The Chemistry of Light-Production in Luminous Organisms. 197 



is well known that the acid prevents light-production. As McDermott 

 (23) has simultaneously failed to extract a photogenic substance with 

 oxygen-free aqueous solvents, we may safely conclude that something 

 connected with light-production undergoes decomposition on standing. 

 We shall see later what this substance is. 



In 1885 Dubois (9) showed that the elaterid beetle Pyrophorus 

 noctilucus contained the substances luciferin and luciferase which are 

 described on page 176. I find that the lampyrid beetles Photinus, 

 Photuris, and Luciola also contain similar substances, but their proper- 

 ties agree with the related bodies previously described in Cypridina 

 rather than those described by Dubois for Pholas (10), and conse- 

 quently I have likewise called them photogenin ( = luciferase) and 

 photophelein ( = luciferin). For instance, firefly photophelein can not 

 be oxidized with light-production by oxidizing agents and is found in 

 many non-luminous forms, the opposite of the condition said to hold 

 for Pholas luciferin ( = photophelein). 



Like Cypridina photogenin, firefly photogenin is prepared by allow- 

 ing an aqueous extract of the luminous organ to stand until the 

 light disappears, and the photophelein is prepared by extracting the 

 firefly with boiling water. Light appears on mixing the two substances. 

 As we shall see, firefly photophelein alone in solution is very stabile, 

 but, together with unboiled extract of luminous or non-luminous parts 

 of the firefly, it is very unstabile. Therefore the photophelein is prob- 

 ably the substance which underwent decomposition when dried pow- 

 dered luminous tissue was allowed to stand in contact with oxygen-free 

 water for one hour in the experiments described above. 



DISTRIBUTION OF PHOTOGENIN AND PHOTOPHELEIN IN THE FIREFLY AND 



OTHER ORGANISMS. 



While photogenin is found only in the luminous gland-cells of the 

 firefly, photophelein is distributed throughout the body of the firefly. 

 An extract of the non-luminous parts of the firefly will give light with 

 photogenin, but only if tested immediately the extract is made. An 

 extract 10 minutes old is found to contain no photophelein unless it 

 has been previously boiled. After boiling the photophelein can be 

 kept for many days without decomposition. There appears to be 

 something in the extract of non-luminous parts of the firefly which 

 causes the photophelein to disappear unless the former is destroyed 

 by heat. That this is the case can be shown by adding unboiled extract 

 of the non-luminous parts to photophelein, when the latter disappears 

 from solution. Because of failure to boil the non-luminous firefly 

 extract, I had for a long time overlooked the existence of photophelein 

 in regions other than the luminous gland. Lack of oxygen retards but 

 probably does not prevent the disappearance of photophelein from 

 non-luminous parts. Note that just as photophelein disappears in 

 contact with photogenin and oxygen with light-production, so it also 



