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 

 devour 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 before 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" periodi- 

 cally, 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 Infusorians, 

 which always abound where there is rotting 

 organic matter. The Infusorians devoured 

 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 part and 



