Negative reaction to the theories forwarded in Dr. Edward H. Clarke's 1873 treatise against coeducation, "Sex in Education or A Fair Chance for the Girls," has been largely neglected. The book appeared at a time when conspicuous numbers of women were extending their activities by campaigning for suffrage; working in factories, schools, and medicine; and entering public high schools and universities. Clarke suggested that women who engaged in sustained vigorous mental activity, studying in a "boy's way," risked atrophy of the uterus and ovaries, masculinization, sterility, insanity, even death. Coeducation was seen as impractical since young women should study no more than four hours each day, with a total remission during the menstrual period, a regime which would be emasculating to boys. Critics of "Sex and Education" pointed to Clarke's faulty methodology and lack of statistics. They presented an impressive array of evidence against his theories: case studies, letters from authorities, and data on the health, career patterns, marriage rates, and fertility of women who had attended college. They argued that coeducation promoted healthy, realistic relationships between women and men, was less expensive and more practical than separate education, and had proven effective and beneficial. However, his theories were used in the decades that followed, not only by opponents of coeducation but also by opponents of the extension of women's roles in other areas. Critiques were not widely circulated or reviewed, nor were any printed in more than one edition. (KC)