Summary. Galenism forms the historical background for the confrontation between vitalism and mechanism that begins in the seventeenth century. In the course of development since antiquity, the original basis of Galenism in Aristotetian natural philosophy was often modified and transformed; thus there arose an extraordinarily complex system of differing explanatory principles and interpretative levels for the physiology of the organism. In 1544, this system, which had remained essentially unchanged until the modern period, was once more presented in comprehensive fashion in Jean Fernel's physiology. Part B offers a survey of the material-somatic-psychic hierarchy of Fernel's system. Of special significance in this context are, on the one hand, the doctrine of the “spirits” as an important pre-idea for the later modern physiologies and, on the other, the traditional view of the function of the heart and circulation.

In addition to this account, various factors are pointed out that contributed to the crisis and downfall of Galenism. Reductionism in particular, to which the modern sciences are inclined, played an essential role. In the place formerly occupied by the hierarchy of explanatory principles in Galenism, Harvey, for example, sets the vitalistic aspect of the organism, harking back to its Aristotelian foundation. In contrast, Descartes extracts the material-mechanistic level from the Galenic hierarchy and declares it, from now on, the only real explanatory principle in the realm of physiology.

History, it is acknowledged, gladly permits the apparent high points of its achievements to carry within themselves the germ of crisis or downfall. Political and cultural phenomena as diverse as, say, the Alexandrian empire or classical physics around 1900 were equally affected by this principle. Such a fate also overtook Galenism, which around 1600 still represented a physiological-medical system of impressive completeness and universality and yet fifty years later had already lost its authority. A point of view that today seems to explain everything is most certain to be relativized or superseded by tomorrow.

With respect to Galenism, even more than in the fields, for example, of philosophy or physics, where Aristotle represented the foremost authority for scholastic learning, we must take care not to identify this system with Aristotelianism or to draw a straight line from Aristotle to Galen and on through the Arab physicians to Jean Fernel in the sixteenth century.