COLD LIGHT—HARVEY 215 
one containing luciferin, which will oxidize with the production of 
light, and the other part containing a catalyst or enzyme which accel- 
erates the oxidation of luciferin. The two substances could be 
separated by a difference in their properties, luciferase being de- 
stroyed on heating, while luciferin was not. We can obtain the two 
substances in solution in water, and they can be precipitated by vari- 
ous reagents. They can be purified and experimented with like any 
other bodies, although we do not yet know what is their exact struc- 
ture. Chemically, luciferin is probably to be placed among the pro- 
teins, among the simplest members of the proteins, the peptones or 
proteoses; luciferase is related to the albumins. 
The question as to whether we shall ever be able to reproduce 
living light becomes the question whether we shall ever be able to 
synthesize the proteins. Personally I think that will come in the 
future. We now synthesize fats, sugars, and some of the polypeptids, 
which are simple proteins. It is only a matter of time for synthesis 
of the more complicated compounds of which luciferin is a member. 
Finally we may ask what happens when luciferin is oxidized. 
Does it go to carbon dioxide like other foodstuffs in our body? Sugar 
and fat are oxidized to water and carbon dioxide. Can we place the 
luminescent oxidation in the same category? I think we can not. 
Experiment has shown that no carbon dioxide is produced from the 
luminescence of an animal, and I believe the change that does occur 
is a very simple change. Although the reaction can be only par- 
tially written we can at least name the material which is oxidized, 
and for convenience I have called this oxidation product, oxy-luci- 
ferin, a similar nomenclature to the one which is used for the red pig- 
ment of blood. The red pigment of our blood, hemoglobin, when 
shaken with air, becomes oxy-hemoglobin. If we place oxy-hemo- 
globin under an air pump, and exhaust all the air, it returns to re- 
duced hemoglobin or hemoglobin proper. This process is reversible 
and will go either one way or the other, depending upon the amount 
of oxygen present. 
Luciferin behaves in a somewhat similar way. We can allow the 
luciferin to become completely oxidized and then by proper methods 
reduce the oxy-luciferin again and recover our luciferin. The 
methods for doing this are not quite so simple as the method for re- 
ducing oxy-hemoglobin, for one can not put it under an air pump 
and get reduction, but there are many other means of reducing oxy- 
luciferin, and I think this occurs in the luminous animal. When a 
firefly flashes, it oxidizes the luciferin to oxy-luciferin. When it is 
resting, in the dark between the flashes, the oxy-luciferin is reduced 
back to luciferin, and the firefly is ready for another flash. 
I do not wish to say that all the luciferin in the firefly becomes 
oxidized in one flash, but part of it does, and in the time between 
