What Is Bacteria

Bacteria are living plants that are so tiny you cannot see them without a microscope. Thousands of them could be put on the period at the end of this sentence. A single one of these tiny plants is called a bacterium; the word bacteria means more than one of them, just as the word dogs means more than one dog.

There are bacteria nearly everywhere -floating in the air, living in the soil, on furniture, on the page of this book, on our hands and in our bodies and so on. Sometimes bacteria are called germs, and sometimes they are called microbes (which means tiny bits of life). Bacteria do not have leaves and stems and roots as do most of the plants you can see. Each one is much like a very tiny bit of living jelly surrounded by a clear, thin covering called a membrane.

There are more than 1,600 different kinds of bacteria. We hear mostly of bacteria that make us sick, and there are many of these; but most bacteria are not harmful at all, and some bacteria are so useful to mankind that we could not live without them. Some of these useful bacteria make it possible for certain plants to use nitrogen, a gas in the air, without which the plants could not grow. Some bacteria cause milk to sour, so that cheese can be made of it. Others turn fruits or grain into alcohol, wine, cider, or vinegar.

Other bacteria help you to digest your food. Some bacteria get their food by living on dead animals or plants. These are called saprophytes, and are very useful bacteria because the dead animals and plants they destroy help to make the soil rich and fruitful. Bacteria that get their food by living on live animals or plants are called parasites. Most of these bacteria cause disease. Some bacteria are shaped like short rods-in fact, the name bacteria comes from a word that means "rod-shaped." The first known bacteria were rodshaped.

Now the rod-shaped bacteria are called bacilli; spiral or corkscrew-shaped bacteria are called spirilla; and round or oval bacteria are called cocci, which means they look like seeds or grain. Some bacteria must have air to live; these are called aerobic. Others die if they come in contact with air; these are called anaerobic. Sunlight kills almost all bacteria. Bacteria increase their numbers very rapidly. They do not have seeds or lay eggs. Instead, each bacterium splits and separates into two bacteria. When it is warm, some bacteria divide every fifteen minutes. In less than one day, one bacterium can become more than a hundred million bacteria, if each one is able to divide itself. This rarely happens. In your blood stream, for instance, your white corpuscles (the disease-fighting ones) catch and destroy most of the bacteria before they have a chance to split.