Medical Thermometer 1866 – Measuring Fever

In 1612, Italian physician Santorio Santorio was among the first to add a numerical scale to thermometer-like devices. However, the effects of air pressure prevented accurate measurements.

German physicist Daniel Gabriel Fahrenheit, who invented the alcohol thermometer in 1709 and the mercury thermometer in 1714, preferred mercury because it could be used across a wide temperature range. It also had a freezing point as low as alcohol and a boiling point high enough to measure temperatures above and below the freezing point of water.

Some early clinical thermometers were almost a foot (25 cm) long, making them difficult to carry in a doctor's bag or apply to patients. Measurements could take more than twenty minutes. In 1866, British physician Thomas Clifford Allbutt invented a clinical thermometer only six inches (15 cm) long that he could always carry in his pocket and use as often as a stethoscope.

An important turning point in medical thermometer history was German physician Carl Wunderlich's work, publishing temperature data from 25,000 patients in 1868. That year, Scottish physician Thomas Maclagan also studied temperatures in patients with typhoid and pneumonia. 

Wunderlich not only published temperature data from a large patient group but also defined the normal human body-temperature range. He considered normal temperature approximately 37°C (98.6°F). Although these values remain generally accepted, later research showed that such averages can vary between individuals and at different times of day.

Electronic and infrared technologies made medical thermometers faster and more accurate in the second half of the 20th century. Electronic thermometers became widespread from the 1980s, being safer and easier to use than mercury thermometers. Infrared sensors are now commonly used in medical thermometers.

Fever is a response to infection or other illness and is usually a defence mechanism. Raising body temperature makes it harder for bacteria and viruses to multiply and increases immune-system effectiveness. A raised temperature may therefore be an early sign of illness and help doctors diagnose infection or disease.

Typical fever curves, patterns of temperature rising and falling at particular times, have been identified during certain diseases. Typhoid fever and malaria, for example, have characteristic fever patterns that can aid diagnosis.

Different thermometers measure temperature orally, rectally, in the ear (tympanic), at the skin surface or on the forehead (temporal). Different types may suit different ages and circumstances.

Historical figures mentioned in the article: Santorio Santorio (1561–1636), Daniel Gabriel Fahrenheit (1686–1736), Carl Reinhold August Wunderlich (1815–1877), Thomas Clifford Allbutt (1836–1925), Thomas Maclagan (1838–1903)

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