The Germ of an Idea: Contagionism, Religion, and Society in Britain, 1660-1730 by Margaret DeLacy (review)
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Margaret DeLacy. The Germ of an Idea: Contagionism, Religion, and Society in Britain, 1660-1730. Basingstoke, UK: Palgrave Macmillan, 2016. xviii + 305 pp. $100.00 ( 978-1-137-57527-2).

Margaret DeLacy has been studying the early roots of contagion theory for many years and has now produced the most important book on the topic to appear for quite some time. Following Edwin Ackerknecht's groundbreaking work, considerable scholarship has explored debates between contagionists and anticontagionists in the nineteenth century, while plague has drawn equal interest in the topic for the Renaissance. In between these poles, however, the issue has been far less studied. DeLacy explores the oft-neglected period of the late seventeenth and early eighteenth centuries to chart the development of ideas that anticipate—but which remained a long way off and quite distinct from—modern germ theory.

Right off the top Delacy must be commended for tackling such an intricate and frankly messy intellectual world. By the Restoration the British medical scene had been strongly influenced by iatrochemistry and would soon feel the impact of Newtonian mechanism but yet still held on to vestiges of humouralism. Contagion [End Page 444] was not a new idea, but DeLacy makes a good case that it took greater form by 1730, thanks to a series of factors that included the influence of the Helmonto-nian belief that diseases were independent entities invading the body, advances in microscopy that led some doctors to believe in animate microorganisms (usually termed animalcules), and the increased presence of medical taxonomies that presented diseases as entities with greater specificity. She points to epidemics like the 1720 Marseilles plague scare and the worrying spread of the cattle disease rinderplast a decade earlier, as well as the advent of inoculation as key events that drew greater attention to the value of contagionism. Readers unfamiliar with the period will likely be astonished at how modern seems a treatise like Benjamin Marten's New Theory of Consumptions, which as long ago as 1720 argued that phthisis (later tuberculosis) was a specific disease spread by contagion thanks to a microscopic organism. But DeLacy correctly resists anachronism. While many of the tools of modern germ theory were at their disposal, almost no seventeenth- or eighteenth-century doctor put them all together. Instead, belief in animalcules, disease-specificity, or medical taxonomy appear here and there, appearing in fits and starts, and almost always contested.

What allows DeLacy to make sense of this intellectual stew, and what must be considered her most valuable contribution, is her ability to link proponents of early contagionism to heterodox religion and unconventional medical education. Contagionists were often medical outsiders, especially those who studied abroad because as dissenters they were barred from Oxford and Cambridge and therefore from becoming Fellows of the Royal College of Physicians. Here DeLacy's work follows on the tradition of Charles Webster (in linking seventeenth-century science to radical religion) as well as Hal Cook (by foregrounding the political struggles of the heterogeneous medical world of Restoration London).1 Her careful prosopography demonstrates how doctors with nontraditional backgrounds and education—especially those who had been exposed to Helmontian chemistry—tended to advance contagionist ideas most clearly. Some of her figures may not seem like "outsiders"—eminent doctors like Hans Sloane, Richard Mead, or Thomas Sydenham—but in each case she teases out their backgrounds and demonstrates their similar intellectual roots.

My only quibble with this fine book is that the Great London Plague of 1665/6 gets almost no coverage. Surely if there was an event that drew attention to the question of contagion after 1660 this was it. It is notable that during the much later 1720 plague scare (to which DeLacy devotes chap. 9) many of the treatises that rolled off the press were reissues of texts from the earlier crisis, such as Nathaniel Hodges' Loimologia, or, an historical Account of the Plague in London in 1665, With precautionary Directions against the like Contagion (1720, originally 1672). Indeed, the well-known pamphlet war between Hodges and Helmontonian physicians like George Thomson during and following the great epidemic would have provided a [End Page 445] rich topic for...