THE MICROBES IN AIR AND WATER 33 
The two most common diseases known to 
be transmitted by water are typhoid fever and 
cholera. Both find their way into water via 
sewage from the homes of people sick with 
one or the other of these diseases. But neither 
germ finds the right food there, and so lives 
only for a short time. Typhoid germs will live 
for four or five days in natural bodies of water; 
they do not ordinarily multiply, but become 
fewer in numbers. Sewage, therefore, is most 
dangerous immediately after it enters the water, 
be it river or lake or drainage canal. But the 
germs can live for some time in the soil, and 
sometimes are washed into rivers and wells after 
they have been in the soil for several weeks. 
They have been known to travel quite a dis¬ 
tance in the water, at least eighty or ninety 
miles. 
The cholera germ is less hardy than the ty¬ 
phoid germ and lives a shorter time in the 
water, for it is killed by other microbes harm¬ 
less to human beings. By boiling water for 
ten minutes, we can completely destroy both 
A river flowing 
through a city is 
usually filled with 
germs 
Do microbes 
cause disease? 
M. 
pit 
