The Black Death Transformed: Disease and Culture in Early Renaissance Europe (review)

In 1894, the biologist Alexandre Yersin, working with victims of the bubonic plague, was the first to identify the bacillus that now bears his name. Yersin, however, went on to make a more dramatic claim, namely, that he had discovered the bacillus responsible for the Black Death. Or had he? Neither Yersin nor those who later confirmed his claims were particularly well qualified to assess the scanty medieval evidence at their disposal. If biologists and historians could do it all over again, and examine without prejudice the massive medieval evidence now available, would they still arrive at the same conclusion?

The answer, according to some recent observers, is almost certainly "no"; the medieval plague behaved more like a virulent virus than Yersinia pestis. To date, however, no historian with the necessary expertise has adequately reexamined the medieval evidence. Cohn sets for himself this very task in The Black Death Transformed. Hundreds of narrative sources show that the signs and symptoms of the medieval plague only superficially resembled those of modern bubonic plague. To take just a few of the most convincing examples, modern buboes appear chiefly in the groin, usually singly, whereas chroniclers of the late medieval plague described multiple boils on the neck, face, and thigh, as well as blotches over the entire body. Victims of modern plague died far more quickly than their medieval counterparts. Late medieval observers also failed to mention the enormous number of rat deaths that are a characteristic sign of the modern bubonic plague. Finally, the medieval evidence shows no association between the plague and grain supplies, a feature of rat-based bubonic plague.

Some evidence would support Yersin, and studies based on signs and symptoms alone are not wholly convincing. Cohn's major set of arguments is built around epidemiology, the distribution and transmission of the disease. Using tens of thousands of death documents—wills and testaments, burial records, obituaries, and other sources almost unknown to earlier historians—Cohn shows that the epidemiology of the late medieval plague was nothing like that of modern bubonic plague. The late medieval mortality rate was exceedingly high, compared to the figure of less than 3 percent characteristic of bubonic plague. The medieval plague infected the victim's family members as well as attending notaries, doctors, and priests, whereas a modern plague ward is a relatively safe place, as long as it is free of rats and fleas. The medieval plague spread with astonishing rapidity and rarely lasted more than a year in a given city; the bubonic plague moves slowly, capable of lasting for five to twenty years at a time in cities. The fleas that carry bubonic plague, finally, cannot stand temperature extremes, whereas the medieval plague, at least in the Mediterranean, often struck at the hottest points of the summer.

The most compelling argument appears in Chapter 8, in which Cohn argues that mortality rates declined noticeably across the fourteenth and fifteenth centuries. This decline, coupled with the tendency of successive episodes to single out children, suggests an immunological response, something that could not have happened with a bacterial disease like Yersinia pestis. Cohn is aware that a declining absolute number of testaments in plague years could have resulted from a multitude of factors, such as a declining overall population, a growing tendency to write precautionary testaments, and variations in record-keeping practices. The uncorrelated figures presented in a series of bar graphs are not especially convincing. Cohn is more persuasive when he sets his absolute figure in the context of known population trends, especially rural-urban migration patterns. By charting "plague figures as ratios of the preceding intervals of non-plague years," Cohn argues that "the steady downward thrust of plague mortality is even more striking than that shown by the raw figures" (200). Yet he provides ratios for only a...