In describing and explaining the sexes, medicine and science participated in the delineation of what was "feminine" and what was "masculine" in the Middle Ages. Hildegard of Bingen and Albertus Magnus, among others, writing about gynecology, the human constitution, fetal development, or the naturalistic dimensions of divine Creation, became increasingly interested in issues surrounding reproduction and sexuality. Did women as well as men produce procreative seed? How did the physiology of the sexes influence their healthy states and their susceptibility to (...) disease? Who derived more pleasure from sexual intercourse, men or women? The answers to such questions created a network of flexible concepts which did not endorse a single model of male-female relations, but did affect views on the health consequences of sexual abstinence for women and men and on the allocation of responsibility for infertility - problems with much social and religious significance in the Middle Ages. Sometimes at odds with, and sometimes in accord with other forces in medieval society, medicine and natural philosophy helped to construct a set of notions that divided significant portions of the world - from the behavior of animals to the operations of astrological signs - into "masculine" and "feminine." Even cases that seemed to exist outside the definitions of this duality, for example, hermaphrodite features or homosexual behavior, were brought under control by the application of gendered labels, such as "masculine women.". (shrink)