by Aristotle
9 · What has been said of the bladder is equally true of the kidneys. For these also are wanting in all animals that are clad with feathers or with scales or with scale-like plates; the sea and land tortoises forming the only exception. In some of the birds, however, there are flattened kidney-like bodies, as though the flesh [30] allotted to the formation of the kidneys, unable to find one single place of sufficient size, had been scattered over several.
The fresh-water tortoise has neither bladder nor kidneys. For the softness of its shell allows of the ready transpiration of fluid; and for this reason neither of the organs mentioned exists in this animal. All other animals, however, whose lung [671b1] contains blood are, as before said, provided with kidneys. For nature uses these organs for two separate purposes, namely for the excretion of the residual fluid, and to subserve the blood-vessels, a channel leading to them from the great vessel.
In the centre of the kidney is a cavity of variable size. This is the case in all [5] animals, excepting the seal. The kidneys of this animal are more solid than those of any other, and resemble the kidneys of the ox. The human kidneys are also like those of the ox; being as it were made up of numerous small kidneys, and not presenting one unbroken surface like the kidneys of sheep and other quadrupeds. For this reason, should the kidneys of a man be once attacked by disease, the [10] malady is not easily expelled. For it is as though many kidneys were diseased and not merely one; which naturally enhances the difficulties of a cure.
The duct which runs to the kidney from the great vessel does not terminate in the central cavity, but is expended on the substance of the organ, so that there is no blood in the cavity, nor does any congeal there after death. A pair of stout ducts, [15] void of blood, run, one from the cavity of each kidney, to the bladder; and other ducts, strong and continuous, lead into the kidneys from the aorta. The purpose of this arrangement is to allow the superfluous fluid to pass from the blood-vessel into the kidney, and the resulting renal excretion to collect, by the percolation of the [20] fluid through the solid substance of the organ, in its centre, where as a general rule there is a cavity. (This by the way explains why the kidney is the most malodorous of all the viscera.) From the central cavity the fluid is discharged into the bladder by the ducts that have been mentioned, having already assumed in great degree the character of excremental residue. The bladder is as it were moored to the kidneys; [25] for, as already has been stated, it is attached to them by strong ducts. These then are the causes for which the kidneys exist, and such the functions of these organs.
In all animals that have kidneys, that on the right is placed higher than that on the left. For, inasmuch as motion commences from the right, and the organs on this [30] side are in consequence stronger than those on the left, they must all push upwards because of this motion in advance of their opposite fellows; indeed, men even raise the right eyebrow more than the left, and the former is more arched than the latter. The right kidney being thus drawn upwards is in all animals brought into contact with the liver; for the liver lies on the right side. [672a1]
Of all the viscera the kidneys are those that have the most fat. This is in the first place the result of necessity, because the kidneys are the parts through which the residual matters percolate. For the blood which is left behind after this excretion, being of pure quality, is of easy concoction, and the final result of thorough blood-concoction is lard and suet. For just as a certain amount of fire is [5] left in the ashes of solid substances after combustion, so also does a remnant of the heat that has been developed remain in fluids after concoction; and this is the reason why oily matter is light, and floats on the surface of other fluids. The fat is not formed in the kidneys themselves, the density of their substance forbidding this, but [10] is deposited about their external surface. It consists of lard or of suet, according as the animal’s fat is of the former or latter character. The difference between these two kinds of fat has already been set forth in other passages. The formation, then, of fat in the kidneys is the result of necessity; being, as explained, a consequence of the necessary conditions which accompany the possession of such organs. But at the [15] same time the fat is there to ensure the safety of the kidneys, and to maintain their natural heat. For placed, as these organs are, close to the surface, they require a greater supply of heat than other parts. For while the back is thickly covered with flesh, so as to form a shield for the heart and neighbouring viscera, the loins, in accordance with a rule that applies to all bendings, are destitute of flesh; and fat is therefore formed as a substitute for it, so that the kidneys may not be without [20] protection. The kidneys, moreover, by being fat are the better enabled to secrete and concoct their fluid; for fat is hot, and it is heat that effects concoction.
Such, then, are the reasons why the kidneys are fat. But in all animals the right kidney is less fat than its fellow. The reason for this is, that the parts on the right [25] side are naturally more dry and more suited for motion than those on the left. But motion is antagonistic to fat, for it tends to melt it.
Animals then, as a general rule, derive advantage from their kidneys being fat; and the fat is often very abundant and extends over the whole of these organs. But, should the like occur in the sheep, death ensues. Be its kidneys, however, as fat as [30] they may, they are never so fat but that some part, if not in both at any rate in the right one, is left free. The reason why sheep are the only animals that suffer in this manner, or suffer more than others, is that in animals whose fat is composed of lard this is of fluid consistency, so that there is not the same chance in their case of breath getting shut in and causing mischief. But it is to this that rot is due. And thus [35] even in men who suffer from kidney trouble, though it is beneficial to them to have fat kidneys, yet should these organs become over-fat, deadly pains ensue. As to [672b1] those animals whose fat consists of suet, in none is the suet so dense as in the sheep, neither is it nearly so abundant; for of all animals there is none in which the kidneys become so soon gorged with fat as in the sheep. Rot, then, is produced by the moisture and the breath getting shut up in the kidneys, and is a malady that carries [5] off sheep with great rapidity. For the disease forthwith reaches the heart, passing thither by the aorta and great vessel, the ducts which connect these with the kidneys being of unbroken continuity.
10 · We have now dealt with the heart and the lung, as also with the liver, [10] spleen, and kidneys. The latter are separated from the former by the midriff or, as some call it, the diaphragm. This divides off the heart and lung, and, as already said, is called the diaphragm in sanguineous animals, all of which have a midriff, just as they all have a heart and a liver. The reason is that the midriff serves to [15] divide the region of the heart from the region of the stomach, so that the centre wherein abides the sensory soul may be undisturbed, and not be overwhelmed, directly food is taken, by its up-steaming vapour and by the abundance of heat then superinduced. For it was to guard against this that nature made a division, [20] constructing the midriff as a kind of partition-wall and fence, and so separated the nobler from the less noble parts, in all cases where a separation of upper from lower is possible. For the upper part is the better and that for the sake of which the rest exists; while the lower part exists for the sake of the upper and constitutes the necessary element in the body, inasmuch as it is the recipient of the food.
[25] That portion of the midriff which is near the ribs is fleshier and stronger than the rest, but the central part has more of a membranous character; for this structure conduces best to its strength and its extensibility. Now that there are as it were outgrowths to prevent heat mounting up from below, is shown by what happens when, owing to their proximity to the stomach, they attract thence the hot and residual fluid. For when this occurs there ensues forthwith a marked disturbance of [30] intellect and sensation. It is indeed because of this that the midriff is called the diaphragm, as though it had some share in the process of thinking.12 In reality, however, it has no part whatsoever itself
in the matter, but, lying in close proximity to organs that have, it makes the changes of intelligence evident. This too explains why its central part is thin—not only by necessity, inasmuch as those portions of the fleshy whole which lie nearest to the ribs must necessarily be fleshier than the rest, [35] but also in order to give it as small a proportion of humour as possible; for, had it been made of flesh throughout, it would have been more likely to attract and hold a [673a1] large amount of this. That heating of it affects sensation rapidly and in a notable manner is shown by the phenomena of laughing. For when men are tickled they are quickly set a-laughing, because the motion quickly reaches this part, and being heated but slightly it nevertheless manifestly so disturbs the mental action as to occasion movements that are contrary to the man’s intention. That man alone is affected by tickling is due firstly to the delicacy of his skin, and secondly to his being [5] the only animal that laughs. For to be tickled is to be set in laughter, the laughter being produced by such a motion as mentioned of the region of the armpit. [10]
It is said also that when men in battle are wounded anywhere near the midriff, they are seen to laugh, owing to the heat produced by the wound. This is asserted by more credible persons than those who tell the story of how a human head speaks after it is cut off. For so some assert, and even call in Homer to support them, representing [15] him as alluding to this when he wrote, ‘His head still speaking rolled into the dust’, instead of ‘The head of the speaker’.13 So fully was the possibility of such an occurrence accepted in Arcadia, that one of that country was actually brought to trial under the following circumstances. The priest of Zeus Hoplosmios had been murdered; but as yet it had not been ascertained who was the assassin; when certain persons asserted that they [20] had heard the murdered man’s head, which had been severed from the body, repeat several times the words, ‘Cercidas slew man on man’. Search was thereupon made and a man of those parts who bore the name of Cercidas hunted out and put upon his trial. But it is impossible that any one should utter a word when the windpipe is severed and no motion any longer derived from the lung. Moreover, among the barbarians, where heads are chopped off with great rapidity, nothing of the kind has ever yet occurred. [25] Why, again, does not the like occur in the case of other animals than man? [For the story about laughing when the midriff is wounded, is but what one would expect; for no animal but man ever laughs. So, too, there is nothing irrational in supposing that the trunk may run forwards to a certain distance after the head has been cut off; seeing that bloodless animals at any rate can live, and that for a considerable time, after decapitation, [30] as has been set forth and explained in other passages.]14
The purposes, then, for which the viscera severally exist have now been stated. It is of necessity upon the inner terminations of the vessels that they are developed; [673b1] for humour, and that of a bloody character, cannot but exude at these points, and it is of this, solidified and coagulated, that the substance of the viscera is formed. Thus they are of a bloody character, and in substance resemble each other while they differ from other parts.
11 · The viscera are enclosed each in a membrane. For they require some [5] covering to protect them from injury, and require, moreover, that this covering shall be light. To such requirements membrane is well adapted; for it is close in texture so as to form a good protection, destitute of flesh so as neither to attract humour nor retain it, and thin so as to be light and not add to the weight of the body. Of the membranes those are the stoutest and strongest which invest the heart and the [10] brain; as is but consistent with reason. For these are the parts which require most protection, seeing that they are the main governing powers of life, and that it is to governing powers that guard is due.
12 · Some animals have all the viscera that have been enumerated; others have only some of them. In what kind of animals this latter is the case, and what is the explanation, has already been stated. Moreover, the self-same viscera present [15] differences in different possessors. For the heart is not precisely alike in all animals that have one; nor, in fact, is any of the others. Thus the liver is in some animals split into several parts, while in others it is comparatively undivided. Such differences present themselves even among those sanguineous animals that are viviparous, but [20] are marked in fishes and in the oviparous quadrupeds, and this whether we compare them with each other or with the Vivipara. As for birds, their liver very nearly resembles that of the Vivipara; for in them, as in these, it is of a pure and blood-like colour. The reason for this is that the body in both these classes of animals admits of the freest exhalation and the amount of foul residual matter within is but small. [25] Hence it is that some of the Vivipara are without any gall-bladder at all. For the liver takes a large share in maintaining the purity of composition and the healthiness of the body. For these are conditions that depend finally upon the blood, and there is more blood in the liver than in any of the other viscera, the heart only excepted. On the other hand, the liver of oviparous quadrupeds and fishes inclines, as a rule, to a yellow hue, and there are even some of them in which it is entirely of [30] this bad colour, in accordance with the bad composition of their bodies generally. Such, for instance, is the case in the toad, the tortoise, and other similar animals.
The spleen in animals that have horns and cloven hoofs, such as the goat, the sheep, and the like, is of a rounded form; excepting when increased size has caused [674a1] some part of it to extend its growth longitudinally, as has happened in the case of the ox. On the other hand, it is elongated in all polydactylous animals. Such, for instance, is the case in the pig, in man, and in the dog. While in animals with solid hoofs it is of a form intermediate to these two and mixed, being broad in one part, narrow in another. Such, for example, is its shape in the horse, the mule, and the ass.
13 · The viscera differ from the flesh not only in the bulkiness of their [5] substance, but also in position; for they lie within the body, whereas the flesh is placed on the outside. The explanation of this is that these parts partake of the character of blood-vessels, and that while the former exist for the sake of the vessels, the latter cannot exist without them.
14 · Below the midriff lies the stomach, placed at the end of the oesophagus [10] when there is one, and in immediate contiguity with the mouth when the oesophagus is wanting. Continuous with this stomach is what is called the gut. These parts are present in animals, for reasons that are self-evident. For it is a matter of necessity that an animal shall receive the incoming food and discharge it when its moisture has been extracted. This residual matter, again, must not occupy [15] the same place as the yet unconcocted nutriment, and there must be a place in which they change. For there must be one receptacle for the ingoing food and another for the useless residue, and as there are separate times for these operations, so there must be distinct places. These, however, are matters which will be more suitably set forth when we come to deal with Generation and Nutrition. What we [20] have at present to consider are the variations presented by the stomach and its subsidiary parts. For neither in size nor in shape are these parts uniformly alike in all animals. Thus the stomach is single in all sanguineous and viviparous animals which are ambidentate. It is single therefore in all the polydactylous kinds, such as man, dog, lion, and the rest; in all the solid-hoofed animals also, such as horse, mule, [25] ass; and in all those which, like the pig, though their hoof is cloven, yet are ambidentate. When, however, an animal is of large size, and feeds on substances of so thorny and ligneous a character as to be difficult of concoction, it may in [30] consequence have several stomachs, as for instance is the case with the camel. A similar multiplicity of stomachs exists also in the horned animals; the reason being that horn-bearing animals are not ambidentate. The camel also, though it has no horns, is not ambidentate. The explanation of this is that it is more essential for the camel to have a multiple stomach than to have front teeth. Its stomach, then, is constructed like that of non-ambidentates, and its teeth match its stomach—for the
[674b1] teeth in question would be of no service. Its food, moreover, being of a thorny character, and its tongue necessarily made of a fleshy substance, nature uses the earthy matter which is saved from the teeth to give hardness to the palate. The [5] camel ruminates like the horned animals, because its multiple stomach resembles theirs. For all animals that have horns, the sheep for instance, the ox, the goat, the deer, and the like, have several stomachs. For since the mouth, owing to its lack of [10] teeth, only imperfectly performs its office as regards the food, the stomachs receive the food one from the other in succession, the first taking the unreduced substances, the second the same when somewhat reduced, the third when reduction is complete, and the fourth when the whole has become a smooth pulp. Such is the reason why there is this multiplicity of parts and cavities in animals with such dentition. The names given to the several cavities are the paunch, the honey-comb bag, the [15] manyplies, and the reed. How these parts are related to each other, in position and in shape, must be looked for in the History of Animals and the Anatomies.
Birds also present variations in the part which acts as a recipient of the food for [20] the same reason. For here again it is because the mouth fails to perform its office—for birds have no teeth at all, nor any instrument whatsoever with which to bite up or grind down their food—it is because of this, that in some of them what is called the crop precedes the stomach and does the work of the mouth; while in others the oesophagus is either broad or a part of it bulges just before it enters the [25] stomach, so as to form a preparatory store-house for the unreduced food; or the stomach itself has a protuberance in some part, or is strong and fleshy, so as to be able to store up the food for a considerable period and to concoct it, in spite of its not [30] having been ground into a pulp. For nature retrieves the inefficiency of the mouth by increasing the efficiency and heat of the stomach. Other birds there are, such, namely, as have long legs and live in marshes, that have none of these provisions, but merely an elongated oesophagus.15 The explanation of this is to be found in the moist character of their food. For all these birds feed on substances easy of reduction, and because of this, [their food being moist and not requiring much concoction]16 their stomachs are moist.