Thanks to Jill for her cogent and well-reasoned exposition of what the hell that “Rx” thing is all about.
In the 1964 edition of the Life/Science Library tome “The Body” (published, at some remove, by the good folks at “Life” magazine and one of my favorite books), this comment appears:
A GOD’S EYE AND A DOCTOR’S PRESCRIPTION
FROM MYTH TO PRESCRIPTION PAD
In the Second Century, Galen used mystic symbols to impress patients. According to one theory, he borrowed from the Egyptian myth of the Eye of Horus [illustration] a symbol which has gradually evolved into today’s familiar sign for “prescription.” The myth tells how Horus, the falcon god, attacked his uncle to avenge his father’s murder. In the fight, Horus’ eye was torn, whereupon Thoth, patron god of physicians, miraculously healed it.
Note the careful hedging (“according to theory”), as well as the stripped-down prose. Clearly, a tome meant for people who have little appreciation of getting paid by the word. Since Galen appears to have influenced Western medicine in a way out of all proportion to his actual medical knowledge (but let’s be fair to folks without a solid grasp of germ theory), this is about as plausible as any notion.
The book’s well worth tracking down, if you haven’t seen it. Oy, such stuff about fistulas is gold.