by Aristotle
The next question to be discussed is that of the kind of movement or action, [30] 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 operating in sanguineous animals generally are identical with those operating in man. Hence we must consider them all on this basis. Now, it has been determined already in another work that sense-perception in [456a1] animals originates in the same part in which movement originates. This is one of three determinate places, viz. that which lies midway between the head and the abdomen. This in sanguineous animals is the region of the heart; for all sanguineous [5] animals have a heart; and from this it is that both motion and the controlling sense-perception originate. Now, as regards movement, it is obvious that the origin of breathing and of the cooling process generally takes its rise there; and it is with a view to the conservation of the heat in this part that nature has provided respiration [10] and the process of being cooled by moisture. Of this per se we shall treat hereafter. In bloodless animals, and insects, and such as do not respire, the connatural spirit is seen puffed up and subsiding in the part which is in them analogous. This is clearly observable in the holoptera as wasps and bees; also in flies and such creatures. And since to move anything, or do anything, is impossible without strength, and holding [15] the breath produces strength—in creatures which inhale, the holding of that breath which comes from without, but in creatures which do not respire, of that which is connatural (which explains why winged insects, when they move, are perceived to make a humming noise, due to the friction of the connatural spirit colliding with the diaphragm of the holoptera); and since every animal moves if some sense-perception, [20] either internal or external, occurs in the primary organ of sense, accordingly if sleeping and waking are affections of this organ, the place in which and the organ in which sleep and waking originate, is evident.
Some persons move in their sleep, and perform many acts like waking acts, but not without an image or an exercise of sense-perception; for a dream is in a certain [25] 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, had been explained in the work on Problems.
3 · The point for consideration next in order to the preceding is:—What are [30] 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 ultimate form is, in sanguineous animals, the natural substance blood, or, in bloodless animals, that which is analogous to this; and since the veins are the place of the blood, while the [456b1] origin of these is the heart—this is clear from the dissections—it is manifest that, when the external nutriment enters the parts fitted for its reception, the exhalation enters into the veins, and there, undergoing a change, is converted into blood, and makes its way to their source. We have treated of all this when discussing the [5] subject of nutrition, but must here recapitulate what was there said, in order that we may consider the beginnings of the process, and come to know what happens to the 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 [10] impotence. And 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 possible that one who had swooned should fall asleep, the image might be a dream. Persons who have fallen into a deep trance, and have come to be regarded as dead, say many [15] things while in this condition. The same view, however, is to be taken of all these cases.
As we observed above, sleep is not any impotence of the perceptive faculty, but this affection is one which arises from the exhalation attendant upon the process of nutrition. The matter exhaled must be driven onwards to a certain point, then turn [20] back and change like a tide-race. Now, in every animal the hot naturally tends to move upwards, but when it has reached the parts above, 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 liquid and the corporeal, which is [25] 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 repulsed the hot, sleep comes on, and the animal is presently asleep. A confirmation of this appears from considering the things which induce sleep; they all, whether potable or edible, for instance [30] poppy, mandragora, wine, darnel, produce a heaviness in the head; and persons borne down and nodding 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 exhalation 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 [457a1] cold, like food 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, [5] 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 [10] 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 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 [15] 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 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 they do not even turn the neck; for in them, as in persons deeply intoxicated, there is ever a large quantity [20] of moisture ascending. It is reasonable, 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 for the moisture to flow down through them; while in the case of dwarfs and those whose heads are abnormally large, the impetus of the [25] exhalation upwards is excessive. Those whose veins are large are, thanks to the easy flow through the veins, not addicted to sleep, unless, indeed, they labour under some other affection which counteracts this. Nor are the ‘atrabilious’ addicted to sleep, for in them the inward region is cooled so that the quantity of exhalation in their case is not great. For this reason they have large appetites, though spare and lean; [30] 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 wheresoever such secretion is potentially present.
[457b1] Hence it is plain from what has been said that sleep is a sort of concentration, or natural recoil, of the hot matter inwards, due to the cause above mentioned. Hence restless movement is a marked feature in the case of a person when drowsy. But where it begins to fail, he grows cool, and owing to this cooling process his eye-lids droop. Accordingly the upper and outward parts are cool, but the inward [5] and lower, i. e. the parts at the feet and in the i
nterior 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 [10] 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 exhalation ascends thither? Or, as those who have hot water poured on them feel a sudden shiver of cold, just so in the case before [15] us, may it be that, when the hot substance ascends, the cold rallying to meet it cools them, deprives their native heat of all its power, and compels it to retire? Moreover, when much food is taken, 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 [20] element 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 it forces the hot back again and flows downwards. Hence it is that men sink down 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 unconsciousness, [25] and afterwards imagination.
Or are the solutions thus proposed possible accounts of the refrigeration which takes place, while, as a matter of fact, the region of the brain is, as stated elsewhere, the main determinant of the matter? For the brain, or in creatures without a brain that which corresponds to it, is of all parts of the body the coolest. Therefore, as [30] 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 water once more; just so the waste exhalation, when [458a1] carried up by the heat to the region of the brain, is condensed into phlegm (which explains why catarrhs are seen to proceed from the head); while that exhalation which is nutrient and not unwholesome, becoming condensed, descends and cools [5] 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 exhalation. This, then, is a sufficient explanation of the cooling which takes place, despite the fact that the exhalation is exceedingly hot.
A person awakes from sleep when digestion is completed: when the heat, which [10] had been previously forced together in large quantity within a small compass from out the surrounding 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 [15] 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 of the two veins, the one called the ‘great’ and the ‘aorta’. It is in the central chamber [20] that the 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 in need of separation, sleep occurs until the purer part of this blood has been separated off into the upper parts of the body, and the more turbid into the lower parts. When this has taken place animals awake from sleep, being released from the heaviness [25] consequent on taking food.
We have now stated the cause of sleeping, viz., that it consists in the recoil by the corporeal element, borne upwards 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 actualize its powers; [30] 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.
**TEXT: W. D. Ross, Aristotle: Parva Naturalia, Clarendon Press, Oxford, 1955
1Reading ἐπεί (Susemihl) for ἔτι.
ON DREAMS**
J. I. Beare
1 · We must, in the next place, investigate the subject of the dream, and first inquire to which of the faculties of the soul it presents itself, i.e. whether the [458b1] affection is one which pertains to the faculty of thought or to that of sense-perception; for these are the only faculties within us by which we acquire knowledge.
If, then, the exercise of the faculty of sight is seeing, that of the auditory faculty, hearing, and, in general that of the faculty of sense-perception, perceiving; and if there are some perceptions common to the senses, such as figure, magnitude, [5] motion, &c, while there are others, as colour, sound, taste, which are special; and further, if all creatures, when the eyes are closed in sleep, are unable to see, and the analogous statement is true of the other senses, it is clear that we perceive nothing when asleep; we may conclude that it is not by sense-perception we perceive a dream.
But neither is it by opinion that we do so. For we not only assert, e.g., that some [10] object approaching is a man or a horse, but that the object is white or beautiful, points on which opinion without sense-perception would say nothing either truly or falsely. It is, however, a fact that the soul makes such assertions in sleep. We seem to see equally well that the approaching figure is a man, and that it is white. Again, we think of something else, over and above the dream, just as we do in waking [15] moments when we perceive something; for we often also reason about that which we perceive. So, too, in sleep we sometimes have thoughts other than the images. This would be manifest to any one who should attend and try, immediately on arising from sleep, to remember. There are cases of persons who have seen such dreams, [20] those, for example, who believe themselves to be mentally arranging a given list of subjects according to the mnemonic rule. They frequently find themselves to be mentally putting into its place some other image apart from the dream. Hence it is plain that not every image in sleep is a dream, and that the thinking which we perform then is due to an exercise of the faculty of opinion. [25]
So much at least is plain on all these points, viz. that the faculty by which, in waking hours, we are subject to illusion when affected by disease, is identical with that which produces illusory effects in sleep. So, even when persons are in excellent health, and know the facts of the case perfectly well, the sun, nevertheless, appears [30] to them to be only a foot wide. Now, whether the imaginative faculty of the soul be identical with, or different from, the faculty of sense-perception, in either case the thing does not occur without our seeing or perceiving something. Even to see wrongly or to hear wrongly can happen only to one who sees or hears something real, though not exactly what he supposes. But we have assumed that in sleep one [459a1] neither sees, nor hears, nor exercises any sense whatever. Perhaps we may regard it as true that the dreamer sees nothing, yet as false that his faculty of sense-perception is unaffected, the fact being that the sense of seeing and the other senses may possibly be then in a certain way affected, while each of these affections, as [5] when he is awake, gives its impulse in a certain manner to his faculty of sense, though not in the same manner as when he is awake. Sometimes, too, opinion says, just as to those who are awake, that it is false; at other times it is inhibited, and follows the image.
It is plain therefore that this affection, which we name dreaming, is no exercise of opinion or thought but yet is not an affection of the faculty of perception in the [10] simple sense. If it were the latter it would be possible to hear and see in the simple sense.
How then, and in what manner, it takes place, is what we have to examine. Let us assume, what is indeed clear enough, that the affection pertains to sense-perception as surely as sleep itself does. For sleep
does not pertain to one organ in animals and dreaming to another; both pertain to the same organ.
[15] But since we have, in our work on the soul, treated of imagination, and the faculty of imagination is identical with that of sense-perception, though the being of a faculty of imagination is different from that of a faculty of sense-perception; and since imagination is the movement set up by a sensory faculty when actually discharging its function, while a dream appears to be an image (for which occurs in [20] sleep—whether simply or in some particular way—is what we call a dream): it manifestly follows that dreaming is an activity of the faculty of sense-perception, but belongs to this faculty qua imaginative.
2 · We can best consider the nature of the dream and the manner in which it originates by regarding it in the light of the circumstances attending sleep. The [25] objects of sense-perception corresponding to each sensory organ produce sense-perception in us, and the affection due to their operation is present in the organs of sense not only when the perceptions are actualized, but even when they have departed.