  Regius first came to Descartes’ attention through a mutual friend, Henricus Reneri (1593–1639), and almost immediately (in August 1638) began a correspondence with Descartes, which continued until 1645. In keeping with the custom at that time, he also presided as a professor over disputations at the University (the equivalent of research seminars, presented by students in the form of a defence of theses that were composed by their supervisor). The texts of disputations were normally printed and distributed in advance of their oral presentation, and some rare copies of Regius’ disputations survive. These were initially concerned with medical matters, such as a controversial disputation supporting Harvey’s theory of blood circulation (Regius 1640a). During the year 1641, Regius considered publishing a book on natural philosophy, and consulted both Descartes and Gisbertus Voetius (1589–1676), the Professor of Theology and University Rector, about his plans. While Descartes recommended that Regius develop his ideas in the form of disputations, Voetius initially advised publication as a monograph, possibly to avoid conflict with faculty members in theology or philosophy. Regius adopted Descartes’ advice and, in April 1641, he began a series of disputations under the title Physiologia sive cognitio sanitatis (Regius 1641a).