THE FRESH WATERS 147 



These minute plants are the chief producers 

 in the fresh-water community. The animals 

 are the consumers, though many of them de- 

 vour their smaller neighbours, who might 

 therefore rank among the producers. When 

 an animal dies in the water, the Bacteria 

 which cause all rotting break down its body 

 into salts and gases. The salts, sooner or later, 

 often with the help of other Bacteria, become 

 the food of aquatic plants, and the gases pass 

 into the air or are captured in the water be- 

 fore they get so far. Thus the Bacteria are 

 the middlemen. 



The experiment has been made of putting 

 mud and manure in boxes round the edge of a 

 fish-pond, which tended to "give out" pe- 

 riodically, apparently because the water was 

 too sparsely peopled. Bacteria worked at the 

 material in the boxes and made it available 

 for the microscopic animals, called Infuso- 

 rians, which always abound where there is 

 rotting organic matter. The Infusorians de- 

 voured what the Bacteria prepared, and some 

 of them devoured the Bacteria too. A living 

 cataract of Infusorians fell into the pond and 

 formed the food of water-fleas or Copepods, 

 which in turn were eaten by fishes. What was 



