Saint Bede said that there are three days in the month of February, that is the Ides of February [13th], the sixth of the kalends of March [24th February], and the 11th day of the kalends of March [19th February], in which if anyone is born male, his body continues uncorrupted until the day of judgement.
Likewise, there are three other days in which there is no necessity nor reason to lessen the blood of man or beast or to take a potion; these are the last Monday in April, and the first Monday on entering August; similarly, the final [Mon]day on leaving December. Those three days are to be observed with great diligence because then all veins are full. For that reason, whoever is cut on those three days, human or animal, will die either within seven days or, for certain, within fourteen days. And if anyone eats goose those three days, male or female, they will die the fortieth day; and if male or female is born, they will without doubt die a bad death.
Likewise, there are another three days and nights on which a female is never conceived; and if a male was conceived on these three days or nights, and was born, his body will never be corrupted right up to Judgement Day. Evidently, these are the last day of December and the first two of January. Rare are those who know this is true.
© 2018 Christopher Monk
Elizabeth Lazenby, 'De minutione sanguinis, sive de phlebotomia: On blood-letting or phlebotomy, by the Venerable Bede: A translation and commentary', in Medicine in Northumbria: Essays in the History of Medicine (The Phebus Society, 1993), pp. 58-80.
Stephen Pollington, Leechcraft: Early English Charms, Plantlore, and Healing (Anglo-Saxon Books, 2000).