Today, libraries across the US and the rest of the world are seen as centers of free learning, presenting enormous opportunities for children and adults alike. However, not too long ago, people in the US and the UK were absolutely terrified by the idea that libraries were dens of disease. In today's episode, the guys explore how fears of tuberculosis, scarlet fever and more led to public hysteria over sharing books -- and how this panic put the concept of libraries as we know them in serious danger.