Blood is mentioned throughout the play and mainly in reference to murder or treason. The first reference to blood is in MacBeth's soliloquy in Act 2, Scene 1, Lines 33-61, when Macbeth sees the bloody dagger floating in the air before him. Also in this soliloquy on line 46 he sees "on thy blade and dudgeon gouts of blood", this means that there is blood on the handle and spots of blood on the handle. This is implying that the dagger was viciously and maliciously used on someone. Shakespeare most likely put this in as premonition of murder and death to come later in the story.
The next reference, although indirect, in Act 2, Scene 2, Lines 5-11 is when Lady MacBeth talks about smearing the blood from the dagger on the faces and hands of the servants that she drugged. In Act 2, Scene 2, Lines 11-12, "I laid their daggers ready; He could not miss them". Notice how she said THEIR daggers. She is setting up the innocent servants of the king, making it look like they committed treason. Also in this scene is the first reference of blood pertaining to guilt. MacBeth says this in Act 2, Scene 3, Line 60, "Will all great Neptune's ocean wash this blood clean from my hand?" This is an example of blood representing guilt, because MacBeth wishes he could just wash his guilt away.
Again, blood is referred to again when in Act 2, Scene 3, Lines 123-134 Malcolm and Donaldbain are discussing what to do and Malcolm says in Line 128, "There's daggers in men's smiles, the nearer in blood, the nearer bloody." Meaning that their closest relatives are likely to kill them. Again, blood is being used to describe treason, murder and death.
Act 5, Scene 1 is the famous sleepwalking scene. While Lady MacBeth is sleepwalking she makes many references to the evil...