MAN’S FIGHT AGAINST MICROBES 
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ing their tremendous importance in the lives 
of human beings. The knowledge we have 
today of the cause?of diseases, and of ways to 
prevent and cure them, is all based on Pasteur’s 
and Koch’s great and priceless discoveries, 
which have saved millions of human lives. 
When the United States first began to build 
the Panama Canal, white laborers were sent 
from this country to the tropical land of Panama 
to do the work. But so many of the laborers 
soon became ill and died with malaria, that 
work on the canal almost came to a stop. It 
became clear that unless a way could be found 
to keep the men from getting malaria, it would 
be impossible to build the canal. 
Fortunately, a few years before, scientists had 
discovered that malaria is caused, as we have 
already seen, by a microbe that lives in the body 
of a single kind of mosquito. The mosquito, 
by its bite, spreads the germs from sick persons 
to healthy ones, who then become sick. The 
army engineers in charge of the work on the 
canal knew of this discovery; so they at once 
What stopped 
wor\ on the 
Panama Canal? 
