Internally, however, the closeness of the connection of the passages is not maintained throughout; for the heart intervening between the base of the two, infuses in the one the powers for respiration, and in the other for nutriment. Now the fiery element is naturally inclined to seek for the material which serves as fuel, and this necessarily happens with regard to the receptacle of nourishment; for the more it becomes penetrated by fire through the neighbouring warmth, the more it draws to itself what nourishes the heat. And this sort of impulse we call appetite. But if the organ which contains the food should obtain sufficient material, not even so does the activity of the fire become quiescent: but it produces a sort of melting of the material just as in a foundry, and, dissolving the solids, pours them out and transfers them, as it were from a funnel, to the neighbouring passages: then separating the coarser from the pure substance, it passes the fine part through certain channels to the entrance of the liver, and expels the sedimentary matter of the food to the wider passages of the bowels, and by turning it over in their manifold windings retains the food for a time in the intestines, lest if it were easily got rid of by a straight passage it might at once excite the animal again to appetite, and man, like the race of irrational animals, might never cease from this sort of occupation. As we saw, however, that the liver has especial need of the co-operation of heat for the conversion of the fluids into blood, while this organ is in position distant from the heart (for it would, I imagine, have been impossible that, being one principle or root of the vital power, it should not be hampered by vicinity with another such principle), in order that the system may suffer no injury by the distance at which the heat-giving substance is placed, a muscular passage (and this, by those skilled in such matters, is called the artery) receives the heated air from the heart and conveys it to the liver, making its opening there somewhere beside the point at which the fluids enter, and, as it warms the moist substance by its heat, blends with the liquid something akin to fire, and makes the blood appear red with the fiery tint it produces.

Ἀλλ' ἐπὶ τὸ βάθος οὐκέτι διαπαντὸς τὸ προσφυὲς παραμένει τῆς συζυγίας τῶν πόρων. Μέση γὰρ τῆς ἑκατέρων ἕδρας ἡ καρδία παρεμπεσοῦσα͵ τῷ μὲν πρὸς ἀναπνοὴν τῷ δὲ πρὸς τροφὴν τὰς δυνάμεις ἐντίθησιν. Πέφυκε γὰρ τὸ πυρῶδες ἐπιζητεῖν τὴν ὑπεκκαίουσαν ὕλην͵ ὃ δὴ καὶ περὶ τὸ δοχεῖον τῆς τροφῆς κατ' ἀνάγκην συμβαίνει. Ὅσῳ γὰρ ἔμπυρον διὰ τῆς γείτονος γίνεται θερμασίας͵ τοσούτῳ μᾶλλον ἐφέλκεται τὰ τὸ θερμὸν ὑποτρέφοντα, τὴν δὲ τοιαύτην ὁρμὴν ὄρεξιν ὀνομάζομεν. [249] Εἰ δὲ περιδράξαιτο τῆς ἀρκούσης ὕλης τὸ περιεκτικὸν τῆς τροφῆς͵ οὐδὲ οὕτως ἠρεμεῖ τοῦ πυρὸς ἡ ἐνέργεια. Ἀλλὰ καθάπερ ἐν χωνευτηρίῳ σύντηξίν τινα τῆς ὕλης ποιεῖ καὶ διαλύσασα τὰ συνεστῶτα καὶ ἀναχέασα͵ καθάπερ ἐκ χοάνης τινὸς μεταχεῖ πρὸς τοὺς ἐφεξῆς πόρους. Εἶτα τὸ παχυμερέστερον τοῦ εἰλικρινοῦς διακρίνασα͵ τὸ μὲν λεπτὸν δι' ὀχετῶν τινων ἐπὶ τὰς τοῦ ἥπατος ἄγει πύλας, τὴν δὲ ὑλώδη τῆς τροφῆς ὑποστάθμην εἰς τοὺς εὐρυχωροτέρους τῶν ἐντέρων πόρους ἀπώσατο καὶ τοῖς πολυτρόποις αὐτῶν ἑλιγμοῖς ἀναστρέφουσα χρόνῳ͵ παρακατέχει τὴν τροφὴν τοῖς σπλάγχνοις͵ ὡς ἂν μὴ δι' εὐθύτητα τοῦ πόρου ῥᾳδίως ἀποβαλόμενον͵ εὐθὺς ἀνακινοίη τὸ ζῶον πρὸς ὄρεξιν καὶ μηδέποτε παύοιτο τῆς τοιαύτης ἀσχολίας κατὰ τὴν τῶν ἀλόγων φύσιν ὁ ἄνθρωπος. Ἐπεὶ δὲ καὶ τῷ ἥπατι μάλιστα τῆς τοῦ θερμοῦ συνεργίας ἦν χρεία πρὸς τὴν τῶν ὑγρῶν ἐξαιμάτωσιν͵ ἀφέστηκε δὲ τοῦτο τῆς καρδίας κατὰ τὴν θέσιν (οὐ γὰρ ἦν͵ οἶμαι͵ δυνατὸν ἀρχήν τινα καὶ ῥίζαν ζωτικῆς οὖσαν δυνάμεως͵ περὶ τὴν ἑτέραν ἀρχὴν στενοχωρεῖσθαι)͵ ὡς ἂν μή τι τῆς οἰκονομίας ἐν τῇ ἀποστάσει τῆς θερμαντικῆς οὐσίας παραβλαβείη, πόρος νευρώδης (ἀρτηρία δὲ τοῦτο παρὰ τῶν ταῦτα σοφῶν ὀνομάζεται) ἀναδεξάμενος τῆς καρδίας τὸ ἔμπυρον πνεῦμα͵ φέρει παρὰ τὸ ἧπαρ͵ αὐτοῦ που παρὰ τὴν εἴσοδον τῶν ὑγρῶν συνεστομωμένος͵ καὶ ἀναζέσας διὰ τῆς θερμότητος τὴν ὑγρασίαν͵ ἐναποτίθεταί τι τῷ ὑγρῷ τῆς τοῦ πυρὸς συγγενείας͵ τῇ πυροειδεῖ χρόᾳ τὸ τοῦ αἵματος εἶδος καταφοινίξας.