THE first tenement New York knew bore the mark of Cain from its birth, though a generation passed before the waiting was deciphered. It was the “rear house,” infamous ever after in our city’s history. There had been tenant-houses before, but they were not built for the purpose. Nothing would probably have shocked their original owners more than the idea of their harboring a promiscuous crowd; for they were the decorous homes of the old Knickerbockers, the proud aristocracy of Manhattan in the early days. It was the stir and bustle of trade, together with the tremendous immigration that followed upon the war of 1812 that dislodged them. In thirty-five years the city of less than a hundred thousand came to harbor half a million souls, for whom homes had to be found.