Macbeth promises to do as she asks and charges her to treat Banquo especially with distinction. Nor does he conceal from her what now tortures him most, “Dear wife, Thou knowest that Banquo, and his Fleance, lives.” And immediately the Lady is her old self: “But in them nature's copy's not eterne.” Though Lady Macbeth is represented as at once prepared for a second murder, Macbeth has now no more need of her: “Be innocent of the knowledge, dearest chuck, Till thou applaud the deed.”
Yet, although he shrinks back no longer from any sort of evil deed, he does so before the horrible pictures of his phantasies, the hallucinations of his unconscious. Here is where Shakespeare's genius enters. The Macbeth of the Chronicle commits throughout all his acts of horror apparently in cold blood. At least nothing to the contrary is reported. With Shakespeare on the other hand Macbeth, who is represented in the beginning as more ambitious than cruel, is pathologically tainted. From his youth on he suffered from frequent visions, which, for example, caused him to see before Duncan's murder an imaginary dagger. This “strange infirmity, which is nothing To those that know me,” comes to light most vividly on the appearance of Banquo's ghost at the banquet. Lady Macbeth must use all her presence of mind to save at least the outward appearance. With friendly exhortation, yet with grim reproof and scornful word, she attempts to bring her husband to himself. In this last scene, when she interposes in Macbeth's behavior, she stands completely at the height. Not until the guests have departed does she grow slack in her replies. In truth neither her husband's resolution to wade on in blood nor his word that strange things haunt his brain can draw from her more than the response, “You lack the season of all natures, sleep.” It seems as if she had collapsed exhausted after her tremendous psychical effort.
Shakespeare has in strange fashion told us nothing of what goes on further in her soul, though he overmotivates everything else, even devotes whole scenes to this one purpose. We first see her again in the last act in the famous sleep walking scene. She begins to walk in her sleep, falls ill with it one might well say, just on that day when Macbeth goes to war. Her lady in waiting saw her from this day on, at night, “rise from her bed, throw her nightgown upon her, unlock her closet, take forth paper, fold it, write upon it, read it, afterwards seal it, and again return to bed; yet all this while in a most fast sleep.”—“A great perturbation in nature! to receive at once the benefit of sleep, and do the effects of watching,” the evidently keen sighted physician thinks. He soon has the opportunity to observe the Lady's sleep walking for himself. She comes, in her hand a lighted candle, which at her express command must be always burning near her bed. Her eyes are open as she walks, but their sense is shut. Then she rubs her hands together as if to wash them, which she does according to the statement of the lady in waiting, often continuously for a quarter of an hour.
Now they hear her speaking: “Yet here's a spot. Out damned spot! out, I say!—One, two, why, then 'tis time to do't.—Hell is murky!—Fie, my lord! a soldier, and afear'd? What need we fear who knows it, when none can call our power to account?—Yet who would have thought the old man to have had so much blood in him?—The Thane of Fife had a wife; Where is she now?—What, will these hands ne'er be clean?—No more o' that, my lord, no more o' that; you mar all with this starting.—Here's the smell of the blood still; all the perfumes of Arabia will not sweeten this little hand. Oh! oh! oh!—Wash your hands, put on your nightgown; look not so pale;—I tell you yet again, Banquo's buried; he cannot come out of his grave.—To bed, to bed; there's knocking at the gate. Come, come, come, come, give me your hand. What's done cannot be undone. To bed, to bed, to bed.” After such appearances she always in fact goes promptly to bed. The physician who observes her pronounces his opinion: “This disease is beyond my practice. Yet have I known those which have walked in their sleep, who have died holily in their beds.” Here however there seems to be something different:
“Foul whisperings are abroad; unnatural deeds
Do breed unnatural troubles.”
And then as if he were a psychoanalyst:
“Infected minds
To their deaf pillows will discharge their secrets.
More needs she the divine, than the physician.—
God, God forgive us all! Look after her;
Remove from her the means of all annoyance,
And still keep eyes upon her.”
Also he answers Macbeth, who inquires after the condition of the patient.
“Not so sick, my lord,
As she is troubled with thick-coming fancies,
That keep her from her rest.…
. . . . . . Therein the patient
Must minister to himself.”
Yet as the king's star declines neither the doctor's foresight nor his skill prevents Lady Macbeth, the “diabolical queen” from laying hands upon herself.