What was behind the mysterious increase in lung cancer deaths at the turn of the 20th century? This episode looks at that early debate about environmental pollution. Along the way, we’re going to talk about toxic vapors -- and not Miasma theory, but the actual literal Great Smog of London in 1952 that killed over 10,000 people -- as well as the birth of the case-control study, Nazi attempts at tobacco control programs, and the rather prosaic beginnings of a debate that rages to this day.