Megalopolis and micro-organism

The story of Dr John Snow’s investigations into the causes of the cholera epidemics in mid-Victorian London has been written up several times, most recently in a book by Sandra Hempel which I reviewed in these pages six months ago. So do we need yet another account of them? Perhaps not, except that Steven Johnson approaches them from an unusually interesting angle: his book is less concerned with medical history than with urban history and, in particular, the rise of mega- cities. ‘We are now, as a species,’ he claims, ‘dependent on dense urban living as a survival strategy.’

If you’re wondering what relevance Snow’s discovery, dismissed and mocked as it was at the time, that the culprit in the devastating 1854 outbreak of cholera in Soho was the water pump in Broad (now Broadwick) Street has to this large claim, Johnson’s answer is, ‘Broad Street marked the first time in history when a reasonable person might have surveyed the state of urban life and come to the conclusion that cities would some day become great conquerors of disease.