Public health used to be enforced by the state, taking measures to isolate the ill and thus spare the community. Such traditional techniques involved a heavy sacrifice of individual liberties as citizens were inconvenienced and worse for the public good. In modern democracies, however, such heavy-handed methods could not continue. Public health therefore shifted its focus from the state imposing the needed behavioral changes on its subjects to citizens themselves voluntarily adopting the kind of conduct that was required to remain safe and healthy. Bacteriology and the increasing knowledge that some diseases were caused not by filth, but by microscopic organisms allowed public health authorities to target their preventive actions more precisely. It also allowed them to specify the kinds of behavioral prescriptions citizens had to follow to avoid spreading disease – not sneezing or coughing in public, avoiding needless physical and sexual contact, maintaining more general social distance, and the like. Citizens became increasingly responsible for their own well-being, learning how to behave to remain healthy.