Medical superstition varies according to the kind and the origin of these supernatural causes, and therefore appears in the greatest variety of forms. If these causes were looked for in celestial regions, medical superstition became vested with the religious garb, and its source was in the religious cult; but if the belief prevailed that God shared the domination of the world with other mysterious elements, such as were embodied in different forms in accordance with the various philosophical systems, medical superstition bore a philosophical and mystical stamp whose origin is revealed in the history of philosophy. But if certain mysterious powers hidden in the womb of nature or active above the earth were considered to influence human life, medical superstition assumed a physical character. However, it frequently followed that the above three factors acted simultaneously or in varying combinations, or certain other elements which were inherent in human nature cooperated. For this reason it is sometimes not quite easy to decide as to the source from which this or that form of medical superstition principally derived its persistent currency. But, nevertheless, it is our intention to divide our subject in accordance with the sources from which the several forms of medical superstition spring, as it is absolutely impossible to obtain a satisfactory view of the extensive material without first attempting a systematic arrangement of the data at hand. But before attempting to inquire why the purest and most valuable fountains of all human knowledge—religion, philosophy, and natural science—have at the same time become sources of medical superstition, it will be advisable to explain the character which medical science had assumed under the exclusive domination of theism, and how conditions shaped themselves when physico-mechanical philosophy appeared and began to do battle with the theistic conception of life. These conditions played such a special part in the development of medico-physical superstition that it becomes necessary first to examine their power and tendency before attempting to contemplate medical superstition proper. II THEISM IN ITS RELATION TO MEDICINE AND IN ITS STRUGGLE WITH THE PHYSICO-MECHANICAL THEORY OF LIFE