Our structure, then, being thus divided, we have carefully to mark that our faculty for life is not supported in any one way by some single organ, but nature, while distributing the means for our existence among several parts, makes the contribution of each individual necessary for the whole; just as the things which nature contrives for the security and beauty of life are also numerous, and differ much among themselves.

We ought, however, I think, first to discuss briefly the first beginnings of the things which contribute to the constitution of our life. As for the material of the whole body which serves as a common substratum for the particular members, it may for the present be left without remark; for a discussion as to natural substance in general will not be of any assistance to our purpose with regard to the consideration of the parts.

As it is then acknowledged by all that there is in us a share of all that we behold as elements in the universe-of heat and cold, and of the other pair of qualities of moisture and dryness-we must discuss them severally.

We see then that the powers which control life are three, of which the first by its heat produces general warmth, the second by its moisture keeps damp that which is warmed, so that the living being is kept in an intermediate condition by the equal balance of the forces exerted by the quality of each of the opposing natures (the moist element not being dried up by excess of heat, nor the hot element quenched by the prevalence of moisture); and the third power by its own agency holds together the separate members in a certain agreement and harmony, connecting them by the ties which it itself furnishes, and sending into them all that self-moving and determining force, on the failure of which the member becomes relaxed and deadened, being left destitute of the determining spirit.

Οὕτω τοίνυν τῆς κατασκευῆς τῆς ἐν ἡμῖν διῃρημένης͵ ἔστιν ἀκριβῶς κατανοῆσαι͵ ὅτι οὐ μονοειδῶς ἡμῖν δι' ἑνός τινος ἡ πρὸς τὸ ζῇν δύναμις διεξάγεται, ἀλλὰ πλείοσι μορίοις ἡ φύσις τὰς πρὸς τὴν σύστασιν ἡμῶν ἀφορμὰς ἐπινείμασα͵ ἀναγκαίαν ποιεῖ πρὸς τὸ ὅλον τὴν παρ' ἑκάστου συνεισφοράν. Ὥστε καὶ ὅσα πρὸς ἀσφάλειαν τῆς ζωῆς καὶ κάλλος ἡ φύσις ἐπετεχνάσατο͵ πλείω τέ ἐστι ταῦτα καὶ πολλὴν πρὸς ἄλληλα τὴν διαφορὰν ἔχει.

Ἀλλ' οἶμαι διελέσθαι πρότερον ἐν ὀλίγῳ χρῆναι τῶν πρὸς τὴν σύστασιν τῆς ζωῆς συντελούντων ἡμῖν τὰς πρώτας ἀρχάς. Ἡ μὲν οὖν τοῦ παντὸς σώματος ὕλη κοινὴ τοῖς καθ' ἕκαστον μέλεσιν ὑποκειμένη͵ σιγάσθω τανῦν· οὐδὲν γὰρ πρὸς τὸν σκοπὸν ἡμῖν συντελέσει ἡ καθόλου φυσιολογία πρὸς τὴν μερικὴν θεωρίαν.

Ὁμολογουμένου τοίνυν παρὰ πᾶσι τοῦ πάντων ἐν ἡμῖν εἶναι τῶν στοιχειωδῶς ἐν τῷ κόσμῳ θεωρουμένων τὴν μοῖραν͵ τοῦ τε θερμοῦ καὶ τοῦ ψύχοντος καὶ τῆς ἑτέρας συζυγίας τῆς κατὰ τὸ ὑγρόν τε καὶ ξηρὸν νοουμένης͵ τὰ καθ' ἕκαστον ἡμῖν διαληπτέον.

Οὐκοῦν ὁρῶμεν τρεῖς τὰς διοικητικὰς τῆς ζωῆς δυνάμεις͵ ὧν ἡ μὲν διαθάλπει τὸ πᾶν τῇ θερμότητι͵ ἡ δὲ ὑπονοτίζει τῇ ἰκμάδι τὸ θερμαινόμενον͵ ὡς ἂν τῇ ἰσοκρατείᾳ τῆς τῶν ἐναντίων ποιότητος͵ ἐπὶ τοῦ μέσου συντηροῖτο τὸ ζῶον͵ μήτε τοῦ ὑγροῦ καταφρυγομένου τῷ πλεονασμῷ τῆς θερμότητος͵ μήτε τοῦ θερμοῦ σβεννυμένου τῇ ἐπικρατείᾳ τοῦ καθυγραίνοντος. Ἡ δὲ τρίτη δύναμις συνέχει δι' ἑαυτῆς κατά τινα συμβολήν τε καὶ ἁρμονίαν τὰ διακεκριμένα τῶν ἄρθρων τοῖς παρ' ἑαυτῆς συνδέσμοις ἁρμόζουσα καὶ πᾶσιν ἐπιπέμπουσα τὴν αὐτοκίνητόν τε καὶ προαιρετικὴν δύναμιν, ἧς ἐπιλειπούσης͵ πέρατον γίνεται καὶ νεκρῶδες τὸ μέρος͵ τοῦ προαιρετικοῦ πνεύματος ἀμοιρῆσαν.