You see, medical bloodletting was an art directly tied to the astrological calendar and the movement of the planets. You couldn't just bleed someone any old time you felt like it--the stars had to align! This German almanac from 1484 gives you all the details. Just the top fourth of the page was a calendar. The rest prescribed the best times to let blood.
While the bleeding might help you keep healthy this year, things didn't look so good in the long run. Saturn and Jupiter were in an unusual alignment, an omen for sixty years of pestilence, wars and even the birth of a false prophet. Actually, thinking about that era, it was probably a pretty safe bet...
This broadside doesn't have a call number yet; to see it, come to Rauner and ask for it in person.