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 Hght-production, as no sensible heat is emitted 

 — the radiation is apparently all cold Ught. 



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 Ught 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 permeability of the surface layer. This, however, 

 will apparently not explain all cases of Hght-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 Ught by 

 means of the oxidation of one or more protein substances 

 secreted by the Uving protoplasm but retaining the power 

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

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

 utiUty 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 metaboUsm, 

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

 protoplasm and resulting in the production of Ught just as of 

 heat in other cases. But where the photogenous secretion 



