160 THE NATURE OF ANIMAL LIGHT 



formed from spontaneous oxidation of luciferin appears to 

 be the same as that formed with luciferase present. Both 

 give hiciferin again on reduction. Perhaps the reaction 

 takes place in two stages, similar to those supposed to 

 occur in other enzyme actions : 



luciferin + luciferase = luciferinlucif erase 

 luciferinlucif erase + (or minus Ho)= oxy luci- 

 ferin + luciferase. 



We may then assume as a tentative hypothesis that 

 luminescence only occurs during oxidation (addition of 

 or removal of H) of the luciferinlucif erase compound. 



We have just seen that the effect of cooling a Cypridina 

 extract containing luciferin and luciferase and lumines- 

 cing with a bluish light, is to reduce the intensity and 

 change the shade toward the yellow. Velocity of oxidation 

 must be lowered and wdth the same concentration of lucif- 

 erase lowered velocity means more light of the longer 

 wave-lengths. A very instructive experiment on color of 

 the light can be carried out with animals having different 

 colored lights and so closely related that their luciferins 

 and lucif erases will interact with each other. Such a case 

 is presented by the American fireflies, Photinus and Pko- 

 turis. PJiotinus emits an orange light, while Photuris 

 emits a greenish yellow light. The difference in color is 

 especially noticeable when the luminous organs of the two 

 forms are ground up in separate mortars. As sho\\Ti by 

 Coblentz, the difference in color is real, the spectrum 

 of Photinus extending farther into the red than that of 

 Photuris (see Fig. 8). We can easily prepare luciferin 

 and luciferase from the two fireflies and make the follow- 

 ing mixtures : 



