Clearly 98.6°F is just an exact-sounding conversion from the less exact sounding 37° Celsius.
But is 37° even the right number or just the center of a range.
Who came up with this “constant” enshrined on every oral thermometer?
This is a guess: the temperature 37 degrees Celsius was found to be the normal temperature to a limited degree of specificity, namely, no tenths of a degree. It was then converted to Fahrenheit precisely, and has been used with that degree of precision since, when of course a better statement would be 98 and a half degrees, give or take…
Just a guess and with class in a couple minutes no time to check it out. Sorry, don’t normally do this, but I’ve thought about this a lot, so will be interested to find out the truth. 
I believe the the practice of measuring oral temperature is for the purpose of uniformity. If everyone takes oral temperature, then useful comparisons with the temperature record over time and from one doctor to the next can be made.
The 98.6 F or 37 C is merely a nominal figure and small departures from it aren’t unususal. A doctor or nurse, however, can judge when a departure is no longer small.
Keith did, in 1967.
Suppose we said that it is 37.0°Celsius. Then 98.6°F would be just as exact.
Right; many people have average temperatures a bit above or below 37 degrees Celsius. I’m pretty sure my average temperature is something like 98 even.
And then, of course, there’s Iceman. 
I always thought it was because Farenheit’s scale was supposed to utilize 0 as the temperature on one of the coldest days in Poland (?), and 100 was supposed to be the human body temperature. Apparently, either he had a fever or his equipment wasn’t totally accurate.
Wikipedia says this is one of the three possible explinations.
According to John Allan Paulos in his book A Mathematician Reads the Newspaper, “Recent investigations involving millions of measurements have revealed that this number is wrong; normal human body temperature is actually 98.2 degrees Fahrenheit.” The study from which the number 98.6 arose was originally conducted in Celsius, and the result was rounded to the nearest degree: 37 C, which just means it was somewhere between 36.5 and 37.5 C, which translates to a Fahrenheit range of 97.7 to 99.5 degrees.
See also 98.6.
I run a little cold myself, usually around 98 flat.
I was amused by a Buffy ep. I saw the other day (4th season), where the Initiative is using
infrared scopes to tell the living from the undead-and every single living person they scanned
read “98.6”…
I’ve always heard that back when the Fahrenheit scale was created, 0 was freezing, 100 body temp, and 200 the boiling point of water. However, this was with alchol thermometers that were not very accruate. As we got more accruate thermometers it became the accepted 32, 98.6, and 212 respectably.
No cite, just something I heard once that made sence to me.
I heard that it was imply the case that the first themometer simply had a scale on it before things were being measured. Don’t remember where I got that idea.
Since freezing is not 0 at all, but 32, I’d have guessed that Fahrenheit simply was measuring the outdoor temp and when he went to divide the scale he picked as the nominal endpoints the high and low recorded that year.
When subsequent years had different highs and lows there was no specific reason to rewrite his logs, it was easier to let the numbers stand. He was recording things for himself alone at that point. Was my guess.
The cite above that lists “the normal range for body temperature is 97 to 100 degrees Fahrenheit” seems more useful than 98.6, but would mean a wide mark on the thermometer instead of a skinny one. I’d bet that’s the main reason for an artificially narrow normal, just the preference of a thermometer manufacturer.
Not to mention that human skin temp is nowhere near 98.6
As I recall the development of the Fahrenheit scale, and no, I wasn’t around at the time, he selected as zero the lowest temperature he could get in his laboratory and body temperature as 100. This made the melting point of ice equal to 32.454F and the boiling point 215.01F. Not liking the decimals on the temperature of the melting point he adjusted his size of his degrees so that it was 32. When this was done the body temperature came out as 98.6F and the boiling point as nearly 212F.
Does no one even bother anymore to see what The Master says?
I like the version I heard better. 
When I was a boy, the magic number was always 98.4. I don’t know whether this was my mother getting it wrong or if it’s just a British thing, but I’m sure my doctor also used 98.4.
One of my favourite Cecil lines: “In short, 100 means nothing on the Fahrenheit scale, 96 used to mean something but doesn’t anymore, and 0 is colder than it ever gets in Denmark. Brilliant.”
96 is a “nicer” number - you can have a half, a third, a quarter, a sixth, an eighth or a twelfth, to name but a few. 100 is a bit less user-friendly.
The C is easy: 0C for freezing pure water, 100C for boiling pure water at 1atm.
The F, as I was told by my college professors, came from a Royal request. 0F was the temperature at which the North Sea freezes; 100F, the temperature of the human body. Farenheit was a tad off, that’s all.