Such as we have seen, is the nature and such are the causes of respiration - the subject in which this discussion originated. For the fire cuts the food and following the breath surges up within, fire and breath rising together and filling the veins by drawing up out of the belly and pouring into them the cut portions of the food; and so the streams of food are kept flowing through the whole body in all animals. And fresh cuttings from kindred substances, whether the fruits of the earth or herb of the field, which God planted to be our daily food, acquire all sorts of colours by their inter-mixture; but red is the most pervading of them, being created by the cutting action of fire and by the impression which it makes on a moist substance; and hence the liquid which circulates in the body has a colour such as we have described. The liquid itself we call blood, which nourishes the flesh and the whole body, whence all parts are watered and empty places filled.

Now the process of repletion and evacuation is effected after the manner of the universal motion by which all kindred substances are drawn towards one another. For the external elements which surround us are always causing us to consume away, and distributing and sending off like to like; the particles of blood, too, which are divided and contained within the frame of the animal as in a sort of heaven, are compelled to imitate the motion of the universe. Each, therefore, of the divided parts within us, being carried to its kindred nature, replenishes the void. When more is taken away than flows in, then we decay, and when less, we grow and increase.

The frame of the entire creature when young has the triangles of each kind new, and may be compared to the keel of a vessel which is just off the stocks; they are locked firmly together and yet the whole mass is soft and delicate, being freshly formed of marrow and nurtured on milk. Now when the triangles out of which meats and drinks are composed come in from without, and are comprehended in the body, being older and weaker than the triangles already there, the frame of the body gets the better of them and its newer triangles cut them up, and so the animal grows great, being nourished by a multitude of similar particles. But when the roots of the triangles are loosened by having undergone many conflicts with many things in the course of time, they are no longer able to cut or assimilate the food which enters, but are themselves easily divided by the bodies which come in from without. In this way every animal is overcome and decays, and this affection is called old age. And at last, when the bonds by which the triangles of the marrow are united no longer hold, and are parted by the strain of existence, they in turn loosen the bonds of the soul, and she, obtaining a natural release, flies away with joy. For that which takes place according to nature is pleasant, but that which is contrary to nature is painful. And thus death, if caused by disease or produced by wounds, is painful and violent; but that sort of death which comes with old age and fulfils the debt of nature is the easiest of deaths, and is accompanied with pleasure rather than with pain.

[80d] Καὶ δὴ καὶ τὸ τῆς ἀναπνοῆς͵ ὅθεν ὁ λόγος ὥρμησεν͵ κατὰ ταῦτα καὶ διὰ τούτων γέγονεν͵ ὥσπερ ἐν τοῖς πρόσθεν εἴρηται͵ τέμνοντος μὲν τὰ σιτία τοῦ πυρός͵ αἰωρουμένου δὲ ἐντὸς τῷ πνεύματι συνεπομένου͵ τὰς φλέβας τε ἐκ τῆς κοιλίας τῇ συναιωρήσει πληροῦντος τῷ τὰ τετμημένα αὐτόθεν ἐπαντλεῖν· καὶ διὰ ταῦτα δὴ καθ΄ ὅλον τὸ σῶμα πᾶσιν τοῖς ζῴοις τὰ τῆς τροφῆς νάματα οὕτως ἐπίρρυτα γέγονεν. νεότμητα δὲ καὶ ἀπὸ συγγενῶν ὄντα͵ τὰ μὲν καρπῶν͵ τὰ δὲ χλόης͵ [80e] ἃ θεὸς ἐπ΄ αὐτὸ τοῦθ΄ ἡμῖν ἐφύτευσεν͵ εἶναι τροφήν͵ παντοδαπὰ μὲν χρώματα ἴσχει διὰ τὴν σύμμειξιν͵ ἡ δ΄ ἐρυθρὰ πλείστη περὶ αὐτὰ χρόα διαθεῖ͵ τῆς τοῦ πυρὸς τομῆς τε καὶ ἐξομόρξεως ἐν ὑγρῷ δεδημιουργημένη φύσις. ὅθεν τοῦ κατὰ τὸ σῶμα ῥέοντος τὸ χρῶμα ἔσχεν οἵαν ὄψιν διεληλύθαμεν ὃ καλοῦμεν αἷμα͵ νομὴν σαρκῶν καὶ σύμπαντος τοῦ σώματος͵ [81a] ὅθεν ὑδρευόμενα ἕκαστα πληροῖ τὴν τοῦ κενουμένου βάσιν·  

ὁ δὲ τρόπος τῆς πληρώσεως ἀποχωρήσεώς τε γίγνεται καθάπερ ἐν τῷ παντὶ παντὸς ἡ φορὰ γέγονεν͵ ἣν τὸ συγγενὲς πᾶν φέρεται πρὸς ἑαυτό. τὰ μὲν γὰρ δὴ περιεστῶτα ἐκτὸς ἡμᾶς τήκει τε ἀεὶ καὶ διανέμει πρὸς ἕκαστον εἶδος τὸ ὁμόφυλον ἀποπέμποντα͵ τὰ δὲ ἔναιμα αὖ͵ κερματισθέντα ἐντὸς παρ΄ ἡμῖν καὶ περιειλημμένα [81b] ὥσπερ ὑπ΄ οὐρανοῦ συνεστῶτος ἑκάστου τοῦ ζῴου͵ τὴν τοῦ παντὸς ἀναγκάζεται μιμεῖσθαι φοράν· πρὸς τὸ συγγενὲς οὖν φερόμενον ἕκαστον τῶν ἐντὸς μερισθέντων τὸ κενωθὲν τότε πάλιν ἀνεπλήρωσεν. ὅταν μὲν δὴ πλέον τοῦ ἐπιρρέοντος ἀπίῃ͵ φθίνει πᾶν͵ ὅταν δὲ ἔλαττον͵ αὐξάνεται.  

νέα μὲν οὖν σύστασις τοῦ παντὸς ζῴου͵ καινὰ τὰ τρίγωνα οἷον ἐκ δρυόχων ἔτι ἔχουσα τῶν γενῶν͵ ἰσχυρὰν μὲν τὴν σύγκλεισιν αὐτῶν πρὸς ἄλληλα κέκτηται͵ συμπέπηγεν δὲ ὁ πᾶς ὄγκος αὐτῆς ἁπαλός͵ [81c] ἅτ΄ ἐκ μυελοῦ μὲν νεωστὶ γεγονυίας͵ τεθραμμένης δὲ ἐν γάλακτι· τὰ δὴ περιλαμβανόμενα ἐν αὐτῇ τρίγωνα ἔξωθεν ἐπεισελθόντα͵ ἐξ ὧν ἂν ᾖ τά τε σιτία καὶ ποτά͵ τῶν ἑαυτῆς τριγώνων παλαιότερα ὄντα καὶ ἀσθενέστερα καινοῖς ἐπικρατεῖ τέμνουσα͵ καὶ μέγα ἀπεργάζεται τὸ ζῷον τρέφουσα ἐκ πολλῶν ὁμοίων. ὅταν δ΄ ἡ ῥίζα τῶν τριγώνων χαλᾷ διὰ τὸ πολλοὺς ἀγῶνας ἐν πολλῷ χρόνῳ πρὸς πολλὰ ἠγωνίσθαι͵ [81d] τὰ μὲν τῆς τροφῆς εἰσιόντα οὐκέτι δύναται τέμνειν εἰς ὁμοιότητα ἑαυτοῖς͵ αὐτὰ δὲ ὑπὸ τῶν ἔξωθεν ἐπεισιόντων εὐπετῶς διαιρεῖται· φθίνει δὴ πᾶν ζῷον ἐν τούτῳ κρατούμενον͵ γῆράς τε ὀνομάζεται τὸ πάθος. τέλος δέ͵ ἐπειδὰν τῶν περὶ τὸν μυελὸν τριγώνων οἱ συναρμοσθέντες μηκέτι ἀντέχωσιν δεσμοὶ τῷ πόνῳ διιστάμενοι͵ μεθιᾶσιν τοὺς τῆς ψυχῆς αὖ δεσμούς͵ ἡ δὲ λυθεῖσα κατὰ φύσιν μεθ΄ ἡδονῆς ἐξέπτατο· [81e] πᾶν γὰρ τὸ μὲν παρὰ φύσιν ἀλγεινόν͵ τὸ δ΄ ᾗ πέφυκεν γιγνόμενον ἡδύ. καὶ θάνατος δὴ κατὰ ταὐτὰ ὁ μὲν κατὰ νόσους καὶ ὑπὸ τραυμάτων γιγνόμενος ἀλγεινὸς καὶ βίαιος͵ ὁ δὲ μετὰ γήρως ἰὼν ἐπὶ τέλος κατὰ φύσιν ἀπονώτατος τῶν θανάτων καὶ μᾶλλον μεθ΄ ἡδονῆς γιγνόμενος ἢ λύπης.