Sight, smell, taste, hearing and touch - these are the five (A16) ... through which we experience the world around us. They can help (A17) ... us from potential danger, for example, when a loud noise warns us to look out for trouble. Similarly, the body's immune system too sends messages through the brain, telling the body how to respond in certain situations. For example, if you catch a virus or a disease and infection is (A18)... in your body, the immune system immediately goes into action and produces a chemical called IL-1 that tells you to feel feverish and sleepy Once, these feelings were (A19) ... of only as symptoms of the infection. However, recent research has modified point of view. Doctors now believe that they represent the system's method of helping us fight the disease fever (A20) ... the growth of harmful bacteria and resting in bed speeds up our recovery.