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Wakefulness has toned what was relaxed. And neither of these remains in perpetuity, but both give way to the presences of each other, so that nature renews itself by these alternations, as if partaking of each in turn it passes uninterruptedly from one to the other. For the animal to be constantly strained in its activities causes a certain rupture and tearing of the overstrained parts; and the continuous relaxation of the body brings about a certain collapse of its constitution and a dissolution. But to attain each of these in due measure at the proper time is a power for the preservation of nature, which through the continuous transition to opposite states rests itself from one in the other. Thus, therefore, taking the body which has been toned by wakefulness, it brings about a release of the tension through sleep, resting the sensory faculties for a time from their activities, as if unyoking horses after the chariot races. And timely relaxation is necessary for the constitution of the body, so that nourishment may be distributed without hindrance throughout the whole body through its channels, with no tension impeding its passage.

For just as from the moist earth, when the sun shines with warmer rays, certain misty vapors are drawn up from the depths; something similar happens also in the earth that is us, when the nourishment from within is heated by the natural warmth. And the vapors, being naturally upward-moving, and airy, and breathing towards what is above, come to be in the regions around the head, like smoke penetrating the joints of a wall; then from there, being exhaled, they spread to the passages of the sense organs, through which perception is necessarily idle, yielding to the passage of those vapors. For the sight is taken over by the eyelids, as if by some leaden device, I mean that sort of weight, which relaxes the eyelid over the eyes. And the hearing, being thickened by these same vapors, as if a door were placed on the auditory parts, keeps quiet from its natural activity; and such a condition is sleep, with the sensation in the body being at rest, and completely inactive from its natural movement, so that the distributions of nourishment may become easy to pass, passing out together with the vapors through each of the pores. And for this reason, if the system around the sense organs should be constricted by the exhalation from within, and sleep should be prevented by some necessity; the sinewy part, having become full of vapors, is naturally stretched by itself, so that through the extension the part thickened by the vapors may be thinned out; something like what those do who by more vigorous twisting squeeze the water from garments. And since the parts around the pharynx are circular, and the sinewy element abounds in them; when the thickness of the vapors must be expelled from these also (since it is impossible to extend the circular part in a straight line, unless it be stretched according to its circumferential shape); for this reason, the breath having been caught in the yawn, when the chin sinks down to the uvula below, and all the inner parts are stretched into the shape of a circle, that sooty thickness which is trapped in the parts is breathed out together with the passage of the breath. And often, such a thing is known to happen even after sleep, whenever some of those vapors has been left behind in those places, unexpelled and unbreathed. From these things, therefore, the human mind clearly shows that it is connected to nature, for when nature is composed and awake, it too works and moves; but when nature is relaxed in sleep, it remains motionless, unless, perhaps, one should suppose the dream-like fantasy to be a movement of the mind operating during sleep. But we say that only the intelligent and composed activity of the intellect ought to be referred to the mind; but the fanciful triflings during sleep we consider to be certain phantoms of the mind's activity to the

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ἐγρήγορσις τὸ ἀνει μένον ἐτόνωσε. Καὶ οὐδέτερον τούτων ἐν τῷ διηνεκεῖ συμμένει, ἀλλ' ὑποχωρεῖ ταῖς παρουσίαις ἀλλήλων ἀμφότερα, οὕτω τῆς φύσεως ἑαυτὴν ταῖς ὑπαλλαγαῖς ἀνακαινιζούσης, ὡς ἑκατέρων ἐν τῷ μέρει μεταλαγ χάνουσαν ἀδιασπάστως ἀπὸ τοῦ ἑτέρου μεταβαίνειν ἐπὶ τὸ ἕτερον. Τό τε γὰρ διαπαντὸς συντετάσθαι ταῖς ἐνεργείαις τὸ ζῶον, ῥῆξίν τινα καὶ διασπασμὸν τῶν ὑπερτεινομένων ποιεῖται μερῶν· ἥ τε διηνεκὴς τοῦ σώματος ἄνεσις διάπτωσίν τινα τοῦ συνεστῶτος καὶ λύσιν ἐργάζεται. Τὸ δὲ κατὰ καιρὸν μετρίως ἑκατέ ρων ἐπιτυγχάνειν, δύναμις πρὸς διαμονήν ἐστι τῆς φύσεως, διὰ τῆς διηνεκοῦς πρὸς τὰ ἀντικείμενα με ταβάσεως ἐν ἑκατέροις ἑαυτὴν ἀπὸ τῶν ἑτέρων ἀνα παυούσης. Οὕτω τοίνυν τετονωμένον διὰ τῆς ἐγρη γόρσεως τὸ σῶμα λαβοῦσα, λύσιν ἐμποιεῖ διὰ τοῦ ὕπνου τῷ τόνῳ, τὰς αἰσθητικὰς δυνάμεις πρὸς καιρὸν ἐκ τῶν ἐνεργειῶν ἀναπαύσασα, οἷόν τινας ἵππους μετὰ τοὺς ἀγῶνας τῶν ἁρμάτων ἐκλύσασα. Ἀναγκαία δὲ τῇ συστάσει τοῦ σώματος ἡ εὔκαιρος ἄνεσις, ὡς ἂν ἀκωλύτως ἐφ' ἅπαν τὸ σῶμα διὰ τῶν ἐν αὐτῷ πόρων ἡ τροφὴ διαχέοιτο, μηδενὸς τόνου τῇ διόδῳ παρεμ ποδίζοντος.

Καθάπερ γὰρ ἐκ τῆς διαβρόχου γῆς, ὅταν ἐπιλάμψῃ θερμοτέραις ἀκτῖσιν ὁ ἥλιος, ἀτμοί τινες ὀμιχλώδεις ἀπὸ τοῦ βάθους ἀνέλκονται· ὅμοιόν τι γίνεται καὶ ἐν τῇ καθ' ἡμᾶς γῇ, τῆς τροφῆς ἔσω θεν ὑπὸ τῆς φυσικῆς θερμότητος ἀναζεούσης. Ἀνω φερεῖς δὲ ὄντες οἱ ἀτμοὶ κατὰ φύσιν, καὶ ἀερώδεις, καὶ πρὸς τὸ ὑπερκείμενον ἀναπνέοντες, ἐν τοῖς κατὰ τὴν κεφαλὴν γίνονται χωρίοις, οἷόν τις καπνὸς εἰς ἁρμονίαν τοίχου διαδυόμενος· εἶτα ἐντεῦθεν ἐπὶ τοὺς τῶν αἰσθητηρίων πόρους ἐξατμιζόμενοι διαφοροῦν, δι' ὧν ἀργεῖ κατ' ἀνάγκην ἡ αἴσθησις, τῇ παρ όδῳ τῶν ἀτμῶν ἐκείνων ὑπεξιοῦσα. Αἱ μὲν γὰρ ὄψεις τοῖς βλεφάροις ἐπιλαμβάνονται, οἷόν τινος μηχανῆς μολυβδίνης, τοῦ τοιούτου λέγω βάρους, τοῖς ὀφθαλ μοῖς ἐπιχαλώσης τὸ βλέφαρον. Παχυνθεῖσα δὲ τοῖς αὐτοῖς τούτοις ἀτμοῖς ἡ ἀκοὴ, καθάπερ θύρας τινὸς τοῖς ἀκουστικοῖς μορίοις ἐπιτεθείσης, ἡσυχίαν ἀπὸ τῆς κατὰ φύσιν ἐνεργείας ἄγει· καὶ τὸ τοιοῦτον πά θος ὕπνος ἐστὶν, ἀτρεμούσης ἐν τῷ σώματι τῆς αἰ 168 σθήσεως, καὶ παντάπασιν ἐκ τῆς κατὰ φύσιν κινήσεως ἀπρακτούσης, ὡς ἂν εὐπόρευτοι γένωνται τῆς τρο φῆς αἱ ἀναδόσεις, δι' ἑκάστου τῶν πόρων τοῖς ἀτμοῖς συνδιεξιούσης. Καὶ τούτου χάριν εἰ στενοχωροῖτο μὲν ὑπὸ τῆς ἔνδοθεν ἀναθυμιάσεως ἡ περὶ τὰ αἰσθητήρια δια σκευὴ, κωλύοιτο δὲ κατά τινα χρείαν ὁ ὕπνος· πλῆρες γενόμενον τῶν ἀτμῶν τὸ νευρῶδες, αὐτὸ ὑφ' ἑαυτοῦ φυσικῶς διατείνεται, ὡς διὰ τῆς ἐκτάσεως τὸ παχυνθὲν ὑπὸ τῶν ἀτμῶν μέρος ἐκλεπτυνθῆναι· οἷόν τι ποιοῦσιν οἱ διὰ τῆς σφοδροτέρας στρεβλώσεως τὸ ὕδωρ τῶν ἱματίων ἐκθλίβοντες. Καὶ ἐπειδὴ κυκλοτερῆ τὰ περὶ τὸν φάρυγγα μέρη, πλεονάζει δὲ τὸ νευρῶδες ἐν τούτοις· ὅταν καὶ ἀπὸ τούτων ἐξωσθῆναι δέοι τὴν τῶν ἀτμῶν παχυμέρειαν (ἐπειδὴ ἀμήχανόν ἐστι δι' εὐθείας ἀποτεῖναι τὸ κυκλοειδὲς μέρος, εἰ μὴ κατὰ τὸ περιφερὲς σχῆμα διαταθείη)· τούτου χάριν ἀπολη φθέντος ἐν τῇ χάσμῃ τοῦ πνεύματος, ὅτε ὁ ἀνθερεὼν ἐπὶ τὸ κάτω τοῖς γαργαρεῶσιν ὑποκοιλαίνεται, καὶ τῶν ἐντὸς πάντων εἰς κύκλου σχῆμα διαταθέντων, ἡ λιγνυώδης ἐκείνη παχύτης ἡ ἐναπειλημμένη τοῖς μέρεσι συνδιαπνεῖται τῇ διεξόδῳ τοῦ πνεύματος. Πολλάκις δὲ, καὶ μετὰ τὸν ὕπνον οἶδε τὸ τοιοῦτον συμ βαίνειν, ὅταν τι τῶν ἀτμῶν ἐκείνων περιλειφθείη τοῖς τόποις ἄπεμπτόν τε καὶ ἀδιάπνευστον. Ἐκ τού των τοίνυν ὁ ἀνθρώπινος νοῦς δείκνυσιν ἐναργῶς, ὅτι τῆς φύσεως ἔχεται, συνεστώσης μὲν καὶ ἐγρηγορυίας, καὶ αὐτὸς συνεργῶν καὶ κινούμενος· παρεθείσης δὲ τῷ ὕπνῳ, μένων ἀκίνητος, εἰ μή τις ἄρα τὴν ὀνει ρώδη φαντασίαν νοῦ κίνησιν ὑπολάβοι κατὰ τὸν ὕπνον ἐνεργουμένην. Ἡμεῖς δέ φαμεν μόνην δεῖν τὴν ἔμ φρονά τε καὶ συνεστῶσαν τῆς διανοίας ἐνέργειαν ἐπὶ τὸν νοῦν ἀναφέρειν· τὰς δὲ κατὰ τὸν ὕπνον φαντα σιώδεις φλυαρίας ἰνδάλματά τινα τῆς κατὰ τὸν νοῦν ἐνεργείας οἰόμεθα τῷ