DURING THE FAMED MAGICAL BOAT RIDE in Cervantes's Don Quixote, the knight-errant describes to Sancho Panza a means of delineating their passage down a slow moving river, which Quixote has taken for an Atlantic crossing:
Listen, Sancho: when the Spaniards, and all those who sail out of
Cadiz, head out toward the East Indies, one of the things that tells
them they've passed over the equatorial line is that all the lice on
board the ship suddenly die, to the very last ...