καὶ γὰρ οὗτοι κτἑ.: the ignorance of the trader is more fully set forth in Gorg. 517 d ff. τούτων γὰρ (sc. σιτίων, ποτῶν, ἱματίων κτἑ.) ποριστικὸν εἶναι ἢ κάπηλον ὄντα ἢ ἔμπορον . . ., οὐδὲν θαυμαστόν ἐστιν ὄντα τοιοῦτον δόξαι καὶ αὑτῷ καὶ τοῖς ἄλλοις θεραπευτὴν εἶναι σώματος, παντὶ τῷ μὴ εἰδότι, ὅτι ἔστι τις παρὰ ταύτας τέχνη γυμναστική τε καὶ ἰατρική, ἣ δὴ τῷ ὄντι ἐστὶ σώματος θεραπεία.—
ὧν... λανγ̂γρεεκ>ἀγωγίμων: depend. on ὅ τι following.
περὶ τὸ σῶμα: with reference to the body. In such expressions the prep. with the acc. brings out the quality of the adj. more distinctly and independently than would a simple gen., and is preferred by Plato, with whom however it becomes almost a mannerism. Cf. πρὸς τὴν ψυχήν below, Gorg. 517 e εἰδέναι ὅ τι τὸ χρηστὸν καὶ πονηρὸν τῶν σιτίων ἢ ποτῶν ἐστὶν εἰς ἀρετὴν σώματος.
ἀεί: often means in each case, every time.
ἐπαινοῦσι: as Protagoras afterwards does, cf. 318
