A medical thermometer or clinical thermometer is a device that is used to measure the body temperature of a human or other animal. The tip of a thermometer is inserted into one of several locations – under the tongue (for oral or sublingual temperature), under the armpit (for axillary temperature), into the rectum via the anus (for rectal temperature), into the ear (for tympanic temperature) – or placed on the forehead (for temporal temperature).
History The medical thermometer began as an instrument called a water thermoscope, constructed by Italian physicist/astronomer Galileo Galilei c. 1592–1593. This instrument lacked an accurate scale with which to measure temperature, and it could be affected by changes in atmospheric pressure. Italian physiologist Santorio Santorio is the first person known to have put a measurable scale on the thermoscope; he wrote about it in 1625, though he may have invented one as early as 1612. His models were bulky, impractical, and took a fair amount of time to take an accurate oral reading of a patient's temperature. Two people switched from using water to using alcohol in the thermometer. The earliest was Ferdinando II de' Medici, Grand Duke of Tuscany (1610–1670), who created an enclosed thermometer that used alcohol c. 1654. Physicist/engineer Daniel Gabriel Fahrenheit (1686–1736) made contributions to thermometers as well. He created an alcohol thermometer in 1709 and later produced the first mercury thermometer in 1714. Mercury, he found, responded more quickly to temperature changes than the previously used water. Fahrenheit also created the temperature scale which is named after him, having recorded the system in 1724. The scale is still used primarily for everyday applications in the United States and its territories and associated states (all served by the U.S. National Weather Service), as well as in the Bahamas, Belize, and the Cayman Islands. Dutch mathematician/physicist Christiaan Huygens created a clinical thermometer in 1665, to which he added an early form of the Celsius scale by aligning the scale to the freezing and boiling points of water. By 1742, Swedish astronomer Anders Celsius created the Celsius temperature scale that was the reverse of the modern scale – 0 represented the boiling point of water, while 100 represented freezing. This scale was reversed by Swedish botanist Carolus Linnaeus in 1744. Working independently of Celsius, French scientist Jean-Pierre Christin – permanent secretary of the Académie des sciences, belles-lettres et arts de Lyon (transl. Academy of Sciences, Belles-Lettres and Arts of Lyon) – developed a similar scale in which 0 represented the freezing point of water and 100 represented boiling. On 19 May 1743, he published the design of a mercury thermometer that used this scale, called the "Thermometer of Lyon", built by the craftsman Pierre Casati. The medical thermometer was used by Hermann Boerhaave, as well as his students Gerard van Swieten and Anton de Haen. It was also utilised around this time by Scottish physician George Martine. De Haen made particular advances in medicine with the thermometer. By observing the correlation between a patient's change in temperature and the physical symptoms of an illness, De Haen concluded that a record of one's temperature could inform the doctor about a patient's health. However, his proposals were not received enthusiastically by his peers, and the medical thermometer remained a scarcely used instrument in medicine. Thermometers remained cumbersome to transport and use during this period. By the mid-19th century, the medical thermometer was still a foot in length (30.28 cm) and took as long as twenty minutes to take an accurate temperature reading. Between 1866 and 1867, English physician Sir Thomas Clifford Allbutt designed a medical thermometer that was much more portable – measuring only six inches long and taking only five minutes to record a patient's temperature. This thermometer was first manufactured in Leeds by a local firm, Harvey & Reynolds, which was established by Quakers Richard Reynolds and Thomas Harvey. In 1868, German physician, psychiatrist, and medical professor Carl Reinhold August Wunderlich published his studies that consisted of more than one million readings of 25,000 patients' temperatures, taken in the underarm. With these findings, he concluded a healthy human's temperature fell within the range of 36.3 to 37.5 °C (97.34 to 99.5 °F). Theodor Benzinger (1905–1999) invented the ear thermometer in 1964. Born in Stuttgart, he immigrated to the United States in 1947 and became a naturalised citizen in 1955. He worked from 1947 to 1970 in the bioenergetics division at the Naval Medical Research Center in Bethesda, Maryland.
Classification by location A person's temperature can be measured in various locations around the body which maintain a fairly stable temperature (mainly oral, axillary, rectal, tympanic, or temporal). Normal temperature varies slightly with location; an oral reading of 37 °C does not correspond to rectal, temporal, or other readings with the same value. When a temperature is quoted, the location should also be specified. If a temperature is stated without qualification (e.g., typical body temperature), this temperature is usually assumed to be sublingual (under the tongue). Differences between core temperature and measurements at different locations – known as clinical bias – are related to normal human body temperature. Measurements are subject to both site-dependent clinical bias and variability between a series of measurements (i.e., standard deviation of the differences). For example, one study found that the clinical bias of rectal temperatures was greater than for ear temperature as measured by a selection of thermometers being tested; however, the variability in rectal temperatures was lower.
… excerpt ends here. Continue reading the full article.
