What injustice did muckraker Jacob Riis document?

Jacob Riis wrote "How the Other Half Lives." He exposed the lives of the many poor Americans living in the slums of the city. These treachers include tenements in which many people crammed together to live in, hot beds which were the poorly made mattresses that they slept in, called hot beds because one person would go to work (usually in a factory) while the other slept and then they would rotate, so the beds would always be warm, and there were often no Windows or it was one or two rooms with bunks and a makeshift stove in the middle of the room. Children would be playing in the dirty streets and illness was easily spread.