HOW THE BODY FIGHTS GERMS
Fortunately, the body is not helpless against germs. It has niters, such as the tiny hairs in the nose, to keep them out, and secretions, such as the tears, to kill them or wash them away. If they do get in, leucocytes (white blood cells) attack and devour them. The number of leucocytes in the blood increases rapidly when they are needed to fight infections. Fevers help the body to destroy some germs that are unable to grow at a temperature much above normal.
The body has still other resources. It manufactures substances that, in a sense, counteract the germs and render their poisons (toxins) harmless. These substances are called antibodies; some are known as antitoxins. After the body has won its battle against a certain disease, these substances remain in the blood and prevent the germs of that disease from getting a foothold again. We say that such people have become immune to the disease; this is called an acquired immunity. People who are immune to a disease without ever having had it are said to have a natural immunity. Many immunities are partial or temporary.
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