th by doing this when other persons are
afraid of the blood.

=90. Healing cuts.=--When your flesh is cut it soon grows together
again. The work of the little white cells in the blood is to help heal
cuts and wounds and bruises. These cells are like little amebas in the
blood. They keep moving around with the blood, and now and then burrow
outside the capillaries to see if all is well. If they find a cut,
hundreds and thousands rush to the spot at once. Some eat up any
specks of dirt on the cut. Others fit themselves into the sides of the
cut and grow long and slender, like strings, and so bind the two edges
of the cut together. In this way all cuts are healed.

[Illustration: =Bacteria growing in a kidney and producing an abscess
(x300).=

_a_ kidney tube.
_b_ white blood cell attacking bacteria.
_c_ bacteria.
_d_ blood vessel of the kidney.]

=91. The white blood cells kill disease germs.=--There are tiny living
beings everywhere in the air, and soil, and water. Some of them can grow
inside a man and make him sick. These tiny things are called _disease
germs_. One kind gives a man typhoid fever, and another diphtheria.
Another kind grows on cuts, and sometimes makes them very sore. The
white cells of the blood are always watching for these enemies, like a
cat hunting mice, and when they find them they at once try to kill them.
But sometimes the white blood cells get killed. Then they look like
cream in the cut. We call this creamy liquid _matter_ or _pus_, and say
"We have caught cold in the cut." In most pricks and cuts the white
cells of the blood can kill all these enemies and also heal the cut.

=92. Catching cold.=--Sometimes the cold air blows on our head and
hurts the cells of the nose. If there are disease germs in the air,
they may grow in the injured part of the nose and make us have a "cold
in the head." Then the white blood cells gather at the spot so as to
kill the disease germs. Also the arteries bring a great deal of blood
to the nose so as to heal the injured parts. Some of the white blood
cells and the liquid from the blood run out, and we have to blow the
nose. The white blood cells help to make us well whenever we catch a
cold or other kind of sickness.

=93. Red blood cells.=--The red blood cells are like tiny flat plates.
They float in the liquid part of the blood and make the blood look
red. They carry air from the lungs to the cells of every part of the
body, and thus help all t