Lewis Hine was born in Oshkosh, Wisconsin, in 1874. As a young boy, he worked long hours in a local factory, experiencing at first hand conditions he would later document so vividly with his camera. In 1903, he acquired a camera and a flashgun, and within a few years became one of the foremost investigative reporters of his days. He first examined the lives of some of the hundreds of thousands of immigrant families who were then crowding the customs sheds at Ellis Island. What happened to them once they set foot on the Promised Land? His photographs showed the appalling conditions that awaited most immigrants: overcrowded, filthy slums; violent, dangerous streets; and poor-paying, enslaving jobs at which men and women roiled to support their young families. Next he turned the illuminating light of his camera on the horrific conditions in America's coal mines. He recorded the squalor(污秽，卑劣) and desperation suffered by miners and their families. Even the government was shocked by photographs of boys--often as young as nine or ten years of age--dirty-faced, pale, undernourished, employed as breaker boys in the unhealthy and dangerous interiors of the nation's coal mines. Hine soon earned the sobriquet that was to stick with him until the end of his days: 'the conscience with a camera.' In 1908, he was hired as a photographer by the federal government's National Child Labor Committee to investigate child labor conditions in the United States. Hine's pictures of children, ill clothed and barefoot, tending machines in cotton mills, stunned America. Hine realized only too clearly that these ragged, exploited children, who had no chance for an education or hope for the future, were not the only victim. By employing a massive child labor force (over forty thousand children under sixteen years of age worked in cotton mills), industry was also enslaving an entire adult labor force, undercut by this cheap child labor. Hine's photographs were published widely in newspapers, magazines, and National Child Labor Committee reports. Many believe that as a direct result of the publication of photographs as disturbing as the vulnerable little girl working in a cotton mill, the federal government introduced legislation to put an end to such child labor practices. In the second paragraph, the word 'filthy' probably means ______.