Aristotle

by Various Works [lit]

  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
r />   way and manner in which this refrigeration occurs.

  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