John Snow, Asiatic Cholera and the inductive-deductive method - republished

Lecture 3: Incubation period and defining a case and numerator

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Snow continues his description of hundreds of cases of cholera which affect communities. Snow remarks that cholera is transmitted from the sick to the healthy over and over again. He corresponded with scores of physicians up and down the country who reported the same set of signs and symptoms: feeling unwell, followed by the excretion of copious amounts of watery faeces (“rice water”), vomiting and anuria (not passing any urine), followed by death by what we would now call hypovolemic shock. 

The post-mortem findings were also typical, with congestion of small bowel mucosa and dryness of tissues. Snow also describes the density of blood, comparing those from the sick with those from the healthy. The acute loss of fluids was the unifying characteristic of all fatal cases, although sometimes of variable s…