Are all water 
microbes harmful? 
34 WORLD OF INVISIBLE LIFE 
typhoid and cholera germs, as well as any other 
harmful microbes which may be present. That 
is why water should be boiled before drinking 
when we are not sure that it is free from such 
microbes. 
The ordinary microbes in water, which are 
not harmful, are of many different kinds. They 
may make water cloudy and bad-smelling, but 
otherwise they do no harm. Many of them 
have complex structures, as compared to the 
simpler microbes. They even have mouth open¬ 
ings and a sort of stomach. Some of these are 
called Infusoria, others are amoebas, and an¬ 
other kind are called rotifers. Some are green 
when seen through the microscope. Though 
these are larger than many of the microbes, they 
are all too small to be seen without one. 
Besides, all bodies of water swarm with the 
countless kinds of tiny microbes that can live 
on dead plant and animal matter, but which, 
as far as we know, cannot thrive on living ani¬ 
mals, and so are not dangerous to man. 
Most of the microbes in water are killed by 
