Formula for the Meditrinalia
The Meditrinalia, 11 October: the end of the vintage, and the first new wine is tasted mixed with old. The formula is spoken over the mouthful.
Novum vetus vinum bibo, novo veteri morbo medeor — new old wine I drink, of new old sickness I am healed. It works by likeness: the same two adjectives are applied to the wine and to the ailment, so that new cures new and old cures old, and one swallow covers both cases at once. The effect is achieved by grammar, not by composition.
This is a carmen in the old sense — efficacious speech built on assonance: novum-novo, vetus-veteri, bibo-morbo-medeor. The sower's formula is put together in the same way (pliny-sowing-001): no god, no request, only words correctly said.
On the etymology. Varro derives the festival's name from mederi, to heal, and from a goddess Meditrina. Modern scholars doubt it: it is likelier that the goddess was extracted from the festival's name than the reverse, and that this whole prayer is a late explanation of a word no longer understood. In that case the formula explains the rite rather than the rite the formula.
Varro quotes it as living usage. He introduces the formula with the words quod facere solent etiam nunc multi cum dicunt — which many still do even now, when they say. That is, this is not a rite recorded from the priestly books but what people in Varro's own day said at table on tasting the new wine. Checked against the edition: the card's text agrees.