In the 14th century doctors were powerless against the plague, and they could only improvise some cures.

Plague would appear in three different forms:
Bubonic: characterized swollen lymph nodes (buboes or pustules) under the armpits, at the groin and wherever people had been bitten by fleas.                                                                                                                                       Pulmonary: the disease would infect lungs and cause cough with haemoptysis.
Septicaemic: the most lethal among the three ones; blood circulation would be rapidly invaded by the noxious bacteria and death would come within a few hours. The doctors of the age would try to draw the “poison” out of the body through bleedings, laxatives and enemas. 
Buboes would be incised or covered with hot cataplasms, poultices prepared with emollient substances.
Medical potions were used, prepared with the most various ingredients, from rare spices to chrome powder and gold compounds. Aromatic wood would be burnt to purify the air and flowers would be watered with rose water and vinegar, but such measures were useful just to cover the smell of rotting flesh. Several sorts of diets were recommended for precautionary purpose, and some of them may have been useful to make people healthier and therefore able to better fight the infection. Nevertheless the fact of being in peace with God was considered the best defence, in fact, at the sick-bed the doctor was always preceded by a priest. Prayers and confessions came before medical cures.
Not all those infected by plague would die, but their recovery had to be considered a miracle.
Only in 1894 the cause of the disease and its vaccine were discovered.