Chinese migrants who converted to Christianity remained at first low. They were mainly Protestants who had already been converted in China where foreign Christian missionaries (who had first come in mass in the 19th century) had strived for centuries to wholly Christianize the nation with relatively minor success. Christian missionaries had also worked in the Chinese communities and settlements in America, but nevertheless their religious message found few who were receptive. It was estimated that during the first wave until the 1882 Chinese Exclusion Act, less than 20% of Chinese immigrants had accepted Christian teachings. Their difficulties with integration were exemplified by the end of the first wave in the mid-20th century when only a minority of Chinese living in the U.S. could speak English. Tanka people women who worked as prostitutes for foreigners also commonly kept a "nursery" of Tanka girls specifically to export them to overseas Chinese communities in Australia or America for prostitution work, or to serve as a Chinese or foreigner's concubine. Of the first wave of Chinese who moved to America, few were women. In 1850, the Chinese community of San Francisco consisted of 4,018 men and only seven women. By 1855, women made up only two percent of the Chinese population in the United States, and even by 1890 this had only increased to 4.8 percent. The lack of visibility of Chinese women in general was due partially to the cost of making the voyage when there was a lack of work opportunities for Chinese women in America. This was exacerbated by the harsh working conditions and the traditional female responsibility of looking after the children and extended family back in China. The only women who did go to America were usually the wives of merchants. Other factors were cultural in nature, such as having bound feet and not leaving the home. Another important consideration was that most Chinese men were worried that by bringing their wives and raising families in America they too would be subjected to the same racial violence and discrimination they had faced. With the heavily uneven gender ratio, prostitution grew rapidly and the Chinese sex trade and trafficking became a lucrative business. Documents from the 1870 U.S. census show that 61 percent of 3,536 Chinese women in California were classified as prostitutes as an occupation. The existence of Chinese prostitution was detected early, after which the police, legislature and