Nasty stereotypes have helped move the merchandise for more than a century, and the history of their use and abuse offers a weird and telling glimpse of race relations in this country. Not surprisingly, the earliest instances were the most egregious. This circa-1900 ad for a rodent-control product called Rough on Rats doesn't just exploit the then-popular urban legend that Chinese people eat rats. It also underscores the intensity of American xenophobia of the day. There were anti-Chinese riots at the time, as well as legislation like the Chinese Exclusion Act, a federal ban on immigration passed in 1882. (It was on the books until 1943.) In the ad, "They must go" refers both to the rodents and the Chinese.