The plague is one of the most deadly diseases of all time and the largest outbreak was called the Black Death. This occurred in mediaeval times and to this day it is still one of the most deadly epidemics of all time. It killed between a third and a half of the inhabitants of Europe at the time.
So what is the name of the bacteria which caused the plague and the black death? It is called Yersinia pestis and it was carried in fleas on the coats of black rats. These rodents travelled along the trade routes of the world in ships in amongst goods such as food and clothing. They transmitted the disease far and wide. The malady entered Europe via the market town of Caffa which was walled and held under siege from the Mongol army for a long time.
They tried to take the town by catapulting their dead over the walls with the aim of infecting the inhabitants. Many of the inhabitants of the city, whilst carrying the disease, fled north into Europe, taking it with them.
The bacteria is spread when the flea regurgitates it's bloodmeal. The germ blocks the alimentary tract of the flea, resulting in vomiting of subsequent meals and transmission of the disease. Fatality rate is 100% without antibiotics, meaning that in mediaeval times everybody who caught it would die. People were desperate. They believed that they were being afflicted with the disease due to wrongdoing during their lives. As a result they would attempt to purify themselves by whipping and other methods such as seeking cleansing by a priest.
In their desperation people strapped live animals to their infected lymph notes. Toads and chickens in particular were fastened to the groin region where buboes developed. These are enlarged lymph nodes, containing infection. By strapping the animals on this would increase the heat in the region, leading to the nodes bursting and pus and other fluids issuing forth. Many believed that this would speed up recovery, although it is probable that it would hasten their demise. The open wounds would be likely to become infected. This would lead to septicaemia. As no antibiotics had been discovered at this time people would have died from overwhelming infection.
It has recently been discovered that the feathers of chickens do contain a compound which has been proven to stop Yersinia pestis. There may have been some truth in this after all.
Doctors at the time were in short supply and very busy. There was very little that they could do to actually cure the disease but there were many quack remedies available at the time. Famously the doctors would wear long thick coats, boots, long gloves and a hood which covered the whole head. This would have a long beak shaped nose which contained sweet smelling herbs and spices. This was worn with the belief that the disease was transmitted in bad air. Unwittingly the doctors were protecting themselves against fleabites. Because every part of the body was covered it would have been very difficult for a flea to get near enough to the skin to bite them.