654 



SCIENCE 



[N. S. Vol. XLIV. No. 1140 



ether and is a very unstable substance. Fire- 

 fly photophelein is not harmed by chloroform 

 and can be preserved for many days. On the 

 other hand, it is the Cypridina photophelein 

 which is the unstable substance. A water solu- 

 tion of Cypridina photogenin preserved with 

 chloroform for 56 days will still give light on 

 mixing with fresh photophelein. It should be 

 borne in mind that photogenin, the source of 

 the light, is not only a very powerful sub- 

 stance, but also a stable substance. If we can 

 see the light from a stable body in a concentra- 

 tion of 1 : 1,600,000,000, what might not be 

 accomplished with the pure substance? We 

 have, perhaps, in the power of photogenin the 

 first indication of a really possible utility of 

 " cold light." My work is not sufficiently ad- 

 vanced to state the chemical nature of pho- 

 togenin except to say that it is probably pro- 

 tein. Many of the properties of photogenin 

 and photophelein will be found in forthcoming 

 papers on Cypridina, Cavernulari-a and the 

 firefly. 



The photogenin and photophelein of Cypri- 

 dina 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 luminous cells. Just 

 as in presence of photogenin, photophelein 

 is rapidly used up with light production, so 

 in presence of extract of the non-luminous 

 cells of Cypridina, photophelein quickly dis- 

 appears, 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 neces- 

 sary to extract them with boiling water to 

 prepare a stable solution giving light with 

 photogenin. Because of failure to boil the ex- 

 tract, I previously had overlooked the exist- 

 ence of photophelein in the non-luminous parts 

 of fireflies. The evidence seems to indicate 

 that boiling destroys a substance existing in 

 non-luminous parts which oxidizes the pho- 

 tophelein. 



Probably photogenin from different forms 

 is different, at least there is a certain amount 

 of specificity in the photogenin-photophelein 

 reaction. Photogenin from Cypridina will 

 give a faint light with photophelein from the 

 firefly, but photogenin and photophelein of 

 the same species or allied species give much 

 the brightest light. Por instance, firefly 

 photogenin will give a brighter light with 

 photophelein from other species of fireflies or 

 even from non-luminous insects (i. e., the 

 boiled cell extracts of non-luminous beetles) 

 than with Cypridina photophelein. Indeed, 

 it may be found that the photogenins from 

 different forms exhibit differences in light- 

 giving power, depending on relationship, sim- 

 ilar to the differences in the hemoglobins, or 

 similar to the specificity of the precipitin re- 

 actions of different animals. 



If Dubois's statement that Pholas luciferin 

 will give light with oxidizing agents, that it is 

 not destroyed by heat and is found only in 

 luminous cells, be confirmed, we may perhaps 

 look to two general methods of light produc- 

 tion in the animal kingdom — one as in Pholas, 

 the oxidation with light production of luci- 

 ferin by luciferase so closely paralleled by 

 pyrogallol and peroxidases; 4 the other, as in 

 Cypridina and the firefly, through the inter- 

 action of photogenin and photophelein, the 

 photogenin giving light by some mechanism 

 which can not at present be definitely stated. 

 The closest parallel is the zymase system. 

 Just as zymase is inactive without its co- 

 enzyme, so photogenin is inactive (will not 

 emit light) without photophelein, and just as 

 there are certain quantitative relations be- 

 tween zymase and co-zymase, so there are 

 similar quantitative relations between photo- 

 genin and photophelein. As oxygen is neces- 

 sary for light production, we may, perhaps, 

 provisionally regard photogenin as a substance 

 auto-oxidizable with light production only in 

 the presence of photophelein. 



E. Newton Harvey 



Princeton University, 

 October 16, 1916 



* Harvey, E. N., Amer. Jour. Physiol., 1916, 

 XLI., 454. 



