OUR “NORMAL” TEMPERATURE
No one today thinks
twice about taking the temperature of someone presenting with illness, but that
wasn’t always so. Physicians in the U.S. rarely recorded temperatures before, and even during, the Civil War. World-wide the practice was much the same. What
made the change?
Human temperature
seems to have been first measured by the remarkable Sanctorio Sanctorius,
professor at the University of
Padua in the early 1600s. In addition to
weighing intake and output to measure insensitive losses, he measured
temperatures using a graduated thermoscope, an open tube sensitive to
atmospheric pressure as well as temperature. Closed tubes, to eliminate
atmospheric pressure effects, were soon invented. Then in 1714 Daniel Gabriel
Fahrenheit, a skilled instrument maker working in Holland, fashioned a
mercury-filled closed tube thermometer with a new scale that proved quite
accurate. He
picked zero as the temperature of a mixture of ice, water, and
sea-salt, 32 of water and ice alone, and boiling water measured 212. The
astronomer Anders Celsius, in 1742, brought back the centigrade scale first promulgated
by Christiaan Huygens in the previous century. Both scales continued in use.
 |
| Sanctorio Sanctorius (from Wikipedia) |
 |
| Daniel Fahrenheit (from Wikipedia) |
Thermometry still had no sex appeal, however. Of a few
prominent medical men who adopted it in their practice one stands out: Anton de
Haen, a former pupil of Hermann Boerhaave. As professor of medicine at the
University of Vienna from 1754-76, de Haen recorded the levels and diurnal
variations in temperatures of normal and diseased subjects, correlated high
temperatures with high pulse rates, and noted the association of rising
temperatures
with chills. But most clinicians saw no practical value in
measuring temperatures. Concepts of the mechanisms of heat production and
regulation, both in physics and biology, were not developed until the early 19th
century, and fever was still a disease, not a symptom.
 |
| Anton de Haen (Wellcome Library) |
The person most influential in bringing the medical world around to using the thermometer was Carl Wunderlich. Wunderlich
studied medicine at the University of Tübingen, graduating in 1837. Grumbling
about the backward status of German medicine at the time he teamed up with two
of his schoolmates, Wilhelm Griesinger and Wilhelm Roser, to literally usher in
a new era. The three founded a new journal, the “Archiv für Physiologische
Heilkunde” (Archives of Physiologic Medicine, or Medical Science) to emphasize
the importance of physiologic investigation in addition to clinical observation.
It was the beginning of a golden age in German medicine, assisted by government
subsidies and attracting students from around the world.
Wunderlich ended up
as professor of medicine at the Univ. of Leipzig, where he conducted his
temperature studies (and where clinical physiology achieved world renown). With
Germanic
thoroughness he recorded around-the-clock temperatures of some 25,000
patients, collecting over a million measurements. Both normals and the sick of
all ages were included. The work culminated in a book, Das Verhalten der Eigenwärme
in Krankheiten (On the temperature in Diseases), that exerted wide
influence.
 |
| Carl Wunderlich (National Library of Medicine) |
Wunderlich used a mercury bulb thermometer and preferred temperatures
taken in “a well-closed axilla” over oral or rectal temperatures. His work
established the now familiar “normal” average temperature of 37C (98.6 F)
degrees, with oscillations seldom exceeding 0.5o C each way. He demonstrated
rather typical fever patterns for various diseases, such as typhoid, typhus,
relapsing fever, smallpox, measles, etc., thus using the thermometer as a
diagnostic aid. Fever patterns, especially high temperatures, could also help
with prognosis.
In spite of the influence of the work, there were problems. Statistical
methods were not well developed at the time and Wunderlich’s measurements are
not tabulated, but rather summarized. More important, how accurate were the
measurements? Wunderlich himself states, “Errors that do not exceed half a
degree Centigrade are hardly worth mention”, suggesting that high precision was
not a priority.
 |
| English version of Wunderlich's book second edition (Hathi Trust) |
And another question: is 37oC really the “normal” average
temperature? In 1992 a group of 148 normal subjects aged 18 to 40 were studied
over three days with modern Diatek electric oral thermometers (700 readings).
Their mean (and median) temperature turned out to be 36.8oC +/-0.4
degrees (98.2oF +/- 0.7 F).
Why the difference? Wunderlich preferred axillary temperatures, known to
be lower than oral ones. He used glass thermometers with a mercury column, most
about 12” long, that could take 15 to 20 minutes to equilibrate – frustrating
to a busy nurse. Another possible source of error is calibration of the thermometers.
The first internationally accepted temperature scale was not established until
1897, ten years after Wunderlich’s death. We cannot test Wunderlich’s own
instrument but a thermometer belonging to one of his students is available (now in the
Mütter Museum in Philadelphia). It is 22.5 cm long (about
9”), and in a water bath it gave readings 1.6oC to 1.8oC
higher than modern electronic thermometers, partially offsetting the lower
readings formerly obtained in the axilla. Physical changes from long storage,
such as change in bulb size, were thought to play a minor role in such a
difference. Finally, as mentioned, Wunderlich did not worry about less than a
half degree variance in measurement.
So we are “cooler” than we thought, though not by much. But Wunderlich’s
work, in spite of some inaccuracies and fuzzy statistical methods, established
thermometry as a permanent clinical practice.
SOURCES:
Wunderlich, W A. On
the Temperature in Diseases: A Manual of
Medical
Thermometry. Eng trans by W B Woodman, London,
1871.
Mackowiak, P and Worden, G. “Carl Reinhold August
Wunderlich and the Evolution
of Clinical Thermometry”.
1994. Clin Infect Dis v18(3) pp 458-67.
Dominguez, A, et al. “Adoption of Thermometry into Clinical
Practice in the United
States”. 1987. Rev Infect Dis v9:
1193-
1201.
Mackowiak,
P A, et al. “A Critical Appraisal of 98.6oF, the Upper
Limit of
the Normal Body Temperature, and Other Legacies
of Carl
August Wunderlich”. 1992. JAMA v268:
1578-80.
Gershon-Cohen,
J. “A Short History of Medical Thermometry”.
1964. Ann
N Y Acad Sci. v121:4-11.
