ambition furnishes ribs of steel to 'the sides of his intent'; and
she is herself wound up to the execution of her baneful project with
the same unshrinking fortitude in crime, that in other circumstances
she would probably have shown patience in suffering. The deliberate
sacrifice of all other considerations to the gaining 'for their
future days and nights sole sovereign sway and masterdom', by the
murder of Duncan, is gorgeously expressed in her invocation on
hearing of 'his fatal entrance under her battlements':

--Come all you spirits
That tend on mortal thoughts, unsex me here:
And fill me, from the crown to th' toe, top-full
Of direst cruelty; make thick my blood,
Stop up the access and passage of remorse,
That no compunctious visitings of nature
Shake my fell purpose, nor keep peace between
The effect and it. Come to my woman's breasts,
And take my milk for gall, you murthering ministers,
Wherever in your sightless substances
You wait on nature's mischief. Come, thick night!
And pall thee in the dunnest smoke of hell,
That my keen knife see not the wound it makes,
Nor heav'n peep through the blanket of the dark,
To cry, hold, hold!--

When she first hears that 'Duncan comes there to sleep' she is so
overcome by the news, which is beyond her utmost expectations, that
she answers the messenger, 'Thou'rt mad to say it': and on receiving
her husband's account of the predictions of the Witches, conscious
of his instability of purpose, and that her presence is necessary to