Although every town in France has a street named for Pasteur, was he alone able to stop people from spitting, persuade them to dig drains, influence them to undergo vaccination? Pasteur's success depended upon a whole network of forces, including the public hygiene movement, the medical profession (both military physicians and private practitioners), and colonial interests. It is the operation of these forces, in combination with the talent of Pasteur, that Bruno Latour sets before us as a prime example of science in action.