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 
