Biolnminescence 667 



per cent efficient, that of Photinns about 87 per cent.^^ For the bluish hght 

 of Cypridina and Chaetopteriis, the maximum emissions of which he still 

 further from the region of maximum sensitivity for the human eye, the 

 luminous efficiencies are of the order of 20 per cent or less. However, all of 

 these exhibit strikinglv higher luminous efficiencies, of course, than does the 

 carbon incandescent lamp, which approximates 0.5 per cent. We must al- 

 ways bear in mind that the luminous efficiencies would have more real com- 

 parative biological significance if they were calculated in terms of the spec- 

 tral energy curves of sensitivity of the photoreceptive mechanisms of those 

 species reacting in nature to these light sources. 



The Mechanism of Li^ht Production. The actual light-yielding reactions 

 of animals have recei\ed considerable study. The solution of the problem of 

 their general nature has been very much simplified through the discovery 

 that these reactions will proceed in vitro in a manner superficially indistin- 

 guishable from those proceeding in vivo. It has been known for many years 

 that the luminescent cells or tissues of certain animals or their products can 

 be dried with a resultant cessation of light emission. When water is again 

 added the materials will again luminesce. Hence the final reactions are ob- 

 viously not dependent on the vital organization of cells, although the pro- 

 duction of the specific materials which participate in these reactions do have 

 such dependence. 



In addition to an aqueous medium, photogenic reactions of most animals 

 require also the presence of free oxygen. This appears equally true, whether 

 the reactions occur within the living organism or in extracts of dried prep- 

 arations of luminous organs. It is true, however, that in some instances the 

 necessary partial pressure of oxygen is extremely small. The only critical ex- 

 periments which have indicated that luminescence can occur in the com- 

 plete absence of oxygen have been performed on certain radiolarians, the 

 jellyfish, Pelagia and Aequorea, and certain ctenophores.-'' •*^- -^^ One must 

 conclude that in these animals either the reactions are basically different from 

 those in most other animals or a source of oxygen is available in the ma 

 terial of the extracts. The latter alternative appears the more probable. 



It was clearly demonstrated many years ago that the photogenic reaction 

 in the beetle, Pyrophonis,^^ and in the mollusc, Pholas,^^' involved two 

 organic substances. These were separated from one another by utilizing the 

 characteristics (1) that one substance was less heat stable than the other, 

 and (2) that when the luminescent reaction had run its course some of one 

 of the substarices, the relatively heat-instable one, remained. The one that 

 was relatively heat stable was named luciferin, the other luciferase. Luciferin 

 solutions could be obtained free from luciferase by extracting the luminous 

 organs in hot water; luciferase could be obtained free from luciferin by ex- 

 tracting the organs in cold water and then permitting the extract to luminesce 

 to exhaustion. 



Luciferin and luciferase have also been identified in the polychaete worm, 

 Odontosyllis, in the ostracods, Cypridina and Pyrocypris, in the deep-sea 

 shrimp, Acanthephyra, and in several species of beetles.-''- -^- '^^ However, 

 careful search has failed to reveal their presence as such in most other com- 

 mon luminous groups. It is reasonable to assume that the functional counter- 

 parts of these substances are nonetheless present in these latter groups. 



