Miasma vs. Germ Theory

In this session, we will discuss the competing causal explanations for infection during the London Cholera Outbreak, specifically miasma theory, which posited that infection was transmitted solely via noxious air, and germ theory, which posited that there was an infectious agent transmitted from person to person. One of the big takeaways from this session’s readings is that Snow used spatial information to make the argument that observed spatial patterns of Cholera could not be explained well at all by miasma theory, but instead was more consistent with the transmission of some infectious agent, i.e. V. Cholerae

Before Class

Continue reading The Ghost Map, Ch 3-4 (pp 56-109) (Johnson 2007)

During Class

We will begin to explore the concept of a natural experiment, which is what Snow’s experimenta crucis (described in the readings) was an early example of. We will discuss both how such studies can be valuable, and also how they can go wrong, or at least open up a number of questions while answering others.

Additional Resources


Spatial density estimation exercise


Johnson, Steven. 2007. The Ghost Map: The Story of London’s Most Terrifying Epidemic–and How It Changed Science, Cities, and the Modern World. Reprint edition. London: Riverhead Books.