Pioneering 19th century German physician Carl Reinhold August Wunderlich is widely known for championing the empirical observation of hospital patients and sagely spreading the idea that fever is a symptom, not a disease, but he is best known for persistently sticking a one-foot rod in the armpits of thousands of people.
The rod was a thermometer, of course, and the temperature measurements he recorded led him to reveal in his 1868 magnum opus, Dos Verhalten der Eigenwarme in Krankenheiten, a number that remains with us even today: 37 °C, or 98.6 °F, the average human body temperature.
Except that number is wrong.
In 1992, researchers at the University of Maryland used the latest equipment and employed rigorous methodology to determine the average human body temperature from a sample of 148 healthy men and women aged 18 through 40 years. Taking over 700 temperature readings spaced out at various times throughout the day, they found that the average human body temperature is closer to 98.2 °F, and, in a bold conclusion that flew in the face of 120 years of common knowledge, stated:
"Thirty-seven degrees centigrade (98.6 °F) should be abandoned as a concept relevant to clinical thermometry."
Even if Mr. Wunderlich is truly wrong -- and it's not looking good for him -- one can't really denigrate his effort. His readings reportedly came from a sizable sample group: as many as 25,000 individuals! But unfortunately, they also came from a now antiquated device. Wunderlich's data almost certainly was hindered by shoddy thermometers.
"Thermometers used by Wunderlich were cumbersome, and had to be read in situ, and, when used for axillary measurements [under the arm] required fifteen to twenty minutes to equilibrate," the researchers noted.
With 98.2 °F now considered to be the correct average human body temperature, it's worth mentioning that, if you took your temperature right now, it almost certainly won't be that number. Your body's temperature fluctuates throughout the day, from roughly 97.6 °F at six in the morning to 98.5 °F at six in the evening. In fact, a temperature as high as 99.5 °F is still considered healthy.
The human body relies on consistent temperatures to function properly. A body temperature ten degrees too warm or twenty degrees too cool more often than not results in death. But there are notable exceptions to the norm. Willie Jones of Atlanta, Georgia survived after reaching an internal temperature of 115.7 °F during a bout of heatstroke. Two-year-old Karlee Kosolofski's body temperature dipped down to 57.5 °F after spending five hours outside in a Canadian winter, yet she lived to tell the tale.
additional reference material on this topic:
Normal Body Temperature _ Rethinking the normal human body temperature - Harvard Health.pdf