• A pregnant woman encounters a wolf in the woods. She is so scared that her strong emotion of fear imprints the wolf’s morphological traces on the fetus in her womb. Another pregnant woman craves strawberries or cherries so intensely that she leaves certain marks or impressions of these fruits on the fetus. The belief that the power of maternal emotions such as desire and fear can imprint certain marks, signs or signatures on the fetus was widespread in the early modern period. This belief was adopted by Renaissance philosophers such as Marsilio Ficino (1433–1499) and Pietro Pomponazzi (1462–1525), who intimately connected it to the traditional theory of imagination or phantasia. Moreover, folkloric tales about the mysterious and extraordinary psychic powers exerted by special groups of women, who were often labeled as witches and healers, might have reinforced this belief, contributing to the propagation of the idea that their forces could exceed the order of nature.
    Recent studies have shed new light on the historical and intellectual background of the issue, although its complete history has yet to be written. In this article I will focus on the intervention of early modern learned medicine in the theorization of this belief. To this end I will address the case of Thomas Feyens or Fienus (1567–1631) of Antwerp, who wrote a monograph devoted to the power of imagination in the embryological framework.
    Fienus was a professor of medicine at the University of Louvain from the end of the sixteenth century until his death and published a series of embryological works. Among these works there is a treatise, entitled “On the Forces of the Imagination” (Louvain, 1608). This was dedicated to Ernest of Bavaria (1554–1612), Count Palatine, Archbishop of Cologne and Prince-Bishop of Liege, now known as a fervent patron of new sciences and arts, including Paracelsian medicine and alchemy.