Chelidonius

In the belly of a swallow, there is a stone found, called chelidonius, “which, if it be lapped in a fair cloth, and tied to the right arm, will cure lunaticks, mad men, make them amiable and merry.”

According to Thomas de Cantimpré the swallow-stone is a talisman for merchants and tradesmen. The merits of the chelidonius, as this stone was called, were fully recognized in Saxon England and are given due prominence in an Anglo-Saxon medical treatise, dating form the first half of the tenth century.

while he discusses the chelidonius, he says nothing of extracting it so soon and describes the colors of its two varieties as black and red, and so does Bartholomew later on.