Aristotle · a new plain-English translation from the original language
1| Why, if a man has intercourse, are his eyes especially weakened? Is it clear that this happens because the moisture is depleted? A proof that seed is cold is this: it does not become moist unless the hot parts heat it through. Nor does it need melting, for it is already in a fluid state within the man, just like blood. E. Problems Connected with Fatigue Why are walks that are long on level ground more tiring than uneven ones, while short ones are less tiring? Is it because both abundant motion and forceful motion produce fatigue? Motion of the jolting kind is forceful, and continuous, uniform motion is abundant. Now on uphill ground, if the walk is long, the change of position becomes a kind of rest, and the motion is not long, nor even for the horses themselves, because of the change; but on level ground, the uniformity of posture does not divide up or rest the parts, but rather works together to make the motion continuous. When the walk is short, on flat ground no fatigue results, because of the sheer quantity of motion required to tire; but on uphill ground, because the change becomes forceful and opposite — now upward, now downward — it produces fatigue. Such change occurs, as we say, on uphill ground, but on level ground the opposite is the case.
2| Why do people who faint, and people who are worn out from exercise, seem to have smaller bodily bulk and shriller voices? Is it because voices that appear smaller also appear shriller (a sign of this is that when people imitate those speaking from far off, they pitch their voice high), and their bulk is smaller as well? Why is the belly the only part that gets thin from exercise? Is it because the fat is greatest around the belly? Why does fat get rubbed away in those who work hard, while flesh does not? Is it because fat melts when heated, and motion produces heat, while flesh does not melt? Why are the parts around the belly the fattest? Is it because they are close to the food? For while the other parts receive their nourishment from the belly, the belly itself often takes it directly and repeatedly. Or is it because the belly does the least work, since it has no joints to bend? Why does fatigue stop more effectively when someone mixes water with oil and rubs it in? Is it because the oil penetrates more when mixed with water? For if it is used by itself, it does not penetrate in the same way, because it tends to float on the surface. So the body is softened more when the mixture penetrates, since oil is by nature hot, and hot things both dry and harden, and dryness and hardness are unfavorable against fatigue; but oil rubbed in with water dries less.
4| Why do they instruct the fatigued to vomit, if vomiting itself is fatiguing? Is it because fatigue arises from bones being bruised, pressed, and strained, and this can happen to them from something outside the body or from something within it, and in two ways: either because the flesh is stretched beyond its own capacity, or because a considerable quantity of matter is mixed into the rest of the body without having a proper place of its own, as is the case with residues? For all external weights fastened onto us are more fatiguing than the body's own parts, even if they happen to be lighter in weight than those parts. A sign of what has been said is this: those who have eaten and drunk more, though they have exerted themselves less than those who are fasting, become more fatigued, because the food, being undigested, does not have its proper place. And since fatigue produces a wasting-away, and this wasting-away is a residue, it is this residue that produces fatigue in us, wandering about in disorder and falling upon the bones and sinews and the loose, open interior parts of the flesh. Vomiting, then, by expelling this very thing, which is the cause of the fatigue, naturally makes people free of fatigue; for the body is left as it was at the start of the exertion. But vomiting is fatiguing not because of any excess in the motion that occurs in it, but when it happens that one does not vomit thoroughly; for when much food is left behind, with residues present in it, the fatigue that comes from vomiting occurs, just as has been said in the case of those who are overfull. If, then, in those cases too the exertion is not the cause of the fatigue, but rather being in that condition and then exerting oneself, then neither would vomiting be the cause of fatigue for those who do not expel the food; for fatigue would have to occur in everyone who vomits, yet many people become less fatigued after vomiting.
5| Why is it more fatiguing for the arm to throw at nothing than to throw a stone? Is it because throwing at nothing produces more of a wrench? For it finds no resistance to brace against, as the thrower does against the missile in his hand. Similarly with this is the pentathlete against his jumping-weights, and the runner swinging his arms. This is why the one jumps farther when he has jumping-weights than when he does not, and the other runs faster swinging his arms than not swinging them. Why does running at speed, in a human being as in other animals, produce diseased conditions in the region of the head? And yet running as a whole seems to draw the residues downward, just as walking does; this is why the legs of those who walk a great deal become thick, because both the nourishment and the residues migrate downward from above. Is it, then, that the motion produces the same effect, but the rapid motion, on account of the strain and the holding of the breath, heats the head excessively, and inflates the veins in it, and makes it susceptible to being seized by external forces, such as cold and heat and the effects coming from the chest, and when these enter, that region is necessarily thrown into disease?
6| Why do people grow more fatigued on level ground than on uneven ground, yet walk a level road faster than an uneven one? Is it because it is less fatiguing not always to make one's motion in the same posture, which happens more in uneven walking? For people walk faster on it because they move less against nature. On level ground the lifting and the setting-down of the foot are small and frequent, while on uneven ground the opposite holds. Now lifting is against nature, for every lifting involves force. And what is small in each single step becomes great over many steps. Why is it more fatiguing to lie down on flat surfaces than on hollow ones? Is it for the same reason that convex surfaces are more fatiguing than flat ones? For weight gathered onto a single spot, in sitting or in lying down, produces distress through the pressure. Now a convex surface has this quality more than a straight one, and a straight one has it more than a hollow one; for our body is more curved than straight, and hollow surfaces come into contact with such shapes over a greater area than flat ones do. For these same reasons, surfaces that give way are less fatiguing to lie and sit on than surfaces that do not give way.
7| Why are short walks fatiguing? Is it because they are uneven? For they often involve stopping. And changing frequently from one state to its opposite is fatiguing, since it allows no habituation to either, and habituation is what makes something free of fatigue. But habituation to both at once is not possible. Why do the eyes of people riding on horseback water more, the faster the horse runs? Is it because the air that keeps striking them is colder the shorter the time it stays in contact with the body, which is what happens with people running unclothed? And cold produces tears. Or is it for the opposite reason? For heat too produces tears, as the sun does, and motion produces heat. Or is it because of the blow from the air? For just as winds blowing against the eyes from the front disturb them, so too the air striking against them delivers a softer blow the faster it drives.
8| Why do other parts of the body become fleshier when rubbed, while the belly becomes thinner? Or does even the belly not become thinner exactly, but rather firmer through this treatment, though not in the same way as the flesh does, which is why this is a problem at all? For in general it is in exercises and exertions above all that the belly grows thin. The cause is that fatty things melt when heated, and things that by nature already have tension melt more readily. Now the skin is by nature possessed of tension; but because it fattens very quickly, it always has some measure of fatness, unless it happens to be afflicted by some disease. The cause of this is that it is close to the nourishment. Since, then, fat as a whole is not present by nature but is acquired, and is not one of the necessary parts as flesh is, both the motion of exercise and the motion of massage, by heating it, melt it away and distribute the excess nourishment to the other parts. This is why sitting still fattens the belly while making the rest of the body thinner, whereas motions and massage make the belly thinner while making the rest of the body thicker.
9| Why is it that after long, hard walks and runs, when a person stands on the tips of the toes, the heels of the feet shake and are pulled downward and forward? Is it because, on account of the continuity and intensity of the motion, the shaking of the sinews does not settle down in a person? For the soul often has control of the whole body, but not of its parts, whenever they are set in motion in some way, as with the heart and the genitals. The cause is that a great deal of breath is kindled around the sinews, and this does not cool off at the same moment that the person stops. So this breath, shaking the sinews as it were pulls them out from under, is dragged down, and makes control least possible over the part that is farthest away; and the heels are just such a part, as the lower lip is for people who are angry. Why is it that people who are not running very intensely breathe in rhythm? Is it because every rhythm is measured by a definite motion, and such is the motion that proceeds by equal steps, which is what people running at a trot do? So as soon as they begin to trot they breathe accordingly, so that the breathing, occurring by equal steps because it is measured by an equal motion, produces rhythm. Or is it because absolutely all breathing occurs by equal steps in those who use it naturally and do not hold it back? So when people are sitting or walking, since the motion of the body is moderate, the rhythm does not become obvious; but when they run intensely, since perception does not keep pace with the motion, we cannot take in the rhythm of the breathing together. But in moderate trotting, the motion, being a perceptible measure of the breathing, makes the rhythm evident.
10| Why is it that in trotting the air seems to us to turn into wind? Is it because, being set in motion by trotting, we set in motion the air that is continuous with our bodies, and this is breath? That is why the air not only seems to but in truth does turn into wind. Or is it because in trotting we strike against the air, and when this happens we perceive the air more, through the motion? So it is reasonable that it seems to us to turn into wind; for this is what happens on account of the forward motion. Why is it that people fall more often running than walking? Is it because they lift the foot more before it moves? For this is how running differs from walking. Why is it that going up we feel the strain in our knees, but going down in our thighs? Is it because when we go up, we throw the body upward, and the great pull on the body comes from the knees as well, which is why we feel it in the knees; whereas on downward slopes, because the legs are carried forward under us, we brace ourselves on the thighs and so feel it in them. And further, everything that occurs contrary to nature produces strain and distress. Now what is natural for the knees is to bend forward, and for the thighs to bend backward. So on upward slopes the knees bend backward, because they want to brace against something, while on downward slopes the thighs bend forward, because our body is inclined to pitch forward.
11| Why is it that on long walks we feel the strain most in the middle of the thighs? Is it because, in anything long and continuous, when the middle is held fixed, the strain occurs there most of all? That is also why breakage occurs there most of all. And the thigh is just such a thing; that is why we feel the strain most in its middle. Why do people who are moist choke quickly when they exert themselves and when they are overheated? Is it because moisture, when heated up, turns into air, and the more there is of it, the more it burns? So when it cannot escape on account of its quantity, no cooling occurs, and it is quickly set ablaze by the innate heat together with the acquired heat. That is also why the sweats that occur in people exercising, and in general in people exerting themselves, and the discharge of breath, are beneficial; for as the moisture is separated out and made thin, breath is produced. Why is it that well-proportioned bodies often fall ill, yet recover more easily? Is it for the same cause in both cases? For what is well-proportioned is uniform, and what is uniform shares more in the same affections; so if some part suffers, at once the whole suffers along with it. But what is disproportionate, being more disjointed, does not share the enjoyment of its parts. So a well-proportioned body falls ill often for this reason, but recovers more easily because the whole body has a share in it; for the affection, being distributed among more parts, becomes weaker, and so is more easily got rid of. The disproportionate body, on the other hand, since it does not share the affection among its parts, falls ill less often, but recovers with more difficulty, since the affection is intense.
12| Why is it that people grow weary more on level ground than on uneven ground, yet walk the level road faster than the uneven one? Is it because it is least wearying not always... (the text breaks off here) on the uneven course more, but they travel faster where, in an equal time, there is less lifting of the foot? So on level ground the lifting is small and frequent, while on uneven ground it is the opposite. And what occurs a little with each step becomes a great deal over many steps. Why is it that going down slopes we feel the strain most in the thighs, but going up in the shins? Is it because in going up we lift the body? For the whole body becomes a burden. So whatever the whole weight rests on, and by which we lift it, feels the strain the most. And this is the shin. For it is the extreme part, having length, and not, like the foot, having breadth; that is why it is unsteady. So it is as though we move weights by the shoulder, and support them on it. That is precisely why we feel the strain most in the shoulder. But going down, since the body falls forward and is thrust ahead contrary to nature, the strain is felt in whatever part the body falls onto most and makes unsteady. Now the shin stays still, and the weight becomes the chest; but the thigh receives the fall and is made unsteady, because it has length and turns from above, at the point where the chest falls onto it.
13| Why does a road seem longer when we walk it without knowing how long it is, than when we know, other things being equal? Is it because to know how long it is, is to know its number; and the indefinite always seems greater than the definite? Just as, if one knew that it was of a certain length, it would necessarily be limited, so too, even when one does not know, the soul reasons falsely as though the reverse were the case, and the road appears unlimited. Further, quantity is what is definite, and the definite is quantity. So whenever something does not appear definite, it appears unlimited, because what is naturally definite, if it is not definite, is unlimited; so what appears undefined must in some way appear unbounded. Why do people feel weary in the thighs more than in the shins? Is it because the thighs are near the region that holds the residue, so that if it becomes excessive through the heat produced by motion, the thighs contract more, and more, than the shins? Or is it because the thighs are more continuous with the trunk? For they feel the strain most through the separation of what is continuous. And indeed even when people have no residue at all and grow weary, they still feel the strain in the thighs and the lower back more. Or is it that, just as swellings in the groin occur from a blow because of the connection of the veins and sinews, so it is here too? And the thigh is nearer to the source. Or is it because the thigh stays in the same posture more than the shin does? And this is more wearying. Or is it because it is fleshy, so that there is much that is natural to it in its own right?
14| Why is it that in some people, when they exert themselves, sores break out? Is it because, when the body is unclean, the motion, by heating it, draws off other residues along with the sweat? And since these are thick and contain bad humors — sharp, bitter, and salty — the residues cannot be excreted because of their thickness, but are lifted up through the flesh and cause sores because of the bitterness of the humor. Why is it that people are not given food right away after exercise or after taking medicine? Is it because the body is still being purged, and has not yet ceased its exertion, and the residues have not yet been separated out? Why is it harder to run than to walk? Is it because the runner carries a greater burden? For whenever the body is airborne, it bears the whole of itself upon itself. But the walker, like people resting against low walls, has part of the weight resting on what is at rest. Why is it that people are not hungry right after exercise? Is it because of the residue left over from the wasting away of the body, until this is digested in turn? Or is it because of the breath that exertion produces out of the moisture? Or is it because of the thirst that arises from being heated by the exertion? For all of these things happen together.
15| Why do the exhausted and the wasting-away have nocturnal emissions? Is it because, in general, the hot and moist are prone to nocturnal emissions? For semen is by nature of that sort. And such a thing arises most from bodies so disposed, when the heat that comes from sleep is added to them; for their bodies need only a slight tip of the scale, and this from within, not from without. Now the consumptive and the exhausted are disposed in just this way: the exhausted are full of hot molten residue because of their fatigue and exertion, while the consumptive are so because of their catarrh and the heat produced by the inflammation. Why is it harder to rub the left leg against itself for a long time than the right? Is it because we are able to labor with the right leg? In movements contrary to nature, the rubbing of the left leg happens in a reversed way, and things done contrary to nature are difficult. But to the left leg the right is nothing noticeable, because it is not strong in either direction. Why is it healthy to cut back on food but do more exercise? Is it because the cause of disease is an abundance of residue? And this arises either from an excess of food or from a deficiency of exertion.
16| Why should one not make the flesh dense for the sake of health, but rather porous? For just as a city is healthy, and a place well-ventilated is healthy (which is also why the sea is healthy), so too a body that is well-ventilated is the more healthy. For either no residue at all must be present, or it must be got rid of as quickly as possible; and bodies must be in such a condition that, as soon as they take in food, they excrete the residue, and be in motion and not at rest. For what stays in place putrefies, like standing water, and what putrefies and is not moved produces disease; but what is excreted before it spoils is removed in time. This, then, does not happen when the flesh is dense (for the pores are as it were blocked up), but it does happen when the flesh is porous. That is also why one should not walk about naked in the sun; for the flesh contracts, and people become altogether stripped of flesh, and the body becomes moister. For what is inside then remains, while what is on the surface is got rid of, just as boiled meats lose more than roasted ones. Nor should one walk about with the chest bare; for from the best-built bodies the sun takes away what least needs taking away, when it ought rather to take from what is inside. From there, then, because it is far off, sweat cannot be drawn up unless with exertion, but from the surface, because it is close at hand, it is easy.
17| Why are short walks tiring? Is it because there is frequent stopping, and the motion around the turns is uneven? And such a thing is tiring. Why do people standing still in the sun grow hotter than those in motion, even though motion produces heat? Is it that not every motion heats, but some cools, as happens also with people who blow on and stir boiled pots? If, then, heat stays with one who stands still, and staying heats more than moving does (for our body is always giving off from itself a certain warm vapor of its own, which heats the air nearby as a firebrand does when present), then when we are at rest the air surrounding us becomes hot for the reasons stated, but when we are in motion it becomes a wind, which cools us; for all wind is cold.
18| Why do those riding on horses weep more from the eyes the faster the horse runs, and likewise those on foot the faster they run? Is it because the air striking them is cold? For cold produces weeping; by contracting and condensing the flesh it purges out the moisture. Or is it for the opposite reason? For heat produces sweats, and a tear is a kind of sweat. That is why both of these arise from heat, and both are equally salty. And motion produces heat. Or is it because of the blow dealt by the air? For just as winds blowing from opposite directions disturb the eyes, so too the air that strikes us, the faster it is driven, or the faster one runs oneself, the more it deals a soft blow, and it is because of this blow that weeping occurs, the pores of the eye being loosened by the blow; for every blow either divides or bruises. Why must summer fatigue be cured with a bath, but winter fatigue with an anointing of oil? Is it because winter fatigue, on account of the shivering and the changes that occur, must be relieved with heat, which the oil will produce by warming (for oil is hot); whereas in summer one must moisten? For the season is dry, and no shivering occurs because of the warmth. And scant eating and heavy drinking occur in summer, the one entirely, the other more: drinking occurs entirely in summer because of the dryness, while scant eating is common to both seasons but more marked in summer, since the body is heated more by food on account of the season.
19| Why do those who run vigorously get the worst strains, when someone stands in their way as they run? Is it because those things are torn apart the most which are pulled and set in motion strongly in opposite directions at once? So when someone stands in the way of a runner whose parts are being thrust forcefully forward, it happens that a counter-pull toward the opposite direction occurs at the very moment that they are still being carried forward, so that the strain becomes stronger the more violently they are running.
20| Why, among walks along roads, are the uneven ones less tiring than the level ones? Is it because an upright bearing is natural to the whole body? Walks on level ground are more tiring than those on uneven ground; for they impose the exertion on the same parts, while walks on uneven ground distribute it more over the whole body. And walks in warm weather make people thinner more than walks in cold weather; for they impose more exertion on the outer parts, and that is why, by producing sweats, they make people thinner. But walks in cold weather make the flesh tighter and make people more desirous of food; for they produce an increase of heat in the inner parts, and, since the outer parts become hard to move because of the cold, they purge the inner region, increasing the heat within it, and they make the flesh solid, being unable to master it throughout. Likewise, uphill walks are more laborious and more thinning than downhill ones. For uphill walks make especially the lower back labor, while downhill ones make the thighs labor; for the whole weight, falling upon the thighs, tends to produce fatigue. For the heat, being carried upward against nature by force, heats thoroughly. That is why uphill walks produce sweats, and by raising the breath make one thinner, and cause pain in the lower back; for the legs, being lifted with difficulty, bend and pull back the lower back, and it is by this that people are compelled to labor most. Walks on resistant ground cause fatigue in the muscles and the stretched parts of the legs; for they produce tension in the sinews and the muscles, since the pressure against them becomes forceful. Walks on soft ground are also tiring to the joints; for they cause frequent bendings of the joints, since the footing gives way beneath them. And this is the same problem.