Sometimes, it is true, it would seem as tho medicine, under some circumstances, had recourse to supernatural factors in explaining various phenomena of physiological as well as pathological conditions; as, for instance, in the primeval pneuma-doctrine, or in those conceptions which attribute to a mental or psychical principle a far-reaching influence upon the performance of all bodily functions. Upon closer investigation, however, we shall find that the pneuma, or spirit, the soul, or whatever else the mysterious mainspring of all phenomena of life may be called, was by no means conceived of by medicine as immaterial or supernatural. On the contrary! Medicine, as often as it required a spiritual something to explain the manifestations of the body, has always regarded this unknown quantity as thoroughly substantial. It has not, indeed, been possible to determine more precisely the material nature of this great unknown, altho such attempts are by no means wanting in Democritus, Galen, and others; still it was always considered a corporeal thing. Supernatural qualities were ascribed to it only after death, but so long as the soul animated the body, united with the latter, it was a terrestrial being, and as such obeyed the laws of terrestrial substance. It was possible for medical science, therefore, to reckon with it in the explanation of pathological processes without necessarily expecting a reproach that supernatural agencies were called in for assistance. Medicine, therefore, altho it has traveled the same diagnostico-theoretical road as natural science, has not, like the latter, directly produced superstition. It is true, it has called forth innumerable erroneous hypotheses. But a wrong hypothesis, altho it may be nonsensical to the utmost and give rise to the most serious practical consequences, is by no means superstition; for both error and superstition—so far as it is a question of medical matters—are two radically different conceptions, because the former concerns itself only with natural, the latter with supernatural factors. Yet it is quite conceivable that the dissemination of an intellectual principle can be furthered and promoted without overt advocacy of the principle itself, and this was the relation that existed for thousands of years between medicine and superstition; for we learn from this investigation that the representatives of medicine were too often ready to admit all kinds of superstitious views into medicine. Whenever religion, philosophy, and natural science have seriously attempted to influence medicine in a manner promoting superstition, medical science yielded to these attempts, and this is the only reproach which can be justly laid at the door of our science.