On Youth and Old Age by Aristotle


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, andwhile it is clear that its essential reality cannot be corporeal, yet manifestly it must exist in some bodily partwhich 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 beingwhat is called an animal and a living thing,we find that in all beings endowedwith both characteristics (viz. being an animal and being alive) there must be a single identical part in virtue ofwhich 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 livewithout having sensation, and it is by sensation thatwe distinguish animal fromwhat 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 inwhich the senseswhen functioning must meet, and this must be situated midway betweenwhat is called before and behind (we call ‘before’ the direction fromwhich 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 aswell), clearly the nutritive principle must be situated midway between these regions. That partwhere food enterswe call upper, considering it by itself and not relatively to the surrounding universe,while downward is that part bywhich 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 inwhich 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 andwhat is called the mouth in animals, by means ofwhich they take in their food,whether the source of supply be the earth or each other’s bodies.

All perfectly formed animals are to be divided into three parts, one that bywhich food is taken in, one that bywhich 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 ofwhich they bear thewhole trunk, towit legs and feet andwhatever 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 towhich 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; plantswhen cut into sections continue to live, and a number of trees can be derived from one single source. A separate accountwill be given of the reasonwhy some plants cannot livewhen 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 toowith 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 onwhich 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 aswell.   Divisible animals are like a number of animals grown together, but animals of superior construction behave differently because their constitution is a unity of the highest possible kind. Hence some of the organs on division display slight sensitiveness because they retain some psychical susceptibility; the animals continue to move after the vitals have been abstracted: tortoises, for example, do so even after the heart has been removed.

The same phenomenon is evident both in plants and in animals, and in plantswe 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 away 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,whenwewish 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 fromwhat has been observed in those caseswhere observation of their growth is possible. Hence in bloodless animals alsowhat 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 fromwhich the members are formed. Hence it is clear that there is one function in nutritionwhich 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 occupiedwith subordinate offices. Certainly, however, all saguineous animals have the supreme organ of the sensefaculties in the heart, for it is here thatwe 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,whereaswith 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 endowedwith sensation. Elsewhere in other workswe have stated the reasonswhy some of the sense-organs are, as is evident, connectedwith 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.)

Thus if, on the one hand,we look to the observed facts,whatwe have said makes it clear that the source of the sensitive soul, togetherwith that connectedwith 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; forwe 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. thatwhich elaborates and thatwhich receives the nutriment in its final formwill best perform their appropriate function; for the soulwill then be close to each, and the central situationwhich itwill, as such, occupy is the position of a dominating power.   Further, thatwhich 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 thatwhich 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 thewhole body possess some connatewarmth of constitution, and hencewhen alive they are observed to bewarm, butwhen dead and deprived of life they are the opposite. Indeed, the source of thiswarmth 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; butwhen thewarmth here is quenched, death always ensues, because the source of heat in all the other members depends on this, and the soul is, as itwere, set aglowwith 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 coincidentwith the maintenance of heat, and whatwe call death is its destruction.

However, it is to be noticed that there are twoways inwhich fire ceases to exist; it may go out either by exhaustion or by extinction. Thatwhich is self-causedwe call exhaustion, that due to its opposites extinction. [The former is that due to old age, the latter to violence.] But either of theseways inwhich fire ceases to be may be brought about by the same cause, for,when there is a deficiency of nutriment and thewarmth 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 casewhat 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 consumedwhen inserted in a large blaze just as is the casewith 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 someway of cooling the heat resident in the source ofwarmth. Take as an illustration what occurswhen 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 heatwhich it possesses. However,we have stated in The Problems the reasonswhy these operations, namely banking up and covering up a fire, have the opposite effects (in the one case the fire goes out, in the other it continues alive for a considerable time).

Everything living has soul, and it, aswe have said, cannot exist without the presence of heat in the constitution. In plants the natural heat is sufficientlywell kept alive by the aidwhich 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 upwhich 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 orwater in pots, for the purpose of cooling the roots of the plants.   Some animals pass their life in thewater, 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 itwill require further application on our part-to give an account of the way and manner inwhich this refrigeration occurs.

A few of the previous physical philosophers have spoken of respiration. The reason, however,why it exists in animals they have either not declared or,when they have, their statements are not correct and show a comparative lack of acquaintancewith the facts. Moreover they assert that all animals respire-which is untrue. Hence these points must first claim our attention, in order thatwe may not be thought to make unsubstantiated charges against authors no longer alive.   First then, it is evident that all animalswith 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 underwater 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 inwater; 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 inwater in theway fishes do. On the other hand, animalswhich have the lung chargedwith blood have greater need of respiration on account of the amount of their heat,while none at all of the otherswhich do not possess lungs breathe.

Democritus of Abdera and certain otherswho 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 inwhich fishes and oysters respire. Anaxagoras says thatwhen 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 dischargewater through their gills, they suck the air out of thewater surrounding the mouth by means of the vacuum formed in the mouth, for he believes there is air in thewater.

But these theories are untenable. Firstly, they state onlywhat is the common element in both operations and so leave out the half of the matter. Forwhat 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 bywhich they draw it in, and this must happen in alternation. Hence, as a result, they must take thewater into their mouth at the same time as they breathe out. But the air and thewater must meet and obstruct each other. Further,when they discharge thewater they must emit their breath by the mouth or the gills, and the resultwill be that theywill breathe in and breathe out at the same time, for it is at that moment that respiration is said to occur. But it is impossible that they should do both at the same time. Hence, if respiring creatures must both exhale and inhale the air, and if none of these animals can breathe out, evidently none can respire at all.

Further, the assertion that they draw in air out of the mouth or out of thewater by means of the mouth is an impossibility, for, not having a lung, they have nowindpipe; rather the stomach is closely juxtaposed to the mouth, so that they must do the suckingwith the stomach. But in that case the other animalswould do so also,which is not the truth; and thewater-animals alsowould be seen to do it when out of thewater,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 bodywhich 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 bothwhen they are in thewater andwhen they are thrown on to dry land and gasp. Moreover, alwayswhen respiring animals are killed by being suffocated inwater, 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 beneathwater. Butwith fishes this result never occurs, inwhatsoever waywe 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 alsowhen they are underwater. For if fishes draw in air out of the surroundingwater by means of their mouthwhy should not men too and other animals do so also; they should also, in the sameway as fishes, draw in air out of the mouth. If in the former case itwere 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 notwant 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 thewater they take in a moderate amount. But that should be a possible occurrencewith 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, andwhat is the organ they employ? The main reasonwhy thesewriters have not given a good account of these facts is that they have no acquaintancewith the internal organs, and that they did not accept the doctrine that there is a final cause forwhatever Nature does. If they had asked forwhat purpose respiration exists in animals, and had considered thiswith reference to the organs, e.g. the gills and the lungs, theywould have discovered the reason more speedily.

Democritus, however, does teach that in the breathing animals there is a certain result produced by respiration; he asserts that it prevents the soul from being extruded from the body. Nevertheless, he by no means asserts that it is for this purpose that Nature so contrives it, for he, like the other physical philosophers, altogether fails to attain to any such explanation. His statement is that the soul and the hot element are identical, being the primary forms among the spherical particles. Hence,when these are being crushed together by the surrounding atmosphere thrusting them out, respiration, according to his account, comes in to succour them. For in the air there are many of those particleswhich he calls mind and soul. Hence,whenwe breathe and the air enters, these enter alongwith it, and by their action cancel the pressure, thus preventing the expulsion of the soulwhich resides in the animal. This explainswhy life and death are bound upwith the taking in and letting out of the breath; for death occurswhen 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 andwhy 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 saidwhether the cause is external or internal. Neither does he assign the cause of the beginning of respiration, nor saywhether 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 bewithin: it is not due to pressure from around. It is absurd also thatwhat surrounds should compress and at the same time by entering dilate. This then is practically his theory, and how he puts it.   But ifwe 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 ofwhichwe all have experience. For in hotweatherwe growwarmer, 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 thiswas just the timewhen the external air should enter and annul the expulsive movement,whereas it is the opposite that occurs. Forwhen the breath is not let out and the heat accumulates too much thenwe need to respire, and to respirewe must draw in the breath.when hot, people breathe rapidly, because they must do so in order to cool themselves, justwhen the theory of Democrituswould make them add fire to fire.

The theory found in the Timaeus, of the passing round of the breath by pushing, by no means determines how, in the case of the animals other than land-animals, their heat is preserved, and whether it is due to the same or a different cause. For if respiration occurs only in land-animalswe should be toldwhat 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 thatwhen the hot air issues from the mouth it pushes the surrounding air,which being carried on enters the very placewhence the internalwarmth issued, through the interstices of the porous flesh; and this reciprocal replacement is due to the fact that a vacuum cannot exist. Butwhen 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 awarm condition. It is said that it is this actionwhich goes on continuouslywhen the breath is taken in and let out.   But according to thisway of thinking itwill follow thatwe breathe out beforewe breathe in. But the opposite is the case, as evidence shows, for though these two functions go on in alternation, yet the last actwhen 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, thosewho give this kind of explanation by no means state the final cause of the presence in animals of this function (towit 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 thatwhen 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,whilewewere 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, andwhat is breathed in is cold.when it is hotwe pant in breathing, for, becausewhat enters does not adequately perform its cooling function,we have as a consequence to draw the breath frequently.

It is certain, however, thatwe 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 itwere, 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 repeatwhat 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 arewe 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 nutrimentwould enter and the refuse be discharged by the same channel, but this does not appear to occur in the other instances.

Empedocles also gives an account of respirationwithout, however, making clearwhat its purpose is, orwhether or not it is universal in animals. Alsowhen dealingwith respiration by means of the nostrils he imagines he is dealingwithwhat is the primary kind of respiration. Even the breathwhich passes through the nostrils passes through thewindpipe out of the chest aswell, andwithout 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 thewindpipe, they die. Nature employs respiration through the nostrils as a secondary function in certain animals in order to enable them to smell. But the reasonwhy it exists in some only is that though almost all animals are endowedwith 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 ofwhich 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 towhat 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 blusteringwindwith swelling billowwild. Butwhen the blood leaps up, backward it breathes. Aswhen withwater-clock of polished bronze a maiden sporting, Sets on her comely hand the narrow of the tube And dips it in the frail-formedwater’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 thewater meet. So also when within the vessel’s deeps thewater 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 maidwithdraws her hand. But then in contrariwise Once more the air comes in andwater 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 rushingwith swellingwave, But,when it backward leaps, in like bulk air flows out.

This then iswhat he says of respiration. But, aswe said, all animals that evidently respire do so by means of thewindpipe,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 tallieswith the explanation given. But the facts seem to be quite opposed. The chest is raised in the manner of a forge-bellowswhen the breath is drawn in-it is quite reasonable that it should be heatwhich 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 uvulawhere 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, bothwhen it enters andwhen it passes out. Such then is the nature and magnitude of the difficulties besetting the theories of otherwriters concerning respiration.

We have already stated that life and the presence of soul involve a certain heat. Not even the digesting process towhich is due the nutrition of animals occurs apart from soul andwarmth, 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 regionwhich is the immediate vehicle of this principle. The region in question is intermediate between thatwhere food enters and thatwhere 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 fromwhich 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 withwhich Nature has set it aglow. But fire, aswe have already stated, is destroyed in twoways, either by extinction or by exhaustion. It suffers extinction from its opposites. Hence it can be extinguished by the surrounding cold bothwhen in mass and (though more speedily)when scattered. Now thisway of perishing is due to violence equally in living and in lifeless objects, for the division of an animal by instruments and consequent congelation by excess of cold cause death. But exhaustion is due to excess of heat; if there is too much heat close at hand and the thing burning does not have a fresh supply of fuel added to it, it goes out by exhaustion, not by the action of cold. Hence, if it is going to continue it must be cooled, for cold is a preventive against this form of extinction.

Some animals occupy thewater, others live on land, and, that being so, in the case of thosewhich are very small and bloodless the refrigeration due to the surroundingwater 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 thewaist, in order to secure cooling through the membrane, which there is thinner. They arewarmer animals and hence require more refrigeration, and such are bees (some ofwhich live as long as seven years) and all that make a humming noise, likewasps, cockchafers, and crickets. They make a sound as if of panting by means of air, for, in the middle section itself, the airwhich exists internally and is involved in their construction, causing a rising and falling movement, produces friction against the membrane. Theway 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, aswe said, in theway 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 greaterwarmth and are indented at thewaist, but the songless variety have no fissure there. Animals alsowhich 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 timewithout breathing; for the lung, containing little blood or fluid, can rise a longway: 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-aswe have already said. For of exhaustion that kindwhich is destruction due to lack of refrigeration is called suffocation, andwhatsoever 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 animalswith little strength tend to breathe more frequently. These, however, die ofwhat is called suffocationwhen the stomach becomes filled and the heat in the central segment is destroyed. This explains alsowhy they revive after being among ashes for a time. Again amongwater-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 theirwant 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.

Concerning the bloodless animalswe 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, allwhich 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 havewings, e.g. birds, and thosewith 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 thewater, e.g. the class ofwater-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 thewater, keep the head above the surface in order to respire. But allwith gills produce refrigeration by taking inwater; the Selachia and all other footless animals have gills. Fish are footless, and the limbs they have get their name (pterugion) from their similarity towings (pterux). But of thosewith 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 bywater. Now for one purpose one organ is adapted and one single means of refrigeration is sufficient in every case. Hence, sincewe see that Nature does nothing in vain, and if therewere two organs onewould be purposeless, this is the reasonwhy some animals have gills, others lungs, but none possess both.

Every animal in order to exist requires nutriment, in order to prevent itself from dying, refrigeration; and so Nature employs the same organ for both purposes. For, as in some cases the tongue serves both for discerning tastes and for speech, so in animalswith lungs the mouth is employed both inworking up the food and in the passage of the breath outwards and inwards. In lungless and non-respiring animals it is employed inworking 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 admitwater. 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 thewindpipe and lying on the lung. Thewindpipe is situated before the oesophagus, throughwhich food passes intowhat is called the stomach, but in quadrupedswhich are sanguineous there is, as it were, a lid over thewindpipe-the epiglottis. In birds and oviparous quadrupeds this covering is absent, but its office is discharged by a contraction of thewindpipe. The latter class contract the windpipewhen 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 thewindpipe is expanded, and the air enters to effect refrigeration. In animalswith gills thewater is first discharged through them and then the food passes in through the mouth; they have nowindpipe and hence can take no harm from liquid lodging in this organ, only from its entering the stomach.

For these reasons the expulsion ofwater 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.

Amongwater-animals the cetaceans may give rise to some perplexity, though they too can be rationally explained. Examples of such animals are dolphins andwhales, 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 whichwe have now stated [refrigeration]; the admission ofwater is not for the purpose of refrigeration. That is effected by respiration, for they have a lung. Hence they sleepwith 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 thewater 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 organswhich are chargedwith blood; but it lies before the brain and thence dischargeswater.   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 surroundingwater. But in feeding they admitwater, and hence must expel it in order to prevent its being swallowed simultaneouslywith 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 inwater must feed in it.

An account must next be given of refrigeration and the manner in which it occurs in respiring animals and those possessed of gills. we have already said that all animalswith lungs respire. The reason why some creatures have this organ, andwhy 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 thosewith most blood and mostwarmth in the lung are of greater size, and animal inwhich the blood in the lung is purest and most plentiful is the most erect, namely man; and the reasonwhy 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;whilewinged 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.

Empedocles is then in errorwhen he says that those animalswhich have the mostwarmth and fire live in thewater 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; forwater has less heat than air. But it iswholly absurd that thewater-animals should in every case originate on dry land, and afterwards change their place of abode to thewater; 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 notwarmer than land-animals, for in some cases they have no blood at all, in others little.

The question, however, as towhat sorts of animals should be calledwarm andwhat cold, has in each special case received consideration. Though in one respect there is reason in the explanationwhich 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 ofwhich any animal is constituted and the states and dispositions of that material. For example, if naturewere to constitute a thing ofwax or of ice, shewould not preserve it by putting it in a hot place, for the opposing qualitywould quickly destroy it, seeing that heat dissolves thatwhich cold congeals. Again, a thing composed of salt or nitrewould not be taken and placed inwater, for fluid dissolves that ofwhich 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 ofwhich is due to the fluid and the cold should have liquid for their medium [and, if they are cold, theywill exist in the cold],while thatwhich is due to the drywill be found in the dry. Thus trees grow not inwater but on dry land. But the same theorywould relegate them to thewater, on account of their excess of dryness, just as it does the things that are excessively fiery. Theywould 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 inwhich they exist; the liquid is found in liquid, the dry on land, thewarm 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 awarm 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 seasonswhich all experience supply the meanswhich 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 ofwhich it is composed can never be so. This, then, is a sufficient explanation ofwhy it is not owing to the heat in their constitution that some animals are aquatic, others terrestrial, as Empedocles maintains, and ofwhy some possess lungs and others do not.

The explanation of the admission of air and respiration in those animals inwhich a lung is found, and especially in those inwhich 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 chargedwith blood of all the visceral organs. All animalswith 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 reasonwhy animalswith a full-blooded lung respire most is hence manifest; the more heat there is, the greater is the need for refrigeration, and at the same time breath can easily pass to the source of heat in the heart.

In order to understand theway inwhich 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 needwhich the animal has for refrigeration, is the union of the soulwith fire that takes place in the heart. Respiration is the means of effecting refrigeration, ofwhich those animals make use that possess a lung aswell as a heart. Butwhen they, as for example the fishes,which on account of their aquatic nature have no lung, possess the latter organwithout the former, the cooling is effected through the gills by means ofwater. For ocular evidence as to how the heart is situated relatively to the gillswe must employ dissections, and for precise detailswe 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 inwhich 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 ofwater through the gills, effect the coolingwhich 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 contactwith the blood, rapidly becomes hot. The heat of the blood counteracts the refrigeration and,when respiring animals can no longer move the lung aquatic animals their gills,whether owing to discase or old age, their death ensues.

To be born and to die are common to all animals, but there are specifically diverseways inwhich 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 occurswhen the cause of death is external, the latterwhen 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 iswithering, 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 iswhy some insects livewhen divided, andwhy, even among sanguineous animals, allwhose vitality is not intense live for a long time after the heart has been removed. Tortoises, for example, do so and make movementswith 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 possessorswhen the heatwith which it is bound up is no longer tempered by cooling, for, as I have often remarked, it is consumed by itself. Hencewhen, 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 disturbancewill 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 flamewhich 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 diseaseswhich harden the lung by forming tumours orwaste residues, or by excess of morbid heat, as happens in fevers, accelerate the breathing owing to the inability of the lung to move far either upwards or downwards. Finally,when motion is no longer possible, the breath is given out and death ensues.

Generation is the initial participation, mediated bywarm 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 towither, in animals to die. Death, in old age, is the exhaustion due to inability on the part of the organ, owing to old age, to produce refrigeration. This then is our account of generation and life and death, and the reason for their occurrence in animals.

It is hence also clearwhy respiring animals are suffocated inwater and fishes in air. For it is bywater 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 ofwhich effects the admission and expulsion of the breath or of water. The following, moreover, is the manner of the constitution of the organ.

In connexionwith 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 orwaste products. It occurs, for example, in the ailment known as ‘spasms’ and in other diseases. It occurs also in fear, forwhen 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 thewalls, 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, ofwhich the food furnishes a constant supply. It occurswhen the fluid rises to the outerwall 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 sowe can perceive in the initial stages of generation, for the heart can be seen to contain blood before the veins become distinct. This explainswhy 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 simultaneouslywith each other, owing to their connexionwith the heart. The heart always beats, and hence they also beat continuously and simultaneouslywith each other and with it.

Palpitation, then, is the recoil of the heart against the compression due to cold; and pulsation is the volatilization of the heated fluid.

Respiration takes placewhen the hot substancewhich 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. Butwhen it increases it necessarily causes the organ to rise. This organwe must to be constructed like the bellows in a smithy, for both heart and lungs conform prettywell 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 occurwhen people respire; they raise their chest because the motive principle of the organ described residentwithin 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, andwhen it collapses the airwhich entered must pass out again.when it enters the air is cold, but on issuing it iswarm owing to its contactwith 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, intowhich it passes, have each a blood-vessel lying alongside, so that thewhole 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 upwith the passage of the breath outwards and inwards. It is in the sameway 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 thewater pass through, butwhen it is chilled and retreats through its channels to the heart, they contract and eject thewater. 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 upwith respiration, so in the other animals class they depend on the admission ofwater.

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 towhich 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 concludewith an account of medical principles.




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