The first clue that the pneumonia diagnosis was wrong lies in Miller’s own apparent uneasiness with it. “The disease,” he wrote, “was not viewed as a case of pure pneumonia; but as this was the most palpable affection, the term pneumonia afforded a succinct and intelligible answer to the innumerable questions as to the nature of the attack.”

Harrison — who had had some medical training as a young man — summoned Miller to the White House on March 26, complaining not of a lung ailment but of anxiety and fatigue. Miller did not bleed him, as was the standard treatment for pneumonia at the time. (More about what he did do in a moment.) But Miller may have overlooked a clue that was in front of his nose.

In those days the nation’s capital had no sewer system. Until 1850, some sewage simply flowed onto public grounds a short distance from the White House, where it stagnated and formed a marsh; the White House water supply was just seven blocks downstream of a depository for “night soil,” hauled there each day at government expense.

That field of human excrement would have been a breeding ground for two deadly bacteria, Salmonella typhi and S. paratyphi, the causes of typhoid and paratyphoid fever — also known as enteric fever, for their devastating effect on the gastrointestinal system.