Aristotle

by Various Works [lit]

  in the treatises on Anatomy and Natural History. Now as there is a

  receptacle for the entire matter taken as food, and also a

  receptacle for its excremental residue, and again a third

  receptacle, namely the vessels, which serve as such for the blood,

  it is plain that this blood must be the final nutritive material in

  such animals as have it; while in bloodless animals the same is the

  case with the fluid which represents the blood. This explains why

  the blood diminishes in quantity when no food is taken, and

  increases when much is consumed, and also why it becomes healthy and

  unhealthy according as the food is of the one or the other

  character. These facts, then, and others of a like kind, make it plain

  that the purpose of the blood in sanguineous animals is to subserve

  the nutrition of the body. They also explain why no more sensation

  is produced by touching the blood than by touching one of the

  excretions or the food, whereas when the flesh is touched sensation is

  produced. For the blood is not continuous nor united by growth with

  the flesh, but simply lies loose in its receptacle, that is in the

  heart and vessels. The manner in which the parts grow at the expense

  of the blood, and indeed the whole question of nutrition, will find

  a more suitable place for exposition in the treatise on Generation,

  and in other writings. For our present purpose all that need be said

  is that the blood exists for the sake of nutrition, that is the

  nutrition of the parts; and with this much let us therefore content

  ourselves.

  4

  What are called fibres are found in the blood of some animals but

  not of all. There are none, for instance, in the blood of deer and

  of roes; and for this reason the blood of such animals as these

  never coagulates. For one part of the blood consists mainly of water

  and therefore does not coagulate, this process occurring only in the

  other and earthy constituent, that is to say in the fibres, while

  the fluid part is evaporating.

  Some at any rate of the animals with watery blood have a keener

  intellect than those whose blood is of an earthier nature. This 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,

  notwithstanding their want of blood, are yet more intelligent than

  some among the sanguineous kinds. Such for 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 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 solid, are turned into so many hot

  embers in the blood, like the embers in a vapour-bath, 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, that is to say if the earthy constituents of which we are

  speaking, are taken out of the blood, the fluid that remains behind

  will no longer coagulate; just as the watery residue of mud will not

  coagulate after removal of the 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 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 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 material intended to serve

  for the formation of the blood.

  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 fatty

  character. This is shown by the unctuous aspect of these substances;

  for such unctuous aspect 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 which contain such fibrous matter. Thus it is

  that in those horned animals that have no front teeth in the upper jaw

  the fat consists of 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 have front teeth in

  both jaws, and whose feet are divided into toes, there is no suet, but

  in its place lard; and this, not being of an earthy character, neither

  coagulates nor dries up into a friable mass.

  Both lard and suet when present in moderate amount are beneficial;

  for they 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 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 se
nsitive;

  as therefore is neither lard nor suet, seeing that they are nothing

  but concocted blood. Were then the whole body composed of these

  substances, it would be utterly without sensation. Such animals,

  again, as are 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 injuriously affected

  by any chance excess of heat or cold. For the same reason fat

  animals are less prolific than others. For that 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 reproductive excretion at all, or only a

  scanty amount.

  6

  So much then of blood and serum, and of lard and suet. Each of these

  has been described, and the purposes told for which they severally

  exist. 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 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

  external 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.

  The consistency of the marrow agrees with that of the fat. For

  when the fat consists of lard, then the marrow also is unctuous and

  lard-like; but when the blood is converted by concoction into suet,

  and does not assume the form of lard, then the marrow also has a suety

  character. In those animals, therefore, that have horns and are

  without upper front teeth, the marrow has the character of suet; while

  it takes the form of lard in those that have front teeth in both jaws,

  and that also have the foot divided into toes. What has ben 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 of unctuous fat or of suet, it could not

  hold together in such a continuous mass as it 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 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 contained within the bones is the

  nutriment out of which these are formed. Now the universal

  nutriment, as already stated, is blood; and 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 that it is perfectly intelligible how the marrow within

  the bone comes to have the character of these substances. So also it

  is easy to understand why, in those animals 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 chine. 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 chine. In 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 of

  the chine, as already mentioned, is somewhat 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 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 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 unctuous 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 clearly shown by many indications. The coldness of

  the brain is also manifest enough. For in the first place it is cold

  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 proper substance. This brain is not

  residual matter, nor yet is it one of the parts which are anatomically

  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 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 rough and

  inaccurate assertion; and it would perhaps be better to say that the

  soul is incorporate in some substance of a fiery character. The 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 mu
ch the same thing

  as to confound the auger or the saw with the carpenter or his craft,

  simply because the work is wrought by the two in conjunction. 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 the true

  and rational position), 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

  an organ, unless indeed it be, as the Poulp, by analogy. For where

  there is no blood, there in consequence there is but little heat.

  The brain, then, tempers the heat and seething of the heart. In order,

  however, that it may not itself be absolutely without heat, but may

  have a moderate amount, branches run from both blood-vessels, that

  is to say from the great vessel 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 abundant and thick.

  We can now understand why defluxions 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 nutriment steams upwards

  through the blood-vessels, its refuse portion is chilled by the

  influence of this region, and forms defluxions of phlegm and serum. We

  must suppose, to compare small things with great, that the like

  happens here as occurs in 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