Today we know that one of the easiest and most effective things you can do to protect yourself from the cold, flu, and other respiratory illnesses (including those like the novel coronavirus) is to wash your hands. But there was a time when that wasn't so obvious. Dana Tulodziecki, a professor at Purdue University, tells the story of Ignaz Semmelweis, the scientist who's credited with discovering the importance of handwashing. We'll hear how he figured it out and why there's more to the story. Follow host Maddie Sofia on Twitter @maddie_sofia. Email the show at shortwave@npr.org.