How did bad weather conditions in the years before the black death impact the spread of the disease?

For there were alot of places to carry the disease for bad living conditions 

Hi! after fertilization occurs, the zygote goes through mitosis and then differentiation (aka specialization of cells) to have a variety of cells that perform different functions. this allows for the creation of tissues and so on, all of which were once stem cells with no specific function.i hope i !