Evidence-Based Medicine in the Eighteenth Century: The Ingen Housz–Jenner Correspondence Revisited

There should be good reasons to re-publish literature, to rewrite history, and among the best is the discovery of new documentation. During recent efforts to find and collate all the surviving original documents of and pertaining to Dr Jan Ingen Housz (1730–1799), we were fortunate to discover previously unpublished letters—the ‘‘fourth’’ and ‘‘sixth’’ letters, below. They belong in the sequence first presented as a significant correspondence in 1838 by John Baron and reappraised by Peter Van der Pas in 1964. It relates to Jenner’s privately published description, in September 1798, of his studies and experiments on cowpox and its apparent power to protect people against smallpox. This paper, universally known as the Inquiry, was a milestone in the history of medicine and is seen by many as the very genesis of immunology. So important is it that any related correspondence must be equally significant. The discovery of the unpublished letters and other insights gained from our researches on Ingen Housz have prompted this article. It adds considerably, we believe, to that of Peter Van der Pas to whom we are personally obliged. Besides the privilege of introducing new material we aim, first, to replace all the letters between the two men into their correct sequence (not alternating as previously assumed); second, to interpret each letter in relation to Jenner’s Inquiry, an early example of ‘‘ordered experience’’, of evidence-based medicine; third, to illustrate, once again, the equal importance of inspiration, perspiration, perseverance, luck and stubborn conviction in scientific advance.