Greco-Christian stream·Corpus Aristotelicum (Complete Works of Aristotle)·On Sleep and Waking

On Sleep and Waking

Περὶ Ὕπνου καὶ Ἐγρηγόρσεως · De Somno et Vigilia · biology

[453b.16] With regard to sleep and waking, we must consider what they are; whether they are peculiar to soul or to body, or common to both; and if common, to what part of soul or body they appertain: further, from what cause it arises s that they are attributes of animals, and whether all animals share in them both, or some partake of the one only, others of the other only, or some partake of neither and some of both. Further, in addition to these questions, we must also inquire what the dream is, and from what cause sleepers sometimes dream, and sometimes do not; or whether the truth is that sleepers always dream but do not always remember (their dream); and if this occurs, what its ex- planation is. Again, [we must inquire] whether it is possible or not to foresee the future (in dreams), and if it be possible, in what manner ; further, whether, supposing it possible, it extends only to things to be accomplished by the agency of Man, or to those also of which the cause lies in supra-human agency, and which result from the workings of Nature, or of Spontaneity. First, then, this much is clear, that waking and sleep appertain to the same part of an animal, inasmuch as they are opposites, and sleep is evidently a privation of waking. For contraries, in natural as well as in all other matters, are seen always to present themselves in the same subject, and to be affections of the same: examples are—health and sickness, beauty and ugliness, strength and weakness, sight and blindness, hearing and deafness. This is also clear from the following considerations. The criterion by which we know the waking person to be awake is identical with that by which we know the sleeper to be asleep; for we assume that one who is exercising sense-perception is awake, CHAPTER I and that every one who is awake perceives either some external movement or else some movement in his own con- sciousness. If waking, then, consists in nothing else than the exercise of sense-perception, the inference is clear, that the organ, in virtue of which animals perceive, is that by which they wake, when they are awake, or sleep, when they are asleep. But since! the exercise of sense-perception ~ does not belong to soul or body exclusively, then (since the subject of actuality is in every case identical with that of potentiality, and what is called sense-perception, as actuality, is a move- ment of the soul through the body) it is clear that its” affection is not an affection of soul exclusively, and that a soulless body has not the potentiality’ of perception”. [Thus sleep and waking are not attributes of pure intelligence, on the one hand, or of inanimate bodies, on the other. | Now, whereas we have already elsewhere distinguished what are called the parts of the soul, and whereas the nutrient is, in all living bodies, capable of existing without the other parts, while none of the others can exist without the nutrient ; it is clear that’ sleep and waking are not affections of such living things as partake only of growth and decay, e.g. not of plants, because these have not the faculty of sense-perception, 1 Since waking is not peculiar to soul or body, neither is sleeping ; for sleeping is the potentiality of waking, and if the actuality can- not be peculiar to body or to soul, neither can the potentiality be so. Sleep is an affection (πάθος) which renders ‘ potential’ the αἴσθησις, whose actuality is waking. But instead of concluding ‘neither is the πάθος peculiar to soul or body’, or ‘neither is the affection peculiar to soul, nor can a body without soul sleep’, he winds up with the conclusion : ‘nor is a body without soul capable of sense-fperception’ ; which involves the other point; and is really what he aims at. For to be capable of incapable of it is to be incapable of sleeping as well as of waking. The nerve of the reasoning is contained in the parenthesis. * Sc. ὕπνος ; see 453> 28, 29. © Cf. 454 11-12, where also what is capable of sleeping is virtually ® Sc. cannot sleep: Sleep, the πάθος, as the parenthesis shows, is II. 1. 412% 23-26. * The clauses preceding δῆλον ὅτι are only the preamble, not the reason, of what follows. For os... ὅτι cf. 443° 23, 24. 454 ἃ -_ oO 454 ἃ 20 whether or not this be capable of separate! existence ; in its potentiality, indeed, and in its relationships, it zs separable | sc. Likewise it is clear that [of those which either sleep or wake] there is no animal which is always awake or always asleep, but that both these affections belong [alter- nately] to the same animals.’ For if there be an animal not endued with sense-perception, it is impossible that this should either® sleep or wake; since both these are affections tive functions. With τῷ εἶναι cf. 4488 20 (note), where τῷ λόγῳ explains it. Nowhere in the world can Aristotle find τὸ αἰσθητικόν apart τύπῳ, OY μεγέθει, yet it is separate τῷ εἶναι, i.e. in its relationship to objects. It is separate also τῇ δυνάμει. This difference may be expressed by τῇ δυνάμει therefore = ‘in respect of its potentiality as part of soul’, or briefly ‘as a faculty’. ‘different animals’. δ The difficulty of this whole passage becomes acute here. The traditional translation involves a misuse of οὔτε before the infinitive. The grammatical version would be —‘it cannot either sleep or wake,’ οὔτε... οὔτε explicating ov. As the text stands this would make no sense. Inserting μή before ἔχον we could restore sense and grammar. This has been assumed in the translation. It is to be observed that the μὲν after ὅσα in 415 has no answering δέ, But Aristotle would naturally have gone on from ‘plants’ to the case of animals which stood on the border line. Having said that φυτά (which have not the organ of sense-perception) cannot sleep or wake, he would naturally say that if there be any animal which has not perception it too cannot sleep or wake. In 778° 23-779" 10 he considers such animals, viz. ἔμβρυα, which (he there says) do not sleep but do something like it, ‘just like plants.’ In Po/. 1335 24, too, he refers ἄμβλωσιν. In another respect the received translation is wrong, for ‘if there be any animal having αἴσθησις ᾽: the former would be repre- gets any meaning, by making it refer to οὐ yap. .. ἔχουσι ἴῃ ἃ 17. Then, however, it appears that ὁμοίως ... ταῦτα ὃ 19-21 is out of its place. If, however, we transfer this to ® 24 after αἰσθητικοῦ we find the next words tautological. So that there is something almost certainly wrong with the text. I believe the insertion of μή to be required absolutely by the grammar, and critically justifiable by the consideration that it would have easily been lost owing to the appearance it has of contradicting Aristotle’s well-known definition of ζῷον. At least its insertion has as good critical ground to stand upon as that of μή in 4493 3 Cun) alo Iaverat. The general sense of * 21-26 (οὐ yap... ἐγρηγορέναι) is—‘ For while without sensation no creature can do either, zw/¢/ sensation every creature must do both.’ An explanation of the passage from 10 to *32 communicated by Mr. Charles Cannan seems so valuable, based as it is on minute and CHAPTER I of the activity of the primary faculty of sense-perception. But it is equally impossible also that either of these two affec- tions should perpetually attach itself to the same animal, e.g. that some species of animal should be always asleep or always - awake, without intermission ; for all organs which have a natural function must lose power when they work beyond the natural time-limit of their working period; for instance, the eyes [must lose power] from |too-long continued] seeing, and must give it up; and so it is with the hand and every other member which has a function. Now, if sense-perception is the function of a special organ, this also, if it continues perceiving beyond the appointed time-limit of its continuous working period, will lose its power, and will do its work no longer. Accordingly, if the waking period is determined by this fact, that in it sense-perception is free; if in the case of some contraries one of the two must be present, while in the case of others this is not necessary'; if waking is the contrary of sleeping, and one of these two must be present to every animal: it must follow that the state of sleeping is necessary. Finally, if such affection is Sleep, and this is a state of powerlessness arising from excess of waking, and excess of waking is in its scholarly analysis of the sense and grammar, that his permission to print it has been gladly accepted. Mr. Cannan suggests that in ἃ 21 we should read ‘But it is equally plain that there is nothing which has one of the two always, but both affections belong to the same farts and kinds of animals [avzma/s, for plants are excluded above]. For [(a) as to parts| it does not follow that, if some part of an animal has sense-perception, it—the mere part—has the faculty either of sleeping or of waking ; for both these affections are incident, not to a single organ, but to the primary faculty of sense-perception [for example, the heart is not always asleep and the brain always awake (cf. Michael, p. 44. 13, Arist. 453” 13), for in the proper sense they do not sleep or wake at all]; nor [(64)’as to Ainds], on the other hand, can either sleeping or waking attach itself for ever, to the exclusion of the other, to the same thing, in the sense that some particular kind of animal [e.g. the weasel] is always awake, and some other [e.g. the dormouse] is always asleep. For (ὅτι) all things having a natural ἔργον become incapable in time of that ἔργον ; therefore, that of which τὸ αἰσθάνεσθαι is an ἔργον will become incapable of τὸ αἰσθάνεσθαι, and leave a blank which must be filled up with sleep, its contrary.’ παρεῖναι, τῶν δ᾽ ot. There are certain pairs of contraries (e.g. κακία and ἀρετή, Cf. 11.45% 25) one of which is not always predicable of living animals ; while there are others of which one must be always present, and to this class belong sleep and waking.

[454a.1] origin sometimes morbid, sometimes not, so that the power- lessness or dissolution of activity will be so or not; it is inevitable that every creature which wakes must also be capable of sleeping, since it is impossible that it should con- tinue actualizing its powers perpetually. So, also, it is impossible for any animal to continue always sleeping. For sleep is an affection of the organ! of sense- perception—a sort of tie or inhibition of function imposed on it, so that every creature that sleeps must needs have the organ of sense-perception. Now, that alone which is capable of sense-perception in actuality has the faculty of sense- perception ; but to realize this faculty, in the proper and unqualified sense, is impossible while one is asleep. All sleep, therefore, must be susceptible of awakening. Accord- ingly, almost all other animals are clearly observed to partake in sleep, whether they are aquatic, aerial, or terrestrial, since fishes of all kinds, and molluscs, as well as all others which have cyes, have been seen sleeping. ‘ Hard-eyed’ creatures and insects manifestly assume the posture? of sleep; but the sleep of all such creatures is of brief duration, so that often it might well baffle one’s observation to decide whether they sleep* or not. Of testaceous animals, on the contrary, no direct sensible evidence is as yet forthcoming to determine whether they sleep, but if the above reasoning be convincing to any one, he who follows it will admit this * [viz. that they do so]. That, therefore, all animals sleep may be gathered from these considerations. For an animal is defined as such by its possessing sense-perception : and we assert that sleep is, in a certain way, an inhibition of function, or, as it were, a tie, imposed on sense-perception, while its loosening or remission constitutes the being awake. But no plant can partake in cither of these affections, for without sense-perception there 1 What affects the ovgun, affects the facu/ty, and there is no need to press the distinction here. > If we cannot see that they are asleep, we can see them ‘couching’, The notion of κοίτη in κοιμώμενα is important ; the allusion to it contains the point here. servation cannot decide the gevera/ question: but with the @ priori * [Read τοῦτο for τούτῳ, with Bywater, Δ ?. xxviii. 243. Edd.]

[454b.1] is neither sleeping nor waking. But creatures which have

[454b.30] sense-perception have likewise the feeling of pain and plea- sure, while those which have these have appetite as well ; but plants have none of these affections. A mark of this" is

[455a.1] that the nutrient part does its own work better when (the animal) is asleep than when it is awake. Nutrition and growth are then especially promoted, a fact which implies that creatures do not need sense-perception to assist these processes. CHAPTER II We must now proceed to inquire into the cause why one sleeps and wakes, and into the particular nature of the sense- perception, or sense-perceptions, if there be several, on which these affections depend. Since, then, some animals possess : all the modes of sense-perception, and some not all, not, for example, sight, while all possess touch and taste, except such animals as are imperfectly developed, a class of which we have already treated in our work on the soul; and since an animal when asleep is unable to exercise, in the simple sense, any particular’ sensory faculty whatever, it follows that in the state called sleep the same affection must extend to all " the special senses ; because, if it attaches itself to one of them but not to another, then an animal while asleep may perceive with the latter; but this is impossible. Now, since every sense has something peculiar, and also something common; peculiar, as, e.g., seeing is to the sense of sight, hearing to the auditory sense, and so on with the other senses severally ; while all are accompanied by a com- mon power, in virtue whereof a person perceives /Aat he sees or hears (for, assuredly, it is not by the special * sense of sight that one sees that he sees; and it is not by mere taste, or Jt O - 1 Separableness of the nutrient from the sentient faculty. which does not preclude such exercise of this as takes place in dreaming. 8. The text is exceedingly doubtful: cf. ἃ 25 2722, (where the conclusion 4 But by the ‘general’ sense, gz related to the ‘ special’. 455 ἃ to Cy 455 Ὁ “yr DE SOMNO IT VIGILIA sight, or both together that one discerns, and has the faculty of discerning, that sweet things are different from white things, but by a faculty connected in common with all the organs of sense; for there is one sensory function, and the controlling sensory faculty is one, though differing as a faculty of percep- tion’ in relation to each genus of sensibles, 6. g., sound or colour); and since this |common sensory activity] subsists in association chiefly with the faculty of touch (for this [touch] can exist apart from all the other organs of sense, but none of them can exist apart from it—a subject of which we have treated in our speculations concerning the Soul); it is therefore evident that waking and sleeping are an affection of this [common and controlling organ of sense-perception ]. This explains why they belong to all animals, for touch [with which this common organ is chiefly connected], alone, [is common] to all [animals]. For if sleeping were caused by the sfeczal senses having each and all undergone some affection, it would be strange that these senses, for which it is neither necessary nor in a manner possible to realize their powers simultaneously, should necessarily all go idle and become motionless simul- taneously. For the contrary experience, viz. that they should not go to rest altogether, would have been more reasonably anticipated. But, according to the explanation just given, all is quite clear regarding those also. For, when the sense organ which controls all the others, and to which all the others are tributary, has been in some way affected, that these others should be all affected at the same time is inevitable, whereas, if one of the tributarics becomes power- less, that the controlling organ should also become powerless need in no wise follow. It is indeed evident from many considerations that sleep does not consist in the mere fact that the special senses do not function or that one does not employ them; and that it does not consist merely in an inability to exercise the sense-perceptions ; for such is what happens in cases of swooning. A swoon means just such impotence of percep- governs τοῦ γένους. Cf. 4403 18 (note). CIIAPTER Il tion, and certain other cases of unconsciousness also are of this nature. Moreover, persons who have the blood-vessels in the neck compressed become insensible. But sleep super- venes when such incapacity of exercise has neither arisen in some casual organ of sense, nor from some chance cause, but when, as has been just stated, it has its seat in the primary organ with which one perceives objects in general.' For when this has become powerless all the other sensory organs also must lack power to perceive; but when one of them has become powerless, it is not necessary for this also to lose its power. We must next state the cause to which it is due, and its quality as an affection. Now, since there are several types of cause (for we assign equaliy the ‘final’, the ‘ efficient’, the ‘ material’, and the ‘ formal’ as causes), in the first place, then, as we assert that Nature operates for the sake of an end, and that this end is a good”; and that to every creature which is endowed by nature with the power to move, but cannot with pleasure ὁ to itself move always and continuously,

[455a.2] rest is necessary and beneficial ; and since, taught by cxperi- ence, men apply to sleep this metaphorical ὁ term, calling it a ‘rest’ [from the strain of movement implied in sense- perception]: we conclude that its end is the conservation of animals, But the waking state is for an animal its highest end, since the exercise of sense-perception or of thought is the highest end for all beings to which either of these appertains ; inasmuch as these are best, and the highest end is what is best: whence it follows that sleep belongs of necessity to each animal. I use the term ‘necessity’ in its conditional sense, meaning that if an animal is to exist and have its own proper nature, it must have certain endowments ; and, if these 2. ἀνάπαυσις is an end, i.e. a@ good ; but ἦε end, i.e. the highest end, of * Anaxagoras held that all αἴσθησις i is pera λύπης. Theophr. de Sens. The metaphor is plain enough in the Greek word ἀνάπαυσις. No word in English seems to meet the case so well as ‘rest’. EM give καταφοράν, which, however, it would be difficult to translate here. But cf.

[455b.1] are to belong to it, certain others likewise must belong to it [as their condition]. The next question to be discussed is that of the kind of movement or action, taking place within their bodies, from which the affection of waking or sleeping arises in animals. Now, we must assume that the causes of this affection in all other animals are identical with, or analogous to, those which operate in sanguineous animals ; and that the causes operat- ing in sanguineous animals generally are identical with those operating in man. Hence we must consider the entire sub- ject in the light of these instances [afforded by sanguineous animals, especially man]. Now, it has been definitely settled already in another work that sense-perception in animals originates in the same part of the organism in which move- ment originates. This locus of origination is one of three determinate loci, viz. that which lies midway between the head and the abdomen. This in sanguineous animals is the region of the heart; for all sanguineous animals have a heart; and from this it is that both motion and the con- trolling sense-perception originate. Now, as regards move- ment, it is obvious that that of breathing and of the cooling process generally takes its rise there ; and it is with a view to the conservation of the [due amount of] heat in this part that nature has formed as she has both the animals which respire, and those which cool themselves by moisture. Of this | cooling process] fev se we shall treat hereafter. In bloodless animals, and insects, and such as do not respire, the ‘con- natural spirit’! is seen alternately puffed up and subsiding in the part which is in them analogous [to the region of the heart in sanguineous animals]. This is clearly observable in the holoptera [insects with undivided wings| as wasps and bees; also in flies and such creatures. And since to move anything, or do anything, is impossible without strength, and holding the breath produces strength—in creatures which inhale, the holding of that breath 2 which comes from without, a... ¢ , ° ε a , ’, , « A CHAPTER II 456 but, in creatures which do not respire, of that which is con- natural (which explains why winged insects of the class holoptera, when they move, are perceived to make a hum- ming noise, due to the friction of the connatural spirit collid- ing with the diaphragm); and since movement’? is, in every animal, attended 2 with some sense-perception, either internal or external , in the primary organ of sense, [we conclude] accordingly that if sleeping and waking are affections of this organ, the place in which, or the organ in which, sleep and waking originate, is self-evident [being that in which move- : ment and sense-perception originate, viz. the heart]. Some persons move in their sleep, and perform many acts like waking acts, but not without a phantasm or an exercise of sense-perception ; for a dream is in a certain way a sense- impression. But of them we have to speak later on. Why it is that persons when aroused remember their dreams, but do not remember these acts which are like waking acts, has been already explained in the work ‘ Of Problems’. to to “ye CHAPTER III The point for consideration next in order to the preceding 50 is:— What are the processes in which the affection of waking and sleeping originates, and whence do they arise? Now, since it is when it has sense-perception that an animal must first take food and receive growth, and in all cases food in its

[455b.35] ultimate form is, in sanguineous animals, the natural sub- stance blood, or, in bloodless animals, that which is analogous

[456b.1] to this; and since the veins are the place of the blood, while the origin of these is the heart—an assertion which is proved by anatomy—it is manifest that, when the external nutriment has an αἴσθησις he moves (or is moved) locally. The κινεῖται here and the κινεῖν * 15 refer to /oca/ movement, involving output of bodily energy, not to the κίνησις (or stimulation) of sense. should be regarded as prompted by the perception—a very important difference. ὅ οἰκείας ἢ ἀλλοτρίας : arising either from an intra-organic or an extra- organic stimulus. * i.e. gua animal; before this, in the embryonic stage, it grows and is nourished like a vegetable. en Io enters the parts fitted for its reception, the evaporation arising from it enters into the veins, and there, undergoing a change, is converted into blood, and makes its way to their source [the heart]. We have treated of all this when discussing the subject of nutrition, but must here recapitulate what was there said, in order that we may obtain a scientific view of the beginnings of the process, and come to know what exactly happens to the primary organ of sense-perception to account for the occurrence of waking and sleep. For sleep, as has been shown, is not any given impotence of the perceptive faculty ; for unconsciousness, a certain form of asphyxia, and swooning, all produce such impotence. Moreover it is an estab- lished fact that some persons in a profound trance have still had the imaginative faculty in play. This last point, indeed, gives rise to a difficulty ; for if it is conceivable that one who had swooned should in this state fall asleep, the phantasm also which then presented itself to his mind might be regarded as a dream. Persons, too, who have fallen into a deep trance, and have come to be regarded as dead, say many things while in this condition. The same view, however, is to be taken of all these cases, |i.e. that they are not cases of sleeping or dreaming]. As we observed above, sleep is not co-extensive with any and every impotence of the perceptive faculty, but this affection is one which arises from the evaporation attendant upon the process of nutrition. The matter evaporated must be driven onwards to a certain point, then turn back, and change its current to and fro, like a tide-race in a narrow strait. Now, in every animal the hot naturally tends to move [and carry other things] upwards, but when it has reached the parts above, [becoming cool, see 457 " 30] it turns back again, and moves downwards in a mass. This explains why fits of drowsiness are especially apt to come on after meals; for the matter, both the

[456b.5] liquid and the corporeal, which is borne upwards in a mass, is then of considerable quantity. When, therefore, this comes to a stand it weighs a person down and causes him to nod, but when it has actually sunk downwards, and by its return has re- pulsed the hot, sleep comes on, and the animal so affected is presently asleep. A confirmation of this appears from consider- CHAPTER III ing the things which induce sleep ; they all, whether potable or edible, for instance poppy, mandragora, wine, darnel, produce a heaviness in the head ; and persons borne down [by sleepi- ness| and nodding [drowsily] all seem affected in this way, i.e. they are unable to lift up the head or the eye-lids. And it is after meals especially that sleep comes on like this, for the evaporation from the foods eaten is then copious. It also follows certain forms of fatigue; for fatigue operates as a solvent, and the dissolved matter acts, if not cold, like food 456 ἢ 20 ae rare)

[457a.1] prior to digestion. Moreover, some kinds of illness have this same effect; those arising from moist and hot secretions, as happens with fever-patients and in cases of lethargy." Extreme youth also has this effect; infants, for example, sleep a great deal, because of the food being all borne upwards —a mark whereof appears in the disproportionately large size of the upper parts compared with the lower during infancy, which is due to the fact that growth predominates in the direction of the former. Hence also they are subject to epileptic * seizures; for sleep is like epilepsy, and, in a sense, actually is a seizure of this sort. Accordingly, the beginning of this malady takes place with many during sleep, and their subsequent habitual seizures occur in sleep, not in waking hours. For when the spirit [evaporation] moves upwards in a volume, on its return downwards it distends the veins, and forcibly compresses the passage through which respiration is effected. This explains why wines are not good for infants or for wet nurses (for it makes no difference, doubtless, whether the infants themselves, or their nurses, drink them), but such persons should drink them [if at all] diluted with water and in small quantity. For wine is spirituous, and of all wines the dark more so than any other. The upper parts, in infants, are so filled with nutriment that within five months [after birth] they do not even turn the neck [sc. to raise the head| ; for in them, as in persons deeply intoxicated, there is

[457a.2] ever a large quantity of moisture ascending. It is reasonable, 1 If ἐν be right, An@apyos may be either a substantive or an adjective in agreement with πυρετοῖς understood. 2 Not merely childish fits and convulsions, but efz/eftic fits. The word in this sense is as old as Hippocrates, and the facts here stated are all medical truths. .) 116) ~ 457 ἃ to oon 30 457 Ὁ oye too, to think that this affection is the cause of the embryo’s remaining at rest in the womb at first. Also, as a general rule, persons whose veins are inconspicuous, as well as those who are dwarf-like, or have abnormally large heads, are addicted to sleep. For in the former the veins are narrow, so that it is not easy forthe moisture to flow down through them ; while in the case of dwarfs and those whose heads are ab- normally large, the impetus of the evaporation upwards is excessive. Those [on the contrary] whose veins are large are, thanks to the easy flow through the veins, not addicted to sleep, unless, indeed, they labour under some other affec- tion which counteracts [this easy flow]. Nor are the ‘atra- bilious’ addicted to sleep, for in them the inward region is cooled so that the quantity of evaporation in their case is not great. For this reason they have large appetites, though spare and lean; for their bodily condition is as if they derived no benefit from what they eat. The dark bile, too, being itself naturally cold, cools also the nutrient tract, and the other parts wheresover such secretion [bile] is potentially present [i.e. tends to be formed]. Hence it is plain from what has been said that sleep is a sort of concentration, or natural recoil,’ of the hot matter inwards |towards its centre], due to the cause above men- tioned. Hence restless movement is a marked feature in the case of a person when drowsy. But where it [the heat in the upper and outer parts] begins to fail, he grows cool, and owing to this cooling process his eye-lids droop. Accord- ingly [in sleep] the upper and outward parts are cool, but ‘What is meant is otherwise expressed, 458% 10 συνεωσμένη κτλ. ἀντιπερίστασις is not here used in its strict sense, in which it involves real σις is defined by Simplicius as a circular process in which ‘ when a body is pushed out of its place that which has expelled it occupies the place, while that which has been thrust out pushes the adjoining body from its place, until the last moved in this series finds itself in the place of the first, which extruded something else’. It depends on the fact that there isno vacuum. (Cf. 266% 25 seqq., 459» 2, 472 17; Zeller, Plato (E.T.), p. 430; Zeller, Avs. i. 515, ii. 378, ἢ.) So Aristotle explained physical facts like the motion of projectiles. Plato, Zz. 79 B-E, uses the word process when on suddenly opening a door in a room the opposite door shuts, or vice versa. Reference to this explains τῆς ἀρχῆς 454” 2, 9.2. CHAPTER III the inward and lower, i.e. the parts at the feet and in the interior of the body, are hot. Yet one might found a difficulty on the facts that sleep is most oppressive in its onset after meals, and that wine. and other such things, though they possess heating properties, are productive of sleep," for it is not probable that sleep should be a process of cooling while the things that cause sleeping are themselves hot. Is the explanation of this, then, to be found in the fact that, as the stomach when empty is hot, while replenishment cools it by the movement it occasions, so the passages and tracts in the head are cooled as the ‘ evapora- tion’ ascends thither? Or, as those who have hot water poured on them feel a sudden shiver of cold, just so in the case before us, may it be that, when the hot substance ascends, the cold rallying to meet it cools [the aforesaid parts], deprives their native heat of all its power, and compels it to retire? Moreover, when much food is taken, which [i.e. the nutrient evaporation from which] the hot substance carries upwards, this latter, like a fire when fresh logs are laid upon it, is itself cooled, until the food has been digested. For, as has been observed elsewhere,” sleep comes on when the corporeal element [in the ‘evaporation’] is conveyed upwards by the hot, along the veins, to the head. But when that which has been thus carried up can no longer ascend, but is too great in quantity [to do 50], it forces the hot back again and flows downwards. Hence it is that men sink down [as they do in sleep] when the heat which tends to keep them erect (man alone, among animals, being naturally erect) is withdrawn ; and this, when it befalls them, causes uncon- sciousness, and afterwards° phantasy. Or are the solutions thus proposed barely conceivable accounts of the refrigeration which takes place, while, as ‘9, There should be only a comma after τοιαῦτα. δέ here gives the argument from the opponent's point of view, and = ‘ for’. 2 De Part. An. ii. 7, 653% 10. ° A new factor—mechanical pressure—is here introduced. τὸ θερμόν alone agree with ἐπιπεσόν, and so Freudenthal translates ‘ wieder- eindringend etzeugt das Warme Bewusstlosigkeit’. ἐπιπίπτειν expresses a hostile attack, an onset. " ‘Afterwards’, i.e. when the process of διάκρισις sets in; cf. 4614 25. AR PN G 457 Ὁ J to O tS 457 Ὁ a matter of fact, the region of the brain is, as stated else- where, the main determinant of the matter? For the brain,

[457a.30] or in creatures without a brain that which corresponds to it, is of all parts of the body the coolest. Therefore, as moisture turned into vapour by the sun’s heat is, when it has ascended to the upper regions, cooled by the coldness of the latter, and becoming condensed, is carried downwards, and turned into

[458a.1] water once more; just so the excrementitious evaporation, when tn 15 20 carried up by the heat to the region of the brain, is condensed into a ‘phlegm’ (which explains why catarrhs are seen to proceed from the head); while that evaporation which is nutrient and not unwholesome, becoming condensed, descends and cools the hot. The tenuity or narrowness of the veins about the brain itself contributes to its being kept cool, and to its not readily admitting the evaporation. This, then, is a sufficient explanation of the cooling which takes place, despite the fact that the evaporation is exceedingly hot. A person awakes from sleep when digestion is completed : when the heat, which had been previously forced together in large quantity within a small compass from out the surround- ing part, has once more prevailed, and when a separation has been effected! between the more corporeal and the purer blood.?. The finest and purest blood is that contained in the head, while the thickest and most turbid is that in the lower parts. The source of all the blood is, as has been stated both here and elsewhere, the heart. Now of the chambers in the heart the central communicates with each of the two others. Each of the latter again acts as receiver from each, respectively, of the two vessels,® called the ‘great’ and the ‘aorta’. It is in the central chamber that the [above-men- tioned] separation takes place. To go into these matters in detail would, however, be more properly the business of a different treatise from the present. Owing to the fact that the blood formed after the assimilation of food is especially > Contained in the ‘ evaporated substance’ now collected back into the heart. * To use the term ‘artery’ here in translation would mislead any mere I-nglish reader into thinking that Aristotle knew the difference between arteries and veins. CHAPTER III 458 a in need of separation, sleep [then especially] occurs |and lasts] until the purest part of this blood has been separated off into the upper parts of the body, and the most turbid into the lower parts. When this has taken place animals awake from sleep, being released from the heaviness conse- quent on taking food. )

[458a.25] We have now stated the cavse' of sleeping, viz., that it consists in the recoil by 2 the corporeal element, upborne by the connatural heat, in a mass upon the primary sense-organ ; we have also stated what* sleep is, having shown that it is a seizure of the primary sense-organ, rendering it unable to

[458a.30] actualize its powers ; arising of necessity (for it is impossible for an animal to exist if the conditions which render it an animal be not fulfilled), i.e., for the sake of its conservation! ; since remission of movement tends to the conservation of animals. material conditions, regarded statically, i.e. in abstraction from their causes the recoil is the cold of the brain: hence ὑπό 8 26 = (not ‘ caused by’, but) ‘undergone by’. The ὑπό in this sense is curious, but ἀντι- of manceuvre effected by the substance. ° i.e. its definition or formal cause. * σωτηρία is the final cause. G we

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