COLOUR AND PHOSPHORESCENCE 185 



result — possibly a quite incidental one — and not the 

 cause of the colour produced. It is highly probable, 

 though it has yet to be definitely proved in all cases, that 

 the pigments of animals are not produced by themselves 

 but are manufactured from vegetable substances which 

 they eat. The exact course which this manufacturing 

 process may take and so the colour of the resultant pigment, 

 appears to depend on the intensity of light. According to 

 one theory feeble light is sufficient for the production of 

 red pigment which may be converted into yellow or white 

 pigment under the influence of light and perhaps other 

 influences. Blue pigment is also produced from red when 

 light is present but is also destroyed by light, so that 

 blue animals are only maintained that colour because the 

 production of pigment keeps pace with its destruction. 

 But we have little definite knowledge on this most important 

 subject which presents problems for the solution of which 

 the combined efforts of biologist and chemist will be 

 necessary. 



Phosphorescence 



Although many land animals, such as the glow-worm 

 and firefly, are able to produce light so that they glow at 

 night, this power of phosphorescence, or " bio-lumines- 

 cence " as it is better called to distinguish it from light 

 produced by the mineral phosphorus, is very much more 

 widespread amongst marine animals. So common is it 

 that it has aroused interest from the earliest times and many 

 theories have been advanced in the attempt to explain the 

 mystery of its production. For instance the explorer 

 Franklin thought that phosphorescence in the sea was due 

 to friction between the salts producing tiny electric sparks. 

 This and other views are now of merely historic interest 

 for, though the power of bio-luminescence is possessed by 



