Catholics who commemorate the Feast of St. Januarius may celebrate two miracles—one ancient, one modern; one Old World, one New World. This past September 19, at the cathedral in Naples, Italy, dedicated to the fourth century martyr, dried blood preserved as a relic of the saint miraculously liquefied, as it has done nearly every year for the last seventeen hundred years. Half a world away, in New York’s Little Italy, descendants of Neapolitan immigrants remembered their Old World patron saint with a ten-day Festival of San Gennaro, much as they have done for the past eighty-seven years. As skeptics sadly...