So, for a quick summary: there were two competing medical theories in the Renaissance. 1) Humoralism, also known as Galenism. Think the four humors and bloodletting. Bile. All that fun stuff stretching back to Hypocrites. And 2) Paracelsianism, which was a combination between a slightly better informed science (emphasis on the slightly) and alchemy. Wedding of elemental opposites, earth, wind, fire, water, turning stones into gold, all that magic. As you can probably imagine, neither of these theories did much to help cure, oh, say, the black plague. Or syphilis. Leprosy. The flu. Gout. Asthma. In-grown toenails. Basically it sucked to live in the Renaissance. And this fact did not escape our astute Mr. Shakespeare.
Shakespeare recognized faults with both medical theories and utilizes Romeo and Juliet to illustrate the flaws in Early Modern medicine. The play offers a deeply skeptical view of medical practice as it often existed in the Early Modern world and is in dialogue with major medical events of the time period. For example, the play was written during one of the many devastating plague outbreaks in the Renaissance. Thus, the plague becomes a very important character within the play. Romeo fails to hear of Juliet’s trick with medicine because the messenger is stopped by a plague quarantine (V. ii. 8). Most memorable, of course, is Mercutio’s famous cry: “a plague a’both your houses!,” cursing the two families to utter demise—a curse assured by the tenuous “glooming peace” brought by the lovers’ deaths (III. i. 83, V. iii. 305).
Along with the placement of disease as a character within the play, Shakespeare inserts medical dialogue into discussions of love and death. A woe-filled Romeo laments, “Hang up philosophy!/ Unless philosophy can make a Juliet,/ Displant a town, reverse a prince’s doom,/ It helps not, it prevails not” (III. iii. 56-59). Philosophy—counsel and preaching self-regulation—were an essential part of Galenic treatments. As Romeo establishes, philosophy has little relevance in dire circumstances; Shakespeare critiques the effectiveness of Galenic medicine. Not only critiquing Galenism, but also Paracelsianism, Shakespeare associates both medical theories with Friar Lawrence. In his famous introductory monologue, Friar Lawrence speaks of the “powerful grace that lies/ In herbs, plants, stones, and their true qualities” (II. ii. 15-16). In one sentence, the friar mentions Galenic herbal cures and alchemical stones. He also describes “the earth that’s nature’s mother”—citing the Paracelsian belief that the divine makes every element “mother” of another (Moss 173). Most significant to the play’s action, however, he muses over cure by contraries, a Galenic concept:
Within the infant rind of this small flower
Poison hath residence, and medicine power:
For this, being smelt, with that part cheers each part,
Being tasted slays all senses with the heart.
Two such opposed kings encamp them still
in man as well as herbs, grace, and rude will
(II. iii. 24-29).
Almost prophetically, Romeo appears in Friar Lawrence’s cell two lines later, foreshadowing his death by poison at the end of the play to subdue the “two such opposed kings”—Lord Montague and Lord Capulet. The play is more traditionally Galenic in outlook, the Friar experiments with the new elements of Paracelsian medicine and spends the entire action attempting to cure a cankerous wound—the feuding families whose “canker’d” hate disturbs the peace—with a Paracelsian slave made from the literal wedding of two Galenic opposites (Romeo and Juliet) (I. i. 91).
Neither medical theory, however, succeeds in saving Romeo and Juliet—and Mercutio, Tybalt, and Paris—from their deaths. Therefore, neither medical theory is especially effective in curing disease.
Romeo and Juliet draws parallels between a medical understanding of the human body—using Galenic and Paracelsian theories—and a political understanding of the social body. Both Friar Lawrence and the Prince describe the Montagues and Capulets in relation to cankers: the Prince describes the “canker’d hate” and Friar Lawrence mentions the canker worm in his famous monologue, a worm that consumes a plant from inside its stem. In terms of the play’s action, the hate between the two families is consuming the characters from the inside out: beginning as a street tousle and culminating in a grand
multi-act killing spree. The five deaths seem to be the only cure for the hatred; the Prince proclaims, “see what a scourge is laid upon your hate” to the heads of the two families, begging for reconciliation at the end of the play (V. iii. 292). Medically, a ‘scourge’ was defined as the cauterizing heat used to burn out infected wounds. This scourge is used to clean out society. Paracelsus introduced new herbal and chemical salves used to heal wounds rather than burning it with hot oil or a fire poker (173). Friar Lawrence tries a Paracelsian salve of a sort to soothe the rivalry by giving Juliet a mysterious liquid that will impart death-like symptoms upon ingestion. Essentially, Juliet uses the liquid both to defy her father and to defy death itself (reviving after a few hours), fulfilling the ultimate desire of all alchemists who sought the elixir of life. The friar’s solution, however, is thwarted by the plague, necessitating the violent and bloody end to the play in order to resolve the familial feud.
Rhetorically, the ‘scourge’ that the Prince mourns can be laterally connected with a critique of bloodletting, another grand theme within the play. As Prince first enters, demanding a cease of violence, he declares:
What, ho! You men, you beasts
That quench the fire of your pernicious rage
With purple fountains issuing from your veins,
On pain of torture, from those bloody hands
Throw your mistemper’d weapons to the ground,
And hear the sentence of your movéd prince.
(I. i. 79-84)
His ‘purple fountains’ refer to the supposedly dangerous purple blood that had to be drained until the red came out of the puncture hole in sustained blood-letting sessions. The sustained bloodletting in the play (the various brawls and deaths) is a temporary release of passions, a more deeply embedded wound, disease, or canker: the humoral imbalance of the young. The duel of the servants that begins the play is obviously the result of an overflow of frustration and hatred, a passion most likely to be associated with an humoral excess of blood. Romeo’s isolationist behavior in the first act is the perfect clinical representation of melancholia (excess of choler). As the play progresses,
each of the principal duelers are described humorally: Romeo’s “fire-eyed fury,” “fiery” Tybalt, etc (III. i. 25, I. i. 106). The young people embody a system out of balance, a kind of disease. The family feud is an internal contamination of the state that is spilling bad blood throughout the city, infecting the populace, and drawing innocent people into a death trap (Mercutio and Paris, though associated with each of the families, are independent from the feud and therefore unjustly killed). The Galenic imbalance transforms into an infective force, invading other parts of society, becoming part of the Paracelsian medical model, mimicking the transformation of medical understanding in the Renaissance. And, like both medical theories as practiced during the Renaissance, neither of the medical models provides a satisfactory cure for the cankerous disease attributed to humoral imbalance.
Shakespeare critiques both medical theories remorselessly. He demonstrates the malleability of and the tenuous relationship between the micro and macrocosms of Galenism, a highly structured medical theory that was out of place in an ever-changing modern world of international trade, an entire new hemisphere, and cyclic plague devastations. He also illustrates the implausibility of Paracelsianism, a magic-and-alchemy-based theory far too concerned with physically impossible alchemical goals. Shakespeare reinforces both system’s failings by interchanging them easily, demonstrating neither could provide a solution to societal ills. The failings of the theories speed the death of a nobleman caught in a racist world and two young lovers trapped between the hatred of members of the Old World. Instead of using disease to illustrate social ills, however, Shakespeare uses social ills—in terms of disease—to illustrate medical issues.
 The most interesting historical medical mystery in the play is Mercutio’s Queen Mab monologue. During the Renaissance, ‘mab’ signified cold sores (Kail 236). Amazingly, in this monologue, Shakespeare hints at the infective nature of the herpes virus by characterizing Mab as the carrier: “O’er ladies lips, who strait on kisses with dream,—/ Which oft the angry Mab with blisters plagues” (I. iv. 71-72). However, understanding the hyper-sexualization of Mercutio’s character and language, it is not beyond possibility that Mab signifies genital herpes instead. Though an understanding and separation of the various types of herpes did not occur until the 20th century, it is possible that genital herpes, and therefore herpes in general, could be connected to smallpox. In the last twelve lines of the monologue, Mercutio mentions, quite clearly, “Spanish blades”—a reference to the Spanish invaders during Elizabeth’s reign and the assumed Spanish origin of syphilis—and illustrates a young woman losing her virginity, undoubtedly connected to venereal diseases. Shakespeare had a remarkable understanding of, or at least ability to characterize, disease.
 Other versions of the play contain “a pox a’both your houses”—a reference to the smallpox epidemic, an equally prevalent disease, though perhaps less devastating in the short-term.