PHOTOPHELEIN AND PHOTOGENIN.
I conclude, therefore, that Dubois's luciferase, a thermolabile sub stance in luminous cells, is the light-producing body. It gives light in contact with many substances not necessarily oxidizable and an espe cially bright light with a thermostabile substance (Dubois's luciferin) found in high concentration throughout the body of Cypridina hilgen dorfii and in small concentration in the blood or juices of other non luminous invertebrates. I therefore propose the new names photogenin (light-producer, from mss, light, and Tevpary, produce) for luciferase and photophelein (light-assister, from (pC.n, light, and c'uveXico, assist), for luciferin.
As we shall see later (p. 189), the photophelein can not be regarded as an enzyme, because it is used up in the reaction and will not give light with an indefinite amount of photogenin. The photogenin corre sponds much more to an enzyme, but it is also slowly used up. At
present we can only speak of photophelein as a definite substance causing in some way the emission of light from photogenin.
Perhaps the comparison of the important facts concerning light production in Pholas and Cypridina shown in table 1 will make clearer Dubois's and my own views, and bring out the contradictory properties of the corresponding substances in the two animals. A more complete table is given on page 200.
Whatever the exact interpretation of the facts may be, it is certain that two substances are concerned in light-production, and these may be separated, because they are destroyed at different temperatures. We may now inquire into each of their properties separately and return to a discussion of the mechanism of light-production, in considering the possible enzyme nature of photogenin.