The Politics of Aristotle

by Aristotle

  Thus much of the heart, its nature, and the end and cause of its existence in such animals as have it.

  [15] 5 · In due sequence we have next to discuss the blood-vessels, that is to say the great vessel and the aorta. For it is into these two that the blood first passes when it quits the heart; and all the other vessels are but offshoots from them. Now that these vessels exist on account of the blood has already been stated. For every fluid requires a receptacle, and in the case of the blood the vessels are that [20] receptacle. Let us now explain why these vessels are two, and why they spring from one single source, and extend throughout the whole body.

  The reason, then, why these two vessels coalesce into one centre, and spring from one source, is that the sensory soul is in all animals actually one, so that the part in which it primarily abides must also be one. In sanguineous animals this oneness is not only actual but potential, whereas in some bloodless animals it is only [25] actual. Hence in the self-same place must necessarily be the source of heat; and this is the cause of the warmth and fluidity of the blood. Thus, then, the oneness of the part in which is lodged the prime source of sensation and of heat explains the oneness of the source in which the blood originates; and this, again, explains why [30] the blood-vessels have one common starting-point.

  The vessels are two because the body of every sanguineous animal that is capable of locomotion is bilateral; for in all such animals there is a distinguishable before and behind, a right and left, an above and below. Now as the front is more honourable and of higher supremacy than the hinder aspect, so also and in like degree is the great vessel superior to the aorta. For the great vessel is placed in front, [668a1] while the aorta is behind; the former again is plainly visible in all sanguineous animals, while the latter is in some indistinct and in some not discernible at all.

  Lastly, the reason for the vessels being distributed throughout the entire body is that in them, or in parts analogous to them, is contained the blood, or the fluid which in bloodless animals takes the place of blood, and that this is the material from which the whole body is made. Now as to the manner in which animals are [5] nourished, and as to the source from which they obtain nutriment and as to the way in which they absorb this from the stomach, these are matters which may be more suitably considered and explained in the treatise on Generation. [But inasmuch as the parts are, as already said, formed out of the blood, it is but rational that the flow [10] of the blood should extend, as it does, throughout the whole of the body. For since each part is formed of blood, each must have blood all about it.]11

  To give an illustration of this. The water-courses in gardens are so constructed as to distribute water from one single source or fount into numerous channels, which [15] convey it to all parts; and, again, in house-building stones are thrown down along the whole ground-plan of the foundation walls; because the garden-plants in the one case take their growth from water, and the foundation walls in the other are built out of the stones. Now just after the same fashion has nature laid down channels for [20] the conveyance of the blood throughout the whole body, because this blood is the material out of which the whole fabric is made. This becomes very evident in bodies that have undergone great emaciation. For in such there is nothing to be seen but the blood-vessels; just as when fig-leaves or vine-leaves or the like have dried up, [25] there is nothing left of them but their vessels. The explanation of this is that the blood, or fluid which takes its place, is potentially body and flesh, or substance analogous to flesh. Now just as in irrigation the largest dykes are permanent, while the smallest are soon filled up with mud and disappear, again to become visible [30] when the deposit of mud ceases; so also do the largest blood-vessels remain permanently open, while the smallest are converted actually into flesh, though potentially they are no whit less vessels than before. This too explains why, so long as the flesh of an animal is in its integrity, blood will flow from any part of it whatsoever that is cut. Now there can be no blood, unless there be a blood-vessel, and yet no vessel is visible—just as the dykes for irrigation are invisible until they [668b1] have been cleared of mud.

  As the blood-vessels advance, they become gradually smaller and smaller, until at last their tubes are too fine to admit the blood. This fluid can therefore no longer find its way through them, though they still give passage to the residue of the moist [5] humour which we call sweat; and especially so when the body is heated, and the mouths of the small vessels are dilated. Instances, indeed, are not unknown of persons who in consequence of a bad general condition have secreted sweat that resembled blood, their body having become loose and flabby, and their blood watery, owing to the heat in the small vessels having been too scanty for its [10] concoction. For, as was before said, every compound of earth and water—and both nutriment and blood are such—becomes thicker from concoction. The inability of the heat to effect concoction may be due either to its being absolutely small in amount, or to the quantity of food, when this has been taken in excess and relative to [15] which it is small. This excess again may be of two kinds, either quantitative or qualitative; for all substances are not equally amenable to concoction.

  The widest passages in the body are of all parts the most liable to haemorrhage; so that bleeding occurs not infrequently from the nostrils, the gums, and the fundament, occasionally also from the mouth. Such haemorrhages are of a painless kind, and not violent as are those from the windpipe.

  [20] The great vessel and the aorta, which above lie somewhat apart, lower down exchange positions, and by so doing give compactness to the body. For when they reach the point where the legs diverge, they each split into two, and the great vessel passes from the front to the rear, and the aorta from the rear to the front. By this [25] they contribute to the unity of the whole fabric. For as in plaited work the parts hold more firmly together, so also by the interchange of position between the blood-vessels are the anterior and posterior parts of the body more closely knit together. A similar exchange of position occurs also in the upper part of the body, between the vessels that have issued from the heart. The details however of the mutual relations [30] of the different vessels must be looked for in the Dissections and the History of Animals.

  So much, then, as concerns the heart and the blood-vessels. We must now pass on to the other viscera and apply the same method of inquiry to them.

  6 · The lung, then, is an organ found in all the animals of a certain class, because they live on land. For there must of necessity be some means or other of tempering the heat of the body; and in sanguineous animals, as they are of an especially hot nature, the cooling agency must be external, whereas in the bloodless [669a1] kinds the innate spirit is sufficient of itself for the purpose. The external cooling agent must be either air or water. In fishes the agent is water. Fishes therefore never [5] have a lung, but have gills in its place, as was stated in the treatise on Respiration. But animals that breathe are cooled by air. These therefore are all provided with a lung.

  All land animals breathe, and even some water animals, such as the whale, the dolphin, and all the spouting Cetacea. For many animals are ambivalent: some that [10] are terrestrial and that inspire air being nevertheless of such a bodily constitution that they abide for the most time in the water; and some that are aquatic partaking so largely of the land character, that respiration constitutes for them the limiting condition of life.

  The organ of respiration is the lung. This derives its motion from the heart; but [15] it is its own large size and spongy texture that affords amplitude of space for the entrance of the breath. For when the lung rises up the breath streams in, and is again expelled when the lung collapses. It has been said that the lung exists as a provision to meet the jumping of the heart. But this is out of the question. For man is practically the only animal whose heart presents this phenomenon of jumping, [20] inasmuch as he alone is influenced by hope and anticipation of the future. Moreover, in most animals it is separated from the lung by a considerable interval and lies above
it, so that the lung can contribute nothing to mitigate any jumping of the heart.

  The lung differs much in different animals. For in some it is of large size and contains blood; while in others it is smaller and of spongy texture. In the vivipara it [25] is large and rich in blood, because of their natural heat; while in the ovipara it is small and dry but capable of expanding to a vast extent when inflated. Among terrestrial animals, the oviparous quadrupeds, such as lizards, tortoises, and the [30] like, have this kind of lung; and, among inhabitants of the air, the animals known as birds. For in all these the lung is spongy, and like foam. For foam contracts from a large mass to a small when it runs together, and the lung of these animals is small and membraneous. In this too lies the explanation of the fact that these animals are little liable to thirst and drink but sparingly, and that they are able to remain for a [35] considerable time under water. For, inasmuch as they have but little heat, the very motion of the lung, airlike and void, suffices by itself to cool them for a considerable [669b1] period.

  These animals, speaking generally, are also distinguished from others by their smaller bulk. For heat promotes growth, and abundance of blood is an indication of heat. Heat, again, tends to make the body erect; and thus it is that man is the most [5] erect of animals, and the vivipara more erect than other quadrupeds. For no viviparous animal, be it footless or be it possessed of feet, is so given to creep into holes.

  The lung, then, exists in general for respiration; but in one order of animals it is bloodless and has the structure described above, to suit the special requirements. There is, however, no one term to denote all animals that have a lung; no [10] designation, that is, like the term bird, applicable to the whole of a certain class. Yet the possession of a lung is a part of their substance, just as much as the presence of certain characters constitutes the essence of a bird.

  7 · Of the viscera some appear to be single, as the heart and lung; others to be [15] double, as the kidneys; while of a third kind it is doubtful in which class they should be reckoned. For the liver and the spleen would seem to be ambivalent. For they may be regarded either as constituting each a single organ, or as a pair of organs resembling each other in character.

  In reality, however, all the organs are double. The reason for this is that the body itself is double, consisting of two halves, which are however combined together [20] under a single origin. For there is an upper and a lower half, a front and a rear, a right side and a left.

  This explains why it is that even the brain and the several organs of sense tend in all animals to consist of two parts; and the same explanation applies to the heart with its cavities. The lung again in Ovipara is divided to such an extent that these [25] animals look as though they had actually two lungs. As to the kidneys, no one can overlook their double character. But when we come to the liver and the spleen, any one might fairly be in doubt. The reason for this is, that, in animals that necessarily have a spleen, this organ is such that it might be taken for a kind of bastard liver; while in those in which a spleen is not an actual necessity but is merely present, as it [30] were, by way of token, in an extremely minute form, the liver plainly consists of two parts; of which the larger tends to lie on the right side and the smaller on the left. Not but what there are some even of the Ovipara in which this condition is comparatively indistinctly marked; while, on the other hand, there are some Vivipara in which the liver is manifestly divided into two parts. Examples of such division are furnished by the hares of certain regions, which have the appearance of having two livers, and by the selachia and some other fishes.

  [670a1] It is the position of the liver on the right side of the body that is the main cause for the formation of the spleen; the existence of which thus becomes to a certain extent a matter of necessity in all animals, though not of very stringent necessity.

  The reason, then, why the viscera are bilateral is, as we have said, that there [5] are two sides to the body, a right and a left. For each of these sides aims at similarity with the other, and so likewise do their several viscera; and as the sides, though dual, are knit together into unity, so also is it with each of the viscera.

  Those viscera which lie below the diaphragm exist one and all on account of [10] the blood-vessels; serving as a bond, by which these vessels, while floating freely, are yet held in connexion with the body. For the vessels give off branches which run to the body through the outstretched structures, like so many anchor-lines. The great vessel sends such branches to the liver and the spleen; and these viscera—the liver [15] and spleen on either side with the kidneys behind—attach the great vessel to the body with the firmness of nails. The aorta sends similar branches to each kidney.

  [20] These viscera, then, contribute in this manner to the animal body. The liver and spleen assist, moreover, in the concoction of the food; for both are of a hot character, owing to the blood which they contain. The kidneys, on the other hand, take part in the separation of the excretion which flows into the bladder.

  The heart then and the liver are essential constituents of every animal; the liver that it may effect concoction, the heart that it may lodge the central source of heat. For some part or other there must be which, like a hearth, shall hold the kindling [25] fire; and this part must be well protected, seeing that it is, as it were, the citadel of the body.

  All sanguineous animals, then, need these two parts; and this explains why these two viscera are found in them all. In such of them, however, as breathe, there is also a third, namely the lung. The spleen, in those animals that have it, is only [30] present of necessity in the same sense as the excretions of the belly and of the bladder are necessary, in the sense, that is, of being a concomitant. Therefore it is that in some animals the spleen is but scantily developed as regards size. This, for instance, is the case in such feathered animals as have a hot stomach. Such are the pigeon, the hawk, and the kite. It is the case also in oviparous quadrupeds, where the [670b1] spleen is excessively minute, and in many of the scaly fishes. These same animals are also without a bladder, because the loose texture of their flesh allows the residual fluid to pass through and to be applied to the formation of feathers and scales. For the spleen attracts the residual humours from the stomach, and owing to [5] its bloodlike character is enabled to assist in their concoction. Should, however, this residual fluid be too abundant, or the heat of the spleen be too scanty, the body becomes sickly from over-repletion with nutriment. Often, too, when the spleen is affected by disease, the belly becomes hard owing to the reflux into it of the fluid; just as happens to those who form too much urine, for they also are liable to a [10] similar diversion of the fluids into the belly. But in those animals that have but little to excrete, such as birds and fishes, the spleen is never large, and in some exists no more than by way of token. So also in the oviparous quadrupeds it is small, compact, and like a kidney. For their lung is spongy, and they drink but little, and such [15] residue as they have is applied to the growth of the body and the formation of scaly plates, just as in birds it is applied to the formation of feathers.

  On the other hand, in such animals as have a bladder, and whose lung contains blood, the spleen is watery, both for the reason already mentioned, and also because the left side of the body is more watery and colder than the right. For each of two [20] contraries has been so placed as to go together with that which is akin to it in another pair of contraries. Thus right and left, hot and cold, are pairs of contraries; and they are in the same column as one another, after the manner described.

  The kidneys when they are present exist not of actual necessity, but as matters of greater finish and perfection. For by their special character they are suited to serve in the excretion of the fluid which collects in the bladder. In animals therefore [25] where this fluid is very abundantly formed, their presence enables the bladder to perform better its proper office.

  Since then both kidneys and bladder exist in animals for one and the same function, we must next treat of the bladder,
though in so doing we disregard the due [30] order of succession in which the parts should be enumerated. For not a word has yet been said of the midriff, which is one of the parts that environ the viscera.

  8 · It is not every animal that has a bladder; those only being apparently [671a1] intended by nature to have one, whose lung contains blood. To such it was but reasonable that she should give this part. For the superabundance in their lung of its natural constituents causes them to be the thirstiest of animals, and makes them require a more than ordinary quantity not merely of solid but also of liquid nutriment. This increased consumption necessarily entails the production of an [5] increased amount of residue; which thus becomes too abundant to be concocted by the stomach and excreted with its own residual matter. The residual fluid must therefore of necessity have a receptacle of its own; and thus all animals whose lung contains blood are provided with a bladder. Those animals, on the other hand, that are without a lung of this character, and that either drink but sparingly owing to [10] their lung being of a spongy texture, or never imbibe fluid at all for drinking’s sake but only as nutriment, insects for instance and fishes, and that are moreover clad with feathers or scales or scaly plates—all these animals, owing to the small amount of fluid which they imbibe, and owing also to such residue as there may be being [15] converted into feathers and the like, are invariably without a bladder. The tortoises, which are comprised among animals with scaly plates, form the only exception; and this is merely due to the imperfect development of their natural conformation; the explanation of the matter being that in the sea-tortoises the lung is flesh-like and contains blood, resembling the lung of the ox, and that in the land-tortoises it is of disproportionately large size. Moreover, inasmuch as the covering which invests [20] them is dense and shell-like, so that the moisture cannot exhale through the porous flesh, as it does in birds and in snakes and other animals with scaly plates, such an amount of secretion is formed that some special part is required to receive and hold it. This then is the reason why these animals, alone of their kind, have a bladder, the [25] sea-tortoise a large one, the land-tortoises an extremely small one.