WHEN THE FRENCH astrologer and physician Geoffrey de Meaux (fl. 1310–49) wrote these words around 1349, he was trying to assess, from a scientific perspective, the great challenge of applying the universal principles of the science of the stars to the very particular task of explaining why some people survived while others around them died in the wake of the Black Death (Horrox 1994: 165). His close contemporary, the Florentine author Giovanni Boccaccio (1313–75) similarly wrote that “not all those who adopted these diverse opinions died, nor did they all escape” (Boccaccio [1353]/1982: 9): suggesting, as Geoffrey did, that a complex selective process was at work during a plague outbreak.

In his treatise on surgery, Guy de Chauliac (d. c. 1368), a leading medical authority and physician to three successive popes, described the causes of mortality as twofold in his discussion of the bubonic plague: one active and universal, one passive and particular. Regarding the latter, Guy wrote: “The particular, passive case was the disposition of each body, such as cachocymia, debility, or obstruction, whence it was that the working men and those living poorly died” (1363/1974: 774). In other words, we can argue that Guy explained that cases of heterogeneous mortality were The image above shows a physician (with a case for medical implements hanging at his belt) lancing a bubo on the neck of a woman afflicted with plague. A young man (probably his assistant) steadies the patient; meanwhile, her husband strips off his tunic to reveal a bubo under his arm, readying himself for the same lancet. A small boy also holds up his arm, perhaps indicating that he, too, feels a bubo developing. A smaller child lies in bed, ill or asleep. Above the scene, a devil brandishes a lancet of his own—one that will inflict plague, rather than treat it—but an angel deflects his aim.