The bubonic plague was the most commonly seen form during the Black Death, with a mortality rate of thirty to seventy-five percent and symptoms including fever of 38–41 °C (101–105 °F), headaches, painful aching joints, nausea and vomiting, and a general feeling of malaise. Of those who contracted the bubonic plague, 4 out of 5 died within eight days.
Septicemic plague was the least common of the three forms, with a mortality rate close to one hundred percent. Symptoms were high fevers and purple skin patches (purpura due to DIC).
David Herlihy identifies another potential sign of the plague: freckle-like spots and rashes. Sources from Viterbo, Italy refer to "the signs which are vulgarly called lenticulae", a word which bears resemblance to the Italian word for freckles, lentiggini. These are not the swellings of buboes, but rather "darkish points or pustules which covered large areas of the body".
In retrospect, it seemed like everything the people thought to do at the time simply made the problem worse. For example, since many equated the plague with God's wrath against sin, and that cats were often considered in league with the Devil, cats were killed en masse. Had this bias toward cats not existed, local rodent populations could have been kept down, lessening the spread of plague-infected fleas from host to host.
The practice of alchemy as medicine, previously considered to be normal for most doctors, slowly began to wane as the citizenry began to realize that it seldom affected the progress of the epidemic and that some of the potions and "cures" used by many alchemists only served to worsen the condition of the sick. Distilled spirit, originally made by alchemists, was commonly applied as a remedy for the Black Death, and, as a result, the consumption of spirits in Europe rose dramatically after the plague. The Church often tried to meet the medical need.
A plague doctor's duties were often limited to visiting victims to verify whether they had been afflicted or not. Surviving records of contracts drawn up between cities and plague doctors often gave the plague doctor enormous latitude and heavy financial compensation, given the risk of death involved for the plague doctor himself. Most plague doctors were essentially volunteers, as qualified doctors had (usually) already fled, knowing they could do nothing for those affected.
A wide-brimmed black hat worn close to the head. At the time, a wide-brimmed black hat would have been identified a person as a doctor, much the same as how nowadays a hat may identify chefs, soldiers, and workers. The wide-brimmed hat may have also been used as partial shielding from infection.
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.
A long, black overcoat. The overcoat worn by the plague doctor was tucked in behind the beak mask at the neckline to minimize skin exposure. It extended to the feet, and was often coated head to toe in suet or wax. A coating of suet may have been used with the thought that the plague could be drawn away from the flesh of the infected victim and either trapped by the suet, or repelled by the wax. The coating of wax likely served as protection against respiratory droplet contamination, but it was not known at the time if coughing carried the plague. It was likely that the overcoat was waxed to simply prevent sputum or other bodily fluids from clinging to it.
A wooden cane. The cane was used to both direct family members to move the patient, other individuals nearby, and possibly to examine the patient with directly.
Leather breeches. Similar to waders worn by fishermen, leather breeches were worn beneath the cloak to protect the legs and groin from infection. Since the plague often tended to manifest itself first in the lymph nodes, particular attention was paid to protecting the armpits, neck, and groin. It is not known how often or widespread plague doctors were, or how effective they were in treatment of the disease. It's likely that while offering some protection to the wearer, they may have actually contributed more to the spreading of the disease than its treatment, in that the plague doctor unknowingly served as a vector for infected fleas to move from host to host.