of the squid (Loligo), Limulus, and Sycotopus (containing 
hemocyanin), and extracts of Chetopterus (a luminous annelid) and the molluse Unio (rich in 
manganese) were tried. Dubois reports that he has obtained light on mixing Pholas luciferin 
with the blood of divers molluscs and marine crustaceans (Ann. Soc. Linn. de Lyons, 1913). Ican 
confirm this statement for an extract of Unio, but obtained no light with Limulus blood, Sycotopus 
blood, squid (Loligo) blood, or turnip or potato juice and Pholas luciferin. Evidently Pholas 
luciferin is much more readily oxidized with light production than Cypridina luciferin. 
3 The following oxidizable substances have been tested: ssculin, lophin, bergamot oil, pyro- 
gallol, gallic acid, anilin, adrenalin, phenol, a-napthol, para-phenylen-diamine, ortol, orcin, 
hydrochinon, resorcin, pyrocatechin, tannin, benzidin, gum guaiac, amidol, a-napthylamine, 
and the chromogen of the false indigo plant (Baptisia tinctoria). Luciferase, with or without H2Os, 
will not accelerate the oxidative color change in any of the above compounds. 
4T have regularly obtained a fair light on mixing luciferase well shaken with chloroform to set 
free any bound luciferin and boiled potato or turnip juice or boiled Limulus blood. The light is 
especially marked about the coagulum in the boiled Limulus blood. The significance of these 
results is not apparent. 
