Why do plague doctors wear a strange mask?

I tried searching for a question like this one but couldn't find any, so I decided to ask this myself. This question may sound silly but its been getting me to wonder all the time. Why do plague doctors wear this mask in a shape of some bird's beak? What did they do? What was its purpose?Why do plague doctors wear a strange mask?
A primitive gas mask in the shape of a bird's beak. A common belief at the time was that the plague was spread by birds. There may have been a belief that by dressing in a bird-like mask, the wearer could draw the plague away from the patient and onto the garment the plague doctor wore. The mask also included red glass eyepieces, which were thought to make the wearer impervious to evil. The beak of the mask was often filled with strongly aromatic herbs and spices to overpower the miasmas or ';bad air'; which was also thought to carry the plague. At the very least, it may have served a dual purpose of dulling the smell of unburied corpses, sputum, and ruptured bouboules in plague victims.Why do plague doctors wear a strange mask?
Because they are chemicals and germs inside your body that could spread in an operation.They use the mask so the germs and chemicals don't go in their mouth,down their throat,into the body and effect the lungs.
http://maskwerks.tripod.com/id8.html





lol its a halloween costume site, but it actually answers the question in the 3rd paragraph I think.
Inside the ';beak'; were various herbs and junk that they believed would keep them from catching the plague.
To stop them from getting the Plague i expect.