BIOL VMINESCENCE 415 



associated with iron, copper and manganese, but whether the presence 

 of these metals is essential to its luminescence has not yet been ascer- 

 tained. The proteolytic enzymes destroy its light-producing power. 

 Photophelein, on the other hand, appears to be a substance related to 

 the proteoses or peptones in many of its properties, but it is not digest- 

 ible by proteolytic enzymes and it is soluble in alcohol. 



The separation of photophelein and photogenin from one another 

 may be accomplished by extracting the luminescent animals or organs 

 with hot water. This extracts the photophelein and destroys the pho- 

 togenin. A solution of photogenin may be prepared by extracting a 

 luminous organ with cold water and allowing the extract to stand until 

 all luminescence has disappeared, when the photophelein has been 

 apparently exhausted. On now mixing these two non-luminous solu- 

 tions a bright luminescence at once appears. 



The actual source of light has been shown by Harvey to be the 

 photogenin, in the following ingenious manner: The light emitted by 

 the Eastern American firefly Photinus is orange in color, while that 

 emitted by Photuris is greenish-yellow. If, now, photinus photogenin 

 is mixed with photophelein from either Photinus or Photuris the color 

 of the luminescence is that emitted by Photinus, namely orange, and 

 conversely Photuris photogenin yields greenish-yellow light whether 

 the source of photophelein be Photuris or Photinus. Evidently, 

 therefore, the character of the light emitted is determined by the 

 photogenin and not by the photophelein. 



The action of photophelein is, to a limited extent, specific. Thus 

 firefly-photophelein will cause emission of light by photogenin derived 

 from other insects, but none from photogenin derived from crusta- 

 ceans. On the other hand photogenin may be caused to luminesce 

 by many substances which are not of animal and vegetable origin, and 

 particularly by fat-solvents and other Cytolytic Agents. Thus lumi- 

 nescence of photogenin may be caused by ether, chloroform, saponins 

 or bile-salts. Harvey believes that these substances promote oxidation 

 of the photogenin by increasing the fineness of the subdivision of the 

 colloidal particles of which it is composed, and thus increasing the 

 area of exposure to oxygen. 



The part played by photogenin itself may also be imitated by a 

 variety of reagents. Thus many aldehydes, polyphenols such as 

 pyrogallol, terpenes, waxes, glucose, lecithin, cholesterol, cetyl and 

 myricyl alcohols, tannic and gallic acids, certain peptones and the bile- 

 acids will emit luminescence when treated in certain concentrations 

 with specific oxidizing-agents. Pyrogallol, for example, will luminesce 

 when treated with plant Peroxidases or with Hemoglobin or by certain 

 salts such as potassium permanganate and potassium ferrocyanide, 

 if hydrogen peroxide is also present. For each oxidizer and oxidizable 

 substance there is an optimal concentration above and below which the 

 light-emission diminishes. Thus one-molecular pyrogallol solution 

 will give no light if mixed with ^ potassium ferrocyanide and a little 



