Communication

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ARTICLES

To the Editor:
In his letter to the editors in the October 2005 AHR (p. 1318), Richard Crane, M.D., responded to the article from Dr. Samuel K. Cohn, Jr., "The Black Death: End of a Paradigm" (AHR, June 2002, 703–738), making the argument, in part, that humans can acquire immunity to modern plague. Dr. Cohn, in his response to Dr. Crane's arguments about immunity to plague, stated that "humans possess little if any natural immunity to this pathogen [Yersinia pestis]." In both his AHR article and his book The Black Death Transformed, Dr. Cohn makes impressive arguments about the nature of the Black Death and how the causative agent could not have been Yersinia pestis. Despite the excellent historical research, Dr. Cohn is mistaken on the issue of immunity and ultimately the causative agent of the Black Death.
Dr. Crane writes about acquired immunity; that is, the immune response upon a second encounter with the same pathogen prevents another onset of acute illness. Natural immunity, in contrast, keeps someone from getting an infection at all. Leprosy is a good example of this, as it is estimated that 90 percent of people cannot acquire an infection from Mycobacterium leprae.
The binding molecules on B cells and T cells have for all practical purposes an unlimited number of genetic variations to adapt to any pathogen. Thus, assuming that a person survived the infection, the next encounter with that antigen would result in a massive secondary immune response, and that pathogen's specific immunological memory would last for a considerable period of time. Due to the stability of the pathogen, a person who encountered Y. pestis again would have the ability to fight off the disease without showing any symptoms—the hallmark of a healthy immune system. This explains the second pandemic as a children's pandemic, since most of the older people would have acquired immunity, whereas the children, never having encountered the antigen, would be vulnerable. Passive immunity may be passed on, but not acquired immunity. Whereas the first wave of the Black Death affected the majority of the population, making immunity to the pathogen apparent, the research of the Indian Plague Commission did not reveal immunity because the percentage of the population infected was too low for a reoccurrence of plague to show any effects of immunity.
Dr. Cohn's argument about effectiveness of the vaccine and how it proves that humans cannot get immunity stems from the way in which the vaccine was created. The vaccine, offered until 1999, was made from whole-cell, killed Y. pestis bacteria. Its ineffectiveness comes from the poor immune response the vaccine would have aroused and the fact that the F1 antigen, which is expressed at 37°C and not 26°C, would not be expressed in a manner to create long-term immune cell memory. In 1978, A. Wake and his colleagues used live, virulent strains of plague to create long-term, cell-mediated immunity—as opposed to short-lived humoral immunity. A severe, acute infection creates a strong acquired immunity.
Unfortunately, none of this science proves much about the Black Death. What, then, caused the Black Death? Unreliable DNA evidence from the work of Didier Rault and Michel Drancourt points to Y. pestis. One group of scientists, led by Carsten Pusch in 2004, pursued a different course to prove that Y. pestis caused the Black Death, so rather than using DNA, they used a dipstick assay for plague's F1 antigen. The results were positive for the F1 antigen in ten of twelve bodies tested. Had the people died of systemic infections of typhoid, the result would have been the same, but descriptions of the Black Death are more similar to plague than typhoid. It is still possible that a pathogen other than Y. pestis caused the Black Death, but the scientific evidence is currently in favor of plague.
Dr. Cohn is right in how unlikely—impossible—it would have been for the Black Death to have been a vector-borne transmitted disease. The rat flea (X. cheopis), which is the most reliable vector for plague, probably did not exist in Europe in the fourteenth century, and the human flea (P. irritans) does not transmit plague efficiently. It certainly was not pneumonic plague. How Y. pestis—or whatever pathogen caused the Black Death in the unlikelihood it was not plague—caused such high mortality in nearly four centuries of reoccurring epidemics still remains a mystery to be solved.
Andrew White Northern Michigan University

Samuel K. Cohn, Jr. does not wish to respond.
To the Editor:
Regarding Atlantic history (AHR, June 2006, 741–757), a bit of historiography. When the Atlantic surfaced as a topic in and of itself in the 1970s and early 1980s, previous accounts of United States history all too often tended to stop at the coasts. As for Latin American history, its practitioners, having worked hard to wrestle it free of Eurocentrism and make it a distinct subject, were shortly thereafter faced with the need to consider a certain amount of reintegration in the lead-up to the five-hundredth anniversary of 1492. Yet reconsideration also evoked recognition of a need to pay greater attention to the history of this nation's cultural diversity, the histories of pre-Columbian inhabitants and the coming of Africans, black slavery, and its aftermath throughout America, and also to the background of the United States' assertion of Free World leadership. It seems to me that the embarking on Atlantic history in that generative time provided a capacious framework within which to introduce (or re-introduce) some broader vistas into consideration of all America's history, as well as into the history of the Western world, and even into the then-burgeoning field of world history.
For my part, it was borne in on me while teaching courses in the histories of both the United States and Latin America that an understanding of the dissolution of old imperial ties throughout America could be improved by examining the interconnections of two then-neglected topics, trade and ideational currents, particularly in their crisscrossing of the Atlantic and their travel along its coasts and between its ports.
Since those earlier days, the Atlantic has obviously fared well as a vantage point and organizing device for the practitioners of many sorts of history; and not least for historians of British Atlantic history and its traditional offshoot, the United States, increasingly viewed as the new empire. Moreover, no one has better demonstrated the value of an Atlantic purview, both directly and indirectly, than J. G. A. Pocock and J. H. Elliott. In effect, John Pocock broke the mold, most notably in The Machiavellian Moment of 1975, freeing us from seeing the Atlantic as a barrier to the continuity of a broadly Western history, and he has most recently made some trenchant observations within current reevaluations of the nature and extent of British empire. And John Elliott, within a comparison of the Spanish and British Atlantic empires, has just produced an extraordinary, a monumental, synthesis and analysis in his Empires of the Atlantic World of seemingly most, if not all, of the work done on the history of the Atlantic world between 1492 and 1830.
Peggy K. Liss Washington, D.C.

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