Section II. THERMOMETERS
HOW IS A PERSON'S TEMPERATURE DETERMINED?
A person's body temperature is measured using an instrument called a
thermometer. The word "thermometer" comes from the Greek word therme (heat) and
the French word metre (measure). There are two general types of thermometers--the
glass thermometer and the electric thermometer. The glass thermometer is easier to
carry than the electric thermometer and is cheaper to replace. The electric thermometer
measures temperatures faster and does not have to be sterilized after each use as does
the glass thermometer.
HOW DOES A GLASS THERMOMETER WORK?
A glass thermometer consists of a stem and bulb. The stem (long part) of the
thermometer has a hollow shaft running almost the entire length of the stem. The bulb
of the thermometer contains a small amount of mercury, a metal that is liquid at ordinary
temperatures. The thermometer is designed so that mercury from the bulb can enter
the hollow shaft in the stem. If you hold the mercury thermometer so that the bulb is
pointed up; however, the mercury will not flow into the shaft. The mercury only enters
the shaft if the mercury in the bulb expands and some of the mercury is forced into the
shaft. The mercury is cooler than body temperature. When the thermometer bulb is
placed next to body tissue, the mercury absorbs some of the body's heat. As the
mercury gets warmer, it expands. Since the mercury has no more room in the bulb,
some of the mercury is forced into the shaft. More and more mercury is forced into the
shaft until the mercury reaches the same temperature as the body tissue and stops
expanding. The patient's temperature is determined by measuring how much the
HOW DO I READ A GLASS THERMOMETER?
Reading the glass thermometer (that is, determining the temperature shown) is
done by holding the thermometer horizontally by the stem end (the end opposite the
bulb) at eye level and rotating the thermometer until the mercury in the shaft can be
clearly seen. This procedure is discussed below.
a. Hold the Thermometer at Eye Level. You must hold the thermometer at the
end of the stem, not the bulb end. (If you held the bulb end, your body heat could cause
the temperature reading to increase if the temperature of your fingers is greater than the
temperature shown on the thermometer.) Normally, the end of the thermometer is held
with the fingertips of the right hand as shown in figure 2-1 A. The thermometer should
be held at eye level to make reading easier.