E. NEWTON HARVEY 135 



I now believe that under the term photophelein I have previously 

 included two separate substances. One of these is the thermostabile 

 dialyzing substance extracted from Cypridina by hot water. Al- 

 though this substance cannot be oxidized with light production by 

 oxidizing agents, it does oxidize spontaneously (also without light 

 production) in the air and loses its power of producing light with 

 photogenin. In the absence of air its solutions are stabile for months. 

 Once oxidized it can again be reduced and will again give light if 

 photogenin is added. It is therefore an oxidizable material and, I 

 beHeve, similar to the luciferin of Pholas. I propose therefore to use 

 Dubois' word luciferin for the thermostabile dialyzing substance of 

 Cypridina in place of photophelein and luciferase for the thermolabile 

 non-dialyzing substance in place of photogenin. The source of the 

 photogenic substances can be designated by prefixing the name of the 

 animal as Cypridina luciferin, Pholas luciferin, etc. I suggest also 

 that luciferin when oxidized be designated oxyluciferin. 



Luciferin is found only in luminous animals. In non-luminous ani- 

 mals and probably also in luminous animals there is a second substance 

 which I have formerly included in the term photophelein, and which 

 may be properly so called, that acts in a manner similar to saponin, 

 NaCl crystals, etc., upon the extract of Cypridina which has stood 

 until the light disappears. When we allow a Cypridina extract con- 

 taining luciferin and luciferase to stand, the luciferin is not completely 

 oxidized, even though the extract is thoroughly aerated, but some 

 of it is bound (adsorbed or combined?) by other substances in the ex- 

 tract. The saponin, NaCl crystals, and extracts of non-luminous 

 animals act by setting free the bound luciferin which is then oxidized 

 and light appears. I suggest that the term photophelein be applied to 

 these substances in tissue extracts. They are not destroyed by boil- 

 ing. On standing some are stable while others are unstable. 



The best way to rid a luciferase solution of the bound luciferin is 

 to shake it thoroughly with chloroform. Such a solution will give no 

 light with extracts of non-luminous animals or saponin, NaCl crystals, 

 etc., but a brilliant light with Cypridina luciferin. 



An insight into the modus operandi of saponin, NaCl crystals, or 

 photophelein may be gained from the following experiments. Both 

 luciferin and luciferase are adsorbed by many finely divided precipi- 



