Susan Shirey, age 11, of Eugene, Ore., for her question:
WHERE WERE GERMS DISCOVERED?
North Americans are considered to be among the healthiest people in the world. Yet despite this, Canadians numbering more than 100,000 have some kind of illness during a year while in the United States two out of every five persons have a chronic, or long continued, disease. In addition, the average American also has two acute, or short and severe, illnesses each year.
It wasn't too long ago that most men believed evil spirits made them sick. Then in about 1400 scientists came up with the theory that some diseases were caused by tiny, invisible particles called germs.
The first theory about germs suggested they developed out of nothing in the blood streams of man and of animals. But then in the 1500s doctors decided that germs were most likely passed from one person to another.
Today we know that infectious diseases are caused by many kinds of germs, including bacteria, viruses and protozoa. The microorganisms cause disease by attacking living tissue. Some germs live in the tissue and multiply so rapidly that the tissue dies. Others produce poisons called toxins that kill tissue.
Some bacteria always live in the bodies of man. They may be found on the skin, in the nose, mouth, throat, lungs, stomach and intestines. These bacteria normally do no harm but they may cause disease when the body's resistance is low for any reason.
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.
Viruses are microorganisms smaller than bacteria. Most viruses can be seen only with the aid of an electron microscope. Many are called filterable viruses because they pass through filters that hold back bacteria.
There are hundreds of kinds of viruses. All are infectious and can cause diseases in most living things. Some even infect other germs. Doctors have found that viruses may sometimes remain inactive for years, but can quickly infect any defenseless cell. After they invade the cell, they multiply rapidly. Millions of polio viruses, for example, crowded together form only a speck. But a single one of these viruses can enter a human nerve cell and produce many more new viruses in a few hours.
Viruses cause many common diseases including mumps, measles, smallpox, chicken pox and influenza.
Bacteria cause many diseases including scarlet fever, whooping cough, diphtheria, tuberculosis, syphillis and gonorrhea.