How do they 
cause sickness? 
64 WORLD OF INVISIBLE LIFE 
work all through the body. Blood-poisoning 
is one of these diseases. Other germs settle in 
special parts of the body, and are unable to 
grow anywhere else. In either case, wherever 
the microbes live and multiply, they form 
poisons that are taken up by the blood and 
carried through the body. This is easy to 
understand when the microbes themselves are 
in the blood, but diseases where the microbes 
causing them remain in one place are like that, 
too. Diphtheria, for instance, is produced by 
germs that grow on the inside surface of the 
throat. The germs themselves do not enter 
the blood or any other part of the body, but, 
as they feed and multiply, they produce a 
powerful poison that is absorbed by the blood 
and thus goes all through the body. Sometimes, 
the microbes grow in the intestines and their 
poisons are absorbed from there. All disease- 
germs act in this way; they produce poisons 
which are absorbed by the body, causing the 
injury and pain known to be a result of what¬ 
ever disease one is suffering with. 
