THE MICROBES THAT MAKE US SICK 65 
The ability of disease-germs to produce illness 
in a person depends also on a number of other 
things. The body has natural means of fighting 
these germs and killing them faster than they 
multiply. This we will explain later on. Only 
under conditions when the body cannot or does 
not fight them hard enough are they able to 
bring about sickness. One of these conditions 
is the age of the person. Children and old 
people become ill from some diseases much 
more easily than adults. Other conditions that 
help the growth of disease germs are hunger, 
thirst, fatigue, exposure to extreme heat or cold, 
a weakened physical condition caused by a 
previous illness, or some severe injury to a 
particular organ of the body. 
Not only does the condition of the body play 
an important part in deciding whether the 
disease germs can attack it, but the condition 
of the germs themselves is also important. At 
certain times their ability to grow in the body 
and produce injury there is less than at others. 
The number of disease-germs that find their 
What can 
prevent them? 
