by Aristotle
Some at any rate of the animals with watery blood have a keener intellect. This [20] is due not to the coldness of their blood, but rather to its thinness and purity; neither of which qualities belongs to the earthy matter. For the thinner and purer its fluid is, the more easily affected is an animal’s sensibility. Thus it is that some bloodless animals are more intelligent than some among the sanguineous kinds. Such for [25] instance, as already said, is the case with the bee and the tribe of ants, and whatever other animals there may be of a like nature. At the same time too great an excess of water makes animals timorous. For fear chills the body; so that in animals whose heart contains so watery a mixture the way is prepared for the operation of this emotion. For water is congealed by cold. This also explains why bloodless animals [30] are, as a general rule, more timorous than such as have blood, so that they remain motionless, when frightened, and discharge their excretions, and in some instances change colour. Such animals, on the other hand, as have thick and abundant fibres in their blood are of a more earthy nature, and of a choleric temperament, and liable to bursts of passion. For anger is productive of heat; and solids, when they have been made hot, give off more heat than fluids. The fibres therefore, being earthy and [651a1] solid, are turned into so many hot embers in the blood and cause ebullition in the fits of passion.
This explains why bulls and boars are so choleric and so passionate. For their blood is exceedingly rich in fibres, and the bull’s at any rate coagulates more rapidly than that of any other animal. If these fibres are taken out of the blood, it will no [5] longer coagulate; just as the watery residue of mud will not coagulate after removal of the earth—for the fibres consist of earth. But if the fibres are left the fluid coagulates, as also does mud, under the influence of cold. For when the heat is expelled by the cold, the fluid, as has been already stated, passes off with it by [10] evaporation, and the residue is dried up and solidified, not by heat but by cold. So long, however, as the blood is in the body, it is kept fluid by animal heat.
The character of the blood affects both the temperament and the sensory faculties of animals in many ways. This is indeed what might reasonably be expected, seeing that the blood is the material of which the whole body is made. For nutriment supplies the material, and the blood is the ultimate nutriment. It makes [15] then a considerable difference whether the blood be hot or cold, thin or thick, turbid or clear.
The watery part of the blood is serum; and it is watery, either owing to its not being yet concocted, or owing to its having become corrupted; so that one part of the serum is the resultant of a necessary process, while another part is for the sake of the blood.
[20] 5 · The differences between lard and suet correspond to differences of blood. For both are blood concocted into these forms as a result of abundant nutrition, being that surplus blood that is not expended on the fleshy part of the body, and is of an easily concocted and well-nourished character. This is shown by the greasiness of [25] these substances; for such grease in fluids is due to a combination of air and fire. It follows from what has been said that no non-sanguineous animals have either lard or suet; for they have no blood. Among sanguineous animals those whose blood is dense have suet rather than lard. For suet is of an earthy nature, that is to say, it contains but a small proportion of water and is chiefly composed of earth; and this it is that makes it coagulate, just as the fibrous matter of blood coagulates, or broths [30] which contain such fibrous matter. Thus it is that non-ambidentate horned animals possess suet. For the very fact that they have horns and huckle-bones shows that their composition is rich in this earthy element; for all such appurtenances are solid and earthy in character. On the other hand in those hornless animals that are [35] ambidentate and possess toes, there is no suet, but in its place lard; and this, not being of an earthy character, neither coagulates nor splits when it dries.
Both lard and suet when present in moderate amount are beneficial; for they [651b1] contribute to health and strength, while they are no hindrance to sensation. But when they are present in great excess, they are injurious and destructive. For were the whole body formed of them it would perish. For an animal is an animal in virtue [5] of its sensory part, that is in virtue of its flesh, or of the substance analogous to flesh. But the blood, as before stated, is not sensitive; as therefore is neither lard nor suet, seeing that they are concocted blood. Were then the whole body composed of these substances, it would be utterly without sensation. Such animals, again, as are [10] excessively fat age rapidly. For so much of their blood is used in forming fat, that they have but little left; and when there is but little blood the way is already open for decay. For decay may be said to be deficiency of blood, the scantiness of which renders it liable, like all bodies of small bulk, to be affected by any chance excess of heat or cold. For the same reason fat animals are less fertile than others. For that [15] part of the blood which should go to form semen and seed is used up in the production of lard and suet, which are nothing but concocted blood; so that in these animals there is either no residue at all, or only a scanty amount.
6 · So much then for blood and serum, and for lard and suet. Each of these, and their causes, have been described.
[20] The marrow also is of the nature of blood, and not, as some think, the germinal force of the semen. That this is the case is quite evident in very young animals. For [25] in the embryo the marrow of the bones has a blood-like appearance, which is but natural, seeing that the parts are all constructed out of blood, and that it is on blood that the embryo is nourished. But, as the young animal grows up and ripens into maturity, the marrow changes its colour, just as do the parts and the viscera. For the viscera also in animals, so long as they are young, have each and all a blood-like look, owing to the large amount of this fluid which they contain.
In those animals which contain lard, the marrow is greasy and lard-like; but when the blood is converted by concoction into suet, and does not assume the form [30] of lard, then the marrow also has a suety character. In those animals, therefore, that have horns and are not ambidentate, the marrow has the character of suet; while it takes the form of lard in those that are ambidentate and have the foot divided into toes. What has been said hardly applies to the spinal marrow. For it is necessary that this shall be continuous and extend without break through the whole backbone, inasmuch as this bone consists of separate vertebrae. But were the spinal marrow either greasy or of suet, it could not hold together in such a continuous mass as it [35] does, but would either be too fluid or too frangible.
There are some animals that can hardly be said to have any marrow. These are those whose bones are strong and solid, as is the case with the lion. For in this animal the marrow is so utterly insignificant that the bones look as though they had [652a1] none at all. However, as it is necessary that animals shall have bones or something analogous to them, such as the fish-spines of water-animals, it is also a matter of necessity that some of these bones shall contain marrow; for the substance [5] contained within the bones is the nutriment out of which these are formed. Now the universal nutriment, as already stated, is blood; and it is reasonable that marrow should be suety or fatty. For the blood within the bone, owing to the heat which is developed in it from its being thus surrounded, undergoes concoction, and self-concocted blood is suet or lard. So also it is easy to understand why, in those animals [10] that have strong and compact bones, some of these should be entirely void of marrow, while the rest contain but little of it; for here the nutriment is spent in forming the bones.
Those animals that have fish-spines in place of bones have no other marrow than that of the backbone. For in the first place they have naturally but a small amount of blood; and secondly the only hollow fish-spine is that of the backbone. In [15] this then marrow is formed; this being the only spine in which there is space for it, and, moreover, being the only one which owing to its division into parts requires a connecting bond. This too is the reason why the marrow here, as already mentioned, is so
mewhat different from that of other bones. For, having to act the part of a clasp, it must be of glutinous character and at the same time sinewy so as to admit of stretching.
Such then are the reasons for the existence of marrow, in those animals that [20] have any, and such its nature. It is evidently the surplus of the sanguineous nutriment apportioned to the bones and fish-spines, which has undergone concoction owing to its being enclosed within them.
7 · From the marrow we pass on in natural sequence to the brain. For there are many who think that the brain itself consists of marrow, and that it forms the [25] commencement of that substance, because they see that the spinal marrow is continuous with it. In reality the two may be said to be utterly opposite to each other in character. For of all the parts of the body there is none so cold as the brain; whereas the marrow is of a hot nature, as is plainly shown by its fat and greasy [30] character. Indeed this is the very reason why the brain and spinal marrow are continuous with each other. For, wherever the action of any part is in excess, nature so contrives as to set by it another part with an excess of contrary action, so that the excesses of the two may counterbalance each other. Now that the marrow is hot is [35] clearly shown by many indications. The coldness of the brain is also manifest enough even to the touch; and, secondly, of all the fluid parts of the body it is the driest and the one that has the least blood; for in fact it has no blood at all in its [652b1] proper substance. Thus brain is not residual matter, nor yet is it one of the parts which are continuous with each other; but it has a character peculiar to itself, as might indeed be expected. That it has no continuity with the organs of sense is plain [5] from simple inspection, and is still more clearly shown by the fact, that, when it is touched, no sensation is produced; in which respect it resembles the blood of animals and their excrement. The purpose of its presence in animals is no less than the preservation of the whole body. For some writers assert that the soul is fire or some such force. This, however, is but a crude assertion; and it would perhaps be better to say that the soul is incorporate in some substance of a fiery character. The [10] reason for this being so is that of all substances there is none so suitable for ministering to the operations of the soul as that which is possessed of heat. For nutrition and the imparting of motion are offices of the soul, and it is by heat that these are most readily effected. To say then that the soul is fire is much the same thing as to confound the auger or the saw with the carpenter or his craft, simply [15] because the work is done when the two are near one another. So far then this much is plain, that all animals must necessarily have a certain amount of heat. But as all influences require to be counterbalanced, so that they may be reduced to moderation and brought to the mean (for in the mean, and not in either extreme, lies their [20] substance and account), nature has contrived the brain as a counterpoise to the region of the heart with its contained heat, and has given it to animals to moderate the latter, combining in it the properties of earth and water. For this reason it is, that every sanguineous animal has a brain; whereas no bloodless creature has such [25] an organ, unless indeed it be, as the octopus, by analogy. For where there is no blood, there in consequence is but little heat. The brain, then, tempers the heat and seething of the heart. In order, however, that it may itself have a moderate amount of heat, branches run from both blood-vessels, that is to say from the great vessel [30] and from what is called the aorta, and end in the membrane which surrounds the brain; while at the same time, in order to prevent any injury from the heat, these encompassing vessels, instead of being few and large, are numerous and small, and their blood scanty and clear, instead of being turbid and thick. We can now [35] understand why fluxes have their origin in the head, and occur whenever the parts about the brain have more than a due proportion of coldness. For when the [653a1] nutriment steams upwards through the blood-vessels, its refuse portion is chilled by the influence of this region, and forms fluxes of phlegm and serum. We must suppose, to compare small things with great, that the like happens here as occurs in [5] the production of showers. For when vapour steams up from the earth and is carried by the heat into the upper regions, so soon as it reaches the cold air that is above the earth, it condenses again into water owing to the refrigeration, and falls back to the earth as rain. These, however, are matters which may be suitably considered in the Principles of Diseases, so far as natural philosophy has anything to say to them. [10]
It is the brain again—or, in animals that have no brain, the part analogous to it—which is the cause of sleep. For either by chilling the blood that streams upwards after food, or by some other similar influences, it produces heaviness in the region in which it lies (which is the reason why drowsy persons hang the head), and [15] causes the heat to escape downwards in company with the blood. It is the accumulation of this in excess in the lower region that produces sleep, taking away the power of standing upright from those animals to whom that posture is natural, and from the rest the power of holding up the head. These, however, are matters which have been separately considered in the treatises on Sensation and on Sleep. [20] That the brain is a compound of earth and water is shown by what occurs when it is boiled. For, when so treated, it turns hard and dry, inasmuch as the water is evaporated by the heat, and leaves the earthy part behind. Just the same occurs when pulse and other fruits are boiled. For these also are hardened and become altogether earthy, because the water which enters into their composition is driven off and leaves the earth, which is their main constituent, behind. [25]
Of all animals, man has the largest brain in proportion to his size; and it is larger in men than in women. This is because the region of the heart and of the lung is hotter and richer in blood. This again explains why man, alone of animals, stands [30] erect. For the heat, overcoming any opposite inclination, makes growth take its own line of direction, which is from the centre of the body upwards. It is then as a counterpoise to his excessive heat that there is this superabundant fluidity and coldness; and it is again owing to this superabundance that the cranial bone which some call the bregma is the last to become solidified; so long does evaporation [35] continue to occur through it under the influence of heat. Man is the only sanguineous animal in which this takes place. Man, again, has more sutures in his skull than any other animal, and the male more than the female. The explanation [653b1] is again to be found in the greater size of the brain, which demands free ventilation, proportionate to its bulk. For if the brain be either too moist or too dry, it will not perform its office, but in the one case will freeze the blood, and in the other will not cool it at all; and thus will cause disease, madness, and death. For the cardiac heat [5] and the centre of life is most delicate in its sympathies, and is immediately sensitive to the slightest change or affection of the blood on the outer surface of the brain.
The fluids which are present in the animal body from the first have now nearly all been considered. Amongst those that appear only at a later period are the residua [10] of the food, which include the deposits of the belly and also those of the bladder. Besides these there is the semen and the milk, in those animals which are of such a nature as to have them. Of these fluids, the excremental residua of the food may be suitably discussed by themselves, when we come to examine and consider the subject of nutrition. Then will be the proper time to explain in what animals they [15] are found, and what are the reasons for their presence. Similarly all questions concerning the semen and the milk may be dealt with in the treatise on Generation, for the former of these fluids is the very starting-point of the generative process, and the latter exists for the sake of generation.
8 · We have now to consider the remaining homogeneous parts, and will [20] begin with flesh, and with the substance that, in animals that have no flesh, takes its place. The reason for so beginning is that flesh forms in animals both a principle and a body in itself. Its right to this precedence can also be demonstrated logically. For an animal is by our definition something that has sensibility and chief of all the prima
ry sensibility, which is that of touch; and it is the flesh, or analogous [25] substance, which is the organ of this sense—either the primary organ, in the same way as the pupil is the organ of sight, or it is the organ and the medium through which the object acts combined, comparable to the pupil with the whole transparent medium attached to it. Now in the case of the other senses it was impossible for nature to unite the medium with the sense-organ, nor would such a junction have served any purpose; but in the case of touch she was compelled by necessity to do so. For of all the sense-organs that of touch is the only one that has corporeal substance, [30] or at any rate it is more corporeal than any other.
It is obvious also to sense that it is for the sake of this that all the other parts exist. By the other parts I mean the bones, the skin, the sinews, and the blood-vessels, and, again, the hair and the various kinds of nails, and anything else there may be of a like character. Thus the bones are a contrivance to give security to [35] the soft parts, to which purpose they are adapted by their hardness; and in animals that have no bones the same office is fulfilled by some analogous substance, as by fish-spine in some fishes, and by cartilage in others.
Now in some animals this supporting substance is situated within the body, [654a1] while in some of the bloodless species it is placed on the outside. The latter is the case in all the Crustacea, as the crabs and the crayfish; it is the case also in the Testacea, as for instance in the several species known by the general name of oysters. For in all these animals the fleshy substance is within, and the earthy matter, which holds the soft parts together and keeps them from injury, is on the [5] outside. For the shell not only enables the soft parts to hold together, but also, as the animal is bloodless and so has but little natural warmth, surrounds it, as a chaufferette does the embers, and keeps in the smouldering heat. Similar to this seems to be the arrangement in another kind of animals, namely the tortoises and [10] the several kinds of water-tortoise. But in Insects and in Cephalopods the plan is entirely different, there being moreover a contrast between these two themselves. For in neither of these does there appear to be any bony or earthy part, worthy of notice, distinctly separated from the rest of the body. Thus in the Cephalopods the main bulk of the body consists of a soft flesh-like substance, or rather of a substance [15] which is intermediate between flesh and sinew, so as not to be so readily destructible as actual flesh. For it is soft like flesh, while it admits of stretching like the sinew. It splits not longitudinally, but into circular segments, like flesh, this being the most advantageous condition, so far as strength is concerned. These animals have also a part inside them corresponding to the spinous bones of fishes. For instance, in the [20] cuttle-fishes there is what is known as the pounce, and in the calamaries there is the so-called pen. In the octopus, on the other hand, there is no such internal part, because the body, or, as it is termed in them, the head, forms but a short sac, whereas it is of considerable length in the other two; and it was this length which led nature to assign to them their hard support, so as to ensure their straightness and [25] inflexibility; just as she has assigned to sanguineous animals their bones or their fish-spines, as the case may be. To come now to Insects. In these the arrangement is quite different from that of the Cephalopods and from that which obtains in sanguineous animals, as indeed has been already stated. For in an insect there is no distinction into soft and hard parts, but the whole body is hard, the hardness, however, being of such a character as to be more flesh-like than bone, and more earthy and bone-like than flesh. The purpose of this is to make the body of the insect [30] less liable to get broken into pieces.