Harvard physician Edward Clarke was one of the group who called attention to the physical dangers of women's education. His provocative book, Sex in Education; or, A Fair Chance for the Girls, published in 1873 (and read by M. Carey Thomas the same year), used descriptive case studies that showed the detrimental effects on young women of school and social regimens that were equal for females and males.

Clarke's thesis-the widely accepted notion of "vital energy," was based on the principle of closed bodily systems with only finite amounts of energy. He argued that when young women studied, blood, nourishment and energy were pulled away from reproductive organs that were in the fragile and critical stages of maturation. At least one week of the month, women should be encouraged, even required to rest regardless of the status of their studies, rather than ignore their menses in an attempt to keep competitive.

The consequences of too much education during the developing years were that fragile girls would become more delicate and robust teenagers would weaken. Those other students, the type with "less adipose and more muscular tissue than is commonly seen, [with] a coarserskin, and, generally, a tougher and more angular makeup" were likely to acquire "an appearance of Amazonian coarseness and force." "Such persons," Clarke insisted, "[were] analogous to the sexless class of termites."

Clarke argued that immigrant and lower-class women were far healthier than their upper class sisters because they worked during their adolescence, rather than studied. Healthier women from this group would produce many healthy children, whereas those with higher levels of education would bear fewer children and frail ones at best. This, Clarke suggested, would deleteriously affect the future well-being of the American nation. His nationalistic, racist and sexist stand, couched in the guise of women's health, was not uncommon in the second half of the nineteenth century.