The Chemistry of Light-Production in Luminous Organisms. 199 



CONCENTRATION OF PHOTOGENIN AND PHOTOPHELEIN NECESSARY TO 



PRODUCE LIGHT. 



The amount of photogenin in the firefly is greater than the amount 

 of photophelein necessary to combine with it; otherwise we would not 

 be able to obtain photogenin, because it would be completely used up 

 in combination with photophelein.^ In some luminous animals (Nodi- 

 luca, CavernuJoria, Watasenia) I have utterly failed to demonstrate a 

 photogenin-photophelein reaction under conditions which should be 

 favorable and after many attempts to demonstrate it. The explana- 

 tion of this result may lie in th-e presence of equivalent amounts of the 

 two substances. 



Both photogenin and photophelein are found in much smaller con- 

 centration in the firefly than in Cypridina. The photogenin from one 

 firefly {Luciola parva), whose average size is 8.2 by 3.1 mm., with 

 luminous organ in the male 2.2 by 1.5 mm. and in the female 2.3 by 

 0.5 mm., will give just visible light in 1.6 c.c. water, and the photo- 

 phelein from 1 firefly in 3.2 c.c. water. The greater possible dilution 

 of the photophelein is due no doubt to the fact that the photophelein 

 comes from the whole body, while the photogenin is derived only from 

 the luminous gland. When we compare this with the crustacean 

 Cypridina, which will give visible light in 25,600 c.c. or one part of 

 luminous gland in 1,700,000,000 parts of water, we see that the firefly, 

 despite the brilliancy of its light, is not a very powerful fight-producer. 



PROPERTIES OF PHOTOGENIN AND PHOTOPHELEIN. 



As to the chemical nature of photogenin and photophelein, nothing 

 definite is known, except that it is not a fat or fat-like substance. The 

 photophelein is much the more stable substance and can be preserved, 

 until attacked by bacteria, or with chloroform for over 6 months. It 

 dialyzes readily through collodion, is not adsorbed by lampblack, and 

 is not readily affected by ether and benzol. Photogenin, on the other 

 hand, disappears in less than 5 hours at 25° C, is quickly destroyed 

 by ether, benzol, and chloroform, and will not dialyze readily if at all. 



In this ready destruction of photogenin by the fat-solvent anesthet- 

 ics, the firefly resembles Pholas dactylus and differs markedly from 

 Cypridina. One sample of Cypridina photogenin was preserved under 

 chloroform for over 54 days and still gave light with photophelein. 



Luciola photogenin is destroyed at about 42°, while the photophelein 

 is still active after 10 minutes' boiling. A bright light is produced on 

 mixing the two at 0° C. Exact destruction temperatures are difficult 

 to determine, however, and Lund (s) finds that in Photuris pennsyl- 

 vanica, if the intact luminous tissues are studied, the light disappears 



'I have not actually made the experiment to show that photogenin is used up in giving light 

 with photophelein, but it seems highly probable that this is the case in the firefly, as it is in 

 Cypridina. 



