SEA WATER 221 



it is these bacteria that are responsible for the production 

 of the sulphuretted hydrogen. Such a condition is unique 

 in salt water. Even in the very greatest depths in the 

 open ocean life is still possible. For the absence of oxygen 

 is a result of stagnant conditions, and in the open ocean 

 such cannot be the case owing to the continual circulation 

 of water in the great ocean currents. 



While we breathe in oxygen we send out into the air 

 again the product resulting from its utilization, carbon 

 dioxide. All animals are therefore constantly giving this 

 gas out to the surrounding water and it is everywhere 

 present. At the same time it is used up again in the upper 

 layers by the floating plants which build up sugars out of 

 it under the action of sunlight, restoring oxygen once more 

 to the water. 



Physical Properties 



Water being the medium in which all marine animals 

 live, there are certain of its physical properties which 

 influence the animals themselves or tend to modify the 

 environment under which they live. On land, for instance, 

 the temperature of the air or the barometric pressure may 

 induce profound changes in our bodies. 



The surface temperature of the sea changes markedly 

 from place to place. In the tropics it is hot compared 

 with the polar regions. The highest tem.perature recorded 

 in the sea is ninety-six degrees Fahrenheit in the Persian 

 Gulf and the lowest twenty-eight degrees Fahrenheit in 

 polar regions.^ Between these two limits all temperatures 

 are to be found. Albeit this range is small compared with 

 the great temperature differences which occur on land, 

 the highest being one hundred and thirty-six degrees 

 Fahrenheit and the lowest minus ninety-four degrees 

 Fahrenheit. But although the changes are not as great 



