Hi I'm looking for some documents or just ideas about the blues symbolism.

We all know that a structure of a piece of blues evoluated (for exemple sometimes there is turn around, sometimes not etc)during this century

So here comes my first question Does someone could tell me about the history of the blues songs musical structures from the early 20th delta blues to the today blues? Then comes my second question What might be the symbolism of each part of a piece of blues?

I thanks you in advance

Sorry for my english I'm french