It’s no secret we share the city with an unquantifiable number of microbial friends, but only recently has anyone tried to survey their population. PathoMap, a mammoth effort by Weill Cornell geneticist Christopher Mason, has, since beginning in June, documented 137 different types of bacteria on five subway lines. “I don’t want to say that the L train is the dirtiest,” Mason notes, “but it did give us a lot of interesting things.”

Illustration by Joan Linder

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