by Aristotle
back to the earth as rain. These, however, are matters which may be
suitably considered in the Principles of Diseases, so far as natural
philosophy has anything to say to them.
It is the brain again-or, in animals that have no brain, the part
analogous to it-which is the cause of sleep. For either by chilling
the blood that streams upwards after food, or by some other similar
influences, it produces heaviness in the region in which it lies
(which is the reason why drowsy persons hang the head), and causes the
heat to escape downwards in company with the blood. It is the
accumulation of this in excess in the lower region that produces
complete sleep, taking away the power of standing upright from those
animals to whom that posture is natural, and from the rest the power
of holding up the head. These, however, are matters which have been
separately considered in the treatises on Sensation and on Sleep.
That the brain is a compound of earth and water is shown by what
occurs when it is boiled. For, when so treated, it turns hard and
solid, inasmuch as the water is evaporated by the heat, and leaves the
earthy part behind. Just the same occurs when pulse and other fruits
are boiled. For these also are hardened by the process, because the
water which enters into their composition is driven off and leaves the
earth, which is their main constituent, behind.
Of all animals, man has the largest brain in proportion to his size;
and it is larger in men than in women. This is because the region of
the heart and of the lung is hotter and richer in blood in man than in
any other animal; and in men than in women. This again explains why
man, alone of animals, stands erect. For the heat, overcoming any
opposite inclination, makes growth take its own line of direction,
which is from the centre of the body upwards. It is then as a
counterpoise to his excessive heat that in man's brain there is this
superabundant fluidity and coldness; and it is again owing to this
superabundance that the cranial bone, which some call the Bregma, is
the last to become solidified; so long does evaporation continue to
occur through it under the influence of heat. Man is the only
sanguineous animal in which this takes place. Man, again, has more
sutures in his skull than any other animal, and the male more than the
female. The explanation is again to be found in the greater size of
the brain, which demands free ventilation, proportionate to its
bulk. For if the brain be either too fluid or too solid, it will not
perform its office, but in the one case will freeze the blood, and
in the other will not cool it at all; and thus will cause disease,
madness, and death. For the cardiac heat and the centre of life is
most delicate in its sympathies, and is immediately sensitive to the
slightest change or affection of the blood on the outer surface of the
brain.
The fluids which are present in the animal body at the time of birth
have now nearly all been considered. Amongst those that appear only at
a later period are the residua of the food, which include the deposits
of the belly and also those of the bladder. Besides these there is the
semen and the milk, one or the other of which makes its appearance
in appropriate animals. Of these fluids the excremental residua of the
food may be suitably discussed by themselves, when we come to
examine and consider the subject of nutrition. Then will be the time
to explain in what animals they are found, and what are the reasons
for their presence. Similarly all questions concerning the semen and
the milk may be dealt with in the treatise on Generation, for the
former of these fluids is the very starting-point of the generative
process, and the latter has no other ground of existence than
generative purposes.
8
We have now to consider the remaining homogeneous parts, and will
begin with flesh, and with the substance that, in animals that have no
flesh, takes its place. The reason for so beginning is that flesh
forms the very basis of animals, and is the essential constituent of
their body. Its right to this precedence can also be demonstrated
logically. For an animal is by our definition something that has
sensibility and chief of all the primary sensibility, which is that of
Touch; and it is the flesh, or analogous substance, which is the organ
of this sense. And it is the organ, either in the same way as the
pupil is the organ of sight, that is it constitutes the primary
organ of the sense; or it is the organ and the medium through which
the object acts combined, that is it answers to the pupil with the
whole transparent medium attached to it. Now in the case of the
other senses it was impossible for nature to unite the medium with the
sense-organ, nor would such a junction have served any purpose; but in
the case of touch she was compelled by necessity to do so. For of
all the sense-organs that of touch is the only one that has
corporeal substance, or at any rate it is more corporeal than any
other, and its medium must be corporeal like itself.
It is obvious also to sense that it is for the sake of the flesh
that all the other parts exist. By the other parts I mean the bones,
the skin, the sinews, and the blood-vessels, and, again, the hair
and the various kinds of nails, and anything else there may be of a
like character. Thus the bones are a contrivance to give security to
the soft parts, to which purpose they are adapted by their hardness;
and in animals that have no bones the same office is fulfilled by some
analogous substance, as by fishspine in some fishes, and by
cartilage in others.
Now in some animals this supporting substance is situated within the
body, while in some of the bloodless species it is placed on the
outside. The latter is the case in all the Crustacea, as the Carcini
(Crabs) and the Carabi (Prickly Lobsters); it is the case also in
the Testacea, as for instance in the several species known by the
general name of oysters. For in all these animals the fleshy substance
is within, and the earthy matter, which holds the soft parts
together and keeps them from injury, is on the outside. For the
shell not only enables the soft parts to hold together, but also, as
the animal is bloodless and so has but little natural warmth,
surrounds it, as a chaufferette does the embers, and keeps in the
smouldering heat. Similar to this seems to be the arrangement in
another and distinct tribe of animals, namely the Tortoises, including
the Chelone and the several kinds of Emys. But in Insects and in
Cephalopods the plan is entirely different, there being moreover a
contrast between these two themselves. For in neither of these does
there appear to be any bony or earthy part, worthy of notice,
distinctly separated from the rest of the body. Thus in the
Cephalopods the main bulk of the body consists of a soft flesh-like
substance, or rather of a substance which is intermediate to flesh and
sinew, so as not to be so read
ily destructible as actual flesh. I call
this substance intermediate to flesh and sinew, because it is soft
like the former, while it admits of stretching like the latter. Its
cleavage, however, is such that it splits not longitudinally, like
sinew, but into circular segments, this being the most advantageous
condition, so far as strength is concerned. These animals have also
a part inside them corresponding to the spinous bones of fishes. For
instance, in the Cuttle-fishes there is what is known as the os
sepiae, and in the Calamaries there is the so-called gladius. In the
Poulps, on the other hand, there is no such internal part, because the
body, or, as it is termed in them, the head, forms but a short sac,
whereas it is of considerable length in the other two; and it was this
length which led nature to assign to them their hard support, so as to
ensure their straightness and inflexibility; just as she has
assigned to sanguineous animals their bones or their fish-spines, as
the case may be. To come now to Insects. In these the arrangement is
quite different from that of the Cephalopods; quite different also
from that which obtains in sanguineous animals, as indeed has been
already stated. For in an insect there is no distinction into soft and
hard parts, but the whole body is hard, the hardness, however, being
of such a character as to be more flesh-like than bone, and more
earthy and bone-like than flesh. The purpose of this is to make the
body of the insect less liable to get broken into pieces.
9
There is a resemblance between the osseous and the vascular systems;
for each has a central part in which it begins, and each forms a
continuous whole. For no bone in the body exists as a separate thing
in itself, but each is either a portion of what may be considered a
continuous whole, or at any rate is linked with the rest by contact
and by attachments; so that nature may use adjoining bones either as
though they were actually continuous and formed a single bone, or, for
purposes of flexure, as though they were two and distinct. And
similarly no blood-vessel has in itself a separate individuality;
but they all form parts of one whole. For an isolated bone, if such
there were, would in the first place be unable to perform the office
for the sake of which bones exist; for, were it discontinuous and
separated from the rest by a gap, it would be perfectly unable to
produce either flexure or extension; nor only so, but it would
actually be injurious, acting like a thorn or an arrow lodged in the
flesh. Similarly if a vessel were isolated, and not continuous with
the vascular centre, it would be unable to retain the blood within
it in a proper state. For it is the warmth derived from this centre
that hinders the blood from coagulating; indeed the blood, when
withdrawn from its influence, becomes manifestly putrid. Now the
centre or origin of the blood-vessels is the heart, and the centre
or origin of the bones, in all animals that have bones, is what is
called the chine. With this all the other bones of the body are in
continuity; for it is the chine that holds together the whole length
of an animal and preserves its straightness. But since it is necessary
that the body of an animal shall bend during locomotion, this chine,
while it is one in virtue of the continuity of its parts, yet its
division into vertebrae is made to consist of many segments. It is
from this chine that the bones of the limbs, in such animals as have
these parts, proceed, and with it they are continuous, being
fastened together by the sinews where the limbs admit of flexure,
and having their extremities adapted to each other, either by the
one being hollowed and the other rounded, or by both being hollowed
and including between them a hucklebone, as a connecting bolt, so as
to allow of flexure and extension. For without some such arrangement
these movements would be utterly impossible, or at any rate would be
performed with great difficulty. There are some joints, again, in
which the lower end of the one bone and the upper end of the other are
alike in shape. In these cases the bones are bound together by sinews,
and cartilaginous pieces are interposed in the joint, to serve as a
kind of padding, and prevent the two extremities from grating
against each other.
Round about the bones, and attached to them by thin fibrous bands,
grow the fleshy parts, for the sake of which the bones themselves
exist. For just as an artist, when he is moulding an animal out of
clay or other soft substance, takes first some solid body as a
basis, and round this moulds the clay, so also has nature acted in
fashioning the animal body out of flesh. Thus we find all the fleshy
parts, with one exception, supported by bones, which serve, when the
parts are organs of motion, to facilitate flexure, and, when the parts
are motionless, act as a protection. The ribs, for example, which
enclose the chest are intended to ensure the safety of the heart and
neighbouring viscera. The exception of which mention was made is the
belly. The walls of this are in all animals devoid of bones; in
order that there may be no hindrance to the expansion which
necessarily occurs in this part after a meal, nor, in females, any
interference with the growth of the foetus, which is lodged here.
Now the bones of viviparous animals, of such, that is, as are not
merely externally but also internally viviparous, vary but very little
from each other in point of strength, which in all of them is
considerable. For the Vivipara in their bodily proportions are far
above other animals, and many of them occasionally grow to an enormous
size, as is the case in Libya and in hot and dry countries
generally. But the greater the bulk of an animal, the stronger, the
bigger, and the harder, are the supports which it requires; and
comparing the big animals with each other, this requirement will be
most marked in those that live a life of rapine. Thus it is that the
bones of males are harder than those of females; and the bones of
flesh-eaters, that get their food by fighting, are harder than those
of Herbivora. Of this the Lion is an example; for so hard are its
bones, that, when struck, they give off sparks, as though they were
stones. It may be mentioned also that the Dolphin, in as much as it is
viviparous, is provided with bones and not with fish-spines.
In those sanguineous animals, on the other hand, that are oviparous,
the bones present successive slight variations of character. Thus in
Birds there are bones, but these are not so strong as the bones of the
Vivipara. Then come the Oviparous fishes, where there is no bone,
but merely fish-spine. In the Serpents too the bones have the
character of fish-spine, excepting in the very large species, where
the solid foundation of the body requires to be stronger, in order
that the animal itself may be strong, the same reason prevailing as in
the case of the Vivipara. Lastly, in the Selachia, as they are called,
the fish-spines are replaced by cartilage. For it is necessary that
the movements of these animals shall be of an undulating character;
and this again requires the framework that supports the body to be
made of a pliable and not of a brittle substance. Moreover, in these
Selachia nature has used all the earthy matter on the skin; and she is
unable to allot to many different parts one and the same superfluity
of material. Even in viviparous animals many of the bones are
cartilaginous. This happens in those parts where it is to the
advantage of the surrounding flesh that its solid base shall be soft
and mucilaginous. Such, for instance, is the case with the ears and
nostrils; for in projecting parts, such as these, brittle substances
would soon get broken. Cartilage and bone are indeed fundamentally the
same thing, the differences between them being merely matters of
degree. Thus neither cartilage nor bone, when once cut off, grows
again. Now the cartilages of these land animals are without marrow,
that is without any distinctly separate marrow. For the marrow,
which in bones is distinctly separate, is here mixed up with the whole
mass, and gives a soft and mucilaginous consistence to the
cartilage. But in the Selachia the chine, though it is
cartilaginous, yet contains marrow; for here it stands in the stead of
a bone.
Very nearly resembling the bones to the touch are such parts as
nails, hoofs, whether solid or cloven, horns, and the beaks of
birds, all of which are intended to serve as means of defence. For the
organs which are made out of these substances, and which are called by
the same names as the substances themselves, the organ hoof, for
instance, and the organ horn, are contrivances to ensure the
preservation of the animals to which they severally belong. In this
class too must be reckoned the teeth, which in some animals have but a
single function, namely the mastication of the food, while in others
they have an additional office, namely to serve as weapons; as is
the case with all animals that have sharp interfitting teeth or that
have tusks. All these parts are necessarily of solid and earthy