Words, like coins, are subject to devaluations and debasement. Big words, like revolution, are particularly vulnerable. Because of its proper coupling with adjectives such as American, French or Industrial, the term ‘revolution’ has been exploited by a myriad writers seeking to hype up some comparatively minor change in, say, the kitchen, the workplace or the high street. In contrast to such insignificant events, a real revolution is something that transforms major aspects of our world and the way we see it. The extraordinary, albeit bloodless, scientific revolution that took place between 1880 and 1900 provides us with a paradigmatic example. For, in this short space of time, medicine underwent perhaps its greatest ever transformation. In just 20 years, the central role of germs in producing illness was for the first time decisively demonstrated and Western doctors abandoned misconceived ideas about the causes and nature of disease that had persisted, in one form or another, for thousands of years.