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What are germs?
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FOR as long as humans have been on this planet, the microscopic life forms that we call germs - bacteria (细菌), viruses, protozoa（原生动物）, fungi（真菌）and others - have been here, too. For all this time, they have been growing and multiplying in the soil, in the water, and in our bodies. Most of the time, people and germs coexist peacefully; in fact, humans couldn't live in a germ-free world. But germs are also the source of many human illnesses.
Let's get to know germs better. What do they look like and how do they live? How do they harm us and how do medications work against them?
Bacteria
Bacteria are living things made of only one cell. Bacteria weigh about one trillionth of an ounce each, and they come in three basic shapes: cocci (球菌), shaped like small balls or spheres; bacilli（杆菌）, shaped like rods or sticks of chewing gum; and small spirals called spirillum （螺菌）.
Under a microscope, scientists can often identify different species of bacteria by their shape and their grouping pattern.
Besides having a characteristic appearance under the microscope, each species of bacteria also has a typical bacterial lifestyle. For example, some bacteria colonize a particular part of a person's body and remain there, often without causing illness.
Others prefer the soil and live there harmlessly - until they find themselves trapped inside a dirty cut on a gardener's hand.
Bacteria differ in their need for oxygen, too, with some living only where there is air and others living without oxygen.
Of the approximately 1,600 species of known bacteria, less than 200 are pathogenic (disease-causing). Pathogenic bacteria can cause illness in at least three different ways: by invasive action, directly invading and attacking a part of the body; by making toxins, chemical byproducts that act as poisons; or by multiplying into large clumps that block tiny blood vessels or interfere with the normal closing of heart valves.
Depending on the type of bacteria and the illness it causes, bacteria can spread in the following ways:
through contaminated water and food.
in the tiny fluid droplets of coughs and sneezes.
through dirty hands.
through contaminated surfaces.
in a sick person's body fluids.
(Part I)(SD-Agencies)
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