144 THE NATURE OF ANIMAL LIGHT 



The sensitivity of our eye is largely responsible for 

 the detection of so small an energy change. As we have 

 seen, recent determinations have proved that the dark 

 adapted eye can detect 18 X 10"^*^ ergs per second. From 

 the heat of complete oxidation of pyrogallol it is 

 possible to calculate the amount of pyrogallol neces- 

 sary to give 18 X 10"^^ ergs if completely oxidized. This 

 quantity is infinitesimally small. When pyrogallol is 

 oxidized by K4Fe(CN)6 and H2O2, it is not completely 

 oxidized and probably only a small amount of the energy 

 is converted into light ; otherwise we should be able to see 

 the luminescence of a very much weaker concentration 

 of pyrogallol. As the reaction luciferin ^ oxyluciferin 

 is so easily reversible, very little energy must be liberated, 

 and, as experiments indicate, very little heat, if any, accom- 

 panies light production. Even though this be true, it is 

 still possible for a very small amount of luciferin to pro- 

 duce a very large amount of light. 



A very small amount of lucif erase only is necessary be- 

 cause it behaves as an enzyme and follows the general rule 

 that catalysts act in minute concentrations. 



On the assumption that luciferase is an enzyme, an 

 organic catalyst oxidizing luciferin with light production, 

 we may appropriately inquire into the relation between the 

 concentration of luciferin and luciferase and intensity 

 and duration of luminescence. Oxygen tension, hydrogen 

 ion concentration and temperature must be maintained 

 constant as these all affect both intensity and duration of 

 luminescence. Before considering luciferin and lucife- 

 rase, however, let us study a few well-known chemilumi- 

 nescent oxidations with special reference to concentration 

 of reacting substances and temperature. 



