2. The body’s ability to resist and overcome disease depends on immunity, a natural defensive mechanism which is due to the presence of certain substances in the blood and lymph stream. These substances are known as antibodies. This immunity is inborn. Antigens, the foreign substances that attack the body, stimulate the production of antibodies.

3. NATURAL I.Species II.Racial III.Individual ACQUIRED I.ACTIVE a.Natural b.Artificial  Live attenuated germs  Killed germs  Toxins II. PASSIVE a. Natural b.Artificial  Antibacterial  Antiserum  Antiviral

4. It is the resistance offered by the body under the normal conditions without any external stimulation of previous infection. It is either possessed from birth or acquired during growth.

5. Types of Natural Immunity I.Species Immunity: e.g. hens against tetanus, dogs, rats against tuberculosis. II.Racial Immunity: e.g. negroes against yellow fever III.Individual immunity: e.g. some human beings cannot catch infection quite often than others.

6. Acquired Immunity It is acquired by the body in two ways : a.Active Acquired Immunity: Antibodies are formed due to reaction of person’s own tissue in acquiring resistance. b.Passive Acquired Immunity: It is acquired by the introduction of antibodies, induced in some other immune person or an animal of the same or another species. Readymade antibodies are given from immune person or animal.

7. Types of Active Acquired I.Natural Acquired: When someone produces his own antibodies against a disease, usually after he has recovered from an illness. The body can produce antibodies, some of which remain effective for years. Such as Measles, Chicken pox. II. Artificial Active Acquired Immunity: It is due to vaccination of certain material containing antigen substances derived from bacteria or viruses, e.g., Rabies, typhoid, tetanus etc.

8. Antigens (Artificial Active Acquired Immunity) A.Live attenuated germs:- In this category living germs with reduced strength are exposed at high temperature. Live vaccines give better protection than the killed vaccine. Vaccines for B.C.G. and M.M.R. are prepared by this method. B.Killed germs:- The vaccines of killed germs are used for Typhoid, Cholera and whooping cough. C.Toxins:- It is the toxin produced by the germs. This is in lower strength and vaccinated. It produces the antibodies. Toxins are used in diseases like Diptheria and Tetanus.

9. Types of Passive Acquired I.Natural Passive Acquired Immunity: Mother’s milk provides antibodies to the infant. Colostrum provides immunity to the child for short period. Immunity is acquired in the womb from mother’s placenta. II.Artificial passive Acquired Immunity: Antibodies or anti-toxins can be taken from the blood of someone who has had a disease, and given to another who is suffering from it. This kind of immunity is always short-lived.

10. Antigens (Artificial passive Acquired Immunity) A.Anti Bacterial:- When bacterial cell is used to produce bacterial serum. This is anti serum which kills the bacteria. Anti bacterial serum is used in plague. B.Anti toxic:- Antibodies from the serum of horse or man are separated who have suffered from the disease. These antibodies are transferred to diseased persons so that those patients can be saved. Antideptheria serum and antitetnus are prepared by this method. C.Anti virus:- Vaccination for those diseases which caused by virus are prepared by this method. The convalescent patients of these diseases have antibodies in their blood. These antibodies are used as protective measures for other people.

11. difference Active ImmunityPassive Immunity a.The antibodies are produced in a person’s own body. b.It takes sometime to provide immunity after immunization. c.It provides immunity for long time sometime for whole life. d.There is no harmful effect of active immunization. Antibodies are supplied from other source than the person himself. It is rapid because antibodies are readymade and action is fast. Its immunity is short lived. Sometimes antitoxins prepared from animals can cause some reaction.