Anything handed down from the distant past had extra authority, and when it came from the East, even more so. Until well into the early modern period, one of the firmest universal beliefs was in the unlucky Egyptian Days.
The Lacnunga Manuscript carefully instructs doctors that there are three days in the year when they must not bleed either animals or men, no matter how sick they were. Blood-letting had not yet acquired the pseudo-scientific footing it had in the 17th and 18th centuries, but it was considered a good, responsible part of health care. Farmers bled their horses once a year (right after Christmas, on St. Stephen’s Day). Monks, the only class of people who received regular, institutionalized health care, had a right to be bled several times a year on a regular schedule, spending a night in the infirmary to recover.
But those scheduled days must never include the Egyptian Days! On those days, it was very unlucky to create a bleeding situation. Within a few days, the man or beast who had thinned his blood would die. He had at most a week, and if he took a strengthening drink to overcome his fate, he would still die within two weeks. Egyptian Days were also terrible luck for births. Such babies could live, but they would die “an evil death.” The last thing that must not be done on an Egyptian Day was to eat roast goose. Due penalty would be paid: death within 40 days.
The concept of Egyptian Days dates back to ancient times, to the Assyrians of Babylon.