In the canon of classical drama, the Shakespearean play Macbeth is one of the most commonly studied. Perhaps what is most interesting about the play is the character Lady Macbeth and the physical and psychological changes she undergoes as a result of the incantation given in Act I Scene V. The monologue is best known for the phrase "unsex me here". What follows is a series of requests that seek the empowerment of an ethereal and malevolent force. Though this is a fairly common theme in renaissance drama, the Shakespearean play Macbeth explores this theme in a radically different way. As the monologue unfolds while seeking supernatural powers likening her to a more masculine presence, she asks explicitly for a physical altering of her being, specifically cessation of her menstrual cycle.
The line "Stop up the access and passage to remorse/ That no compunctious visitings of nature/ Shake my fell purpose" can of course be considered on a more metaphysical term, meaning that no human compassion be waiver her resolve to murder Duncan. But, when dissecting the verbiage of the sentence, perhaps the most enigmatic in this translation would be the phrases "make thick my blood" and "compunctious visitings of nature". When considered in the light of the physiological effects she experiences as the play unfolds, predominantly the bouts of somnambulism, that while the goal of the aforementioned incantation may be developing a more steely resolve, there is physical affectation, namely cessation of all the functions making her innately female. Digging deeper, there is a wealth of resources on medicinal practices and thought on the functioning of the human body. There are several correlations between the physiological changes she requests, undergoes and suffers from as the play progresses and that of the times in which Shakespeare did a majority of his writing. Primarily, a loose attachment that still existed between the supernatural and the natural. The idea that spirits still played some role in illness, healing and physiology in general was still a predominant concept.
There is another recurrent theme in many Shakespearean plays that this image is built heavily on. Many of Shakespeare's female characters crave development of a masculine identity. Most commonly seen in the comedies as a woman cross-dressing as a man to infiltrate a situation, this is a unique example of that recurring motif, because Lady Macbeth seeks to and conceivably permanently alters her physiological state in an attempt to make herself a masculine presence capable of murder.
Certainly, the soliloquy can be glossed over, hanging only on the incantation as a call for strength. But, looking further into the the text of Lady Macbeth, there are many physiological effects, most notedly the somnambulism and ultimately suicide, which brings to mind the idea that indeed some demonic possession had occurred. With that established, and referring back to the requests made in the soliloquy, it is easy to see that in offering to be unsexed, she had full intention of sacrificing the natural functions of both her body and soul. Thus seeking thickening of the blood to cease the visiting of nature and taking of her milk for gall permanently altered her physiological state.