During the Middle Ages faith was one of the things most frequently appealed to, and even the physicians made use of religious belief to secure a favorable attitude of the patient's mind toward the remedies. One of the men who particularly realized the importance of this was Mondeville, the great French surgeon.

Pagel has called attention to Mondeville's insistence on preparing the patient's mind properly for venesection. The patient should be made to feel that this procedure was sure to do him good, and various reasons should be given him why the removal of a certain amount of blood carried with it poisons from the body, and so gave a better opportunity to nature to conquer the disease. If the patients were unfavorably disposed towards venesection, Mondeville thought that it should not be performed, as it was not likely to do good. It was not that he felt that the mental influence was the more important of the two therapeutic factors, but that a combination of the remedial force of blood-letting with a favorable state of the patient's mind meant so much more than could be accomplished by venesection alone that it was worth while to take pains to have the combination of the two. We in modern times realize that in most cases blood-letting rather did physical harm than good. It continued to hold a place in medicine because patients were so much impressed by it that they were given renewed vigor after its use.