troublemakers (like bacteria and viruses) are
denied entry. Other things we can’t make use
of inside, like undigested food and fiber, are
also turned away.
The bouncers take their jobs very
seriously, as experience has taught them that
all outsiders have the potential to cause a lot
of trouble if they get inside. There are only so
many ways into the club, however, so as long
as the bouncers guard all the doors and screen
out any unsavory characters, things inside
should (theoretically) stay healthy and safe.
BACTERIAL FRIENDS AND
FOES
Since keeping your inside healthy and
secure is so important, your body has assigned
your security force some additional agents—a
group of unlikely allies on the outside. Your
body is home to trillions (yes, trillions) of
bacteria, and most of them are in your gut.