The body is under the attack of germs, such as bacteria and viruses, which cause diseases. A healthy body has ways to defend itself. The cuts in the skin close to prevent germs from entering. White blood cells eat germs or release chemicals called antibodies to destroy them.
One way to prevent dangerous diseases is to inject small amounts of the germ into the body. Thus, the white blood cells learn to recognize the enemy and prepare to defend themselves against it. This is called immunization.
Some white blood cells "remember" the identity of invading bacteria or viruses. If the germs reappear, those globules immediately release the chemicals, called antibodies, to destroy them. Other white blood cells chase germs and destroy them by devouring them.
When the body temperature rises above normal, we have a fever. The fever is usually caused by germs that invade the body. Fever accelerates the body's defenses and helps fight the disease. Body temperature can be taken with an instrument called a thermometer.
Many parts of the body heal themselves. A broken bone is healed if the two ends meet. First, the blood coagulates in the break. Then, the cells produce a flexible material called cartilage, which is eventually replaced by bone.
As a curious fact, viruses are so tiny that billions could be placed on the head of a pin. And another curious fact is that the bacteria divide every 20 minutes.
Author of the separators 1-2
