by Aristotle
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.)
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.
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).
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
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.
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.
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.
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, accord
ing 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