Conrad Gessner (1516–65) was town physician and lecturer at the Zwinglian reformed lectorium in Zurich. His approach towards the world and mankind was centred on his preoccupation with the human soul, an object of study that had challenged classical writers such as Aristotle and Galen, and which remained as important in post-Reformation debate. Writing commentaries on Aristotle's De Anima (On the Soul) was part of early-modern natural philosophy education at university and formed the preparatory step for studying medicine. This article uses the case study of Gessner's commentary on De Anima (1563) to explore how Gessner's readers prioritised De Anima's information. Gessner's intention was to provide the students of philosophy and medicine with the most current and comprehensive thinking. His readers' responses raise questions about evolving discussions in natural philosophy and medicine that concerned the foundations of preventive healthcare on the one hand, and of anatomically specified patho- logical medicine on the other, and Gessner's part in helping these develop.