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.