Aristotle

by Various Works [lit]

  heat, the very motion of the lung, airlike and void, suffices by

  itself to cool them for a considerable period.

  These animals, speaking generally, are also distinguished from

  others by their smaller bulk. For heat promotes growth, and

  abundance of blood is a sure indication of heat. Heat, again, tends to

  make the body erect; and thus it is that man is the most erect of

  animals, and the vivipara more erect than other quadrupeds. For no

  viviparous animal, be it apodous or be it possessed of feet, is so

  given to creep into holes as are the ovipara.

  The lung, then, exists for respiration; and this is its universal

  office; 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

  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

  essence, 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 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 lie half-way between the single and the double

  organs. 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 under one supreme centre. 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 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 of 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 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 cartilaginous and some

  other fishes.

  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 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 do the viscera tend to be bilateral and

  yet one by unity of constitution.

  Those viscera which lie below the diaphragm exist one and all on

  account of 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 anchorlines thrown

  out from a ship. The great vessel sends such branches to the liver and

  the spleen; and these viscera-the liver 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,

  but none to the liver or spleen.

  These viscera, then, contribute in this manner to the compactness of

  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 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, and these two alone, are invariably

  found in them all. In such of them, however, as breathe, there is also

  as invariably a third, namely the lung. The spleen, on the other hand,

  is not invariably present; and, in those animals that have it, is only

  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 an inevitable 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 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 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 similar diversion of the fluids

  into the belly. But in those animals that have but little

  superfluous fluid 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 superfluous fluid 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 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 right is conjoined with hot, after the manner

  described, and left with cold.

  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 where this fluid is very

  abundantly formed, their presence enables the bladder to perform its

  proper office with greater perfection.

  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 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 and therefore has

  to be considered with them.

  8

  It is not every animal that has a bladder; those only being

  apparently 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 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 it comes to pass that 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 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 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 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 sea-tortoise a large

  one, the land-tortoises an extremely small one.

  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 allotted

  to the formation of the kidneys, unable to find one single place of

  sufficient size, had been scattered over several.

  The Emys 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 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 animals, excepting the seal. The kidneys of this

  animal are more solid than those of any other, and in form resemble

  the kidneys of the ox. The human kidneys are of similar shape; 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 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 is any

  coagulum found there after death. A pair of stout ducts, 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 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 ill-savoured 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; for, as already has been stated, it is attached to them by

  strong ducts. These then are the purposes 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 side are in consequence stronger than

  those on the left, they must all push upwards in advance of their

  opposite fellows; as may be seen in the fact that men even raise the

  right eyebrow more than the left, and that 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.

  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

  kidne
ys 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 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 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 same time the fat has a

  final cause, namely 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 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 side are naturally more solid and

  more suited for motion than those on the left. But motion is