by Aristotle
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