Plague doctors

 in 1656 the plague broke out and it was the most horrifying and lethal disease in human history.

It killed 10s million people and had at best was at best a 40% survival rate.

It started in the Asian and African countries and spread around the world and in western Europe in the 17th century that's when the "plague doctor" emerged.

As described it had a hood with crystal eyepiece (somewhat like glasses), and a beak with a strong combination of herbs and spices, it may have had pepper, cinnamon, turpentine, roast copper, and sometimes powdered viper flesh, the uniform used was somewhat like the modern-day hazmat suit, as it was designed to block miasma from entering the pores on the skin.

This concoction was inspired by the famous 2nd-century Greco-Roman physician Galen and was thought to ward off poisoned air, known as miasma, people believed the plague from originating from swamps, and sources of decay such as dead animals and plants. 

In earlier centuries Doctors around Europe used metal pomanders (which looked like Christmas ornaments filled with the above, and most guess that the beak from the doctor's mask was a hands-free alternative to holding the pomander.

People did not know that the culprit behind the plague was a tiny flea named Yersinia pestis.

The Doctors who wore the coat were protected from flea since the fleas cannot fit through the cloth.

In the 20th century, there were no treatments for the plague, but people did try some things, such as taking the blood of the patent and cupping, and a hot poker to pop the bubbles filled with pus.  

Well with all things, it (luckily) disappeared with enough time.