Samuel K. Cohn, Jr., does not mince words. The opening sentence of his new book announces the author’s discovery: the so-called Black Death, the fearsome pandemic that killed Europeans on a massive scale in the fourteenth century, was “any disease other than the rat-based bubonic plague” (p. 1). Coming from anyone else, such an assertion might be dismissed out of hand. It flies in the face of an almost unanimous conviction, among both historians and natural scientists, that the Black Death was indeed the bubonic plague. Coming from Cohn, however, this heretical stance needs to be taken very seriously indeed, given the author’s reputation and his well-known expertise when it comes to tabulating burials and testaments in early Renaissance Italy.
Bubonic plague is a disease of rats. As the infected rats die, they fall from rafters like over-ripe fruit and climb out of holes, stumbling awkwardly, in broad daylight. Indian peasants have been known to run for their lives at this point. Those who stay behind risk being bitten by the fleas who abandon the cold rodent corpses and carry the plague bacillus, Yersinia pestis, identified by Alexandre Yersin in Hong Kong in 1894. Modern episodes of bubonic plague were thoroughly investigated in the early years of the twentieth century, especially by the British colonial Indian Plague Commission, whose reports Cohn studied carefully. Before him, the British zoologist Graham Twigg went over the evidence with a fine-tooth comb and concluded, in 1984, that it was a mistake to see the disease caused by Yersinia pestis as identical with the Black Death. Cohn’s mentor, the late David Herlihy, seems to have accepted Twigg’s conclusion, but it was left to Cohn to advance the research to the point where historians can no longer accept the conventional diagnosis without the most serious reservations. In the pages of this journal (June 2002), Cohn made his case. He now develops it in greater detail in the book under review.
First of all, there is not a single mention of dying rats in the eyewitness reports produced by the pandemic of the fourteenth century and later aftershocks. I leave it to Cohn to explain why historians failed to notice this simple fact. To claim that the dead rats were surely there but benighted medieval physicians failed to notice them is not an argument that finds much favor with Cohn. He studied very large numbers of plague tracts and discovered that their authors were often good empirical observers.
A rare peculiarity of Yersinia pestis is that humans cannot acquire lasting immunity if they survive the disease. Cohn’s meticulous research establishes that the disease, after striking virgin-soil populations with devastating effect, became less and less deadly with each assault. After the third or fourth visitation, it tended to single out young children born since the last episode, presumably because adults had acquired some level of immunity. Bubonic plague, by contrast, is equally virulent with each outburst, and it strikes all age groups.
Unlike the medieval pandemic, which killed on a massive scale—Florence may have lost fifty percent of its population—bubonic plague never kills more than three percent. It is also not very contagious: it cannot be transferred from one person to another. In Bombay, crowded hospitals awash with plague victims but with effective rat control were reckoned the safest places to be. This is dramatically at odds with all early modern accounts of the Black Death’s ravages: they stress instant contagion and the effectiveness of quarantine regulations.
If the Black Death was not the bubonic plague, what was it? Cohn can do no more than speculate, as Herlihy and Twigg did before him. The question becomes even more perplexing with the recent claim made by members of a French archeological team. Having extracted DNA from two ancient graves in Provence, they claimed to have found traces of Yersinia pestis in the remains, but their claim has been vigorously challenged by rival scientists.
Even without the author’s intriguing discussion of the cultural consequences of the Black Death, the evidence presented in this book will have far-reaching effects. I only wish that the publishers had taken more care with proofreading: the book is filled with typographical errors.
By Samuel K. Cohn, Jr
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