(p. 108) It is worth pausing for a second to reflect on Snow’s willingness to pursue his investigation this far. Here we have a man who had reached the very pinnacle of Victorian medical practice—attending on the queen of England with a procedure that he himself had pioneered—who was nonetheless willing to spend every spare moment away from his practice knocking on hundreds of doors in some of London’s most dangerous neighborhoods, seeking out specifically those houses that had been attacked by the most dread disease of the age. But without that tenacity, without that fearlessness, without that readiness to leave behind the safety of professional success and royal patronage, and venture into the streets, his "grand experiment"—as Snow came to call it—would have gone nowhere. The miasma theory would have remained unchallenged,
Johnson, Steven. The Ghost Map: The Story of London’s Most Terrifying Epidemic – and How It Changed Science, Cities, and the Modern World. New York: Riverhead Books, 2006.