350 BC
by Aristotle
translated by G. R. T. Ross

WE must now treat of youth and old age and life and death. We must
probably also at the same time state the causes of respiration as
well, since in some cases living and the reverse depend on this.
We have elsewhere given a precise account of the soul, and while
it is clear that its essential reality cannot be corporeal, yet
manifestly it must exist in some bodily part which must be one of
those possessing control over the members. Let us for the present
set aside the other divisions or faculties of the soul (whichever of
the two be the correct name). But as to being what is called an animal
and a living thing, we find that in all beings endowed with both
characteristics (viz. being an animal and being alive) there must be a
single identical part in virtue of which they live and are called
animals; for an animal qua animal cannot avoid being alive. But a
thing need not, though alive, be animal, for plants live without
having sensation, and it is by sensation that we distinguish animal
from what is not animal.
This organ, then, must be numerically one and the same and yet
possess multiple and disparate aspects, for being animal and living
are not identical. Since then the organs of special sensation have one
common organ in which the senses when functioning must meet, and
this must be situated midway between what is called before and
behind (we call 'before' the direction from which sensation comes,
'behind' the opposite), further, since in all living things the body
is divided into upper and lower (they all have upper and lower
parts, so that this is true of plants as well), clearly the
nutritive principle must be situated midway between these regions.
That part where food enters we call upper, considering it by itself
and not relatively to the surrounding universe, while downward is that
part by which the primary excrement is discharged.
Plants are the reverse of animals in this respect. To man in
particular among the animals, on account of his erect stature, belongs
the characteristic of having his upper parts pointing upwards in the
sense in which that applies to the universe, while in the others these
are in an intermediate position. But in plants, owing to their being
stationary and drawing their sustenance from the ground, the upper
part must always be down; for there is a correspondence between the
roots in a plant and what is called the mouth in animals, by means
of which they take in their food, whether the source of supply be
the earth or each other's bodies.


All perfectly formed animals are to be divided into three parts, one
that by which food is taken in, one that by which excrement is
discharged, and the third the region intermediate between them. In the
largest animals this latter is called the chest and in the others
something corresponding; in some also it is more distinctly marked off
than in others. All those also that are capable of progression have
additional members subservient to this purpose, by means of which they
bear the whole trunk, to wit legs and feet and whatever parts are
possessed of the same powers. Now it is evident both by observation
and by inference that the source of the nutritive soul is in the midst
of the three parts. For many animals, when either part-the head or the
receptacle of the food-is cut off, retain life in that member to which
the middle remains attached. This can be seen to occur in many
insects, e.g. wasps and bees, and many animals also besides insects
can, though divided, continue to live by means of the part connected
with nutrition.
While this member is indeed in actuality single, yet potentially
it is multiple, for these animals have a constitution similar to
that of Plants; plants when cut into sections continue to live, and
a number of trees can be derived from one single source. A separate
account will be given of the reason why some plants cannot live when
divided, while others can be propagated by the taking of slips. In
this respect, however, plants and insects are alike.
It is true that the nutritive soul, in beings possessing it, while
actually single must be potentially plural. And it is too with the
principle of sensation, for evidently the divided segments of these
animals have sensation. They are unable, however, to preserve their
constitution, as plants can, not possessing the organs on which the
continuance of life depends, for some lack the means for seizing,
others for receiving their food; or again they may be destitute of
other organs as well.
Divisible animals are like a number of animals grown together, but
animals of superior construction behave differently because their
constitution is a unity of the highest possible kind. Hence some of
the organs on division display slight sensitiveness because they
retain some psychical susceptibility; the animals continue to move
after the vitals have been abstracted: tortoises, for example, do so
even after the heart has been removed.


The same phenomenon is evident both in plants and in animals, and in
plants we note it both in their propagation by seed and in grafts
and cuttings. Genesis from seeds always starts from the middle. All
seeds are bivalvular, and the place of junction is situated at the
point of attachment (to the plant), an intermediate part belonging
to both halves. It is from this part that both root and stem of
growing things emerge; the starting-point is in a central position
between them. In the case of grafts and cuttings this is
particularly true of the buds; for the bud is in a way the
starting-point of the branch, but at the same time it is in a
central position. Hence it is either this that is cut off, or into
this that the new shoot is inserted, when we wish either a new
branch or a new root to spring from it; which proves that the point of
origin in growth is intermediate between stem and root.
Likewise in sanguineous animals the heart is the first organ
developed; this is evident from what has been observed in those
cases where observation of their growth is possible. Hence in
bloodless animals also what corresponds to the heart must develop
first. We have already asserted in our treatise on The Parts of
Animals that it is from the heart that the veins issue, and that in
sanguineous animals the blood is the final nutriment from which the
members are formed. Hence it is clear that there is one function in
nutrition which the mouth has the faculty of performing, and a
different one appertaining to the stomach. But it is the heart that
has supreme control, exercising an additional and completing function.
Hence in sanguineous animals the source both of the sensitive and of
the nutritive soul must be in the heart, for the functions relative to
nutrition exercised by the other parts are ancillary to the activity
of the heart. It is the part of the dominating organ to achieve the
final result, as of the physician's efforts to be directed towards
health, and not to be occupied with subordinate offices.
Certainly, however, all saguineous animals have the supreme organ of
the sensefaculties in the heart, for it is here that we must look
for the common sensorium belonging to all the sense-organs. These in
two cases, taste and touch, can be clearly seen to extend to the
heart, and hence the others also must lead to it, for in it the
other organs may possibly initiate changes, whereas with the upper
region of the body taste and touch have no connexion. Apart from these
considerations, if the life is always located in this part,
evidently the principle of sensation must be situated there too, for
it is qua animal that an animal is said to be a living thing, and it
is called animal because endowed with sensation. Elsewhere in other
works we have stated the reasons why some of the sense-organs are,
as is evident, connected with the heart, while others are situated
in the head. (It is this fact that causes some people to think that it
is in virtue of the brain that the function of perception belongs to


Thus if, on the one hand, we look to the observed facts, what we
have said makes it clear that the source of the sensitive soul,
together with that connected with growth and nutrition, is situated in
this organ and in the central one of the three divisions of the
body. But it follows by deduction also; for we see that in every case,
when several results are open to her, Nature always brings to pass the
best. Now if both principles are located in the midst of the
substance, the two parts of the body, viz. that which elaborates and
that which receives the nutriment in its final form will best
perform their appropriate function; for the soul will then be close to
each, and the central situation which it will, as such, occupy is
the position of a dominating power.
Further, that which employs an instrument and the instrument it
employs must be distinct (and must be spatially diverse too, if
possible, as in capacity), just as the flute and that which plays
it-the hand-are diverse. Thus if animal is defined by the possession
of sensitive soul, this soul must in the sanguineous animals be in the
heart, and, in the bloodless ones, in the corresponding part of
their body. But in animals all the members and the whole body
possess some connate warmth of constitution, and hence when alive they
are observed to be warm, but when dead and deprived of life they are
the opposite. Indeed, the source of this warmth must be in the heart
in sanguineous animals, and in the case of bloodless animals in the
corresponding organ, for, though all parts of the body by means of
their natural heat elaborate and concoct the nutriment, the
governing organ takes the chief share in this process. Hence, though
the other members become cold, life remains; but when the warmth
here is quenched, death always ensues, because the source of heat in
all the other members depends on this, and the soul is, as it were,
set aglow with fire in this part, which in sanguineous animals is
the heart and in the bloodless order the analogous member. Hence, of
necessity, life must be coincident with the maintenance of heat, and
what we call death is its destruction.


However, it is to be noticed that there are two ways in which fire
ceases to exist; it may go out either by exhaustion or by
extinction. That which is self-caused we call exhaustion, that due
to its opposites extinction. [The former is that due to old age, the
latter to violence.] But either of these ways in which fire ceases
to be may be brought about by the same cause, for, when there is a
deficiency of nutriment and the warmth can obtain no maintenance,
the fire fails; and the reason is that the opposite, checking
digestion, prevents the fire from being fed. But in other cases the
result is exhaustion,-when the heat accumulates excessively owing to
lack of respiration and of refrigeration. For in this case what
happens is that the heat, accumulating in great quantity, quickly uses
up its nutriment and consumes it all before more is sent up by
evaporation. Hence not only is a smaller fire readily put out by a
large one, but of itself the candle flame is consumed when inserted in
a large blaze just as is the case with any other combustible. The
reason is that the nutriment in the flame is seized by the larger
one before fresh fuel can be added, for fire is ever coming into being
and rushing just like a river, but so speedily as to elude
Clearly therefore, if the bodily heat must be conserved (as is
necessary if life is to continue), there must be some way of cooling
the heat resident in the source of warmth. Take as an illustration
what occurs when coals are confined in a brazier. If they are kept
covered up continuously by the so-called 'choker', they are quickly
extinguished, but, if the lid is in rapid alternation lifted up and
put on again they remain glowing for a long time. Banking up a fire
also keeps it in, for the ashes, being porous, do not prevent the
passage of air, and again they enable it to resist extinction by the
surrounding air by means of the supply of heat which it possesses.
However, we have stated in The Problems the reasons why these
operations, namely banking up and covering up a fire, have the
opposite effects (in the one case the fire goes out, in the other it
continues alive for a considerable time).


Everything living has soul, and it, as we have said, cannot exist
without the presence of heat in the constitution. In plants the
natural heat is sufficiently well kept alive by the aid which their
nutriment and the surrounding air supply. For the food has a cooling
effect [as it enters, just as it has in man] when first it is taken
in, whereas abstinence from food produces heat and thirst. The air, if
it be motionless, becomes hot, but by the entry of food a motion is
set up which lasts until digestion is completed and so cools it. If
the surrounding air is excessively cold owing to the time of year,
there being severe frost, plants shrivel, or if, in the extreme
heats of summer the moisture drawn from the ground cannot produce
its cooling effect, the heat comes to an end by exhaustion. Trees
suffering at such seasons are said to be blighted or star-stricken.
Hence the practice of laying beneath the roots stones of certain
species or water in pots, for the purpose of cooling the roots of
the plants.
Some animals pass their life in the water, others in the air, and
therefore these media furnish the source and means of refrigeration,
water in the one case, air in the other. We must proceed-and it will
require further application on our part-to give an account of the
way and manner in which this refrigeration occurs.


A few of the previous physical philosophers have spoken of
respiration. The reason, however, why it exists in animals they have
either not declared or, when they have, their statements are not
correct and show a comparative lack of acquaintance with the facts.
Moreover they assert that all animals respire-which is untrue. Hence
these points must first claim our attention, in order that we may
not be thought to make unsubstantiated charges against authors no
longer alive.
First then, it is evident that all animals with lungs breathe, but
in some cases breathing animals have a bloodless and spongy lung,
and then there is less need for respiration. These animals can
remain under water for a time, which relatively to their bodily
strength, is considerable. All oviparous animals, e.g. the frog-tribe,
have a spongy lung. Also hemydes and tortoises can remain for a long
time immersed in water; for their lung, containing little blood, has
not much heat. Hence, when once it is inflated, it itself, by means of
its motion, produces a cooling effect and enables the animal to remain
immersed for a long time. Suffocation, however, always ensues if the
animal is forced to hold its breath for too long a time, for none of
this class take in water in the way fishes do. On the other hand,
animals which have the lung charged with blood have greater need of
respiration on account of the amount of their heat, while none at
all of the others which do not possess lungs breathe.


Democritus of Abdera and certain others who have treated of
respiration, while saying nothing definite about the lungless animals,
nevertheless seem to speak as if all breathed. But Anaxagoras and
Diogenes both maintain that all breathe, and state the manner in which
fishes and oysters respire. Anaxagoras says that when fishes discharge
water through their gills, air is formed in the mouth, for there can
be no vacuum, and that it is by drawing in this that they respire.
Diogenes' statement is that, when they discharge water through their
gills, they suck the air out of the water surrounding the mouth by
means of the vacuum formed in the mouth, for he believes there is
air in the water.
But these theories are untenable. Firstly, they state only what is
the common element in both operations and so leave out the half of the
matter. For what goes by the name of respiration consists, on the
one hand, of inhalation, and, on the other, of the exhalation of
breath; but, about the latter they say nothing, nor do they describe
how such animals emit their breath. Indeed, explanation is for them
impossible for, when the creatures respire, they must discharge
their breath by the same passage as that by which they draw it in, and
this must happen in alternation. Hence, as a result, they must take
the water into their mouth at the same time as they breathe out. But
the air and the water must meet and obstruct each other. Further, when
they discharge the water they must emit their breath by the mouth or
the gills, and the result will be that they will breathe in and
breathe out at the same time, for it is at that moment that
respiration is said to occur. But it is impossible that they should do
both at the same time. Hence, if respiring creatures must both
exhale and inhale the air, and if none of these animals can breathe
out, evidently none can respire at all.


Further, the assertion that they draw in air out of the mouth or out
of the water by means of the mouth is an impossibility, for, not
having a lung, they have no windpipe; rather the stomach is closely
juxtaposed to the mouth, so that they must do the sucking with the
stomach. But in that case the other animals would do so also, which is
not the truth; and the water-animals also would be seen to do it
when out of the water, whereas quite evidently they do not. Further,
in all animals that respire and draw breath there is to be observed
a certain motion in the part of the body which draws in the air, but
in the fishes this does not occur. Fishes do not appear to move any of
the parts in the region of the stomach, except the gills alone, and
these move both when they are in the water and when they are thrown on
to dry land and gasp. Moreover, always when respiring animals are
killed by being suffocated in water, bubbles are formed of the air
which is forcibly discharged, as happens, e.g. when one forces a
tortoise or a frog or any other animal of a similar class to stay
beneath water. But with fishes this result never occurs, in whatsoever
way we try to obtain it, since they do not contain air drawn from an
external source. Again, the manner of respiration said to exist in
them might occur in the case of men also when they are under water.
For if fishes draw in air out of the surrounding water by means of
their mouth why should not men too and other animals do so also;
they should also, in the same way as fishes, draw in air out of the
mouth. If in the former case it were possible, so also should it be in
the latter. But, since in the one it is not so, neither does it
occur in the other. Furthermore, why do fishes, if they respire, die
in the air and gasp (as can be seen) as in suffocation? It is not want
of food that produces this effect upon them, and the reason given by
Diogenes is foolish, for he says that in air they take in too much air
and hence die, but in the water they take in a moderate amount. But
that should be a possible occurrence with land animals also; as
facts are, however, no land animal seems to be suffocated by excessive
respiration. Again, if all animals breathe, insects must do so also.
many of them seem to live though divided not merely into two, but into
several parts, e.g. the class called Scolopendra. But how can they,
when thus divided, breathe, and what is the organ they employ? The
main reason why these writers have not given a good account of these
facts is that they have no acquaintance with the internal organs,
and that they did not accept the doctrine that there is a final
cause for whatever Nature does. If they had asked for what purpose
respiration exists in animals, and had considered this with
reference to the organs, e.g. the gills and the lungs, they would have
discovered the reason more speedily.


Democritus, however, does teach that in the breathing animals
there is a certain result produced by respiration; he asserts that
it prevents the soul from being extruded from the body.
Nevertheless, he by no means asserts that it is for this purpose
that Nature so contrives it, for he, like the other physical
philosophers, altogether fails to attain to any such explanation.
His statement is that the soul and the hot element are identical,
being the primary forms among the spherical particles. Hence, when
these are being crushed together by the surrounding atmosphere
thrusting them out, respiration, according to his account, comes in to
succour them. For in the air there are many of those particles which
he calls mind and soul. Hence, when we breathe and the air enters,
these enter along with it, and by their action cancel the pressure,
thus preventing the expulsion of the soul which resides in the animal.
This explains why life and death are bound up with the taking in and
letting out of the breath; for death occurs when the compression by
the surrounding air gains the upper hand, and, the animal being unable
to respire, the air from outside can no longer enter and counteract
the compression. Death is the departure of those forms owing to the
expulsive pressure exerted by the surrounding air. Death, however,
occurs not by haphazard but, when natural, owing to old age, and, when
unnatural, to violence.
But the reason for this and why all must die Democritus has by no
means made clear. And yet, since evidently death occurs at one time of
life and not at another, he should have said whether the cause is
external or internal. Neither does he assign the cause of the
beginning of respiration, nor say whether it is internal or
external. Indeed, it is not the case that the external mind
superintends the reinforcement; rather the origin of breathing and
of the respiratory motion must be within: it is not due to pressure
from around. It is absurd also that what surrounds should compress and
at the same time by entering dilate. This then is practically his
theory, and how he puts it.
But if we must consider that our previous account is true, and
that respiration does not occur in every animal, we must deem that
this explains death not universally, but only in respiring animals.
Yet neither is it a good account of these even, as may clearly be seen
from the facts and phenomena of which we all have experience. For in
hot weather we grow warmer, and, having more need of respiration, we
always breathe faster. But, when the air around is cold and
contracts and solidifies the body, retardation of the breathing
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.


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
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.


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.


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

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.


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
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

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 breathing 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.


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.


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
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.


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


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
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.


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.


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.


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
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
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.


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.


It is hence also clear why respiring animals are suffocated in water
and fishes in air. For it is by water in the latter class, by air in
the former that refrigeration is effected, and either of these means
of performing the function is removed by a change of environment.
There is also to be explained in either case the cause of the
cause of the motion of the gills and of the lungs, the rise and fall
of which effects the admission and expulsion of the breath or of
water. The following, moreover, is the manner of the constitution of
the organ.


In connexion with the heart there are three phenomena, which, though
apparently of the same nature, are really not so, namely
palpitation, pulsation, and respiration.
Palpitation is the rushing together of the hot substance in the
heart owing to the chilling influence of residual or waste products.
It occurs, for example, in the ailment known as 'spasms' and in
other diseases. It occurs also in fear, for when one is afraid the
upper parts become cold, and the hot substance, fleeing away, by its
concentration in the heart produces palpitation. It is crushed into so
small a space that sometimes life is extinguished, and the animals die
of the fright and morbid disturbance.
The beating of the heart, which, as can be seen, goes on
continuously, is similar to the throbbing of an abscess. That,
however, is accompanied by pain, because the change produced in the
blood is unnatural, and it goes on until the matter formed by
concoction is discharged. There is a similarity between this
phenomenon and that of boiling; for boiling is due to the
volatilization of fluid by heat and the expansion consequent on
increase of bulk. But in an abscess, if there is no evaporation
through the walls, the process terminates in suppuration due to the
thickening of the liquid, while in boiling it ends in the escape of
the fluid out of the containing vessel.
In the heart the beating is produced by the heat expanding the
fluid, of which the food furnishes a constant supply. It occurs when
the fluid rises to the outer wall of the heart, and it goes on
continuously; for there is a constant flow of the fluid that goes to
constitute the blood, it being in the heart that the blood receives
its primary elaboration. That this is so we can perceive in the
initial stages of generation, for the heart can be seen to contain
blood before the veins become distinct. This explains why pulsation in
youth exceeds that in older people, for in the young the formation
of vapour is more abundant.
All the veins pulse, and do so simultaneously with each other, owing
to their connexion with the heart. The heart always beats, and hence
they also beat continuously and simultaneously with each other and
with it.
Palpitation, then, is the recoil of the heart against the
compression due to cold; and pulsation is the volatilization of the
heated fluid.


Respiration takes place when the hot substance which is the seat
of the nutritive principle increases. For it, like the rest of the
body, requires nutrition, and more so than the members, for it is
through it that they are nourished. But when it increases it
necessarily causes the organ to rise. This organ we must to be
constructed like the bellows in a smithy, for both heart and lungs
conform pretty well to this shape. Such a structure must be double,
for the nutritive principle must be situated in the centre of the
natural force.
Thus on increase of bulk expansion results, which necessarily causes
the surrounding parts to rise. Now this can be seen to occur when
people respire; they raise their chest because the motive principle of
the organ described resident within the chest causes an identical
expansion of this organ. When it dilates the outer air must rush in as
into a bellows, and, being cold, by its chilling influence reduces
by extinction the excess of the fire. But, as the increase of bulk
causes the organ to dilate, so diminution causes contraction, and when
it collapses the air which entered must pass out again. When it enters
the air is cold, but on issuing it is warm owing to its contact with
the heat resident in this organ, and this is specially the case in
those animals that possess a full-blooded lung. The numerous
canal-like ducts in the lung, into which it passes, have each a
blood-vessel lying alongside, so that the whole lung is thought to
be full of blood. The inward passage of the air is called respiration,
the outward expiration, and this double movement goes on
continuously just so long as the animal lives and keeps this organ
in continuous motion; it is for this reason that life is bound up with
the passage of the breath outwards and inwards.
It is in the same way that the motion of the gills in fishes takes
place. When the hot substance in the blood throughout the members
rises, the gills rise too, and let the water pass through, but when it
is chilled and retreats through its channels to the heart, they
contract and eject the water. Continually as the heat in the heart
rises, continually on being chilled it returns thither again. Hence,
as in respiring animals life and death are bound up with
respiration, so in the other animals class they depend on the
admission of water.
Our discussion of life and death and kindred topics is now
practically complete. But health and discase also claim the
attention of the scientist, and not mercly of the physician, in so far
as an account of their causes is concerned. The extent to which
these two differ and investigate diverse provinces must not escape us,
since facts show that their inquiries are, to a certain extent, at
least conterminous. For physicians of culture and refinement make some
mention of natural science, and claim to derive their principles
from it, while the most accomplished investigators into nature
generally push their studies so far as to conclude with an account
of medical principles.



Default Template for Easy Text To HTML Converter