Body temperature. Gloved hand holding a thermometer displaying a normal temperature of 36 degrees Celsius. Normal body temperature varies between 36-38 degrees Celsius. If the temperature goes above this range, a fever is indicated. If it goes below, hypothermia is diagnosed. This thermometer can measure body temperature in the mouth, underarm or rectum. It consists of a sealed narrow-bore glass tube with a bulb containing mercury (bottom left). Mercury (grey) inside the tube expands when heated and extends along the scale.