MAN’S FIGHT AGAINST MICROBES 
87 
other curious ideas as to what caused sickness, 
all of them just as useless and stupid as the 
ones we have mentioned. 
With such ideas about sickness, it is no 
wonder that a serious illness in those days 
nearly always meant death. Since men did not 
know what caused illness, or how it spread 
from one person to another, they could not 
know how to fight it. When plague appeared 
in a city during the Middle Ages, as it so often 
did, a person could only hope and pray that 
he would not get it. People had no idea that 
it was caused by germs that could be carried 
from one person to another. 
They did not know that the terribly dirty and 
unhealthful way they lived in the towns, 
crowded closely together in houses that were 
dark and overrun with rats, was a sure means 
of spreading disease germs. We know now that 
the worst disease they suffered from, the Black 
Death, is caused by a germ which is carried 
by rats, but they did not know it. So every 
now and then frightful outbreaks of disease 
What was the 
Blac\ Plague? 
