Page 28 - The Miracle in the Immune System

26 THE MIRACLE OF THE IMMUNE SYSTEM

This picture, which is magnified 5900 times, shows the cells
in the trachea (blue). They use their glands (yellow) to
secrete a substance that traps the particles in the air.

from the inner section of the skin towards the surface.
While doing this, the liquid element (cytoplasm) of the
cell interior transforms into a resistant protein known
as keratin. During the process, the cell dies. The newly
formed keratin substance has a very hard structure and
is not therefore subject to decomposition by digestive
enzymes, which is a sign of its resistance. Thus, invaders
such as bacteria and fungi will be unable to find anything
to rip off from the outer layer of the skin.
Moreover, dead outer cells containing keratin are
constantly shed from the skin surface. The new cells
that come from beneath to replace the discarded ones
form an impenetrable barrier in that area.
The organisms on the skin fulfill another protective
function of the skin. A group of harmless microbes live
on the skin, which have adapted to its acidic medium.