xii CONTENTS 



PAET III. 

 METABOLISM IN THE SEA. 



CHAPTER X. 



THE CONDITIONS OF LIFE IN THE SEA. 



The nutrition of marine organisms — Plankton as food-stufif — Ultimate 

 food-stuffs in the sea — Modes of nutrition among marine organisms — Holo- 

 phytic organisms — Saprophytic organisms — Myxotroj)hic animals — Saprozoic 

 animals — Law of the minimum — Physical conditions and the metabolism of 

 marine organisms — Temperature — Salinity — Migrations of fishes and salinity 

 changes — Sunlight — Photo-synthesis — Colour of sea water . , . 206 



CHAPTER XL 



BACTERIA IN THE SEA. 



Types of bacteria — Biological reactions — Distribution of bacteria in the 

 sea — Halibacteria — Luminous bacteria — Putrefactive bacteria — Prototrophic, 

 metatrophic and paratrophic bacteria — Fermentation bacteria — Sulphur 

 bacteria — Nitrifying bacteria — Nitrogen-fixing bacteria — Denitrifying bacteria 

 — Temperature and denitrification ....... 253 



CHAPTER XIL 



THE CIRCULATION OF NITROGEN. 



Atmospheric, organic, and inorganic nitrogen — Animal and plant metabo- 

 lism — Elimination of waste products — Putrefactive decomposition — Breaking 

 down of dead organic matter — Nitrification — Sewage and its jDurification — 

 Denitrification — Drainage of nitrogen from land to sea — Mass of nitrogen 

 annually added to the sea — Utilisation of land drainage by marine organisms 

 — Transmutation of nitrogen through series of marine organisms — Production 

 by marine plants — Transfer of nitrogen from the sea to the land — Destruction 

 of nitrogen compounds in the sea — Denitrification in the sea — Density of life 

 in polar and tropical seas — Circulation of inorganic food-stufFs — Structural 

 and current metabolism 273 



