DEPARTMENT OF MARINE BIOLOGY. 205 



duction. The preparation of photogenin and photophelein is described in my 

 paper in Science (n. s., xliv, 652.) Contrary to Dubois's results for Pholas, 

 I find photogenin (luciferase) only in the light organs of luminous animals 

 and photophelein (luciferin) widely distributed in the animal kingdom. In 

 the case of Cypridina, photogenin is a very stable substance and may be 

 preserved in solution for over 56 days with chloroform. In the case of the 

 firefly and Pholas photophelein is the more stable substance. 



Photophelein and photogenin are both adsorbed by animal charcoal or 

 Fe(0H)3, but will easily pass a Pasteur-Chamberlain porcelain filter. Photo- 

 phelein dialyzes easily, photogenin only with extreme difficulty. The 

 reaction between photophelein and photogenin is not specific, although 

 photogenin gives a better light with photophelein from the same species than 

 from other luminous species. Neither photogenin nor photophelein are true 

 enzymes, although the photogenin from one Cypridina will use up the photo- 

 phelein from at least 100 others. 



The photogenin and photophelein of Cypridina are secreted together into 

 the sea-water as a perfectly clear granule-free secretion from gland cells on 

 the upper lip, but as already mentioned, in the body, photophelein is found 

 throughout the animal, probably in the blood; photogenin only in the lumi- 

 nous cells. Just as in the presence of photogenin, photophelein is rapidly 

 used up with light-production, so in the presence of the extract of the non- 

 luminous cells of Cypridina, photophelein quickly disappears but without 

 light-production. If we boil the non-luminous cell extract or exclude oxygen, 

 the photophelein is not so rapidly used up. In the case of the firefly, the 

 photophelein disappears so rapidly from an extract of non-luminous cells 

 that it is necessary to extract them with boiling water to prepare a stable 

 solution giving light with photogenin. Because of failure to boil the extract, 

 I previously had overlooked the existence of photophelein in the non-luminous 

 parts of fireflies. The evidence seems to indicate that boiling destroys a 

 substance existing in the non-luminous parts which oxidizes the photophelein. 



Further facts concerning the properties and the effects of temperature, 

 acids and alkalies, protein coagulants, anesthetics, etc., on photophelein and 

 photogenin, as well as a discussion of the theory of Dubois and my own, will 

 be found in my complete papers on Cypridina, Cavernularia, and the firefly, 

 and Mrs. Harvey's paper on Noctiluca. A fact of considerable interest is 

 the comparative harmlessness of KCN, which has no effect on light produc- 

 tion, although this process is an oxidation in all forms. 



Regarding the chemical nature of photogenin, nothing definite can as yet 

 be said, except that it is not a fat or fat-like body, but is probably protein. 

 Cypridina is an excellent form for such investigation, and I expect to report 

 more definitely concerning photogenin in the near future. Photohlepharon, a 

 surface fish of the East Indies, whose large light-organs glow for many hours 

 even when excised, seems also highly favorable for chemical work. 



The present work can be considered only as a beginning, and opens up a 

 large field for future study. There are many organisms as yet almost wholly 

 uninvestigated, and those forms which have been investigated, if we may 

 rely upon the statements recorded, differ in such very essential points that 

 we may perhaps look to several distinct methods of light production. The 

 production of colored light and the distribution of photogenin and photo- 

 phelein among luminous animals offer problems of fascinating interest. 



In conclusion, I wish to express my sincerest thanks to my Japanese 

 friends, particularly to Professor C. Ishikawa, of the Agricultural College, 

 Imperial University of Tokyo, for his interest and assistance, and to Profes- 

 sor Ijima, of the Zoology Department, Imperial University of Tokyo, for the 

 hospitality of the Marine Biological Station at Misaki. I am also greatly 



