On The Parts Of Animals   

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.
Part 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 land 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