Mortiferum magis est quod Graecis hemitritaeon
vulgatum verbis; hoc nostra dicere lingua
non potuere ulli, puto, nec voluere parentes.
inscribes chartae quod dicitur abracadabra
saepius et subter repetes, sed detrahe summam,
et magis atque magis desint elementa figuris
singula, quae semper rapies, et cetera figes,
donec in angustum redigatur littera conum:
his lino nexis collum redimire memento.
(Serenus Sammonicus, Liber Medicinalis 932-942)

Rather more deadly is what in Greek words is commonly called hemitritaion*. This no one could express in our language, I believe, and neither did parents wish for that. Write on a sheet (of papyrus) the word ABRACADABRA, repeat it rather more often underneath, but omit the last letter, so that more and more individual letters will be missing from the lines, the elements that you remove, which you continually snatch away, while you commit to writing the others, until a single letter is to be rendered as the narrow end of a cone. Remember to attach this to the neck with a linen thread.

*  half-of-three, i.e. a fever whose attacks last for approximately 1 1/2 days = 36 hours; ‘tertian fever’ in English.

(tr. Peter Kruschwitz, with his note)