228 FOUNDERS OF OCEANOGRAPHY 



the appropriate conditions. Harvey suggests that the 

 steady luminescence of organisms such as Bacteria, which 

 go on glowing day and night, may be due to continuous 

 oxidation of luciferine to oxy-luciferine and reduction of 

 oxy-luciferine to luciferine again in different parts of the 

 protoplasm of the same cell. This is a highly economical 

 process of light-production, as no sensible heat is emitted 

 — the radiation is apparently all cold Hght. 



The two essential substances can be isolated, and when 

 the reaction is performed in a test-tube the light is only 

 produced on the surface of the fluid where the luciferine 

 can obtain oxygen from the air. Any shake or other 

 stimulation of the tube which enables the fluid to dissolve 

 more oxygen is enough to cause an increased glow or a 

 flash of light like that produced by many luminous animals 

 on stimulation. This observation suggests that, in some 

 cases at least, the light produced in the living animal, either 

 by external or internal stimulus, is a consequence of more 

 oxygen reaching the photogenous cells as the result of some 

 increase of permeabiUty of the surface layer. This, however, 

 will apparently not explain all cases of light-production 

 on stimulation, and Newton Harvey thinks it doubtful 

 whether stimulation can cause any sudden increase in the 

 permeability of the luminescent cells to oxygen. 



Finally, it may be asked — What is the use to the organism 

 concerned of this remarkable production of cold light by 

 means of the oxidation of one or more protein substances 

 secreted by the living protoplasm but retaining the power 

 of light -production, in some cases, at least, long after separa- 

 tion from the body ? It is not necessary to suppose direct 

 utility in all cases. In the lowest organisms where there 

 is a steady glow not depending upon any stimulation, it may 

 be that the light is merely a by-product of metabolism, 

 that is, of the chemical processes going on in the living 

 protoplasm and resulting in the production of light just as of 

 heat in other cases. But where the photogenous secretion 



