On the Chemistry of Light Production in Luminous Organisms. 79 
agents, it does oxidize spontaneously (also without light production) 
in the air and loses its power of producing light with photogenin. In 
the absence of air its solutions are stable for months. Once oxidized, 
it can again be reduced and will again give light if photogenin is added. 
It is therefore an oxidizable material and, I believe, similar to the 
luciferin of Pholas. I propose, therefore, to use Dubois’s word luciferin 
for the thermostable dialyzing substance of Cypridina in place of 
photophelein, and to use luciferase for the thermolable non-dialyzing 
substance in place of photogenin. The source of the photogenic sub- 
stances can be designated by prefixing the name of the animal, as 
Cypridina luciferin, Pholas luciferin, etc. I suggest also that luciferin, 
when oxidized, be designated oxyluciferin. 
Luciferin is found only in luminous animals. In non-luminous ani- 
mals and probably also in luminous animals there is a second substance, 
which I have formerly included in the term photophelein (and which 
may be properly so called), that acts in a manner similar to the action 
of saponin, NaCl crystals, etc., upon the extract of Cypridina which has 
stood until the light disappears. When we allow a Cypridina extract 
containing luciferin and luciferase to stand, the luciferin is not com- 
pletely oxidized, even though the extract is thoroughly aerated, but 
some of it is bound (adsorbed or combined?) by other substances in 
the extract. The saponin, NaCl crystals, and extracts of non-luminous 
animals act by setting free the bound luciferin, which is then oxidized 
and light appears. I suggest that the term photophelein be now 
applied to these substances in tissue extracts. They are not destroyed 
by boiling. On standing some are stable, while others are unstable. 
The best way to rid a luciferase solution of the bound luciferin is to 
shake it thoroughly with chloroform. Such a solution will give no 
light with extracts of non-luminous animals or saponin, NaCl crystals, 
ete., but a brilliant light with Cypridina luciferin. 
An insight into the modus operandi of saponin, NaCl crystals, or 
photophelein may be gained from the following experiment: Both 
luciferin and luciferase are adsorbed by many finely divided precipi- 
tates and colloidal particles, such as boneblack, Fe(OH)s, kaolin, and 
others. If we take a colloidal Fe(OH)s solution of the proper con- 
centration (which can only be determined by experiment), add some 
dilute luciferase to it, and then (after a minute) luciferin, no light 
will appear. This is because the luciferase has been completely ad- 
sorbed by the colloidal Fe(OH);, for if we now add some dilute luci- 
ferase to the above mixture, light will appear, but it will very quickly 
disappear, because the new luciferase added is again very rapidly 
adsorbed, but not so rapidly adsorbed that we fail to get light at first. 
On adding more luciferase we may again get a momentary light, but 
the additions can not be made indefinitely, because we finally reach 
a point where the colloidal Fe(OH); has become saturated with luci- 
