Helen Lefkowitz Horowitz says that she was puzzled by the stir in 1994 when Joycelyn Elders made a mild comment mentioning that masturbation might be taught about as part of sex education in schools. Our nation is used to hearing daytime talk show chatter about sexual abuse, homosexuality, prostitution, and more, but mentioning this universal and enjoyable practice as something that should be taught about (the religious right twisted her words into "should be taught") was enough to get Elders fired as Surgeon General. Why was there such a hysterical reaction to a mention of masturbation? Horowitz is a historian, a professor of American studies, and the one thing she could do to find an answer is historical research. She has done a mountain of it, looking into obscure court cases, journals, and newspapers, to produce the monumental _Rereading Sex: Battles over Sexual Knowledge and Suppression in Nineteenth Century America_ (Knopf). As the title reveals, Horowitz has not just covered ideas about masturbation (although ridiculous fears of that "evil" seem to have percolated through the minds of every parent and preacher of the time), but has covered the huge topic of what our predecessors thought about many aspects of sex.The evangelical Christian movement sweeping across the country in the first half of the nineteenth century seized upon such worries about masturbators and lustful women, and "sinful lust became a chief way of comprehending sexual desire." The American Tract Society was particularly vehement on such issues, and was aghast at the scientific understanding of sexual function that was beginning at the time. Especially important was the protection of female virginity, and fear of pregnancy was a vital shield of the nation's maidenheads. Physiological explanations of birth control were seen as a special danger; unimpeded by fear of impregnation, there was no telling what the women would get up to. Tractarians saw the freethinkers who promoted sexual knowledge as blasphemers. Nothing shocked them more than the non-religious (and it was generally the freethinkers who promoted the spread of physiological ideas) insisting that women had similar sexual desires and need for satisfaction as men, or that birth control would promote happiness, health, and economic freedom. It is surprising that the Young Men's Christian Association looms large in these pages. The YMCA had as a goal the promotion of evangelical religion, and during the Civil War, it was worried about Union soldiers, displaced from home, and in 1865 the YMCA was able to advocate for a post office bill that would forbid mailing erotic prints and books, the first time the federal government tried to regulate moral content of mailed material. The anti-sex activities of the YMCA were linked to the famous and foolish reformer, Anthony Comstock, whose censorious aims even kept birth control information out of medical texts.Horowitz has summarized four "frameworks" out of the confusing discourse about sex during the period. The Vernacular Tradition consists of sexual information (and misinformation) passed generally by word of mouth. Evangelical Christianity hated lust and equated most sexual activities with sin. Reform Physiology looked to the science of the body (often composed of wildly inaccurate assertions) to promote sexual freedom, and sometimes sexual restraint. And then there were Utopians, who thought sex was the central part of human existence and should be untouched by the government. These four voices, in the printed works and journals of the time, often overlapped and swamped each other with rhetoric. The huge number of philosophies and personalities which played a role in the debate, and made a foundation for our current sexual ideas, are brilliantly distilled into this large, well-referenced book, which is an entertaining academic tome without ever being fusty or tedious.