LUCIFERIN AND LUCIFERASE 383 



according to the same investigator,^ '* has many properties in 

 common with the proteoses and peptones, but its chemical nature 

 cannot be definitely stated at present." 



From experiments made upon extracts of the ostracod crustacean 

 Cypridina, Harvey ^ concludes that it is safe to say : (1) that one 

 part of pure luciferin in between 4,000,000,000 and 40,000,000,000 

 parts of sea water gives, upon oxidation in the presence of luciferase, 

 light which is visible to the naked eye, and (2) that one part of pure 

 luciferase in between 800,000,000 and 8,000,000,000 parts of sea 

 water will oxidise a stock luciferin solution with visible lumines- 

 cence. It thus appears that the eye can detect the luminescence 

 of extraordinarily weak solutions of luciferin and luciferase. Indeed, 

 as Harvey points out, the concentrations of luciferin and luciferase 

 which can be detected by the sight test are far smaller than those 

 of other substances required for detection by ordinary chemical 

 reactions.^ 



The light given out by luminous animals may not be always 

 functionally useless. It is possible that certain deep-sea fish, as well 

 as squids and shrimps, which have complex luminous organs, use 

 them as lamps. The light organs of Photoblepharon and Anomalops, 

 the two surface fishes recently investigated by Harvey, are believed 

 to be used as search-lights to attract prey.^ The light given out by 

 fireflies, by the toad fish, Porichthys, which is only luminous in the 

 spawning season, and by the worm Odontosyllis of Bermuda, which 

 is brilliantly luminous when swarming, may serve as a means of 

 recognition or as a sex signal to bring together the sexes for mating.^ 

 It has always been suggested that the light of the sea-pens serves 

 to scare away predaceous animals.*' In many animals, however, 

 the emission of light appears to be quite useless. Useless, too, we 

 must consider the emission of light by luminescent bacteria and by 



1 E. N. Harvey, The Nature of Animal Light, 1920, p. 142. 



2 E. N. Harvey, " The Minimum Concentration of Luciferin to give a Visible 

 Luminescence," Science, 1923, pp. 501-503. 



3 It is remarkable that the eye can detect the flash of light that is given out by 

 the impact of a single charged helium atom on fluorescent zinc sulphide, but here 

 the light has a mechanical origin, not a chemical. 



* E. N. Harvey, The Production of Light by the Fishes Photoblepharon and 

 Anomalops, Publication No. 312 of the Carnegie Institution of Washington, p. 48. 

 5 E. N. Harvey. The Nature of Animal Light, 1920, p. 83. " Ibid. 



