Helen Gustafson, in her lovely, illustrated book Hanky Panky: A History of the Handkerchief (published by Ten Speed Press), tells how schoolchildren were required to have a clean handkerchief to show the teacher. Mothers sent their children to school with two handkerchiefs - one to show the teacher and another working handkerchief that could stand up to blowings and washings. Thus Blow and Show or, as some called it, Show and Blow.