On the other hand, body temperature is also a general indication of body condition. Normal human body temperature is (98.6 ° F ± 0.7°F) and it varies activity of the person as well as place of measurement. When a person is too hot, the blood vessels in his/her skin expand to carry the excess heat to his/her skin's surface. And for this reason the person begins to sweat. Then the sweat evaporates and this process helps to cool his/her body. When a person is too cold, his/her blood vessels narrow so that blood flow to his/her skin gets reduced to conserve body heat. As a result he/she starts shivering and it is an involuntary, rapid contraction of the muscles.