E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Kiss the Place to make it Well.
A relic of a very common custom all over the world of sucking poison from wounds. St. Martin of Tours, when he was at Paris, observed at the city gates a leper full of sores; and, going up to him, he kissed the sores, where-upon the leper was instantly made whole (Sulpicius Sevrus: Dialogues). Again, when St. Mayeul had committed some grave offence, he was sent, by way of penance, to kiss a leper who was begging alms at the monastery. St. Mayeul went up to the man, kissed his wounds, and the leprosy left him. Half a score similar examples may be found in the Bollandistes, without much searching.