154 THE OCEAN FLOOR 



assisted by an enzymatic component called luciferase. 

 Very often this process is occasioned or accelerated by 

 bacterial action. 



Some of the bathypelagic fish have highly perfected 

 li^ht-emitting organs, evidently used for attracting their 

 prey of smaller organisms. In other cases the emission 

 of light may serve the propagation of the species, the 

 individuals recognizing each other at some distance by 

 the light they emit. 



The very fact that animal light plays an important 

 part in the life of deep-sea animals confirms the assump- 

 tion that water in great depths, including the layers im- 

 mediately above the bottom, must have a high degree 

 of transparency, that is, it must be almost free from 

 suspended particles. Investigations made by Jerlov from 

 the "Albatross," mentioned in Chapter 9, bear out this 

 assumption. 



The third factor which limits animal life (besides 

 scarcity of nutrients and lack of illumination) is the 

 high pressure. To the supporters of the theory that the 

 great ocean depths are azoic this factor seemed of para- 

 mount importance. It certainly is astounding that living 

 creatures can support pressures comparable to those 

 inside a modern field gun when the projectile is leaving 

 its barrel — pressures from 10,000 to 15,000 pounds 

 per square inch. Obviously, such enormous external 

 pressures must be counterbalanced by equally high 

 pressures existing in the tissues of the animals support- 

 ing them. A swimbladder containing gas of this 



