Developments in biology and medicine a hundred years ago were to have a dramatic impact on human society. As Roy Porter has argued: ‘the latter part of the nineteenth century brought one of medicine’s few true revolutions: bacteriology. Seemingly resolving age-old controversies over pathogenesis, a new and immensely powerful aetiological doctrine rapidly established itself …’.1 The work of scientists of the calibre of Koch in Germany and Pasteur in France demonstrated that specific micro-organisms caused specific diseases in humans, animals and plants. The knowledge gained in this ‘Golden Age of Bacteriology’ was quickly applied to medical practice. The British Royal Army Medical Corps training manual of 1908, for example, graphically reads: diseases like enteric fever, cholera, dysentery, small-pox, plague, malaria and a number of others, all of which are caused by the entering into the body from without of the cause, which is a living thing or germ. It is quite clear that, from the nature of their causation, the various diseases … are more or less preventable …2 (emphasis added)