COLOUR AND PHOSPHORESCENCE 



187 



but if the tube is shaken further oxygen is admitted and 

 more light is produced either as a glow or as a sudden 

 flash of light. 



The oxy-luciferin can be deprived of the oxygen with 

 which it has united — can be " reduced " in chemical 

 phraseology — and so converted into luciferin again, 

 and can then be used, when luciferase and oxygen are 

 present, to produce more light. This process may ap- 

 parently also go on in nature, there being a continuous 

 change in the light organs of some animals from luciferin to 

 oxy-luciferin with the production of light and then back 

 again. 



Certain bacteria are the 

 lowest form of life to pro- 

 duce light. They are re- 

 sponsible for the light 

 which appears on dead fish, 

 and they occasionally in- 

 vade living animals giving 

 them a luminous appear- 

 ance. According to a cer- 

 tain school of investigators 

 similar bacteria live within 

 the luminous organs of 

 many animals and are 

 the cause of the light 

 produced there. Of the 

 single-celled animals, the 

 Protozoa, two especially, 



Noctiluca miliaris and Pyrocystis noctiluca, have ex- 

 ceptional powers of phosphorescence (Fig. 38). They 

 have no special organs for light production but contain 

 innumerable minute granules which are responsible 

 for the luminescence. The presence of these animals 



Fig. 38. — Noctiluca miliaris, a flagellate 



protozoan which is phosphorescent, 



greatly enlarged. 



