8 SURVEY OF LUMINOUS ORGANISMS 



cule, such as a luciferin-luciferase combination, or an oxidized lucif- 

 erin molecule, or a molecule of an intermediate step, is the emitter. 

 The actual molecule emitting might be designated the "photogen." 



It has long been recognized that a substance whose molecules are 

 readily excited to fluoresce by the energy of radiation is most likely 

 to be chemiluminescent from the energy of a chemical reaction. Bac- 

 terial luciferin, firefly luciferin and Cypridina luciferin are all fluores- 

 cent, and it was early observed (Harvey, 1925) that fluorescence of 

 the light organs of luminous animals is a widespread phenomenon. 

 The fluorescence of ctenophore luminous organs is particularly notice- 

 able immediately after the bioluminescence has ceased (Harvey, 

 1925, 1926). The distribution of marked fluorescence in the luminous 

 organs of various groups is given in column 8 of Table I. 



In addition to bacteria, Cypridina, and fireflies, the only other lumi- 

 nous system which has received chemical attention in recent time 

 is that of earthworms, studied by a group of Czech investigators, 

 Komarek, Backovsky, and Wenig (see Wenig, 1946). They have 

 demonstrated the presence of riboflavin, not flavin phosphate or flavin 

 adenine dinucleotide (Wenig and Kubista, 1949), in the yellow lym- 

 phocytes of the luminous earthworm Eisenia suhmontana, as well as 

 in those of a nonluminous form, E. foetida. The luminous lymph of 

 E. submontarm fluoresces yellow- greenlike riboflavin until the bio- 

 luminescence has disappeared, at which time the fluorescence color 

 changes to blue, that of lumichrome. A corresponding change in the 

 yellow-green fluorescence of the nonluminous lymph of E. foetida 

 does not take place. Consequently the Czech workers first postulated 

 that the bioluminescence of the earthworm is connected with a change 

 from riboflavin to lumichrome, a reaction which does not occur in 

 the nonluminous species. Later they state that the molecules of ribo- 

 flavin are believed to be "absorbed in an oriented layer on the surface 

 of granula of lipoid character . . . [and] the activation energy which 

 brings them into an excited state is probably derived from an oxidative 

 reaction in which molecular oxygen takes part." 



It is interesting to note that the luminous granules of the earthworm 

 are yellow. The luciferin of Cypridina is also yellow (although its 

 luminescence is blue ) , and a yellow color has been observed associated 

 with luminous cells in at least seven additional groups — Hydrome- 



