The faculty of smell does not admit of differences of kind; for all smells are of a half formed nature, and no element is so proportioned as to have any smell. The veins about the nose are too narrow to admit earth and water, and too wide to detain fire and air; and for this reason no one ever perceives the smell of any of them; but smells always proceed from bodies that are damp, or putrefying, or liquefying, or evaporating, and are perceptible only in the intermediate state, when water is changing into air and air into water; and all of them are either vapor or mist. That which is passing out of air into water is mist, and that which is passing from water into air is vapour; and hence all smells are thinner than water and thicker than air. The proof of this is, that when there is any obstruction to the respiration, and a man draws in his breath by force, then no smell filters through, but the air without the smell alone penetrates. Wherefore the varieties of smell have no name, and they have not many, or definite and simple kinds; but they are distinguished only painful and pleasant, the one sort irritating and disturbing the whole cavity which is situated between the head and the navel, the other having a soothing influence, and restoring this same region to an agreeable and natural condition.

περὶ δὲ δὴ τὴν τῶν μυκτήρων δύναμιν͵ εἴδη μὲν οὐκ ἔνι. τὸ γὰρ τῶν ὀσμῶν πᾶν ἡμιγενές͵ εἴδει δὲ οὐδενὶ συμβέβηκεν συμμετρία πρὸς τό τινα σχεῖν ὀσμήν· ἀλλ΄ ἡμῶν αἱ περὶ ταῦτα φλέβες πρὸς μὲν τὰ γῆς ὕδατός τε γένη στενότεραι συνέστησαν͵ πρὸς δὲ τὰ πυρὸς ἀέρος τε εὐρύτεραι͵ διὸ τούτων οὐδεὶς οὐδενὸς ὀσμῆς πώποτε ᾔσθετό τινος͵ ἀλλὰ ἢ βρεχομένων ἢ σηπομένων ἢ τηκομένων ἢ θυμιωμένων γίγνονταί τινων. [66e] μεταβάλλοντος γὰρ ὕδατος εἰς ἀέρα ἀέρος τε εἰς ὕδωρ ἐν τῷ μεταξὺ τούτων γεγόνασιν͵ εἰσίν τε ὀσμαὶ σύμπασαι καπνὸς ἢ ὁμίχλη͵ τούτων δὲ τὸ μὲν ἐξ ἀέρος εἰς ὕδωρ ἰὸν ὁμίχλη͵ τὸ δὲ ἐξ ὕδατος εἰς ἀέρα καπνός· ὅθεν λεπτότεραι μὲν ὕδατος͵ παχύτεραι δὲ ὀσμαὶ σύμπασαι γεγόνασιν ἀέρος. δηλοῦνται δὲ ὁπόταν τινὸς ἀντιφραχθέντος περὶ τὴν ἀναπνοὴν ἄγῃ τις βίᾳ τὸ πνεῦμα εἰς αὑτόν· τότε γὰρ ὀσμὴ μὲν οὐδεμία συνδιηθεῖται͵ τὸ δὲ πνεῦμα τῶν ὀσμῶν ἐρημωθὲν αὐτὸ μόνον ἕπεται. [67a] δύ΄ οὖν ταῦτα ἀνώνυμα τὰ τούτων ποικίλματα γέγονεν͵ οὐκ ἐκ πολλῶν οὐδὲ ἁπλῶν εἰδῶν ὄντα͵ ἀλλὰ διχῇ τό θ΄ ἡδὺ καὶ τὸ λυπηρὸν αὐτόθι μόνω διαφανῆ λέγεσθον͵ τὸ μὲν τραχῦνόν τε καὶ βιαζόμενον τὸ κύτος ἅπαν͵ ὅσον ἡμῶν μεταξὺ κορυφῆς τοῦ τε ὀμφαλοῦ κεῖται͵ τὸ δὲ ταὐτὸν τοῦτο καταπραῧνον καὶ πάλιν ᾗ πέφυκεν ἀγαπητῶς ἀποδιδόν.