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Immunity

Infectious diseases are caused by the invasion and growth of microorganisms in the human body. Infection may result from direct contact with patients or from indirect one.

But the human organism has a specific capacity of resistance against infection. It is called immunity,it may be natural and artificial. A previous attack of an infectious disease produces a more or less permanent protection against its subsequent infection.

In the course of their growth in the body many pathogenic microorganisms produce virulent poisons or toxins. These toxins cause the characteristic symptoms of a particular disease. To meet the infection the cells of the body produce a chemical antidote which is specific for this particular infection and is known as an antitoxin. If a patient can produce a sufficient amount of this antidote to neutralize the toxins before the vital organs are injured, recovery occurs. If the human body had not this capacity we should suffer from all infectious diseases.

If the toxin can be isolated from bacterial cultures and injected into men, an artificial immunity can be produced which results from the formation of antitoxin.

The cellular elements of the tissues also take an active part in the protection of the organism against the infection. The presence of any infection usually produces leucocytosis. Bacteria in the tissues are surrounded by white cells or phagocytes. They prevent the spread of bacteria and destroy them.

If the reaction against invading bacteria is insufficient, vaccines may be injected subcutaneously to produce a more active resistance of the protective mechanisms of the body. Vaccines are employed not only to contribute to the treatment of a disease, but to establish an active artificial immunity.

5. Give the definition ( определение ) of “immunity”

Immunity is … .

Answer the questions

1. What causes the infectious diseases?

2. How may the infection result?

3. What do the pathogenic microorganisms produce?

4. What do the body cells produce to meet the infection?

5. When does the recovery occur?

6. How is an artificial immunity produced?

Fill in the gaps and tell what part the cellular elements play in the protection

1. … also take part in the protection of the body against the infection.

2. … usually produces leucocytosis.

3. …surround the bacteria in the tissues and destroy them.

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