Explanation: The preparations that contains the weakened or live form of biological agents are injected in the body to protect the body against pathogens is known as vaccine.
This is used to create a memory of the pathogens inside the body so that when the body is affected by it for the second time, antibodies for the particular antigen is already present in the body.
This helps in prevention of the body from harmful disease.
These preparations are called Vaccines. <span>A </span>vaccine<span> is a biological preparation that
provides active acquired immunity to a particular disease. A </span>vaccine<span> typically contains an agent that
resembles a disease-causing micro-organism and is often made from weakened or
killed forms of the microbe, its toxins or one of its surface proteins</span>. I
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Hormones -- such as melatonin and cortisol; the former signals the body to go to bed, while the latter signals for the sleeping person to wake up -- are created by physiological changes.
