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 (3) finds that in Photuris pennsyl vanica, if the intact luminous tissues are studied, the light disappears between 45° and 54° and returns on cooling. The maximum tempera ture from which the light revived was 84° and it usually returned about 50°. These effects are similar to those observed with Cypridina.
Very weak concentrations of acids prevent the production of light of the firefly, less weak concentrations of alkalies are necessary, and KCN does not affect light-production in strong (m/100) concentrations.
Table 10 summarizes the characters of photogenin and photophelein (luciferase and luciferin) as found by Dubois for Pholas and by myself for Cypridina and the firefly. Where a statement runs through both photogenin and photophelein columns it applies to a mixture of the two substances. A blank indicates that the experiment has not been tried.