Stories for Thinking Children-2

rial called mucus, which helps to re-
duce friction to the lowest level when
we're moving in the water. That
allows us to move faster. Also, its
slipperiness makes it very difficult
for enemies to catch us. Another
characteristic of mucus is that it
protects us against illness."
Omar agreed: "Yes, I once tried
to take hold of the fish in my fa-
ther's bucket with my hand but
they slid out of my hand again
right away!"
The fish smiled: "The special things
about our skin don't stop there. In our
upper skin there is a special layer made of
keratin. Keratin is a hard, tough material
which is formed by the death of old cells in
the lower level that lose contact with their
sources of food and oxygen."
"This layer made of keratin prevents water
from entering the body and is useful in bal-
ancing inside and outside pressure. If this