(Image: Everett Collection/Rex Features) A document has just gone on display at Mount Vernon, Virginia - the museum in the former home of George Washington, first US President. It is an order dated 1777 and signed by Washington himself to send troops that had not been vaccinated for smallpox - or survived it - to Philadelphia to be vaccinated. These troops were then to join up with the main army, where the disease was raging. It sounds like amazing foresight for its day. "Washington's careful handling of the smallpox epidemic at the beginning of the war was a significant...