v] THE SOURCES OF FOOD 131 



surface of the sea at some distance from the land. 

 Many analyses have also been made of coastal water 

 and water from the deep, and without quoting these 

 we may remark that the coastal water contains more 

 inorganic nitrogen and more carbonic acid, and 

 also more organic dissolved carbon and nitrogen 

 compounds than does the water at some distance 

 from the land. The amounts of these substances 

 also increase regularly the deeper in the sea we go, 

 and the difference between the surface and the 

 bottom is very like the extreme difference found in 

 the surface waters of the Antarctic and tropics. 



Considering the results a little more closely we 

 notice that : (1) The amount of inorganic nitrogen in 

 sea-water is very small, varying from one-tenth to 

 about one-half per million of water ; nevertheless 

 upon this minute trace depends all the life of the 

 sea : it is so small because it is continually being 

 absorbed by plant organisms. (2) It is greatest in 

 the Antarctic where the temperature was nearly that 

 of freezing water ; much less in the North Atlantic, 

 where the temperature varied from about 5 C to 10 C. ; 

 and least in the tropics, where the temperature was 

 about 28 C. (3) The proportion of inorganic nitrogen 

 was least in August, when the temperature was 

 highest ; and greatest in February, when the tem- 

 perature was lowest. (4) The proportion was greatest 

 at the bottom of the sea and least at the surface. It 



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