Aristotle · a new plain-English translation from the original language
1| For it stands to reason that the cycles of the less authoritative things should follow those of the more authoritative ones. For wind too has a kind of life, and generation and decay. But of the revolution of these heavenly bodies there might perhaps be certain other principles again. Nature, then, wishes to number the generations and endings of things by the numbers proper to these bodies, but does not achieve exactness, both because of the indeterminacy of matter and because many principles arise, which, by obstructing the generations and destructions that occur in accordance with nature, are often the causes of the things that happen contrary to nature. Concerning, then, the nourishment of animals from within and their generation to the outside, we have spoken, both about each severally and in common about all.
2| Now we must consider the affections by which the parts of animals differ. I mean by such affections of the parts, for example, blue-grayness of eyes and blackness, and sharpness and deepness of voice, and difference of color [or of body] and of hairs or feathers. Now it happens that some of such things belong to whole kinds, while in others it is a matter of chance, as this has come about especially in the case of humans. Further, in accordance with the changes of age, some of these belong alike to all animals, while others are opposite, as with voices and with the color of hairs; for some animals do not visibly turn gray toward old age, while man is affected by this most of all animals. And some follow immediately upon birth, while others become evident as age advances and as animals grow old. But concerning these and all such matters we must no longer suppose the cause to be of the same kind. For whatever things are not works of nature in common, nor peculiar to each kind, none of these exists or comes to be for the sake of anything. For the eye exists for the sake of something, but its being blue-gray is not for the sake of anything, except insofar as this affection is peculiar to the kind.
3| But in some cases the account does not bear on substance at all; rather, since these things come about of necessity, the causes must be traced back to matter and to the principle that produced the motion. For as was said at the outset, in the first arguments, it is not because each thing comes to be of a certain quality that it is of that quality—at least as regards all those works that are ordered and determinate products of nature—but rather, because it is of a certain quality, it comes to be such: for generation follows on substance and is for the sake of substance, and substance is not for the sake of generation. But the ancient natural philosophers thought the opposite. The reason for this is that they did not see that the causes are several; they saw only the cause of matter and the cause of motion, and even these without making distinctions, while they gave no consideration at all to the cause that operates through the account and the cause that operates through the end. Each thing, then, exists for the sake of something, but it comes to be for the sake of this cause and also for the sake of the rest, all those that are contained in the account of each thing, whether as being for the sake of something or as being that for the sake of which. But for those things that are not of this kind, of which there is nevertheless generation, the cause must now be sought in the motion and the generation, on the supposition that the differentia is taken in the very process of formation.
4| For an animal will have an eye of necessity (since it is posited as being an animal of a certain kind), but it will have an eye of such-and-such a kind of necessity too—not the same kind of necessity, but in another way, because it is the nature of such-and-such a thing to act on and be acted on by such-and-such another. Now that these points have been distinguished, let us speak of what happens next in order. First, then, when the young of all animals are born—especially the incomplete ones—they are accustomed to sleep, because even in the mother, once they first receive perception, they continue sleeping. But there is a puzzle about the generation from the beginning: whether waking belongs to animals before sleep, or the reverse. Because it is observed that as age advances they wake more, it would seem reasonable that the opposite holds at the beginning of generation—namely sleep. And further, because the transition from not-being to being comes about through an intermediate state; and sleep seems by its nature to be a thing of this kind, a kind of boundary between living and not living, and the sleeper neither altogether is not, nor altogether is. For it is by waking, above all, through perception, that living belongs to a thing. But if it is necessary that an animal have perception, and it is first an animal precisely when perception first arises in it, then the disposition it has from the beginning must be reckoned not as sleep but as something like sleep, the sort of disposition the class of plants also has;
5| for indeed it happens that during this time the animals live the life of a plant. But it is impossible for sleep to belong to plants; for no sleep is unwakable, whereas the affection in plants that is analogous to sleep is unwakable. Now it is necessary that animals sleep for the greater part of the time, because growth and weight bear down on the upper regions—we have stated the cause of sleeping, of this kind, elsewhere. But nevertheless they are observed to wake even in the womb (this becomes clear from dissections and in egg-laying animals), and then immediately they sleep again and sink back down. That is also why, once they have come out, they spend the greater part of the time sleeping. And infants do not laugh while awake, but while asleep they both weep and laugh. For perceptions do occur to animals even while asleep—not only what are called dreams, but also apart from the dream, just as with those who get up and do many things while asleep without dreaming. For there are some who, while sleeping, get up and walk about, seeing as those awake do. In these people perception of what is going on does occur, though they are not awake, yet not in the manner of a dream either. And infants seem, as if unacquainted with waking, to perceive and to live by habit in the state of sleep.
6| As time goes on, and growth shifts toward the lower part of the body, they now wake more, and spend the greater part of the time this way. But more than the other animals, in the first period they continue in sleep, for they are born the most incomplete among complete animals, and have their growth chiefly in the upper part of the body. The eyes of infants are all bluer-gray immediately at birth, but later they change to the coloring that is going to belong to them; in the other animals this does not happen in any noticeable way. The cause of this is that the eyes of the other animals are, on the whole, more single-colored—for example, cattle are black-eyed, the eyes of sheep are all watery-pale, while the whole class of some animals is gray-blue or bluish-gray, and some are goat-eyed, just as the goat kind itself, as a whole, is. But the eyes of human beings turn out to be many-colored: for there are some who are bluish-gray, some gray-blue, some black-eyed, and some goat-eyed. That is also why, just as they do not differ from one another, so too they do not differ from themselves; for it is not natural for an eye to have more than one color. But of the other animals, the horse is the most many-colored: for some of them even have eyes of two different colors. This happens to none of the other animals noticeably, but some human beings are born with eyes of two different colors.
7| Now the fact that the other animals show no noticeable change when young and when older, while this does happen with infants, should be reckoned a sufficient cause too: that the part in question is single-colored in the one case, many-colored in the other. And the cause of their being bluer-gray and not yet having their other color is that the parts of the young are weaker, and bluish-grayness is a kind of weakness. One must grasp, in general, concerning the difference among eyes, for what cause some are bluish-gray, some gray-blue, some goat-eyed, some black-eyed. Now the supposition that the bluish-gray are fiery, as Empedocles says, while the black have more of water than of fire, and that for this reason the bluish-gray do not see sharply by day, from lack of water, while the others do not see sharply by night, from lack of fire—this is not well said, at least if one must posit that vision belongs to water and not to fire, for all eyes alike. Further, it is possible to give the cause of the colors in another way as well; but if it is as was said earlier in the works on the senses, and even earlier than these in the works on the soul, that the organ of sight is of water, and for what cause it is of water and not of air or fire, that must be supposed to be the cause of what has been said.
8| For some eyes have more of the moisture, others less than the proportionate amount of motion, and others a proportionate amount. Now those eyes that have much moisture are black-eyed, because the moisture is for the most part not easily seen through, while those with little are bluish-gray, just as is also apparent in the case of the sea: the part of it that is easily seen through appears bluish-gray, the part that is less watery appears darker, and the part that is indistinct through depth appears black and dark blue. The eyes in between these differ, at this point, by a matter of more and less. And the same cause must be supposed also for the fact that the bluish-gray eyes are not sharp-sighted by day, while the black eyes are not sharp-sighted by night. For the bluish-gray, because of the scantiness of the moisture, are moved more by the light and by visible objects, insofar as it is moist and insofar as it is transparent. And further, the motion of this part is vision insofar as it is transparent, but not insofar as it is moist. The black-eyed, because of the abundance of the moisture, are moved less. For the light at night is weak; and at the same time, at night, the moisture as a whole becomes hard to move. But it must neither fail to be moved at all, nor be moved more than as transparent; for the stronger motion drives out the weaker.
9| This is also why people fail to see when they change from strong colors, and when they pass from sunlight into darkness: since the motion already present in the eye is strong, it blocks the motion coming from outside. And in general, sight that is neither strong nor weak is unable to see bright things well, because the moisture is affected more and set in motion by them. The disorders of each kind of sight make this clear too. For glaucoma occurs more in gray eyes, while what is called night-blindness occurs in black eyes. Glaucoma is rather a kind of dryness of the eyes, and this is why it happens more as people grow old: for these parts, like the rest of the body, dry out toward old age. Night-blindness, on the other hand, is an excess of moisture, and this is why it occurs more in the young, since their brain is moister. The vision that is intermediate between much and little moisture is best: for it is neither so scant that its disturbance impedes the motion of the colors, nor does its abundance make it hard to move. But it is not only the causes stated that account for dull or sharp sight, but also the nature of the skin over what is called the pupil. This must be transparent, and for that it must necessarily be thin and white, and even, so that it does not cast a shadow when it wrinkles (and this, indeed, is why old people do not see sharply
10| — for like the rest of the skin, the skin of the eye too wrinkles and grows thicker as people age), and it must be white because black is not transparent: for this is exactly what black is, that which does not let light show through it. This is also why lanterns cannot give light if they are made from such skin. So in old age and in diseases people do not see sharply for these causes, while children's eyes appear gray at first because of the small amount of moisture. Human beings and horses in particular develop eyes of two different colors, for the same reason that man alone among animals goes gray-haired, while of the other animals only the horse, as it visibly grows old, turns white in its hair. For grayness of hair is a kind of weakness of the moisture in the brain and a failure of concoction, and so is grayness of the eye: for being excessively thin or excessively thick has the same effect, the one through too little moisture, the other through too much. So whenever nature is unable to bring the moisture in both eyes to completion in the same way — either concocting it in both alike, or leaving it unconcocted in both alike, but instead concocts it in one and not the other — then it happens that eyes of two different colors result. As for why some animals have sharp sight and others do not, there are two ways in which the cause is given.
11| For 'sharp' is said in roughly two senses, and the same holds for hearing and smelling. Seeing sharply is said in one sense of being able to see from far off, in another of perceiving the differences among the things seen as precisely as possible. These two do not occur together in the same creatures. For the very same person, shading his eyes with his hand or looking through a tube, judges the differences of colors no more and no less than before, but will see farther. Certainly people at the bottom of pits and wells sometimes see the stars. So if some animal has a great projection to its eye, but the moisture in the pupil is not clear nor proportioned to the motion coming from outside, and the skin covering it is not thin, this animal will not be exact about the differences of colors, but will be able to see far off just as if it were near, more so than animals whose moisture is clear and whose covering of it is clear too, but which have no brow ridge in front of their eyes. For the cause of seeing so sharply as to perceive the differences lies in the eye itself: just as on a clean garment even small stains show up clearly, so too in a clear sight even small motions are conspicuous and produce perception.
12| The cause of seeing far off, and of the motion from far-off visible things arriving at the eye, is the position of the eyes: for prominent, bulging eyes do not see well at a distance, while eyes that are set within, lying in a hollow, are able to see far-off things, because the motion is not scattered into empty space but travels in a straight line. For it makes no difference whether one says, as some do, that seeing occurs by the sight going out (for if there is nothing in front of the eyes, the sight, being scattered, must strike the things seen with less force and see distant things less well), or that seeing occurs by the motion coming from the things seen. For it is equally necessary, either way, that sight sees by means of motion. Now distant things would be seen best of all if there were a continuous channel straight from the sight to the thing seen, like a tube: for then the motion from the visible things would not be dissolved. But since this is not so, the further off the projecting structure extends, the more exactly distant things must be seen. Let these, then, be the causes of the difference among eyes.
13| The same holds in the same way for hearing and smell. For it is one thing to hear and smell precisely — perceiving all the differences among the underlying objects of perception as fully as possible — and another thing to hear and smell from far off. Now the cause of judging the differences well is the sense-organ, just as with sight, provided that it itself and the membrane around it are clear. For the channels of all the sense-organs, as has been said in the works on perception, extend to the heart, or, in animals without a heart, to the corresponding part. Now the organ of hearing, since it is a sense-organ of air, is connected by way of the air through which the connate breath produces, in some animals, the pulse, and in others, respiration and inhalation; it terminates there. This is also why learning of what is said occurs, such that one can echo back what was heard: for whatever sort of motion entered through the sense-organ, the same sort of motion again — as if from one and the same imprint — comes about through the voice, so that one says what one heard. And people yawning and exhaling hear less well than when inhaling, because the origin of the organ of hearing lies at the breath-part, and the breath is shaken and set in motion at the same time as the organ that moves it —
14| — for the organ that moves it is itself moved. And the same affection occurs in moist seasons and climates, and the ears seem to fill up with breath because they lie close to the origin of the breath-region. Now the precision of judgment concerning the differences of sounds and smells lies in the sense-organ and the surface membrane being clear: for all the motions are conspicuous, just as with sight, and the same holds in these cases too. As for perceiving from far off and not perceiving from far off, this occurs in the same way as with sight. For those animals that have, in front of their sense-organs, something like long channels running through their parts, perceive from far off. This is why animals with long nostrils, such as Laconian hound-puppies, have keen smell: for since the sense-organ lies at the far end, the motions from a distance are not dispersed but travel in a straight line, just as happens for people shading their eyes in front. Likewise for those whose ears are long and project out at a distance, as some four-footed animals have, and whose inner coil is long: for these too, receiving the motion from far off, deliver it to the sense-organ. So, one might say, man has the least precision of the senses at a distance, in proportion to his size among animals, but is the most keenly sensitive of all to differences.
15| The cause is that his sense-organ is clear and least earthy and corporeal, and man is by nature the thinnest-skinned of animals in proportion to his size. Nature has also worked out the case of the seal reasonably: for although it is four-footed and viviparous, it has no ears but only passages. The cause is that its life is spent in water: the part that forms the ears is added onto the passages in order to preserve the motion of air coming from a distance; so this part is of no use to the seal, but would even produce the opposite effect, by taking in a quantity of water. So much, then, has been said about sight, hearing, and smell.
16| Coats of hair differ, in human beings themselves, according to age, and they differ also as compared with the other kinds of animals that have hair at all. Now nearly all the animals that bear their young alive within themselves have hair; for even those of this class that have spiny growths instead must be reckoned to have a certain form of hair, for example the spines of land hedgehogs and of any other such live-bearing animal. There are differences among hairs in respect of hardness and softness, length and shortness, straightness and curliness, abundance and scantiness, and besides these in respect of color, in whiteness and blackness and the shades between these. Some of these differences also vary with age, as animals grow young or grow old. This is most conspicuous in human beings; for people grow shaggier as they grow older, and some go bald at the front of the head. Children do not go bald, nor do women; men do, once their age is already advancing. And as people grow old their heads turn gray. In none of the other animals, one may say, is this conspicuous, though it is most so in the horse among the rest. Human beings go bald at the front of the head, and turn gray first at the temples;
17| but no one goes bald either at the temples or at the back of the head. As for the animals that do not have hair but something analogous to it — birds having feathers, for instance, and the class of fishes having scales — some of these same conditions befall them too, in the corresponding way. Now for what end nature made the class of hairs for animals has been stated earlier, among the causes concerning the parts of animals; but to show what conditions must be present, and through what necessities each of these results comes about, belongs to the present inquiry. The chief cause of thickness and thinness of hair is the skin; for in some animals it is thick, in others thin, and in some loose-textured, in others dense. A further contributing cause is the difference in the moisture present in it; for in some it is oily, in others watery. For in general the nature of the skin is, as a substrate, earthy — since, being on the surface, it becomes solid and earthy as the moisture evaporates from it — while the hairs, and what is analogous to them, are formed not out of the flesh but out of the skin, the moisture in them evaporating and rising off as vapor. That is why thick hairs come from thick skin, and thin hairs from thin skin.
18| If, then, the skin is looser-textured and thicker, the hairs are thick, both because of the abundance of the earthy matter and because of the size of the pores; but if the skin is denser, the hairs are thin, because of the narrowness of the pores. Further, if the moisture is watery, since it dries up quickly, the hairs do not attain size; but if it is oily, the opposite happens, for oily matter is not easily dried. This is why, in general, the thicker-skinned animals are the thicker-haired, though not the very thickest-skinned the very thickest-haired, for the reasons stated — for example the pig kind stands to the ox and to the elephant, and to many others, in just this relation. For the same reason the hairs on the head are thickest in human beings; for here the skin is thickest and in the greatest degree of moisture, and besides it has much looseness of texture. The cause of hairs being long or short is also the fact that the moisture which evaporates is not easily dried. Of its not being easily dried there are two causes, quantity and quality; for if the moisture is abundant it is not easily dried, and likewise if it is oily. And this is why, in human beings, the hairs from the head are the longest;
19| for the brain, being moist and cool, supplies a great abundance of moisture. Hair becomes straight or curly because of the vapor rising within the hairs. For if this vapor is smoky, being hot and dry, it makes the hair curly. For the hair bends because it is carried in two motions at once: the earthy element is carried downward, the hot element upward. Being thus easily bent, through weakness it is twisted; and this twisting is the curliness of the hair. It is possible to grasp the cause in this way; but it is also possible that, because there is little moisture but much earthy matter, the hairs are drawn together as they are dried out by the surrounding air. For what is straight bends if it evaporates, and shrinks together just as a hair does when it is burned in fire, curliness being a kind of contraction due to lack of moisture, caused by the heat of the surrounding air. A sign of this is that curly hairs are harder than straight ones; for what is dry is hard. Hair is straight in those animals that have abundant moisture; for in these the moisture proceeds by flowing, not by dripping out drop by drop. And this is why the Scythians about the Pontus, and the Thracians, have straight hair; for they themselves are moist, and the air surrounding them is moist too;
20| whereas the Ethiopians and those who live in hot regions have curly hair; for their brains are dry, and so is the surrounding air. Some of the thick-skinned animals have thin hair, for the cause stated before; for the thinner the pores are, the thinner the hairs must necessarily become. This is why the sheep kind has hair of this sort; for wool is nothing but a mass of hairs. There are some animals that have soft hair but not correspondingly thin, for example the hare kind as compared with sheep; for in animals of this sort the hair lies at the surface of the skin. This is why it does not attain length, but the result is similar to what happens with fibers carded from flax; for these too have no length at all, yet are soft and do not admit of being woven. Sheep in cold regions are affected in the opposite way to human beings: for the Scythians have soft hair, while the Sarmatian sheep have hard hair. The cause of this is the same as in the case of all wild animals generally. For cold hardens by drying, through its freezing action; for as the heat is squeezed out, the moisture evaporates along with it, and both the hairs and the skin become earthy and hard. In wild animals the cause is their living out of doors; in the sheep it is the character of the region itself.
21| A sign of this is also what happens with the sea-urchins that are used against strangury. For these, because they live in cold sea-water on account of the depth (for they occur at sixty fathoms and even more), are themselves small, but have spines that are large and hard — large because the growth of the body is diverted to that point (for having little heat and not concocting their nourishment, they have much residue, and spines and hairs and things of this kind are formed out of residue), and hard and stone-like because of the cold and the freezing. In the same way it happens that other growing things too become harder and more earthy and more stony in northern regions than in southern ones, and in exposed places than in hollows; for everything is chilled more there, and the moisture evaporates. Now both heat and cold produce hardness; for moisture is made to evaporate by both, by heat in its own right, and by cold accidentally (for the moisture departs together with the heat, since no moisture exists without heat). But cold not only hardens but also compresses, whereas heat makes things looser in texture. For this same reason, too, as animals grow older, in those that have hair the hairs become harder, and in the feathered and scaly ones the feathers and the scales become harder.
22| For the skin becomes harder and thicker as animals grow older; for it dries out, and old age is, in accordance with its name, earthy, because heat leaves it and, along with the heat, moisture leaves as well. Humans go bald more conspicuously than any other animal. But this sort of affection is something general: some plants are evergreen while others shed their leaves, and among birds those that hibernate shed their feathers. Baldness in humans, in those to whom it happens, is an affection of the same sort. For leaves fall from all plants gradually, part by part, and so do feathers and hairs from those that have them, but when the affection happens all at once, it takes on the names just mentioned. For it is called going bald, and shedding leaves, [and shedding feathers]. The cause of the affection is a deficiency of hot moisture, and of moist substances the oily is most of this sort. That is why oily plants are more evergreen. But the cause of these matters must be discussed elsewhere; for there are other contributing causes for this affection as well. In plants the affection occurs in winter (for this change is more decisive than age), and likewise in the animals that hibernate (for these too are by nature less moist and hot than humans).
23| But humans have their winter and summer in the stages of life. That is why no one goes bald before engaging in sexual intercourse; it happens then, and more so in those of that natural constitution. For by nature the brain is the coldest part of the body, and sexual intercourse cools it further, for it is a discharge of pure, natural heat. It is reasonable, then, that the brain is affected first; for what is weak and in poor condition is at the mercy of a small cause and a small tipping-point. So if one reasons that the brain itself has little heat, and that the skin surrounding it must be even more so, and the nature of the hair on it, being furthest removed from the source, still more so, it would seem reasonable that going bald happens, around that age, to those capable of producing seed. For the same reason, people go bald only at the front of the head, and among animals humans alone go bald: at the front, because that is where the brain is; among animals, only humans, because a human has by far the largest brain, and the moistest. Women do not go bald, for their nature is similar to that of children: both are incapable of the discharge of seed. A eunuch, too, does not go bald, because he changes over toward the female. And eunuchs either do not grow the later-appearing hairs, or shed them if they happen to have them already, except for the pubic hair.
24| For women too lack some of these hairs, but grow others at puberty. This mutilation is a change from the male toward the female. The reason that hibernating animals grow thick coats again, and plants that have shed their leaves grow leaves again, but bald men do not grow hair again, is that for the former the seasons are more truly turning-points of the body's condition, so that when the seasons change, growing and shedding change with them—feathers and hair in the one case, leaves in plants in the other. For humans, winter and summer and spring and autumn occur according to the stage of life, so that, since the stages of life do not turn back, the affections that depend on them do not change back either, even though the cause is similar. On the other affections of the hair, then, this is roughly what has been said.
25| In the other animals, the cause of their colors—both of being one uniform color and of being variegated—is the nature of the skin. In humans, it is responsible for nothing except gray hairs—not those due to old age, but those due to disease. For in the disease called leuke, the hairs become white. But if the hairs are white, the whiteness does not follow through to the skin. The reason is that the hairs grow out of the skin; so when the skin has become diseased and white, the hair falls sick along with it, and the disease of hair is grayness. But the grayness of hair that comes with age arises through weakness and a deficiency of heat. For every stage of life, as the body declines, tends toward coldness, and in old age especially; for old age is cold and dry. One must understand that the nourishment arriving at each part is concocted by the heat proper to that part, and when that heat is unable to concoct it, the nourishment spoils and a defect or disease results. A more precise account of this sort of cause must be given later, in the treatise on growth and nourishment. So in those people whose hair is by nature low in heat, and in whom the moisture entering is more abundant, since the heat proper to the hair is unable to concoct it, it putrefies through the heat present in the surrounding air.
26| All putrefaction comes about through heat, but not heat that is innate, as has been said elsewhere. Putrefaction occurs in water and earth and all bodily things of that kind, and so also in earthy vapor, such as what is called mold; for mold is the decay of earthy vapor. So the nourishment in the hairs, being of this kind, when it is not concocted, putrefies, and what is called grayness results. And it is white, because mold, too, is practically the only one of decayed things that is white. The cause of this is that it contains much air; for all earthy vapor has the character of thick air. For mold is, as it were, the inverse of frost: if the rising vapor freezes, frost results; if it decays, mold results. That is why both occur on the surface, since vapor is a surface phenomenon. And the poets do well when, joking in comedies, they use the metaphor and call gray hairs the mold and frost of old age. For the one is the same in genus, the other in species: frost is the same in genus (since both are vapor), while mold is the same in species (since both are putrefaction). A sign that this is so is the following:
27| In many people, gray hairs have grown in from illness, and afterward, when they recovered, black hairs grew in place of these. The reason is that in sickness, just as the rest of the body is deficient in natural heat, so too the other parts, even the very small ones, share in this weakness. And a great deal of residue arises in bodies and their parts; that is precisely why the failure of concoction in the flesh produces grayness. But when people recover their health and regain strength, they change back again and become, as it were, young again out of old; and that is why the affections change along with them. It is also correct to say that disease is acquired old age, and old age is natural disease; certain diseases, at any rate, produce the very same effects as old age. People go gray at the temples first. The parts behind are lacking in moisture because they contain no brain, while the crown of the head has a great deal of moisture; and a great abundance is not easily putrefied. But the hairs at the temples have neither so little moisture that it can be concocted, nor so much that it cannot putrefy; for being a place intermediate between the two, it lies outside both of the affections. On the cause of grayness in humans, then, this has been said.
28| In the other animals, the fact that this change does not occur on account of this age has clearly the same cause as was stated in the case of baldness: they have a small brain and a less moist one, so that the heat is not overpowered in concocting it. Horses [of them] show this most markedly of all the animals we know, because they have, relative to their size, the thinnest bone around the brain of any animal. Evidence of this is that a blow struck to this spot proves fatal to them; that is why Homer put it this way: "where the horse's hairs first grow upon the skull, there above all is the fatal spot." Since moisture, then, easily flows in because of the thinness of the bone, while heat runs short because of age, these hairs go gray. Red hair also turns gray faster than black hair; for redness is a kind of weakness in a hair, and weak things all age faster. Cranes are said to grow blacker as they age. The cause of this condition would be that the nature of their feathers is naturally whiter, and that as they age there is more moisture in the feathers than is proportionate, which makes them more prone to decay. That grayness comes about through a kind of decay, and is not, as some suppose, a drying-out, is shown by what was said just before: hairs that are covered by caps or coverings go gray faster (for currents of air hinder decay, and covering shuts the air out), and by the fact that rubbing them with water and oil mixed together helps.
29| For the water cools, while the oil mixed in prevents quick drying; for water dries out readily. That it is not a drying-out, and that hair does not whiten the way grass whitens as it dries, is shown by the fact that some hair grows gray right from the start; and nothing that is only now coming to be is yet dried out. Hairs also whiten most often at the tip; for in the extremities, which are the thinnest parts, the least heat is present. In the other animals, wherever hairs turn white, this comes about by nature and not by an affection. In other animals the cause of their colors is the skin: white animals have white skin, black animals black skin, and dappled animals, which arise from a mixture, show white skin in one place and black in another. In the case of humans, however, the skin is not the cause at all; for even very white-skinned people have black hair. The cause is that, relative to size, a human being has the thinnest skin of all animals, so that it has no power over the change of the hair; rather, because of its weakness the skin itself changes color and grows darker from sun and wind, while the hairs do not change along with it at all. In the other animals the skin, because of its thickness, has the governing power over color.
30| That is why the hairs change to match the skins, while the skins do not change at all to match the winds and the sun. Of animals, some are single-colored (by single-colored I mean those whose whole kind has one color, as lions are all tawny; and this holds equally among birds and fish and other animals), others are many-colored yet uniform in body (I mean those whose whole body has the same color, as an ox may be wholly white or wholly black), and others are dappled. This last happens in two ways: some are dappled by their whole kind, as the leopard and the peacock, and some fish, such as the so-called thrattai; in others the kind as a whole is not dappled, but individuals become dappled, as oxen and goats, and among birds, pigeons; and other kinds of birds undergo the same thing. Uniformly-colored animals change far more than single-colored ones, and change into each other's simple color, for instance from white into black and from black into white, and into mixtures of both, because it belongs to the whole kind by nature not to be fixed to one color; for such a kind is readily moved in both directions, so that it both changes into the other color and becomes more dappled. Single-colored animals are the opposite:
31| for they do not change unless through some affection, and this is rare; a white partridge has in fact been seen before now, and a white raven and sparrow and bear. These occur when the animal has been distorted in its generation; for what is small is easily destroyed and easily moved, and what is coming to be is of just this sort, since for things coming to be, the starting-point lies in something small. Animals single-colored by nature but many-colored by kind change most of all through the action of waters; for warm waters make hair white, cold waters black, just as with plants too. The cause is that warm waters contain more air than water, and air, showing through, produces whiteness, just as it does in foam as well. So just as skins that are white through an affection differ from skins that are white by nature, so too in hairs the whiteness that comes through disease or age differs from the whiteness that comes by nature, in that the cause is different: natural heat makes some hairs white, while a foreign cause makes others white. It is the vaporous air, shut up inside, that supplies the white color in every case; that is why, in animals that are not single-colored, all the parts under the belly are whiter.
32| For, generally speaking, all the white parts are also warmer and sweeter in flesh, through this same cause; for concoction makes things sweet, and heat produces concoction. The same cause applies also to single-colored animals that are black or white: heat and cold are the cause of the nature of the skin and of the hairs, since each of the parts has a heat proper to itself; and further the tongues differ in color too, both among single-colored and among dappled animals, and even among single-colored animals that nonetheless differ, as white-tongued from black-tongued. The cause is what was said before: the skins of dappled animals are dappled, and among white-haired and black-haired animals, some have white skin and some black. One should take the tongue to be like one of the external parts, not on the ground that it is sheltered inside the mouth, but as a hand or a foot is external; so that, since the skin of dappled animals is not single-colored, this same cause accounts for the color of the skin on the tongue. Some birds and some wild quadrupeds also change color with the seasons. The cause is that, just as humans change with age, the same thing happens to these animals with the seasons;
33| for this difference is greater than the change that comes with age. Animals that eat more indiscriminately are, as a rule, more dappled, and reasonably so — bees, for example, are more single-colored than hornets and wasps; for if foods are the cause of the change, then those with varied food are reasonably dappled. Varied foods produce more varied movements, and more varied residues of food, and it is from these residues that hairs and feathers and skins arise. Let colors and hairs be distinguished in this way.
34| Concerning voice — the fact that some animals are deep-voiced, others high-voiced, others well-toned and moderately disposed toward both extremes; further that some are loud-voiced, others soft-voiced, and that they differ from one another in smoothness and roughness and flexibility and inflexibility — we must examine through what causes each of these belongs to them. Now concerning high pitch and low pitch, one should suppose the cause to be the same as for the change that occurs with age, in younger and older animals. For in almost all other animals the younger sound higher-pitched, but the calves of cattle sound lower-pitched. The same thing happens too in the case of males and females: in other kinds the female sounds higher-pitched than the male (this is most evident in humans, since nature has given this capacity to them above all, because they alone among animals use speech, and the matter of speech is voice), but among cattle it is the opposite, for the females sound lower-pitched than the bulls. For what purpose animals have voice, and what voice is, and sound in general, has been discussed partly in the works on perception, partly in the works on the soul.
35| Since lowness of pitch consists in the motion being slow, and sharpness in its being fast, there is some difficulty as to whether the cause of the slowness or the speed is the mover or the thing moved. For some say that what is much moves slowly, and what is little moves quickly, and that this is the cause of some voices being low-pitched and others sharp-pitched — speaking correctly up to a point, but not correctly as a whole. For it does seem rightly said, in general terms, that lowness lies in a certain magnitude of what is moved. For if this is so, it is not easy for something small also to sound low, nor likewise for something to be both low and sharp at once. And low-voicedness seems to belong to a nobler nature, and among melodies the low note is better than the strained one; for the better lies in a kind of superiority, and lowness is a kind of superiority. But since being low or sharp in voice is a different thing from having a loud or a soft voice (for there are sharp voices that are loud, and soft voices that are likewise low, and similarly also with respect to the middle pitch between these), by what else would one distinguish loudness and softness of voice than by the quantity, much or little, of what is moved? If, then, sharpness and lowness are to be distinguished by the distinction just given, it will follow that the same things are low-voiced and loud-voiced, and sharp-voiced and soft-voiced.
36| But this is false, and the cause is that 'great' and 'small', 'much' and 'little', are said in some cases without qualification, in others relative to each other. Loud voices, then, consist in what is moved being much without qualification, soft voices in its being little; but low and sharp voices consist in this differentia held relative to each other. For if what is moved exceeds the strength of the mover, what is carried must be carried slowly, but if it is exceeded, quickly. And what is strong, because of its strength, sometimes, in moving much, makes the motion slow, but sometimes, because it prevails, makes it fast. By the same reasoning, among weak movers, those that move more than their power allows make the motion slow, while those that, through weakness, move little, make it fast. These, then, are the causes of the opposed cases — why not all the young are sharp-voiced nor all low-voiced, nor all the old, nor uniformly the males and the females; and besides these, also the cause of the sick speaking sharply, and those in good bodily condition too, and further of people becoming more sharp-voiced as they become old men, the old age being opposite to the condition of the young.
37| Most young creatures, then, and females, moving little air because of weakness, are sharp-voiced; for what is little moves quickly, and what is quick is sharp in voice. But calves and female cattle — the former because of their age, the latter because of the nature of femaleness — do not have strong the part by which they move breath, but in moving much air they are low-voiced; for what moves slowly is low, and much air moves slowly. These move much air, while the others move little, because the vessel through which the breath first travels has, for these, a large gap, and they are forced to move much air, while for the others it is easily managed. As age advances, this moving part grows stronger in each case, so that they change to the opposite: the sharp-voiced become lower-voiced than they themselves were, and the low-voiced become sharper-voiced than themselves; that is why bulls are sharper-voiced than calves and than female cattle. In all creatures, then, strength lies in the sinews, which is why those in their prime are stronger; for the young are more jointless and more without sinew. Further, in the young the tautness has not yet been stretched taut, while in those growing old the tension is already relaxed;
38| that is why both are weak and incapable with respect to motion. Bulls especially are sinewy, and so is the heart; that is why they have this part, by which they move the breath, taut, like a stretched sinewy string. That the heart of cattle has this nature is shown by the fact that bone forms in some of them; for bones seek out the nature of sinew. All castrated animals change toward the female, and because the sinewy strength relaxes, the source emits, at first, a voice similar to that of females. And the relaxation comes about in much the way it would if one, having stretched a string taut, then slackened it by hanging some weight from it — as women who weave on looms do; for they too stretch the warp taut by attaching what are called the 'weights'. For in just this way the nature of the testicles is attached to the seminal ducts, and these come from the vein whose origin is from the heart, at the very point of the part that moves the voice. That is why, when the seminal ducts change with age, at the age when they are now able to secrete seed, this part changes along with them. And as this part changes, the voice also changes — more in males, though the same thing happens in females too, only less noticeably — and there occurs what some call 'breaking', whenever the voice becomes uneven.
39| After this it settles into the lowness or sharpness proper to the age that follows. When the testicles are removed, the tautness of the ducts is relaxed, just as when the weight is removed from the string and the warp. As this relaxes, the source that moves the voice is slackened by the same reasoning. This, then, is the cause why castrated animals change toward the female both in voice and in the rest of their form — because the source from which the tautness of the body derives happens to be relaxed — and not, as some suppose, because the testicles themselves are a bundle of many sources. Rather, small displacements become causes of great effects, not in their own right, but whenever it happens that a source changes along with them. For sources, though small in magnitude, are great in power; for this is what it is to be a source — itself to be the cause of many things, while nothing further above is the cause of it. As to why some animals are by nature so constituted as to be low-voiced and others sharp-voiced, the heat and the cold of the place also contribute. For hot breath, because of its thickness, produces low-voicedness, while cold breath, because of its thinness, produces the opposite.
40| This is clear also in the case of pipes: those who use hotter breath, and emit such breath as those who wail do, play the pipe in a lower register. The cause of roughness of voice, and of the voice being smooth, and of every such unevenness, is that the part and the instrument through which the voice is carried is either rough or smooth, or altogether even or uneven. This is clear whenever some moisture is present around the windpipe, or roughness arises from some affection; for then the voice too becomes uneven. The cause of flexibility is whether the instrument is soft or hard. For the soft can be managed and become all manner of things, while the hard cannot. And the soft can utter both small and great sounds, and hence both sharp and low; for it manages the breath easily, and itself readily becomes great or small; but hardness cannot be managed. So much, then, concerning voice
41| Concerning teeth, that animals do not have them for one purpose, nor all for the same purpose, but some for the sake of nutrition, others also for defense and for articulate speech, has been said before. But as to why the front teeth come first and the molars later, and why the latter do not fall out while the former fall out and grow again, we must take the cause to be akin to what has been said in our accounts of generation. Democritus too has spoken about these matters, but not well. For he states the cause universally without having examined it in all cases. He says that they fall out because they come to be in animals before their season; since teeth grow, so to speak, according to nature only when the animal is at its prime. And he blames suckling for their coming to be before their season. And yet the pig also suckles, but does not shed its teeth; moreover all the saw-toothed animals suckle, but some of them do not shed their teeth except the canines, as for example lions. In this, then, he erred in speaking universally without examining what happens in every case; and this one must do, for a person who states something universally must speak of all cases. Since we posit nature — positing it from what we observe — as neither falling short nor doing anything in vain of what is possible in each case, and since it is necessary for those animals that are going to take nourishment after the enjoyment of milk to have organs for the working of that nourishment;
42| if then this happened, as he says, only at puberty, nature would be falling short of something possible for it to do, and the work of nature would come about contrary to nature. For what happens by force is contrary to nature, and he says the generation of the teeth happens by force. That this is not true is clear from these considerations and others like them. These come to be before the broad ones, first because their function too is prior (for dividing is prior to grinding smooth, and those serve for grinding smooth, these for dividing), and next because the smaller, even if it starts out at the same time as the larger, is naturally disposed to come to be faster than the larger. These are smaller in size than the molars, and the bone of the jaw is broad there but narrow toward the mouth. From the larger, then, more nourishment must necessarily flow in, and from the smaller, a scantier supply. Suckling itself contributes nothing, but the heat of the milk makes the teeth sprout faster. A sign of this is that even among suckling infants, those that feed on warmer milk cut their teeth faster; for what is warm promotes growth. Once they have come to be, they fall out for the sake of the better, because what is sharp quickly grows blunt;
43| others, then, must succeed them for the task. But there is no such bluntness for the broad teeth; through time, being worn down, they only become smoother. The front teeth fall out of necessity, because the roots of the broad teeth are set in a broad and strong bone, while those of the front teeth are set in a thin one, and are therefore weak and easily dislodged. They grow again because their shedding occurs while the bone is still growing, and while it is still the season for teeth to come to be. A sign of this is that the broad teeth too grow over a long time; for the last of them rise up around the twentieth year, and in some people the very last ones have come up only when they are already growing old, altogether because there is abundant nourishment in the wide space of the bone. The front part of the jaw, on account of its thinness, quickly reaches completion, and no residue forms in it, but its own proper nourishment is used up entirely in growth. Democritus, however, having given up speaking of the that-for-the-sake-of-which, reduces everything to necessity in the things nature makes use of — things that are indeed of a certain sort, but that are nonetheless for the sake of something, and for the sake of what is better in each case. So that nothing prevents their coming to be and falling out in this way, but not on account of these things, but on account of the end;
44| and these factors are causes as movers and instruments, and as matter, since it is reasonable that in most cases the work is done by breath, used as an instrument; for just as some of the tools used in the crafts serve many purposes — as in bronze-working the hammer and the anvil — so too does breath in things constituted by nature. To state the causes as being purely a matter of necessity seems like supposing that it is the knife, and nothing else, that has made the water drain out of a dropsical patient, and not health, for the sake of which the knife made the cut. Concerning teeth, then, why some fall out and grow again while others do not, and in general for what cause they come to be, has been stated. And it has also been stated concerning the other affections that occur in the parts, all those that happen to come about not for the sake of anything but from necessity and through the moving cause.