Quoted from Pliny by Aulus Gellius,
Noct. Att. III. xvi. 24.
Erasmus, in his Colloquies, bids one say to him who sneezes, "Sit faustum ac felix," or "Servet te Deus," or "Sit salutiferum" or "Bene vertat Deus."
"Quare homines sternutant?
"Respondetur, ut virtus expulsiva et visiva, per hoc purgetur, et cerebrum a sua superfluitate purgetur, etc. Etiam qui sternutat frequenter, dicitur habere forte cerebrum."—Aristotelis Problemata: Amstelodami, anno 1690.
Query whether from some such idea of the beneficial effect of sneezing, arose the practice of calling for the divine blessing on the sneezer?
When Themistocles was offering sacrifice, it happened that three beautiful captives were brought him, and at the same time the fire burnt clear and bright, and a sneeze happened on the right hand. Hereupon Euphrantides the soothsayer, embracing him, predicted the memorable victory which was afterwards obtained by him, &c.
There is also mention of this custom (the observation of sneezing) in Homer, who has introduced Penelope rejoicing at a sneeze of her son Telemachus:
"Οὐχ ὁράας ὅ μοι υἱὸς ἐπέπταρεν"
Sneezing was not always a lucky omen, but varied according to the alteration of circumstances—"Τῶν πταρμῶν οἱ μὲν εἰσὶν ὠφέλιμοι, οἱ δὲ βλαβεροί," "Some sneezes are profitable, others prejudicial"—according to the scholiast upon the following passage of Theocritus, wherein he makes the sneezing of the Cupids to have been an unfortunate omen to a certain lover:
"Σιμιχίδα μὲν ἔρωτες ἐπέπταρον."