Smartly designed, sometimes comic posters warning against syphilis, gonorrhea, malaria, and tuberculosis were once as common as all of the above. In An Iconography of Contagion: An Exhibition of 20th Century Health Posters at the National Academy of Sciences in Washington (through December 19), these and more recent posters about AIDS show how the advertising industry and public health officials have long fought battles against ignorance in the war against contagious disease. For more on the exhibit, read Amanda Schaffer's New York Times article or download the catalog. And for information on William Helfand's 2003 exhibit To Your Health: An Exhibition of Posters for Contemporary Public Health Issues at the National Library of Medicine, go here.