by Aristotle
direction in which their motion occurs.
The heart again is abundantly supplied with sinews, as might
reasonably be expected. For the motions of the body commence from
the heart, and are brought about by traction and relaxation. The heart
therefore, which, as already said,' as it were a living creature
inside its possessor, requires some such subservient and strengthening
parts.
In no animals does the heart contain a bone, certainly in none of
those that we have ourselves inspected, with the exception of the
horse and a certain kind of ox. In these exceptional cases the
heart, owing to its large bulk, is provided with a bone as a
support; just as the bones serve as supports for the body generally.
In animals of great size the heart has three cavities; in smaller
animals it has two; and in all has at least one, for, as already
stated, there must be some place in the heart to serve as a receptacle
for the first blood; which, as has been mentioned more than once, is
formed in this organ. But inasmuch as the main blood-vessels are two
in number, namely the so-called great vessel and the aorta, each of
which is the origin of other vessels; inasmuch, moreover, as these two
vessels present differences, hereafter to be discussed, when
compared with each other, it is of advantage that they also shall
themselves have distinct origins. This advantage will be obtained if
each side have its own blood, and the blood of one side be kept
separate from that of the other. For this reason the heart, whenever
it is possible, has two receptacles. And this possibility exists in
the case of large animals, for in them the heart, as the body
generally, is of large size. Again it is still better that there shall
be three cavities, so that the middle and odd one may serve as a
centre common to both sides. But this requires the heart to be of
greater magnitude, so that it is only in the largest hearts that there
are three cavities.
Of these three cavities it is the right that has the most abundant
and the hottest blood, and this explains why the limbs also on the
right side of the body are warmer than those on the left. The left
cavity has the least blood of all, and the coldest; while in the
middle cavity the blood, as regards quantity and heat, is intermediate
to the other two, being however of purer quality than either. For it
behoves the supreme part to be as tranquil as possible, and this
tranquillity can be ensured by the blood being pure, and of moderate
amount and warmth.
In the heart of animals there is also a kind of joint-like division,
something like the sutures of the skull. This is not, however,
attributable to the heart being formed by the union of several parts
into a compound whole, but is rather, as already said, the result of a
joint-like division. These jointings are most distinct in animals of
keen sensibility, and less so in those that are of duller feeling,
in swine for instance. Different hearts differ also from each other in
their sizes, and in their degrees of firmness; and these differences
somehow extend their influence to the temperaments of the animals. For
in animals of low sensibility the heart is hard and dense in
texture, while it is softer in such as are endowed with keener
feeling. So also when the heart is of large size the animal is
timorous, while it is more courageous if the organ be smaller and of
moderate bulk. For in the former the bodily affection which results
from terror already pre-exists; for the bulk of the heart is out of
all proportion to the animal's heat, which being small is reduced to
insignificance in the large space, and thus the blood is made colder
than it would otherwise be.
The heart is of large size in the hare, the deer, the mouse, the
hyena, the ass, the leopard, the marten, and in pretty nearly all
other animals that either are manifestly timorous, or betray their
cowardice by their spitefulness.
What has been said of the heart as a whole is no less true of its
cavities and of the blood-vessels; these also if of large size being
cold. For just as a fire of equal size gives less heat in a large room
than in a small one, so also does the heat in a large cavity or a
large blood-vessel, that is in a large receptacle, have less effect
than in a small one. Moreover, all hot bodies are cooled by motions
external to themselves, and the more spacious the cavities and vessels
are, the greater the amount of spirit they contain, and the more
potent its action. Thus it is that no animal that has large cavities
in its heart, or large blood-vessels, is ever fat, the vessels being
indistinct and the cavities small in all or most fat animals.
The heart again is the only one of the viscera, and indeed the
only part of the body, that is unable to tolerate any serious
affection. This is but what might reasonably be expected. For, if
the primary or dominant part be diseased, there is nothing from
which the other parts which depend upon it can derive succour. A proof
that the heart is thus unable to tolerate any morbid affection is
furnished by the fact that in no sacrificial victim has it ever been
seen to be affected with those diseases that are observable in the
other viscera. For the kidneys are frequently found to be full of
stones, and growths, and small abscesses, as also are the liver, the
lung, and more than all the spleen. There are also many other morbid
conditions which are seen to occur in these parts, those which are
least liable to such being the portion of the lung which is close to
the windpipe, and the portion of the liver which lies about the
junction with the great blood-vessel. This again admits of a
rational explanation. For it is in these parts that the lung and liver
are most closely in communion with the heart. On the other hand,
when animals die not by sacrifice but from disease, and from
affections such as are mentioned above, they are found on dissection
to have morbid affections of the heart.
Thus much of the heart, its nature, and the end and cause of its
existence in such animals as have it.
5
In due sequence we have next to discuss the blood-vessels, that is
to say the great vessel and the aorta. For it is into these two that
the blood first passes when it quits the heart; and all the other
vessels are but offshoots from them. Now that these vessels exist on
account of the blood has already been stated. For every fluid requires
a receptacle, and in the case of the blood the vessels are that
receptacle. Let us now explain why these vessels are two, and why they
spring from one single source, and extend throughout the whole body.
The reason, then, why these two vessels coalesce into one centre,
and spring from one source, is that the sensory soul is in all animals
actually one; and this one-ness of the sensory soul determines a
corresponding one-ness of the part in which it primarily abides. In
sanguineous animals this one-ness is not only actual but pot
ential,
whereas in some bloodless animals it is only actual. Where, however,
the sensory soul is lodged, there also and in the selfsame place
must necessarily be the source of heat; and, again, where this is
there also must be the source of the blood, seeing that it thence
derives its warmth and fluidity. Thus, then, in the oneness of the
part in which is lodged the prime source of sensation and of heat is
involved the one-ness of the source in which the blood originates; and
this, again, explains why the blood-vessels have one common
starting-point.
The vessels, again, are two, because the body of every sanguineous
animal that is capable of locomotion is bilateral; for in all such
animals there is a distinguishable before and behind, a right and
left, an above and below. Now as the front is more honourable and of
higher supremacy than the hinder aspect, so also and in like degree is
the great vessel superior to the aorta. For the great vessel is placed
in front, while the aorta is behind; the former again is plainly
visible in all sanguineous animals, while the latter is in some
indistinct and in some not discernible at all.
Lastly, the reason for the vessels being distributed throughout
the entire body is that in them, or in parts analogous to them, is
contained the blood, or the fluid which in bloodless animals takes the
place of blood, and that the blood or analogous fluid is the
material from which the whole body is made. Now as to the manner in
which animals are nourished, and as to the source from which they
obtain nutriment and as to the way in which they absorb this from
the stomach, these are matters which may be more suitably considered
and explained in the treatise on Generation. But inasmuch as the parts
are, as already said, formed out of the blood, it is but rational that
the flow of the blood should extend, as it does, throughout the
whole of the body. For since each part is formed of blood, each must
have blood about and in its substance.
To give an illustration of this. The water-courses in gardens are so
constructed as to distribute water from one single source or fount
into numerous channels, which divide and subdivide so as to convey
it to all parts; and, again, in house-building stones are thrown
down along the whole ground-plan of the foundation walls; because
the garden-plants in the one case grow at the expense of the water,
and the foundation walls in the other are built out of the stones. Now
just after the same fashion has nature laid down channels for the
conveyance of the blood throughout the whole body, because this
blood is the material out of which the whole fabric is made. This
becomes very evident in bodies that have undergone great emaciation.
For in such there is nothing to be seen but the blood-vessels; just as
when fig-leaves or vine-leaves or the like have dried up, there is
nothing left of them but their vessels. The explanation of this is
that the blood, or fluid which takes its place, is potentially body
and flesh, or substance analogous to flesh. Now just as in
irrigation the largest dykes are permanent, while the smallest are
soon filled up with mud and disappear, again to become visible when
the deposit of mud ceases; so also do the largest blood-vessels remain
permanently open, while the smallest are converted actually into
flesh, though potentially they are no whit less vessels than before.
This too explains why, so long as the flesh of an animal is in its
integrity, blood will flow from any part of it whatsoever that is cut,
though no vessel, however small, be visible in it. Yet there can be no
blood, unless there be a blood-vessel. The vessels then are there, but
are invisible owing to their being clogged up, just as the dykes for
irrigation are invisible until they have been cleared of mud.
As the blood-vessels advance, they become gradually smaller and
smaller, until at last their tubes are too fine to admit the blood.
This fluid can therefore no longer find its way through them, though
they still give passage to the humour which we call sweat; and
especially so when the body is heated, and the mouths of the small
vessels are dilated. Instances, indeed, are not unknown of persons who
in consequence of a cachectic state have secreted sweat that resembled
blood, their body having become loose and flabby, and their blood
watery, owing to the heat in the small vessels having been too
scanty for its concoction. For, as was before said, every compound
of earth and water-and both nutriment and blood are such-becomes
thicker from concoction. The inability of the heat to effect
concoction may be due either to its being absolutely small in
amount, or to its being small in proportion to the quantity of food,
when this has been taken excess. This excess again may be of two
kinds, either quantitative or qualitative; for all substances are
not equally amenable to concoction.
The widest passages in the body are of all parts the most liable
to haemorrhage; so that bleeding occurs not infrequently from the
nostrils, the gums, and the fundament, occasionally also from the
mouth. Such haemorrhages are of a passive kind, and not violent as are
those from the windpipe.
The great vessel and the aorta, which above lie somewhat apart,
lower down exchange positions, and by so doing give compactness to the
body. For when they reach the point where the legs diverge, they
each split into two, and the great vessel passes from the front to the
rear, and the aorta from the rear to the front. By this they
contribute to the unity of the whole fabric. For as in plaited work
the parts hold more firmly together because of the interweaving, so
also by the interchange of position between the blood-vessels are
the anterior and posterior parts of the body more closely knit
together. A similar exchange of position occurs also in the upper part
of the body, between the vessels that have issued from the heart.
The details however of the mutual relations of the different vessels
must be looked for in the treatises on Anatomy and the Researches
concerning Animals.
So much, then, as concerns the heart and the blood-vessels. We
must now pass on to the other viscera and apply the same method of
inquiry to them.
6
The lung, then, is an organ found in all the animals of a certain
class, because they live on land. For there must of necessity be
some means or other of tempering the heat of the body; and in
sanguineous animals, as they are of an especially hot nature, the
cooling agency must be external, whereas in the bloodless kinds the
innate spirit is sufficient of itself for the purpose. The external
cooling agent must be either air or water. In fishes the agent is
water. Fishes therefore never have a lung, but have gills in its
place, as was stated in the treatise on Respiration. But animals
that breathe are cooled by air. These therefore are all provided
with a lung.
All la
nd animals breathe, and even some water animals, such as the
whale, the dolphin, and all the spouting Cetacea. For many animals lie
half-way between terrestrial and aquatic; some that are terrestrial
and that inspire air being nevertheless of such a bodily
constitution that they abide for the most time in the water; and
some that are aquatic partaking so largely of the land character, that
respiration constitutes for them the man condition of life.
The organ of respiration is the lung. This derives its motion from
the heart; but it is its own large size and spongy texture that
affords amplitude of space for entrance of the breath. For when the
lung rises up the breath streams in, and is again expelled when the
lung collapses. It has been said that the lung exists as a provision
to meet the jumping of the heart. But this is out of the question. For
man is practically the only animal whose heart presents this
phenomenon of jumping, inasmuch as he alone is influenced by hope
and anticipation of the future. Moreover, in most animals the lung
is separated from the heart by a considerable interval and lies
above it, so that it can contribute nothing to mitigate any jumping.
The lung differs much in different animals. For in some it is of
large size and contains blood; while in others it is smaller and of
spongy texture. In the vivipara it is large and rich in blood, because
of their natural heat; while in the ovipara it is small and dry but
capable of expanding to a vast extent when inflated. Among terrestrial
animals, the oviparous quadrupeds, such as lizards, tortoises, and the
like, have this kind of lung; and, among inhabitants of the air, the
animals known as birds. For in all these the lung is spongy, and
like foam. For it is membranous and collapses from a large bulk to a
small one, as does foam when it runs together. In this too lies the
explanation of the fact that these animals are little liable to thirst
and drink but sparingly, and that they are able to remain for a
considerable time under water. For, inasmuch as they have but little