How an Unpopular Policy Based on Incorrect Science Saved Philadelphia from Yellow Fever

Yellow fever devastated Philadelphia four times in the 1790s, killing more than 10,000 residents and casting into doubt the future viability of the city itself—at the time, the nation’s capital and largest city. Local health officials responded with a set of policies that were widely resented as burdensome and denounced as ineffective. They were based on theories of disease that seem laughably outdated today. Almost immediately, however, yellow fever epidemics became much less frequent and much less deadly than before. David Barnes examines some possible explanations for this unlikely success.