Page 69 - Reading Success B9

The body is a battleground in which a never ending war is waged against
disease producing germs. The air we breathe teems with potential killers, and

bacteria, invisible to the unaided eye, which are fortunately vanquished by the
natural defenses of a healthy body. Bacteria, or the even smaller viruses, can
invade through any opening, such as the mouth, nose, and ears, or a cut or
scratch in the skin.

Illness or infection is caused only when they penetrate into the tissue or
bloodstream. The first defenses of the body are the outer skin and the membranes

around the interior organs. Saliva and tears, both liquids protect areas prone to
invasion, such as the mouth and eyes. Stomach acids, besides digesting food, kill
off dangerous invaders that are often swallowed with it.

Once a germ has penetrated into a vulnerable area, the body’s infantry, the
white cells of the blood, spring to its defense. The average human body

contains 25 to 30 billion of these. When germs invade, the white cells rally and
multiply at the site of the infection and kill the invaders by absorbing and digesting
them - hence the name phagocytes (eating cells) are given to these very useful
fighters. Many white blood cells die in the battle that rages in an infected area,
such as a boil . During the battle the germs release poisonous substances called

toxins. These act as antigens and stimulate certain white and other cells of the
body to produce the defense chemicals called antibodies. Each antibody evolves
to deal with a particular infection. In a lifetime the body may encounter as many as

100,000 different antigens, each one bringing forth the army of antibodies.
Even when the battle is won, the victorious body does not disband its

antibodies. They persist in the bloodstream sometimes for life, being reinforced
occasionally by fresh ones manufactured in the liver and the lymphatic system.
So, if the same germs should return, the correct antibodies are ready and waiting
to repel the attack. This is the natural defense system that gives the body

immunity to an onslaught of certain diseases.

Main Idea

What is the main idea of this story?

a. the body’s natural defenses from disease and infection

b. how some diseases affect one’s body
c. how bacteria and viruses enter the body

d. the physical signs of disease or infection

72_Reading Success B 9