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On Youth and Old Age, On Life and Death, On Breathing
By Aristotle

Translated by G. R. T. Ross

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SECTION 1

Part 1

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.

Part 2

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.

Part 3

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 animals.)

Part 4

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.

Part 5

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 observation.

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).

Part 6

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.

Part 7

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.

Part 8

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.

Part 9

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.

Part 10

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.

Part 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.

Part 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.

Part 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.

----------------------------------------------------------------------

SECTION 2

Part 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.

Part 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.

Part 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
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.

Part 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.

Part 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.

Part 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.

Part 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.

Part 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.

Part 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.

Part 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 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.

Part 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.

Part 25

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.

Part 26

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.

Part 27

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.

THE END

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