[481a1] 1 · What is the mode of growth of the natural breath and its mode of maintenance? For we see that it increases in volume and strength in accordance with both changes of age and the varying condition of the body. May we suppose that it increases as the other parts do, through the addition of some substance to it? [5] Now it is nutriment that is thus added to living creatures; so that we must consider the nature and origin of the nutriment in this case.
Nutrition may result in either of two ways—by means of respiration, or, as in the case of the other parts of the body, by the digestive process consequent on the introduction of the nutriment; and of the two the process by means of the nutriment is perhaps the more likely; for body is nourished by body, and the breath is of the nature of body.
[10] What then is the method? Clearly we must suppose that the breath is nourished by drawing and digesting nutriment from the vein-system, for the blood is the ultimate and universal nutriment. So the breath receives nutriment into the hot element as into its vessel and receptacle.1
The air draws the nutriment and imparts the activity, and applying to itself the [15] digestive power is the cause of its own growth and nutrition.
Perhaps there is nothing absurd in this, but rather in the proposition that the breath is originally derived from the nutriment; for that which is akin to the soul is purer—unless we were to say that the soul itself is a later product than the body, arising when the seeds are sorted out and move towards the development of their nature.
[20] Again, if2 there is some residue left from all nutriment, by what passage is it ejected in this case? It is not reasonable to suppose that it is by the process of exhalation, for this succeeds immediately to the inhalation. Clearly there remains only the explanation that it is through the ducts of the wind-pipe.
The residue which is secreted from it must be either finer or coarser; in either case there is a grave difficulty, if the breath is assumed to be the purest of all substances. But if it is coarser we shall have to assume that there are certain ducts of larger size.
The assumption that we take in and expel the breath by the same ducts is again [25] strange and unreasonable.
Such then are the questions raised by the theory that the breath is maintained and increased by nutriment.
2 · Aristogenes supposes that the growth of the breath is due to respiration, the air being digested in the lungs; for the breath, he holds, is also a form of nutriment, and is distributed into the various vessels, and the refuse is ejected [30] again.
This theory involves more difficulties, for what can cause this digestion? [481b1] Apparently the breath digests itself, as it digests other things; but this is strange intrinsically, unless the breath is different from the external air. If it is different, perhaps the bodily warmth in it may cause digestion.
However, it may be reasonably maintained that the breath3 is coarser than the [5] outside air, since it is combined with the moisture from the vessels and from the solid parts in general; so that digestion will be a process towards corporeality; but the theory that it is finer is not convincing.
Moreover, the rapidity of its digestion is contrary to reason; for the exhalation follows immediately on the inhalation. What then is the agent which so quickly changes and modifies it? [10]
We must naturally suppose that it is the warmth of the body, and the evidence of sense supports this, for the air when exhaled is warm.
Again, if the substance which is digested is in the lungs and the wind-pipe, the active warmth must also reside there: but the common view is that it is not so, but that the nutriment is evaporated by the motion of the breath.
It is still more astonishing if the breath in process of digestion attracts the warmth to itself or receives it because some other agent sets it in motion; moreover, [15] on this theory it is not in itself the primary moving cause.
Then again, respiration extends as far as the lungs only, as the followers of Aristogenes themselves state; but the natural breath is distributed throughout the whole body. If it is from the lungs that the breath is distributed to all parts of the body, including those lower than the lungs, how can the process of its digestion be so [20] rapid? This is more remarkable and involves a greater difficulty; for the lungs cannot distribute the air to the lower parts during the actual process of its digestion. And yet to some extent it would seem that this must be the case, if the digestion takes place in the lungs, and the lower parts also are affected by the respiration.
But the conclusion in this case is still more remarkable and important[25]—namely that the digestion is effected, as it were, entirely by transit and contact.
This also is unreasonable, and still more untenable,4 since it assumes that the same duct is used by the nutriment and the excretions; while if we assume that digestion is effected by any of the other internal parts, the objections already stated will apply: unless we were to assume that excrement is not formed from all [482a1] nutriment, nor in all animals, any more than in plants, for we cannot find it in every one of the bodily parts, or even if we do, at least not in all animals.5
But according to this view the vessels grow just like the other parts, and as they [5] become broadened and distended, the volume of air which flows in and out is increased: and if there must inevitably be some air contained in them, the actual question which we are now asking,6 ‘What is the air which naturally exists in them; and how does this increase under healthy conditions?’ will be obvious from the preceding statement.
How is the natural breath nourished and developed in the case of creatures which have not respiration? For in their case the nutriment can no longer come from without. If in the former case it was from forces within, and from the common [10] nutriment of the body, it is reasonable to say that the same is true in their case also, for similar effects come in like manner from the same causes—unless really in the case of these creatures too it is from without, like their perception of smell; but then they must have some process similar to respiration.7
Under this head we might raise the question whether such creatures can truly be called non-respiratory—pointing to this argument and also to the way in which [15] they take in nutriment; for we should say that they must draw in some breath at the same time; and we should further urge that they must respire for the sake of refrigeration, which they must require just as other creatures do.
But if in their case the refrigeration takes place through the diaphragm, it is clear that the entry of the air must also be by the same pressure; so that there is some process similar to respiration.
But it cannot be determined how or by what agency the air is drawn in; or if [20] there is a drawing in, how the entry takes place—unless, indeed, it is spontaneous. This is a subject for separate investigation.
But how is the natural breath nourished and increased in the case of creatures that live in the water? Apart from their inability to respire, we say further that air cannot exist in water: so it only remains to say that in their case it is by means of the food: and so either all creatures are not uniform in their methods, or else in the case [25] of the others also it is by means of the food. Such are the three possible theories, of which one must be right. So much, then, as regards the nutrition and growth of the breath.
3 · With regard to respiration, some philosophers—such as Empedocles and Democritus—do not deal with its purpose, but only describe the process; others do [30] not even deal with the process at all, but assume it as obvious. But we ought further to make it quite clear whether its purpose is refrigeration. For if the bodily heat is inherent in the upper parts, it follows that the lower parts would have no need of refrigeration: but as a matter of fact the innate breath pervades the whole body, and its origin is from the lungs.
The inspired breath also is thought to be distributed uniformly over all parts, so that it remains to be proved that this is not the case. [35]
Again, it is strange if the lower parts do not require some motive force and, as it were, some nutriment. And it would no longer be for the sake of refrigeration, if it [482b1] does pervade the whole.
Further, the process of the breath’s distribution in general is imperceptible, and so is its speed; and again, the matter of its counter-flow, if, as assumed, it is from all parts, is remarkable, unless it flows back from the most remote parts in some different way, while in its proper and primary sense the action takes place [5] from the regions about the heart.
In many instances such a want of symmetry in functions and faculties may be observed.
However, it is at any rate8 strange if breath is distributed even into the bones—for they say that this is the case, and that it passes there from the air-ducts. Therefore, as I have shown, we must consider the respiration—its purpose, and the parts which it affects, and how it affects them. Again, nutriment is not carried by [10] the air-ducts to all parts, for instance to the vessels themselves and certain other parts; but nevertheless plants live and receive nourishment.9 This question belongs rather to a treatise on methods of nutrition.
4 · Whereas there are three motions belonging to the breath in the windpipe—respiration, pulsation, and a third which introduces and assimilates the [15] nutriment—we must define how and where and for what purpose each takes place.
Of these, the motion of the pulse is perceptible by the senses wherever we touch the body. That of the respiration is perceptible up to a certain point, but is recognized in the majority of parts by a reasoning process. That of nutrition is in practically all parts determinable by reasoning, but by sense in so far as it can be [20] observed from its results.
Now clearly the respiration has its motive principle from the inward parts, whether we ought to call this principle a power of the soul, the soul, or some other combination of bodies which through their agency causes this attraction, and the nutritive faculty would seem to be caused by the respiration, for the respiration [25] corresponds to it, and is in reality similar to it. And to discover whether the whole body is not uniform with regard to the time taken by such motion, or whether there is no difference as to its simultaneity, we must consider all the parts.10
The pulse is something peculiar and distinct from the other motions and in some respects may be seen to be contingent, assuming that when there is an excess [30] of warmth in a fluid, that fluid which is evaporated must set up a pulsation owing to the air being intercepted in the interior, and pulsation must arise in the originating part and in the earliest stage, since it is inborn in the earliest parts. For it arises firstly and in the greatest degree in the heart, and thence extends to the other parts.11 Perhaps this must be an inseparable consequence of the essential nature [35] underlying the living creature, which is manifested when the creature is in a condition of activity.
That the pulse has no connexion with the respiration is shown by the following [483a1] indication—whether one breathes quickly or regularly, violently or gently, the pulse remains the same and unchanged, but it becomes irregular and spasmodic owing to certain bodily affections and in consequence of fear, hope, and anguish affecting the soul.
[5] Next we ought to consider whether the pulse occurs also in the arteries and with the same rhythm and regularity. This does not appear to be so in the case of parts widely separated, and, as has been noted, it seems to serve no purpose whatsoever.
For, on the other hand, the respiration and reception of food, whether they are [10] regarded as quite independent or as correlated, clearly exist for a purpose, and admit of rational explanation.
And of the three, we may reasonably say that the pulsatory and respiratory motions are prior to the other, for nutrition assumes their pre-existence. Or is this not so? for respiration begins when the young is separated from the mother; the reception of nutriment, and nutrition, occur both while the embryo is forming and [15] after it is formed; but the pulsation occurs at the earliest stage, as soon as the heart begins to form, as is evident in the case of eggs. So the pulse comes first, and resembles an activity and not an interception of the breath, unless that also can conduce towards its activity.
5 · They say that the breath which is respired is carried into the belly, not [20] through the gullet—that is impossible—but there is a duct along the loins through which the breath is carried by the respiration from the trachea into the belly and out again: and this can be perceived by the sense.
The question of this perception raises a difficulty: for if the windpipe alone has perception, does it perceive by means of the wind which passes through it, or by its [25] bulk or by its bodily constitution? Or if the air comes first below soul, may it perceive by means of this air which is superior and prior in origin?
What then is the soul? They make it out to be a potentiality which is the cause of such a motion as this. Or is it clear that you will not be right in impugning those who say it is the rational and spirited faculty? for they too refer to these as potentialities.
[30] But if the soul resides in this air, the air is at any rate a neutral substance. Surely, if it becomes animate or becomes soul, it suffers some change and alteration, and so naturally moves towards what is akin to it, and like grows by the addition of like. Or is it otherwise? for it may be contended that the air is not the whole of soul but is something which contributes to this potentiality or in this sense makes it,12 and that which has made it is its principle and foundation.
In the case of non-respiring creatures, where the internal air is not mixed with [483b1] the external13—or is this not the case, is it rather mixed in some other way than by respiration?—what is the difference between the air in the air-duct and the outside air? It is reasonable—perhaps inevitable—to suppose that the former surpasses the latter in fineness.
Again, is it warm by its inherent nature or by the influence of something else? [5] For it seems that the inner air is just like the outer, but it is helped by the cooling. But which is really the case? for when outside it is soft, but when enclosed the air becomes breath, being as it were condensed and in some manner distributed through the vessels. Or must it be mixed in some way, when it moves about in the fluids, and among the solid particles of the body? It is not, therefore, the finest of substances, if it is mixed. We may, however, reasonably expect that the substance [10] which is first capable of receiving soul should be the finest, unless, indeed, soul is something such as has been described, i.e. something not pure nor unmixed: and that the air-duct should be capable of receiving the breath, while the sinew is not.
There is this difference too, that the sinew is tensible, but the air-duct is easily broken, just like a vein.
The skin contains veins, sinews, and air-ducts—veins because when pricked it [15] exudes blood, sinews because it is elastic, air-ducts because air is breathed through it—for only an air-duct can admit air.
The veins must have pores in which resides the bodily heat which heats the blood as if in a cauldron; for it is not hot by nature, but is diffused like molten [20] metals. For this reason too the air-duct becomes hardened, and has moisture both in itself and in the coats which surround its hollow passage.
It is also proved both by dissection and by the fact that the veins and air-ducts, [25] which apparently conduct the nutriment, connect with the intestines and the belly. From the veins the nutriment is distributed to the flesh—not sideways from the veins but out at their mouths, as it were through pipes. For fine veins run sideways14 from the great vein and the windpipe along each rib, and a vein and an air-duct [30] always run side by side.
The sinews and veins form the connexion between the bones, joining them with the centre of the body, and also form the meeting-place between the head and the body, through which fishes receive nutriment and breathe; if they did not respire, they would die immediately on being taken out of the water.
But it is plain even from observations of sense that the veins and air-ducts [484a1] connect with each other; but this would not occur if the moisture did not require breath and the breath moisture,—because there is warmth both in sinew, in air-duct, and in vein, and that which is in the sinew is hottest and most similar to [5] that of the veins. Now the heat seems unsuited to the space where the breath is located, especially with a view to refrigeration: but if the animal produces and as it were re-kindles the heat by heat from without, then there may well be heat there. Besides this, permanence is in a sense natural to all things which have warmth, [10] provided that nothing resists or cools it;15 for that all things require refrigeration is practically proved by the fact that the blood retains its heat in the veins and as it were shelters it there; so when the blood has flowed out it loses its heat, and the creature dies, through the liver having no air-duct.
6 · Does the seed pass through the air-duct? Is its passage due also to [15] pressure, and does this take place only in process of emission? Through this we have evidence of the transformation of the blood into flesh—through the fact that the sinews are nourished from the bones; for they join the bones together. Or is this not true? For sinew is found in the heart, and sinews are attached to the bones: but those in the heart do not connect with anything else, but they end in the flesh. Or does this [20] amount to nothing, and would those which connect the bones be nourished from the bones? But we might say, that rather the bones themselves get their nutriment from the sinew. For this too is strange—since the bone is dry by nature and has no ducts for fluid;16 while the nutriment is fluid. But we must consider first, if the nutriment of the sinews is from the bones, what is the nutriment of the bone. Do the ducts [25] carry it both from the veins and from the air-duct into the bone itself? In many parts these ducts are visible, particularly those leading to the spine, and those leading from the bones are continuous, e.g. in the case of the ribs; but how do we suppose that these ducts lead from the belly, and how does the drawing of the nutriment take place?
Surely most bones are without cartilage like the spine, in no way adapted to [30] motion. Or are they designed to form connexions? And similarly, if bone is nourished from sinew, we must know the means by which sinew is nourished. We say that it is from the fluid surrounding the sinew, which is of a glutinous nature: but we must determine whence and how this arises. To say that the flesh is nourished from vein and air-duct, on the ground that blood comes from any point [35] where you prick it, is false in the case of the other animals, e.g. birds, snakes, and fishes, and oviparous creatures in general. The universal dispersion of the blood is a peculiarity of creatures with a large blood-supply: for e.g. even when a small bird’s breast is cut, not blood but serum flows.
Empedocles says that nail is formed from sinew by a hardening process. Is the [484b1] same true of skin in relation to flesh?
But how can hard and soft-shelled creatures get their nutriment from outside? On the contrary it seems that they get it from inside rather than out. Again, how and by what course does the passage of foods from the belly take place, and again [5] their return into the form of flesh, unaccountable as it is? For this process seems extraordinary and absolutely impossible.
Do different things, then, have different nutriment, not all things being nourished by the blood except indirectly?
7 · We must then consider the nature of bone, whether it exists with a view to motion or to support, or covering and surrounding, and further, whether some bones [10] are as it were originators of motion, like the axis of the universe.
By motion I mean, e.g. that of the foot, the hand, the leg, or the elbow, both the bending motion and motion from place to place—for the latter cannot take place either without the bending, and usually the supporting functions belong to these same bones. And by covering and surrounding I mean as e.g. the bones in the head [15] surround the brain; and those who make the marrow the originator of motion treat the bones as primarily meant to protect it. The ribs are for the purpose of locking together; the originator of motion, itself immovable, is the spine, from which spring the ribs for the purpose of locking the body together: for there must be something of this kind, since everything that is in motion depends on something that is in a state of rest.
At the same time a final cause must exist—under which head some class the [20] originator of motion; i.e. the spinal marrow and the brain.
Besides these there are others which are at a joining17 and whose purpose is locking together, e.g. the collar-bone, which perhaps is named the ‘key-bone’ from its functions. Every one is well adapted for its purpose, for there could be no flexion either of whole or parts, if the parts were not such as they are: e.g. the spine, foot, [25] and elbow: for the bending of the elbow must be inwards to serve our purpose. Similarly, the bending of the foot and the other parts must be such as it is. All exist for a purpose, and so do the smaller bones contained in these larger ones—e.g. the radius in the fore-arm to enable us to twist the fore-arm and the hand; for we should not be able to turn the palm down or up nor lift nor bend the feet if there were not [30] the two radii which are used in these motions. Similarly we must investigate the other details, e.g. whether the motion of the neck is due to only one bone or more. Also we must examine all that are for the purpose of gripping or knitting together, e.g. the patella over the knee; and why other parts have no such bone.
Now all parts which are capable of motion are connected with sinews—and [35] perhaps those concerned with action in a positive way are especially so—thus we find sinews in the elbow, the legs, the hands, and the feet; the other sinews are for the purpose of fastening together all those bones which require fastening; for perhaps some, e.g. the spine, have little or no function except that of bending,18 for the substance which connects the vertebrae is a serum or mucous fluid; others are [485a1] bound together by sinews—thus we find sinews in the joints of the limbs.
8 · The best description of everything may be obtained by an investigation like the present; but we must adequately investigate the final causes. We must not [5] suppose that the bones are for the sake of movement; that is rather the purpose of the sinews or what corresponds to them, viz. the immediate receptacle of the breath which causes motion, since even the belly moves and the heart has sinews—but only some, not all parts have bones: every part must have sinews appropriate for [10] performing such motion or for . . . 19 For the octopus walks little and walks badly. We must take as a starting-point the fact that all animals have different organs for different purposes with a view to the peculiar motion of each, e.g. terrestrial animals have feet—those that are upright having two; others which move altogether upon the earth, the material of whose bodies is more earthy and colder, have several.
[15] Some creatures again may be entirely without feet, for it is possible for them under these conditions to be moved only by external force. Similarly, flying creatures have wings, and their shape is appropriate to their nature. The parts differ in proportion as they are to fly faster or slower. They have feet for the purpose of seeking food and to enable them to stand; bats are an exception; as they cannot use [20] their feet, they get their food in the air, and do not need to rest for the purpose; for they certainly do not need to do so for any other reason.
The hard-shelled aquatic animals have feet on account of their weight; thus they are enabled to move from place to place: all that concerns their other needs is as ordered by the individual requirements of each, even if the principle is not [25] clear—e.g. why many-footed creatures are the slowest, and yet quadrupeds are swifter than bipeds. Is it because the whole of their body is on the ground or because they are naturally cold and hard to move, or for some other reason?
9 · We cannot agree with those who say that it is not the heat-principle which is active in bodies, or that fire has only one kind of motion and one [30] power—the power to cleave. For in the case of inanimate things the action of fire is not universally20 the same on all—some it condenses, others it rarefies; some it dissolves, others it hardens; and so we must suppose that in the case of animate creatures the same results are found, and we must investigate the fire of nature by comparing her processes to those of an art; for different results are achieved by fire [35] in the work of the goldsmith, the coppersmith, the carpenter, and the cook—though, perhaps, it is truer to say that the arts themselves achieve these different results, for [485b1] that by using fire as an instrument they soften, liquefy, and desiccate substances, and some they temper.
Individual natures work in the same way, and so they differ one from another; so that it is ridiculous to judge by externals; for whether we regard the heat as [5] separating or refining, or whatever the effect of warming or burning is, the results will be different according to the different natures of the agencies which employ it. But while the crafts use the fire merely as an instrument, nature uses it as a material as well.
Certainly no difficulty is involved in this; but rather it is remarkable that nature, who employs the instrument, is herself an intelligent agent, who will assign to objects their proper symmetry together with the visible effects of her action: for [10] this is no longer a function either of fire or of breath, so it is remarkable that we should find such a faculty combined with these two bodies. Again, with regard to soul we find the same cause of wonder, for it must be assumed in the functions of these two, and therefore there is some sense in referring to the same agent—either generally or to some particular creative part—the fact that its motion always operates21 in the same way; for nature, from which they are generated, is always [15] constant. But now what variation can there be in individual heat, whether we regard it as an instrument or material, or both? The variations in fire are simply quantitative; but this is practically a question of whether it is mixed with other substances or unmixed, for the purer substance has the proper qualities of its kind in a higher degree.
The same statement applies in the case of all other simple things; for whereas [20] there is a difference between the bone and flesh of a horse and those of an ox,22 this must be the case either because they are produced from different materials, or because the materials are used differently. Now if they are different, what are the distinctive characteristics of each of the simple things and what is . . .?23 for it is these that we are seeking.
But if they are the same in nature, they may be different in their proportions: for one or the other must be the case—as holds good with other things—for the consistencies of wine and honey are different on account of the difference of [25] substance; difference in wine itself, if there is any, is a matter of proportion.
And so Empedocles stated the nature of bone too simply;24 for,25 on the supposition that all bones follow the same proportion in the mixture of elements, the bones of a lion, a horse, and a man ought to be indistinguishable; whereas they actually differ in hardness and softness, density, and other qualities. Similarly with [30] the flesh and other parts of the body.
Further, the various parts in the same creature differ in density and rarity, and in other qualities, so that the blending of their constituents cannot be identical; for, granted that coarseness and fineness, greatness and smallness are quantitative differences, hardness, density, and the opposites certainly depend on the qualitative nature of the mixing. But those who give this account of it must know how the creature element can vary, by excess or deficiency, by being in isolation or in [486a1] combination or heated in something else, like food that is boiled or baked,—which last is perhaps the true explanation; for in the process of mixing it produces the effect designed by nature.
So I suppose we must give the same account of flesh; for the variations are the [486b1] same; and practically the same observations apply to the veins and air-ducts and the rest; so that, in conclusion, either the proportion observed in their mixture is not constant, or the definitions must not be stated in terms of hardness, density, and their opposites.