Aristotle

by Various Works [lit]

lungs, but none possess both.

  17

  Every animal in order to exist requires nutriment, in order to

  prevent itself from dying, refrigeration; and so Nature employs the

  same organ for both purposes. For, as in some cases the tongue

  serves both for discerning tastes and for speech, so in animals with

  lungs the mouth is employed both in working up the food and in the

  passage of the breath outwards and inwards. In lungless and

  non-respiring animals it is employed in working up the food, while

  in those of them that require refrigeration it is the gills that are

  created for this purpose.

  We shall state further on how it is that these organs have the

  faculty of producing refrigeration. But to prevent their food from

  impeding these operations there is a similar contrivance in the

  respiring animals and in those that admit water. At the moment of

  respiration they do not take in food, for otherwise suffocation

  results owing to the food, whether liquid or dry, slipping in

  through the windpipe and lying on the lung. The windpipe is situated

  before the oesophagus, through which food passes into what is called

  the stomach, but in quadrupeds which are sanguineous there is, as it

  were, a lid over the windpipe-the epiglottis. In birds and oviparous

  quadrupeds this covering is absent, but its office is discharged by

  a contraction of the windpipe. The latter class contract the

  windpipe when swallowing their food; the former close down the

  epiglottis. When the food has passed, the epiglottis is in the one

  case raised, and in the other the windpipe is expanded, and the air

  enters to effect refrigeration. In animals with gills the water is

  first discharged through them and then the food passes in through

  the mouth; they have no windpipe and hence can take no harm from

  liquid lodging in this organ, only from its entering the stomach.

  For these reasons the expulsion of water and the seizing of their food

  is rapid, and their teeth are sharp and in almost all cases arranged

  in a saw-like fashion, for they are debarred from chewing their food.

  18

  Among water-animals the cetaceans may give rise to some

  perplexity, though they too can be rationally explained.

  Examples of such animals are dolphins and whales, and all others

  that have a blowhole. They have no feet, yet possess a lung though

  admitting the sea-water. The reason for possessing a lung is that

  which we have now stated [refrigeration]; the admission of water is

  not for the purpose of refrigeration. That is effected by respiration,

  for they have a lung. Hence they sleep with their head out of the

  water, and dolphins, at any rate, snore. Further, if they are

  entangled in nets they soon die of suffocation owing to lack of

  respiration, and hence they can be seen to come to the surface owing

  to the necessity of breathing. But, since they have to feed in the

  water, they must admit it, and it is in order to discharge this that

  they all have a blow-hole; after admitting the water they expel it

  through the blow-hole as the fishes do through the gills. The position

  of the blow-hole is an indication of this, for it leads to none of the

  organs which are charged with blood; but it lies before the brain

  and thence discharges water.

  It is for the very same reason that molluscs and crustaceans admit

  water-I mean such animals as Carabi and Carcini. For none of these

  is refrigeration a necessity, for in every case they have little

  heat and are bloodless, and hence are sufficiently cooled by the

  surrounding water. But in feeding they admit water, and hence must

  expel it in order to prevent its being swallowed simultaneously with

  the food. Thus crustaceans, like the Carcini and Carabi, discharge

  water through the folds beside their shaggy parts, while cuttlefish

  and the polyps employ for this purpose the hollow above the head.

  There is, however, a more precise account of these in the History of

  Animals.

  Thus it has been explained that the cause of the admission of the

  water is refrigeration, and the fact that animals constituted for a

  life in water must feed in it.

  19

  An account must next be given of refrigeration and the manner in

  which it occurs in respiring animals and those possessed of gills.

  We have already said that all animals with lungs respire. The reason

  why some creatures have this organ, and why those having it need

  respiration, is that the higher animals have a greater proportion of

  heat, for at the same time they must have been assigned a higher

  soul and they have a higher nature than plants. Hence too those with

  most blood and most warmth in the lung are of greater size, and animal

  in which the blood in the lung is purest and most plentiful is the

  most erect, namely man; and the reason why he alone has his upper part

  directed to the upper part of the universe is that he possesses such a

  lung. Hence this organ as much as any other must be assigned to the

  essence of the animal both in man and in other cases.

  This then is the purpose of refrigeration. As for the constraining

  and efficient cause, we must believe that it created animals like

  this, just as it created many others also not of this constitution.

  For some have a greater proportion of earth in their composition, like

  plants, and others, e.g. aquatic animals, contain a larger amount of

  water; while winged and terrestrial animals have an excess of air

  and fire respectively. It is always in the region proper to the

  element preponderating in the scheme of their constitution that things

  exist.

  20

  Empedocles is then in error when he says that those animals which

  have the most warmth and fire live in the water to counterbalance

  the excess of heat in their constitution, in order that, since they

  are deficient in cold and fluid, they may be kept in life by the

  contrary character of the region they occupy; for water has less

  heat than air. But it is wholly absurd that the water-animals should

  in every case originate on dry land, and afterwards change their place

  of abode to the water; for they are almost all footless. He,

  however, when describing their original structure says that, though

  originating on dry land, they have abandoned it and migrated to the

  water. But again it is evident that they are not warmer than

  land-animals, for in some cases they have no blood at all, in others

  little.

  The question, however, as to what sorts of animals should be

  called warm and what cold, has in each special case received

  consideration. Though in one respect there is reason in the

  explanation which Empedocles aims at establishing, yet his account

  is not correct. Excess in a bodily state is cured by a situation or

  season of opposite character, but the constitution is best

  maintained by an environment akin to it. There is a difference between

  the material of which any animal is constituted and the states and

  dispositions of that material. For example, if nature were to

  constitute a thing
of wax or of ice, she would not preserve it by

  putting it in a hot place, for the opposing quality would quickly

  destroy it, seeing that heat dissolves that which cold congeals.

  Again, a thing composed of salt or nitre would not be taken and placed

  in water, for fluid dissolves that of which the consistency is due

  to the hot and the dry.

  Hence if the fluid and the dry supply the material for all bodies,

  it is reasonable that things the composition of which is due to the

  fluid and the cold should have liquid for their medium [and, if they

  are cold, they will exist in the cold], while that which is due to the

  dry will be found in the dry. Thus trees grow not in water but on

  dry land. But the same theory would relegate them to the water, on

  account of their excess of dryness, just as it does the things that

  are excessively fiery. They would migrate thither not on account of

  its cold but owing to its fluidity.

  Thus the natural character of the material of objects is of the same

  nature as the region in which they exist; the liquid is found in

  liquid, the dry on land, the warm in air. With regard, however, to

  states of body, a cold situation has, on the other hand, a

  beneficial effect on excess of heat, and a warm environment on

  excess of cold, for the region reduces to a mean the excess in the

  bodily condition. The regions appropriate to each material and the

  revolutions of the seasons which all experience supply the means which

  must be sought in order to correct such excesses; but, while states of

  the body can be opposed in character to the environment, the

  material of which it is composed can never be so. This, then, is a

  sufficient explanation of why it is not owing to the heat in their

  constitution that some animals are aquatic, others terrestrial, as

  Empedocles maintains, and of why some possess lungs and others do not.

  21

  The explanation of the admission of air and respiration in those

  animals in which a lung is found, and especially in those in which

  it is full of blood, is to be found in the fact that it is of a spongy

  nature and full of tubes, and that it is the most fully charged with

  blood of all the visceral organs. All animals with a full-blooded lung

  require rapid refrigeration because there is little scope for

  deviation from the normal amount of their vital fire; the air also

  must penetrate all through it on account of the large quantity of

  blood and heat it contains. But both these operations can be easily

  performed by air, for, being of a subtle nature, it penetrates

  everywhere and that rapidly, and so performs its cooling function; but

  water has the opposite characteristics.

  The reason why animals with a full-blooded lung respire most is

  hence manifest; the more heat there is, the greater is the need for

  refrigeration, and at the same time breath can easily pass to the

  source of heat in the heart.

  22

  In order to understand the way in which the heart is connected

  with the lung by means of passages, we must consult both dissections

  and the account in the History of Animals. The universal cause of

  the need which the animal has for refrigeration, is the union of the

  soul with fire that takes place in the heart. Respiration is the means

  of effecting refrigeration, of which those animals make use that

  possess a lung as well as a heart. But when they, as for example the

  fishes, which on account of their aquatic nature have no lung, possess

  the latter organ without the former, the cooling is effected through

  the gills by means of water. For ocular evidence as to how the heart

  is situated relatively to the gills we must employ dissections, and

  for precise details we must refer to Natural History. As a summarizing

  statement, however, and for present purposes, the following is the

  account of the matter.

  It might appear that the heart has not the same position in

  terrestrial animals and fishes, but the position really is

  identical, for the apex of the heart is in the direction in which they

  incline their heads. But it is towards the mouth in fishes that the

  apex of the heart points, seeing that they do not incline their

  heads in the same direction as land-animals do. Now from the extremity

  of the heart a tube of a sinewy, arterial character runs to the centre

  where the gills all join. This then is the largest of those ducts, but

  on either side of the heart others also issue and run to the extremity

  of each gill, and by means of the ceaseless flow of water through

  the gills, effect the cooling which passes to the heart.

  In similar fashion as the fish move their gills, respiring animals

  with rapid action raise and let fall the chest according as the breath

  is admitted or expelled. If air is limited in amount and unchanged

  they are suffocated, for either medium, owing to contact with the

  blood, rapidly becomes hot. The heat of the blood counteracts the

  refrigeration and, when respiring animals can no longer move the

  lung aquatic animals their gills, whether owing to discase or old age,

  their death ensues.

  23

  To be born and to die are common to all animals, but there are

  specifically diverse ways in which these phenomena occur; of

  destruction there are different types, though yet something is

  common to them all. There is violent death and again natural death,

  and the former occurs when the cause of death is external, the

  latter when it is internal, and involved from the beginning in the

  constitution of the organ, and not an affection derived from a foreign

  source. In the case of plants the name given to this is withering,

  in animals senility. Death and decay pertain to all things that are

  not imperfectly developed; to the imperfect also they may be

  ascribed in nearly the same but not an identical sense. Under the

  imperfect I class eggs and seeds of plants as they are before the root

  appears.

  It is always to some lack of heat that death is due, and in

  perfect creatures the cause is its failure in the organ containing the

  source of the creature's essential nature. This member is situate,

  as has been said, at the junction of the upper and lower parts; in

  plants it is intermediate between the root and the stem, in

  sanguineous animals it is the heart, and in those that are bloodless

  the corresponding part of their body. But some of these animals have

  potentially many sources of life, though in actuality they possess

  only one. This is why some insects live when divided, and why, even

  among sanguineous animals, all whose vitality is not intense live

  for a long time after the heart has been removed. Tortoises, for

  example, do so and make movements with their feet, so long as the

  shell is left, a fact to be explained by the natural inferiority of

  their constitution, as it is in insects also.

  The source of life is lost to its possessors when the heat with

  which it is bound up is no longer tempered by cooling, for, as I

  have often remarked, it is consumed by itself. Hence when, owing to
<
br />   lapse of time, the lung in the one class and the gills in the other

  get dried up, these organs become hard and earthy and incapable of

  movement, and cannot be expanded or contracted. Finally things come to

  a climax, and the fire goes out from exhaustion.

  Hence a small disturbance will speedily cause death in old age.

  Little heat remains, for the most of it has been breathed away in

  the long period of life preceding, and hence any increase of strain on

  the organ quickly causes extinction. It is just as though the heart

  contained a tiny feeble flame which the slightest movement puts out.

  Hence in old age death is painless, for no violent disturbance is

  required to cause death, and there is an entire absence of feeling

  when the soul's connexion is severed. All diseases which harden the

  lung by forming tumours or waste residues, or by excess of morbid

  heat, as happens in fevers, accelerate the breathing owing to the

  inability of the lung to move far either upwards or downwards.

  Finally, when motion is no longer possible, the breath is given out

  and death ensues.

  24

  Generation is the initial participation, mediated by warm substance,

  in the nutritive soul, and life is the maintenance of this

  participation. Youth is the period of the growth of the primary

  organ of refrigeration, old age of its decay, while the intervening

  time is the prime of life.

  A violent death or dissolution consists in the extinction or

  exhaustion of the vital heat (for either of these may cause

  dissolution), while natural death is the exhaustion of the heat

  owing to lapse of time, and occurring at the end of life. In plants

  this is to wither, in animals to die. Death, in old age, is the

  exhaustion due to inability on the part of the organ, owing to old

  age, to produce refrigeration. This then is our account of

  generation and life and death, and the reason for their occurrence

  in animals.