Daniel Ackerstein, age 8, of Sarasota, Fla., for his question:
WHAT EXACTLY IS A GERM?
A germ, also called a microorganism, is any tiny, disease producing plant or animal that can be seen only through a microscope. Infectious diseases can be caused by many kinds of germs, including bacteria, viruses and protozoa.
Some germs live in the tissue and multiply so rapidly that the tissue dies. Other germs produce toxins, or poisons, that kill the tissue.
Bacterial diseases are caused by one celled germ organisms called bacteria. Scientists don't know exactly how many kinds of bacteria exist but they do know that a single grain of soil may hold more than 100 million bacteria of many different kinds.
Fortunately, most bacteria do not cause disease, and many are useful.
Some bacteria always live in the bodies of man and animals. They can be found on the skin, in the nose, mouth and throat as well as the lungs, stomach and intestines.
Virus diseases are caused by germs called viruses, which are even smaller than bacteria. Most are so small that scientists can see them only by means of a powerful electron microscope.
There are hundreds of kinds of viruses. All are infectious and can cause diseases in most living things. Some even infect other germs. Scientists have found that viruses may sometimes remain inactive for years, but can quickly infect any defenseless cell.
After a virus invades a cell, it multiplies rapidly. Millions of polio viruses, for example, can cover a spot no larger than a speck.
Germs that cause the common cold ride on moisture in the air. They enter the nose and lungs when we breathe. Food carries the germs of dysentery and other diseases into the stomach and intestines while germs that cause boils and blood poisoning can enter the body through a scratch or pin prick in the skin.
A disease's incubation period is the time between invasion of the body by a disease producing germ and the appearance of the first symptoms of the disease. The period of communicability is the time during which contagious diseases are most easily passed from sick persons to healthy persons.
Your body's skin is the first line of defense against disease germs. Tears wash germs from the eyes, mucus catches germs in the nose and saliva and acids in the stomach kill germs.
The body sets up a stronger defense that centers in the blood stream. Antitoxins neutralize poisons produced by certain germs while other kinds of antibodies kill or weaken germs in different ways.