Are smallpox and measles the same disease?

That time, that place

Born in Rey in Persia, al-Razi came to run the hospital in Baghdad. The story goes that to choose its site he hung meat in several places and picked where it spoiled last. Whether or not it happened, it tells you how he was remembered.

Why this question

In his day smallpox and measles were treated as one thing. Both bring fever and cover the body in a rash, and nothing in Galen separated them.

But to someone who had watched patients long enough, they looked different: the order in which the rash appears, the pattern of the fever, the course the illness runs.

What was found

He separated the two in writing: what comes first and what follows, which is the more dangerous, symptom by symptom. It is the first record distinguishing them.

More important, though, is the stance he took. He revered Galen. And when a patient in front of him did not match Galen's account, he chose the patient. He gathered those mismatches into a book called Doubts About Galen. Revering someone, he showed, is not the same as following them.