226 FOUNDERS OF OCEANOGRAPHY 



greatest depths, but inhabit intermediate waters, and may 

 even appear at the surface of the sea at night. 



Here, then, we have a great phenomenon of the ocean 

 — of all oceans — and at aU depths, appearing sometimes in 

 one form and sometimes in another : it may be as a duU 

 continuous glow, or it may be seen as mjrriads of briUiant 

 sparks, hke a pyrotechnic display, and in all cases caused 

 by the presence in the water of living creatures. These 

 luminescent organisms are of the most varied kinds, from 

 the lowest and simplest up to fishes, from particles of 

 microscopic size up to the gigantic Pyrosoma, and the light 

 may be produced within a simple protoplasmic cell, or it 

 may be emitted from a complicated organ composed of 

 many layers of cells. It may be a constant, steady hght 

 apparently independent of surrounding conditions, or an 

 instantaneous flash produced as the result of direct stimula- 

 tion, and evidently under nerve-control. And yet the actual 

 method of production of the Hght is probably in all cases 

 the same, and is essentially a physico-chemical process, 

 consisting of the slow oxidation of one or more protein 

 substances secreted by the living protoplasm. Moreover, 

 in many cases, it may be so in all, it has been shown that 

 two substances must be produced — the protein, called luci- 

 ferine, and an enzyme, luciferase — which must be brought 

 into contact in the presence of oxygen in order to produce 

 the characteristic apparently cold light. Bio -luminescence 

 differs from all artificial illuminants in being an emission 

 of light without any sensible heat. It is a conversion of 

 chemical energy into radiant energy. The light is a physical 

 accompaniment of the chemical metaboHsm of the organism, 

 part of the energy set free taking this form in place of the 

 more usual one of heat. It is a highly efficient method of 

 light production ; and it has been stated that the best 

 artificial iUuminant has only about four per cent, of the 

 luminous efficiency of the fire-fly. 



