One of the best allies that Roosevelt had was Jacob A. Riis, that extraordinary man with the heart of a child, the courage of a lion, and the spirit of a crusader, who came from Denmark as an immigrant, tramped the streets of New York and the country roads without a place to lay his head, became one of the best police reporters New York ever knew, and grew to be a flaming force for righteousness in the city of his adoption. His book, "How the Other Half Lives", did more to clean up the worst slums of the city than any other single thing. When the book appeared, Roosevelt went to Mr. Riis's office, found him out, and left a card which said simply, "I have read your book. I have come down to help." When Roosevelt became Police Commissioner, Riis was in the Tribune Police Bureau in Mulberry Street, opposite Police Headquarters, already a well valued friend. Roosevelt took him for guide, and together they tramped about the dark spots of the city in the night hours when the underworld slips its mask and bares its arm to strike. Roosevelt had to know for himself. He considered that he had two duties as Police Commissioner: one to make the police force an honest and effective public servant; the other to use his position "to help in making the city a better place in which to live and work for those to whom the conditions of life and labor were hardest." These night wanderings of "Haroun al Roosevelt," as some one successfully ticketed him in allusion to the great Caliph's similar expeditions, were powerful aids to the tightening up of discipline and to the encouragement of good work by patrolmen and roundsmen. The unfaithful or the easy-going man on the beat, who allowed himself to be beguiled by the warmth and cheer of a saloon back-room, or to wander away from his duty for his own purposes, was likely to be confronted by the black slouch hat and the gleaming spectacles of a tough-set figure that he knew as the embodiment of relentless justice. But the faithful knew no less surely that he was their best friend and champion.