Should we need proof that in the Middle Ages rings were believed to have remedial powers, this is offered by a passage in the statutes of the Hôtel Dieu of Troyes, dated in 1263. Here it is decreed that the nuns should not be permitted to wear rings set with precious stones, _except in case of illness_.[557] Probably in this event the appropriate stone was selected by those versed in this branch of knowledge, after they had determined, as well as they were able, the real nature of the disease. If the owner of a garnet ring who was not an expert in precious stones wished to assure himself of the genuineness of his garnet, the following rather troublesome experiment was at his disposal. He was to disrobe, still wearing his ring, and then to have his body smeared with honey. This done, he was to lie down where flies or wasps were about. If in spite of the sweet temptation they failed to light on his body, this was a proof that the garnet was genuine, an added proof being that when he took off the garnet ring the insects would hasten to make up for lost time and suck up the honey.[558] Jacinth as a ring-setting was said to preserve a traveller from all perils on his journey and to make him well received everywhere. Another merit was that he was protected against plague and pestilence, and would enjoy good sleep.[559] Certainly if this were true, the traveller could ask for no better amulet to bear about with him on his trip. A toadstone set in an open ring, so that the stone could touch the skin, was thought to give notice of the presence of poison by producing a sensation of heat in the skin at the point of contact. A ring made out of narwhal tusk was believed to be an effective antidote to poisons. Apart from these materials, several precious or semi-precious stones, such as emeralds, agates, and also amber and coral, were assumed to be especially sensitive to the approach of poison, so much so that when worn suspended from the neck or set in rings, they would lose their natural color, thus giving timely warning to their wearers.[560]