External Link - Source: Nature
On an unseasonably warm February morning, Mark Pierson takes a 20-minute drive to one of Minneapolis’s larger pet shops. Pierson, a researcher in an immunology laboratory at the University of Minnesota, often comes here to buy mice, so most of the staff know him. Today he asks for ten, and an employee fishes them out of a glass box. Pierson requests the smaller mice because they’re typically younger, but he isn’t too picky. They probably all have what he wants: germs.