Aristotle

by Various Works [lit]

  direction in which their motion occurs.

  The heart again is abundantly supplied with sinews, as might

  reasonably be expected. For the motions of the body commence from

  the heart, and are brought about by traction and relaxation. The heart

  therefore, which, as already said,' as it were a living creature

  inside its possessor, requires some such subservient and strengthening

  parts.

  In no animals does the heart contain a bone, certainly in none of

  those that we have ourselves inspected, with the exception of the

  horse and a certain kind of ox. In these exceptional cases the

  heart, owing to its large bulk, is provided with a bone as a

  support; just as the bones serve as supports for the body generally.

  In animals of great size the heart has three cavities; in smaller

  animals it has two; and in all has at least one, for, as already

  stated, there must be some place in the heart to serve as a receptacle

  for the first blood; which, as has been mentioned more than once, is

  formed in this organ. But inasmuch as the main blood-vessels are two

  in number, namely the so-called great vessel and the aorta, each of

  which is the origin of other vessels; inasmuch, moreover, as these two

  vessels present differences, hereafter to be discussed, when

  compared with each other, it is of advantage that they also shall

  themselves have distinct origins. This advantage will be obtained if

  each side have its own blood, and the blood of one side be kept

  separate from that of the other. For this reason the heart, whenever

  it is possible, has two receptacles. And this possibility exists in

  the case of large animals, for in them the heart, as the body

  generally, is of large size. Again it is still better that there shall

  be three cavities, so that the middle and odd one may serve as a

  centre common to both sides. But this requires the heart to be of

  greater magnitude, so that it is only in the largest hearts that there

  are three cavities.

  Of these three cavities it is the right that has the most abundant

  and the hottest blood, and this explains why the limbs also on the

  right side of the body are warmer than those on the left. The left

  cavity has the least blood of all, and the coldest; while in the

  middle cavity the blood, as regards quantity and heat, is intermediate

  to the other two, being however of purer quality than either. For it

  behoves the supreme part to be as tranquil as possible, and this

  tranquillity can be ensured by the blood being pure, and of moderate

  amount and warmth.

  In the heart of animals there is also a kind of joint-like division,

  something like the sutures of the skull. This is not, however,

  attributable to the heart being formed by the union of several parts

  into a compound whole, but is rather, as already said, the result of a

  joint-like division. These jointings are most distinct in animals of

  keen sensibility, and less so in those that are of duller feeling,

  in swine for instance. Different hearts differ also from each other in

  their sizes, and in their degrees of firmness; and these differences

  somehow extend their influence to the temperaments of the animals. For

  in animals of low sensibility the heart is hard and dense in

  texture, while it is softer in such as are endowed with keener

  feeling. So also when the heart is of large size the animal is

  timorous, while it is more courageous if the organ be smaller and of

  moderate bulk. For in the former the bodily affection which results

  from terror already pre-exists; for the bulk of the heart is out of

  all proportion to the animal's heat, which being small is reduced to

  insignificance in the large space, and thus the blood is made colder

  than it would otherwise be.

  The heart is of large size in the hare, the deer, the mouse, the

  hyena, the ass, the leopard, the marten, and in pretty nearly all

  other animals that either are manifestly timorous, or betray their

  cowardice by their spitefulness.

  What has been said of the heart as a whole is no less true of its

  cavities and of the blood-vessels; these also if of large size being

  cold. For just as a fire of equal size gives less heat in a large room

  than in a small one, so also does the heat in a large cavity or a

  large blood-vessel, that is in a large receptacle, have less effect

  than in a small one. Moreover, all hot bodies are cooled by motions

  external to themselves, and the more spacious the cavities and vessels

  are, the greater the amount of spirit they contain, and the more

  potent its action. Thus it is that no animal that has large cavities

  in its heart, or large blood-vessels, is ever fat, the vessels being

  indistinct and the cavities small in all or most fat animals.

  The heart again is the only one of the viscera, and indeed the

  only part of the body, that is unable to tolerate any serious

  affection. This is but what might reasonably be expected. For, if

  the primary or dominant part be diseased, there is nothing from

  which the other parts which depend upon it can derive succour. A proof

  that the heart is thus unable to tolerate any morbid affection is

  furnished by the fact that in no sacrificial victim has it ever been

  seen to be affected with those diseases that are observable in the

  other viscera. For the kidneys are frequently found to be full of

  stones, and growths, and small abscesses, as also are the liver, the

  lung, and more than all the spleen. There are also many other morbid

  conditions which are seen to occur in these parts, those which are

  least liable to such being the portion of the lung which is close to

  the windpipe, and the portion of the liver which lies about the

  junction with the great blood-vessel. This again admits of a

  rational explanation. For it is in these parts that the lung and liver

  are most closely in communion with the heart. On the other hand,

  when animals die not by sacrifice but from disease, and from

  affections such as are mentioned above, they are found on dissection

  to have morbid affections of the heart.

  Thus much of the heart, its nature, and the end and cause of its

  existence in such animals as have it.

  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

  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; and this one-ness of the sensory soul determines a

  corresponding one-ness of the part in which it primarily abides. In

  sanguineous animals this one-ness is not only actual but pot
ential,

  whereas in some bloodless animals it is only actual. Where, however,

  the sensory soul is lodged, there also and in the selfsame place

  must necessarily be the source of heat; and, again, where this is

  there also must be the source of the blood, seeing that it thence

  derives its warmth and fluidity. Thus, then, in the oneness of the

  part in which is lodged the prime source of sensation and of heat is

  involved the one-ness of the source in which the blood originates; and

  this, again, explains why the blood-vessels have one common

  starting-point.

  The vessels, again, 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, 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 the blood or analogous fluid is the

  material from which the whole body is made. Now as to the manner in

  which animals are 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 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 about and in its substance.

  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 divide and subdivide so as to 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 grow at the expense of the 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 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, 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 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,

  though no vessel, however small, be visible in it. Yet there can be no

  blood, unless there be a blood-vessel. The vessels then are there, but

  are invisible owing to their being clogged up, just as the dykes for

  irrigation are invisible until they 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 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 cachectic state 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 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 its being small in proportion to the quantity of food,

  when this has been taken excess. 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 passive kind, and not violent as are

  those from the windpipe.

  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 they

  contribute to the unity of the whole fabric. For as in plaited work

  the parts hold more firmly together because of the interweaving, 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 of the different vessels

  must be looked for in the treatises on Anatomy and the Researches

  concerning 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 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 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 la
nd animals breathe, and even some water animals, such as the

  whale, the dolphin, and all the spouting Cetacea. For many animals lie

  half-way between terrestrial and aquatic; some that 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 man condition of life.

  The organ of respiration is the lung. This derives its motion from

  the heart; but it is its own large size and spongy texture that

  affords amplitude of space for 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, inasmuch as he alone is influenced by hope

  and anticipation of the future. Moreover, in most animals the lung

  is separated from the heart by a considerable interval and lies

  above it, so that it can contribute nothing to mitigate any jumping.

  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 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

  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 it is membranous and collapses from a large bulk to a

  small one, as does foam when it runs together. 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

  considerable time under water. For, inasmuch as they have but little