v] THE SOURCES OF FOOD 129 



Nitrogen present in the form of organisms O'OOS 

 milligram per litre (O'OOS part per million). 



Thus there are apparently about 110 times as 

 much organic carbon, and about 16 times as much 

 organic nitrogen present in solution in sea-water as 

 is contained in the form of the organised substance 

 of plants and animals of the plankton. These sub- 

 stances are capable of assimilation by saprozoic 

 animals and we may take it that there are creatures 

 in the sea which do feed on them. Nevertheless this 

 does not prevent the final destruction of organic 

 carbon and nitrogen compounds, for of all such 

 resulting from the waste of the animal metabolism 

 only a part will be directly utilised in this way by 

 the saprozoic animals, the rest being broken down by 

 bacteria. And the part thus built up into animal 

 tissue is again broken down in metabolism and part 

 of it becomes the prey of the bacteria. Finally all 

 must undergo this fate. 



We know a great deal more with reference to the 

 amounts of the ultimate food-stuffs present in the 

 "sea. The amount of carbonic acid varies very greatly 

 according to the salinity, the temperature and the 

 depth. It may be stated in round numbers to 

 amount to 50 milligrams per litre of sea-water. 

 There are also a good many facts with regard to the 

 amount of inorganic compounds present in the sea. 

 Analyses by modern methods have been made from 



