How did fourteenth-century living conditions and the state of medical knowledge leave the population defenceless against serious disease?

The streets during the time of the black death
were dumping grounds for sewerage, rubbish and
 plague ridden bodies. 

14th century living conditions were very different to the way we live today.  During this time people did not know about germs or how diseases form and spread. Because of this many people including doctors believed that it was caused by foul smells or even other people such as the Jews.  The inhabitants of cities and towns saw the streets as dumping grounds and would throw all of their rubbish, scraps and raw sewage out the window. The people of that time didn't realise that it was the rats and the fleas causing the plague so they continued to throw their waste outside giving the rodents a source of food. Most families lived in a small dirty box shaped house along with other families and their animals which is a good reason why the disease spread so fast. Labourers worked all day in fields or with animals such as pigs or cows and did not even think to take a bath or change their clothes which is what we now consider to be unhygienic. There were many “cures” however which just made things worse most of the time. Priests and religious groups blamed the citizens and claimed it was Gods punishment to them for doing bad things.  The doctors of the time and people who believed they were magic created cures that didn't help such as carrying sweet smelling herbs around in your pocket or not bathing or exercising.  Although there were thousands of cures, barley any of them worked and by the time the plague had left Europe, one third of the continents population had died.  

This Horrible histories you tube clip explains what the plague was like
http://www.youtube.com/watch?v=KA6nij1kdjE

sources
http://dnausers.d-n-a.net/cbs/pages/bdth/life.htm
http://academic.mu.edu/meissnerd/plague.htm