Baltus[7] says: "De tous les anciens auteurs ecclesiastiques, n'y en ayant pas un qui n'ait parle de ce pouvoir admirable que les Chretiens avoient de chasser les demons," and Gregory of Tours (538-594) says that exorcism was common in his time, having himself seen a monk named Julian cure by his words a possessed person. This testimony of Gregory's concerning the prevalence of exorcisms at the end of the sixth century is interesting in view of the facts that the Council of Laodicea, in the fourth century, forbade any one to exorcise, except those duly authorized by the bishop, and that in the very beginning of the fifth century a physician named Posidonius denied the existence of possession. The fathers of the church, however, ridiculed the solemn assertion of physicians that many of these alleged demoniacal infirmities were attributable to material agencies, and were fully persuaded in their own minds that demons took possession of the organism of the human body. At about this time, such a broad-minded man as Gregory the Great (540-604) solemnly related that a nun, having eaten some lettuce without making the sign of the cross, swallowed a devil, and that, when commanded by a holy man to come forth, the devil replied: "How am I to blame? I was sitting on the lettuce, and this woman, not having made the sign of the cross, ate me along with it." This is but an example of the ideas concerning the entrance of demons into the possessed.[8] Besides the possibility of being taken into the mouth with one's food, they might enter while the mouth was opened to breathe. Exorcists were therefore careful to keep their mouths closed when casting out evil spirits, lest the imps should jump into their mouths from the mouths of the patients. Another theory was that the devil entered human beings during sleep, and at a comparatively recent period a king of Spain, Charles II (1661-1700), kept off the devil while asleep by the presence of his confessor and two friars.[9] Shortly before the reign of Gregory, there came into vogue the fashion of exorcising demons by means of a written formula rather than by the earlier means of making the sign of the cross and invoking the name of Jesus. The theory of demonology was never very clear nor consistent. By some it was claimed that in the practice of the magical arts evil spirits provided cure for sickness, others maintained that they could not heal any diseases, and hence the true test of Christianity was the ability to cure bodily ills. A compromise position was that demons were only successful in eliminating diseases which they had themselves caused. There was not a little doubt in some cases about the character of the possessing spirits, and it behooved people to be careful; demons might use men as habitations, and while posing as good angels vitiate health and provoke disease.