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| Immunity |
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| Immunity is the ability of an organism to recognise the foreign material or chemicals that enter the body and to mobilise the cells and cell products to quickly remove the foreign material. |
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| A person may develop immunity in three different ways. |
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| Immunity through diseases |
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| The first time a person gets an infection, he is likely to develop the disease because the antibody production is slow and the virus has time to multiply and spread throughout the body. |
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| The cells capable of producing antibodies persist in the body as memory cells for a long time, sometimes even for life after the first infection. They quickly become active on further infection and produce antibodies of the same type. These antibodies quickly overcome the infection, so the disease does not appear again. |
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| Vaccination |
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| This is a technique where immunity is developed without infection. Weakened or dead pathogens are injected into a person. The pathogen given is unable to cause the disease, but are sufficient to stimulate the formation of antibodies by the hosts immune system that recognises the pathogen, if it enters the body later. |
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| Example: Small pox, polio, measles and rabies. |
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| Antitoxins |
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| Antibodies that neutralize toxins produced in the body like bacterial toxins or introduced from outside like snake venom are called antitoxins. They are produced artificially these days. |
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| The antigen for e.g., snake venom is injected in low doses into an animal like horse or rabbit. After the animal develops antibodies for the antigen, its blood is drawn and allowed to clot. The serum left behind contains antibodies. It is injected into a person bitten |
| by a snake to neutralize the snake venom as he would not be able to produce antibodies in sufficient quantity quickly. It gives a temporary immunity against the antigen for a few hours or a few months. |
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