Wunderlich's clinical thermometry

Carl Reinhold August Wunderlich (1815 to 1877), a German physician, began taking his patients' temperatures every day early in his career. Over the years he built up a record of how different diseases changed body heat from one day to the next.

In 1868 he published the results as Das Verhalten der Eigenwärme in Krankheiten, The Course of Temperature in Diseases. The book rested on more than a million readings taken in the armpit from some 25,000 patients. From them Wunderlich put average normal body temperature at 37.0°C (98.6°F) and gave the first numerical definition of fever, 38.0°C (100.4°F) or above. He showed that a disease, and the stage a patient had reached, could often be recognized from the shape of the temperature curve.

According to the Science Museum, thermometry was controversial at first but became an important diagnostic tool. Édouard Séguin, a follower of Wunderlich, introduced clinical thermometry in the United States in the mid-1860s, and an American volume combining Wunderlich's work with Séguin's own suggestions on thermometry was published in New York in 1871.

Attempts to check Wunderlich's figures date from 1935. The most careful came in 1992, when Philip Mackowiak and colleagues took 700 readings with electronic oral thermometers from 148 healthy volunteers. They found a mean of 36.8°C (98.2°F), an upper limit of normal of 37.7°C (99.9°F), and a daily swing of about 0.5°C, lowest at 6 a.m. and highest in the late afternoon. They put part of the gap down to differences in instruments and in where and how temperature was measured.