The Plague Doctor
The Toxic Virus
The plague doctor's job was, obviously, to diagnose and treat the plague.
The plague caused it's victims to vomit so much and so violently that their internal organs ruptured. They would suffer massive internal bleeding and this would turn their skin black.
Buboes would form in the victim's armpits, neck... Buboes are large pus filled and spot covered boils which grew as large then burst, the pus leaking into the bloodstream, killing the patient.