to facilitate the concoction of the food, some of them, as the
Cestreus (mullet), have a fleshy stomach resembling that of a bird;
while most of them have numerous processes close against the
stomach, to serve as a sort of antechamber in which the food may be
stored up and undergo putrefaction and concoction. There is contrast
between fishes and birds in the position of these processes. For in
fishes they are placed close to the stomach; while in birds, if
present at all, they are lower down, near the end of the gut. Some
of the Vivipara also have processes connected with the lower part of
the gut which serve the same purpose as that stated above.
The whole tribe of fishes is of gluttonous appetite, owing to the
arrangements for the reduction of their food being very imperfect, and
much of it consequently passing through them without undergoing
concoction; and, of all, those are the most gluttonous that have a
straight intestine. For as the passage of food in such cases is rapid,
and the enjoyment derived from it in consequence but brief, it follows
of necessity that the return of appetite is also speedy.
It has already been mentioned that in animals with front teeth in
both jaws the stomach is of small size. It may be classed pretty
nearly always under one or other of two headings, namely as resembling
the stomach of the dog, or as resembling the stomach of the pig. In
the pig the stomach is larger than in the dog, and presents certain
folds of moderate size, the purpose of which is to lengthen out the
period of concoction; while the stomach of the dog is of small size,
not much larger in calibre than the gut, and smooth on the internal
surface.
Not much larger, I say, than the gut; for in all animals after the
stomach comes the gut. This, like the stomach, presents numerous
modifications. For in some animals it is uniform, when uncoiled, and
alike throughout, while in others it differs in different portions.
Thus in some cases it is wider in the neighbourhood of the stomach,
and narrower towards the other end; and this explains by the way why
dogs have to strain so much in discharging their excrement. But in
most animals it is the upper portion that is the narrower and the
lower that is of greater width.
Of greater length than in other animals, and much convoluted, are
the intestines of those that have horns. These intestines, moreover,
as also the stomach, are of ampler volume, in accordance with the
larger size of the body. For animals with horns are, as a rule,
animals of no small bulk, because of the thorough elaboration which
their food undergoes. The gut, except in those animals where it is
straight, invariably widens out as we get farther from the stomach and
come to what is called the colon, and to a kind of caecal
dilatation. After this it again becomes narrower and convoluted.
Then succeeds a straight portion which runs right on to the vent. This
vent is known as the anus, and is in some animals surrounded by fat,
in others not so. All these parts have been so contrived by nature
as to harmonize with the various operations that relate to the food
and its residue. For, as the residual food gets farther on and lower
down, the space to contain it enlarges, allowing it to remain
stationary and undergo conversion. Thus is it in those animals
which, owing either to their large size, or to the heat of the parts
concerned, require more nutriment, and consume more fodder than the
rest.
Neither is it without a purpose, that, just as a narrower gut
succeeds to the upper stomach, so also does the residual food, when
its goodness is thoroughly exhausted, pass from the colon and the
ample space of the lower stomach into a narrower channel and into
the spiral coil. For so nature can regulate her expenditure and
prevent the excremental residue from being discharged all at once.
In all such animals, however, as have to be comparatively moderate
in their alimentation, the lower stomach presents no wide and roomy
spaces, though their gut is not straight, but has a number of
convolutions. For amplitude of space causes desire for ample food, and
straightness of the intestine causes quick return of appetite. And
thus it is that all animals whose food receptacles are either simple
or spacious are of gluttonous habits, the latter eating enormously
at a meal, the former making meals at short intervals.
Again, since the food in the upper stomach, having just been
swallowed, must of necessity be quite fresh, while that which has
reached the lower stomach must have had its juices exhausted and
resemble dung, it follows of necessity that there must also be some
intermediate part, in which the change may be effected, and where
the food will be neither perfectly fresh nor yet dung. And thus it
is that, in all such animals as we are now considering, there is found
what is called the jejunum; which is a part of the small gut, of the
gut, that is, which comes next to the stomach. For this jejunum lies
between the upper cavity which contains the yet unconcocted food and
the lower cavity which holds the residual matter, which by the time it
has got here has become worthless. There is a jejunum in all these
animals, but it is only plainly discernible in those of large size,
and this only when they have abstained from food for a certain time.
For then alone can one hit on the exact period when the food lies
half-way between the upper and lower cavities; a period which is
very short, for the time occupied in the transition of food is but
brief. In females this jejunum may occupy any part whatsoever of the
upper intestine, but in males it comes just before the caecum and
the lower stomach.
15
What is known as rennet is found in all animals that have a multiple
stomach, and in the hare among animals whose stomach is single. In the
former the rennet neither occupies the large paunch, nor the honeycomb
bag, nor the terminal reed, but is found in the cavity which separates
this terminal one from the two first, namely in the so-called
manyplies. It is the thick character of their milk which causes all
these animals to have rennet; whereas in animals with a single stomach
the milk is thin, and consequently no rennet is formed. It is this
difference in thickness which makes the milk of horned animals
coagulate, while that of animals without horns does not. Rennet
forms in the hare because it feeds on herbage that has juice like that
of the fig; for juice of this kind coagulates the milk in the
stomach of the sucklings. Why it is in the manyplies that rennet is
formed in animals with multiple stomachs has been stated in the
Problems.
Book IV
1
THE account which has now been given of the viscera, the stomach,
and the other several parts holds equally good not only for the
oviparous quadrupeds, but also for such apodous animals as the
Serpents. These two classes of animals are indeed nearly akin, a
; serpent resembling a lizard which has been lengthened out and deprived
of its feet. Fishes, again, resemble these two groups in all their
parts, excepting that, while these, being land animals, have a lung,
fishes have no lung, but gills in its place. None of these animals,
excepting the tortoise, as also no fish, has a urinary bladder. For
owing to the bloodlessness of their lung, they drink but sparingly;
and such fluid as they have is diverted to the scaly plates, as in
birds it is diverted to the feathers, and thus they come to have the
same white matter on the surface of their excrement as we see on
that of birds. For in animals that have a bladder, its excretion
when voided throws down a deposit of earthy brine in the containing
vessel. For the sweet and fresh elements, being light, are expended on
the flesh.
Among the Serpents, the same peculiarity attaches to vipers, as
among fishes attaches to Selachia. For both these and vipers are
externally viviparous, but previously produce ova internally.
The stomach in all these animals is single, just as it is single
in all other animals that have teeth in front of both jaws; and
their viscera are excessively small, as always happens when there is
no bladder. In serpents these viscera are, moreover, differently
shaped from those of other animals. For, a serpent's body being long
and narrow, its contents are as it were moulded into a similar form,
and thus come to be themselves elongated.
All animals that have blood possess an omentum, a mesentery,
intestines with their appendages, and, moreover, a diaphragm and a
heart; and all, excepting fishes, a lung and a windpipe. The
relative positions, moreover, of the windpipe and the oesophagus are
precisely similar in them all; and the reason is the same as has
already been given.
2
Almost all sanguineous animals have a gall-bladder. In some this
is attached to the liver, in others separated from that organ and
attached to the intestines, being apparently in the latter case no
less than in the former an appendage of the lower stomach. It is in
fishes that this is most clearly seen. For all fishes have a
gall-bladder; and in most of them it is attached to the intestine,
being in some, as in the Amia, united with this, like a border,
along its whole length. It is similarly placed in most serpents
There are therefore no good grounds for the view entertained by some
writers, that the gall exists for the sake of some sensory action. For
they say that its use is to affect that part of the soul which is
lodged in the neighbourhood of the liver, vexing this part when it
is congealed, and restoring it to cheerfulness when it again flows
free. But this cannot be. For in some animals there is absolutely no
gall-bladder at all--in the horse, for instance, the mule, the ass,
the deer, and the roe; and in others, as the camel, there is no
distinct bladder, but merely small vessels of a biliary character.
Again, there is no such organ in the seal, nor, of purely sea-animals,
in the dolphin. Even within the limits of the same genus, some animals
appear to have and others to be without it. Such, for instance, is the
case with mice; such also with man. For in some individuals there is a
distinct gall-bladder attached to the liver, while in others there
is no gall-bladder at all. This explains how the existence of this
part in the whole genus has been a matter of dispute. For each
observer, according as he has found it present or absent in the
individual cases he has examined, has supposed it to be present or
absent in the whole genus. The same has occurred in the case of
sheep and of goats. For these animals usually have a gall-bladder;
but, while in some localities it is so enormously big as to appear a
monstrosity, as is the case in Naxos, in others it is altogether
wanting, as is the case in a certain district belonging to the
inhabitants of Chalcis in Euboea. Moreover, the gall-bladder in fishes
is separated, as already mentioned, by a considerable interval from
the liver. No less mistaken seems to be the opinion of Anaxagoras
and his followers, that the gall-bladder is the cause of acute
diseases, inasmuch as it becomes over-full, and spirts out its
excess on to the lung, the blood-vessels, and the ribs. For, almost
invariably, those who suffer from these forms of disease are persons
who have no gall-bladder at all, as would be quite evident were they
to be dissected. Moreover, there is no kind of correspondence
between the amount of bile which is present in these diseases and
the amount which is exuded. The most probable opinion is that, as
the bile when it is present in any other part of the body is a mere
residuum or a product of decay, so also when it is present in the
region of the liver it is equally excremental and has no further
use; just as is the case with the dejections of the stomach and
intestines. For though even the residua are occasionally used by
nature for some useful purpose, yet we must not in all cases expect to
find such a final cause; for granted the existence in the body of this
or that constituent, with such and such properties, many results
must ensue merely as necessary consequences of these properties. All
animals, then, whose is healthy in composition and supplied with
none but sweet blood, are either entirely without a gall-bladder on
this organ, or have merely small bile-containing vessels; or are
some with and some without such parts. Thus it is that the liver in
animals that have no gall-bladder is, as a rule, of good colour and
sweet; and that, when there is a gall-bladder, that part of the
liver is sweetest which lies immediately underneath it. But, when
animals are formed of blood less pure in composition, the bile
serves for the excretion of its impure residue. For the very meaning
of excrement is that it is the opposite of nutriment, and of bitter
that it is the opposite of sweet; and healthy blood is sweet. So
that it is evident that the bile, which is bitter, cannot have any
use, but must simply be a purifying excretion. It was therefore no bad
saying of old writers that the absence of a gall-bladder gave long
life. In so saying they had in mind deer and animals with solid hoofs.
For such have no gall-bladder and live long. But besides these there
are other animals that have no gall-bladder, though those old
writers had not noticed the fact, such as the camel and the dolphin;
and these also are, as it happens, long-lived. Seeing, indeed, that
the liver is not only useful, but a necessary and vital part in all
animals that have blood, it is but reasonable that on its character
should depend the length or the shortness of life. Nor less reasonable
is it that this organ and none other should have such an excretion
as the bile. For the heart, unable as it is to stand any violent
affection, would be utterly intolerant of the proximity of such a
fluid; and, as to the rest of the viscera, none excepting the liver
are nece
ssary parts of an animal. It is the liver therefore that alone
has this provision. In conclusion, wherever we see bile we must take
it to be excremental. For to suppose that it has one character in this
part, another in that, would be as great an absurdity as to suppose
mucus or the dejections of the stomach to vary in character
according to locality and not to be excremental wherever found.
3
So much then of the gall-bladder, and of the reasons why some
animals have one, while others have not. We have still to speak of the
mesentery and the omentum; for these are associated with the parts
already described and contained in the same cavity. The omentum, then,
is a membrane containing fat; the fat being suet or lard, according as
the fat of the animal generally is of the former or latter
description. What kinds of animals are so distinguished has been
already set forth in an earlier part of this treatise. This
membrane, alike in animals that have a single and in those that have a
multiple stomach, grows from the middle of that organ, along a line
which is marked on it like a seam. Thus attached, it covers the rest
of the stomach and the greater part of the bowels, and this alike in
all sanguineous animals, whether they live on land or in water. Now
the development of this part into such a form as has been described is
the result of necessity. For, whenever solid and fluid are mixed
together and heated, the surface invariably becomes membranous and
skin-like. But the region in which the omentum lies is full of
nutriment of such a mixed character. Moreover, in consequence of the
close texture of the membrane, that portion of the sanguineous
nutriment will alone filter into it which is of a greasy character;
for this portion is composed of the finest particles; and when it
has so filtered in, it will be concocted by the heat of the part,
and will be converted into suet or lard, and will not acquire a
flesh-like or sanguineous constitution. The development, then, of
the omentum is simply the result of necessity. But when once formed,
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