Various Works

results. Yet this was just the time when the external air should enter

  and annul the expulsive movement, whereas it is the opposite that

  occurs. For when the breath is not let out and the heat accumulates

  too much then we need to respire, and to respire we must draw in the

  breath. When hot, people breathe rapidly, because they must do so in

  order to cool themselves, just when the theory of Democritus would

  make them add fire to fire.

  11

  The theory found in the Timaeus, of the passing round of the

  breath by pushing, by no means determines how, in the case of the

  animals other than land-animals, their heat is preserved, and

  whether it is due to the same or a different cause. For if respiration

  occurs only in land-animals we should be told what is the reason of

  that. Likewise, if it is found in others also, but in a different

  form, this form of respiration, if they all can breathe, must also

  be described.

  Further, the method of explaining involves a fiction. It is said

  that when the hot air issues from the mouth it pushes the

  surrounding air, which being carried on enters the very place whence

  the internal warmth issued, through the interstices of the porous

  flesh; and this reciprocal replacement is due to the fact that a

  vacuum cannot exist. But when it has become hot the air passes out

  again by the same route, and pushes back inwards through the mouth the

  air that had been discharged in a warm condition. It is said that it

  is this action which goes on continuously when the breath is taken

  in and let out.

  But according to this way of thinking it will follow that we breathe

  out before we breathe in. But the opposite is the case, as evidence

  shows, for though these two functions go on in alternation, yet the

  last act when life comes to a close is the letting out of the

  breath, and hence its admission must have been the beginning of the

  process.

  Once more, those who give this kind of explanation by no means state

  the final cause of the presence in animals of this function (to wit

  the admission and emission of the breath), but treat it as though it

  were a contingent accompaniment of life. Yet it evidently has

  control over life and death, for it results synchronously that when

  respiring animals are unable to breathe they perish. Again, it is

  absurd that the passage of the hot air out through the mouth and

  back again should be quite perceptible, while we were not able to

  detect the thoracic influx and the return outwards once more of the

  heated breath. It is also nonsense that respiration should consist

  in the entrance of heat, for the evidence is to the contrary effect;

  what is breathed out is hot, and what is breathed in is cold. When

  it is hot we pant in breathing, for, because what enters does not

  adequately perform its cooling function, we have as a consequence to

  draw the breath frequently.

  12

  It is certain, however, that we must not entertain the notion that

  it is for purposes of nutrition that respiration is designed, and

  believe that the internal fire is fed by the breath; respiration, as

  it were, adding fuel to the fire, while the feeding of the flame

  results in the outward passage of the breath. To combat this

  doctrine I shall repeat what I said in opposition to the previous

  theories. This, or something analogous to it, should occur in the

  other animals also (on this theory), for all possess vital heat.

  Further, how are we to describe this fictitious process of the

  generation of heat from the breath? Observation shows rather that it

  is a product of the food. A consequence also of this theory is that

  the nutriment would enter and the refuse be discharged by the same

  channel, but this does not appear to occur in the other instances.

  13

  Empedocles also gives an account of respiration without, however,

  making clear what its purpose is, or whether or not it is universal in

  animals. Also when dealing with respiration by means of the nostrils

  he imagines he is dealing with what is the primary kind of

  respiration. Even the breath which passes through the nostrils

  passes through the windpipe out of the chest as well, and without

  the latter the nostrils cannot act. Again, when animals are bereft

  of respiration through the nostrils, no detrimental result ensues,

  but, when prevented from breathing through the windpipe, they die.

  Nature employs respiration through the nostrils as a secondary

  function in certain animals in order to enable them to smell. But

  the reason why it exists in some only is that though almost all

  animals are endowed with the sense of smell, the sense-organ is not

  the same in all.

  A more precise account has been given about this elsewhere.

  Empedocles, however, explains the passage inwards and outwards of

  the breath, by the theory that there are certain blood-vessels, which,

  while containing blood, are not filled by it, but have passages

  leading to the outer air, the calibre of which is fine in contrast

  to the size of the solid particles, but large relatively to those in

  the air. Hence, since it is the nature of the blood to move upwards

  and downwards, when it moves down the air rushes in and inspiration

  occurs; when the blood rises, the air is forced out and the outward

  motion of the breath results. He compares this process to what

  occurs in a clepsydra.

  Thus all things outwards breathe and in;- their flesh has tubes

  Bloodless, that stretch towards the body's outmost edge,

  Which, at their mouths, full many frequent channels pierce,

  Cleaving the extreme nostrils through; thus, while the gore

  Lies hid, for air is cut a thoroughfare most plain.

  And thence, whenever shrinks away the tender blood,

  Enters the blustering wind with swelling billow wild.

  But when the blood leaps up, backward it breathes. As when

  With water-clock of polished bronze a maiden sporting,

  Sets on her comely hand the narrow of the tube

  And dips it in the frail-formed water's silvery sheen;

  Not then the flood the vessel enters, but the air,

  Until she frees the crowded stream. But then indeed

  Upon the escape runs in the water meet.

  So also when within the vessel's deeps the water

  Remains, the opening by the hand of flesh being closed,

  The outer air that entrance craves restrains the flood

  At the gates of the sounding narrow,

  upon the surface pressing,

  Until the maid withdraws her hand. But then in contrariwise

  Once more the air comes in and water meet flows out.

  Thus to the to the subtle blood, surging throughout the limbs,

  Whene'er it shrinks away into the far recesses

  Admits a stream of air rushing with swelling wave,

  But, when it backward leaps, in like bulk air flows out.

  This then is what he says of respiration. But, as we said, all

  animals that evidently respire do so by means of the windpipe, when

  they breathe either through the mouth or through the nostrils.

  Hence, if it is of this kind of respiration
that he is talking, we

  must ask how it tallies with the explanation given. But the facts seem

  to be quite opposed. The chest is raised in the manner of a

  forge-bellows when the breath is drawn in-it is quite reasonable

  that it should be heat which raises up and that the blood should

  occupy the hot region-but it collapses and sinks down, like the

  bellows once more, when the breath is let out. The difference is

  that in a bellows it is not by the same channel that the air is

  taken in and let out, but in breathing it is.

  But, if Empedocles is accounting only for respiration through the

  nostrils, he is much in error, for that does not involve the

  nostrils alone, but passes by the channel beside the uvula where the

  extremity of the roof of the mouth is, some of the air going this

  way through the apertures of the nostrils and some through the

  mouth, both when it enters and when it passes out. Such then is the

  nature and magnitude of the difficulties besetting the theories of

  other writers concerning

  respiration.

  14

  We have already stated that life and the presence of soul involve

  a certain heat. Not even the digesting process to which is due the

  nutrition of animals occurs apart from soul and warmth, for it is to

  fire that in all cases elaboration is due. It is for this reason,

  precisely, that the primary nutritive soul also must be located in

  that part of the body and in that division of this region which is the

  immediate vehicle of this principle. The region in question is

  intermediate between that where food enters and that where excrement

  is discharged. In bloodless animals it has no name, but in the

  sanguineous class this organ is called the heart. The blood

  constitutes the nutriment from which the organs of the animal are

  directly formed. Likewise the bloodvessels must have the same

  originating source, since the one exists for the other's behoof-as a

  vessel or receptacle for it. In sanguineous animals the heart is the

  starting-point of the veins; they do not traverse it, but are found to

  stretch out from it, as dissections enable us to see.

  Now the other psychical faculties cannot exist apart from the

  power of nutrition (the reason has already been stated in the treatise

  On the Soul), and this depends on the natural fire, by the union

  with which Nature has set it aglow. But fire, as we have already

  stated, is destroyed in two ways, either by extinction or by

  exhaustion. It suffers extinction from its opposites. Hence it can

  be extinguished by the surrounding cold both when in mass and

  (though more speedily) when scattered. Now this way of perishing is

  due to violence equally in living and in lifeless objects, for the

  division of an animal by instruments and consequent congelation by

  excess of cold cause death. But exhaustion is due to excess of heat;

  if there is too much heat close at hand and the thing burning does not

  have a fresh supply of fuel added to it, it goes out by exhaustion,

  not by the action of cold. Hence, if it is going to continue it must

  be cooled, for cold is a preventive against this form of extinction.

  15

  Some animals occupy the water, others live on land, and, that being

  so, in the case of those which are very small and bloodless the

  refrigeration due to the surrounding water or air is sufficient to

  prevent destruction from this cause. Having little heat, they

  require little cold to combat it. Hence too such animals are almost

  all short-lived, for, being small, they have less scope for deflection

  towards either extreme. But some insects are longer-lived though

  bloodless, like all the others), and these have a deep indentation

  beneath the waist, in order to secure cooling through the membrane,

  which there is thinner. They are warmer animals and hence require more

  refrigeration, and such are bees (some of which live as long as

  seven years) and all that make a humming noise, like wasps,

  cockchafers, and crickets. They make a sound as if of panting by means

  of air, for, in the middle section itself, the air which exists

  internally and is involved in their construction, causing a rising and

  falling movement, produces friction against the membrane. The way in

  which they move this region is like the motion due to the lungs in

  animals that breathe the outer air, or to the gills in fishes. What

  occurs is comparable to the suffocation of a respiring animal by

  holding its mouth, for then the lung causes a heaving motion of this

  kind. In the case of these animals this internal motion is not

  sufficient for refrigeration, but in insects it is. It is by

  friction against the membrane that they produce the humming sound,

  as we said, in the way that children do by blowing through the holes

  of a reed covered by a fine membrane. It is thus that the singing

  crickets too produce their song; they possess greater warmth and are

  indented at the waist, but the songless variety have no fissure there.

  Animals also which are sanguineous and possess a lung, though that

  contains little blood and is spongy, can in some cases, owing to the

  latter fact, live a long time without breathing; for the lung,

  containing little blood or fluid, can rise a long way: its own

  motion can for a long time produce sufficient refrigeration. But at

  last it ceases to suffice, and the animal dies of suffocation if it

  does not respire-as we have already said. For of exhaustion that

  kind which is destruction due to lack of refrigeration is called

  suffocation, and whatsoever is thus destroyed is said to be

  suffocated.

  We have already stated that among animals insects do not respire,

  and the fact is open to observation in the case of even small

  creatures like flies and bees, for they can swim about in a fluid

  for a long time if it is not too hot or too cold. Yet animals with

  little strength tend to breathe more frequently. These, however, die

  of what is called suffocation when the stomach becomes filled and

  the heat in the central segment is destroyed. This explains also why

  they revive after being among ashes for a time.

  Again among water-animals those that are bloodless remain alive

  longer in air than those that have blood and admit the sea-water,

  as, for example, fishes. Since it is a small quantity of heat they

  possess, the air is for a long time adequate for the purposes of

  refrigeration in such animals as the crustacea and the polyps. It does

  not however suffice, owing to their want of heat, to keep them finally

  in life, for most fishes also live though among earth, yet in a

  motionless state, and are to be found by digging. For all animals that

  have no lung at all or have a bloodless one require less

  refrigeration.

  16

  Concerning the bloodless animals we have declared that in some cases

  it is the surrounding air, in others fluid, that aids the

  maintenance of life. But in the case of animals possessing blood and

  heart, all which have a lung admit the air and produce the cooling

  effect by breat
hing in and out. All animals have a lung that are

  viviparous and are so internally, not externally merely (the

  Selachia are viviparous, but not internally), and of the oviparous

  class those that have wings, e.g. birds, and those with scales, e.g.

  tortoises, lizards, and snakes. The former class have a lung charged

  with blood, but in the most part of the latter it is spongy. Hence

  they employ respiration more sparingly as already said. The function

  is found also in all that frequent and pass their life in the water,

  e.g. the class of water-snakes and frogs and crocodiles and hemydes,

  both sea- and land-tortoises, and seals.

  All these and similar animals both bring forth on land and sleep

  on shore or, when they do so in the water, keep the head above the

  surface in order to respire. But all with gills produce

  refrigeration by taking in water; the Selachia and all other

  footless animals have gills. Fish are footless, and the limbs they

  have get their name (pterugion) from their similarity to wings

  (pterux). But of those with feet one only, so far as observed, has

  gills. It is called the tadpole.

  No animal yet has been seen to possess both lungs and gills, and the

  reason for this is that the lung is designed for the purpose of

  refrigeration by means of the air (it seems to have derived its name

  (pneumon) from its function as a receptacle of the breath (pneuma)),

  while gills are relevant to refrigeration by water. Now for one

  purpose one organ is adapted and one single means of refrigeration

  is sufficient in every case. Hence, since we see that Nature does

  nothing in vain, and if there were two organs one would be

  purposeless, this is the reason why some animals have gills, others

  lungs, but none possess both.