I am going to prove that in the play Macbeth, a symbol of blood is portrayed often (and with different meanings), and that it is a symbol that is developed until it is the dominating theme of the play towards the end. .
To begin with, I found the word "blood", or different forms of it forty-two times (ironically, the word fear is used forty-two times), with several other passages dealing with the symbol. Perhaps the best way to show how the symbol of blood changes throughout the play is to follow the character changes in Macbeth. First he is a brave honoured soldier, but as the play progresses acknowledged and trusted by his king, he becomes a treacherous person who has become identified with death and bloodshed, and ends up killing Duncan who put so much trust in him. This is ironic because the previous thane of Cawdor was executed for treason, which is the first thought that comes into his mind when he is appointed thane. He knows that the king's trust was misplaced; the fact that he murdered his king plays upon his conscience and shows his guilt in different forms. The situation worsens for him after he murders Banquo, who was one of his most loyal and trusted friends. A similar idea can also be applied to lady Macbeth, as her character changes dramatically throughout the course of the play. Hers and Macbeth's roles can be seen to swap in a way. When the idea of killing Duncan comes into the minds of Macbeth and lady Macbeth, Macbeth is uncertain, he seems withdrawn about the whole idea. Lady Macbeth comes across as evil and bloodthirsty, for it is she who ensures that the murder takes place. Towards the end of the play though, although both characters show the immense guilt of what they have done, it is lady Macbeth who is now withdrawn, and Macbeth who comes across as evil, for the full spell of the witches has now taken effect, he does not believe that the Scots will be defeated, so he ridicules the idea of an English invasion.