by Aristotle
same term-as, for example, is the case with blood-vessel and bit of
blood-vessel-while in another sense they are not; but a portion of a
heterogeneous part, such as face, in no sense has the same designation
as the whole.
The first question to be asked is what are the causes to which these
homogeneous parts owe their existence? The causes are various; and
this whether the parts be solid or fluid. Thus one set of
homogeneous parts represent the material out of which the
heterogeneous parts are formed; for each separate organ is constructed
of bones, sinews, flesh, and the like; which are either essential
elements in its formation, or contribute to the proper discharge of
its function. A second set are the nutriment of the first, and are
invariably fluid, for all growth occurs at the expense of fluid
matter; while a third set are the residue of the second. Such, for
instance, are the faeces and, in animals that have a bladder, the
urine; the former being the dregs of the solid nutriment, the latter
of the fluid.
Even the individual homogeneous parts present variations, which
are intended in each case to render them more serviceable for their
purpose. The variations of the blood may be selected to illustrate
this. For different bloods differ in their degrees of thinness or
thickness, of clearness or turbidity, of coldness or heat; and this
whether we compare the bloods from different parts of the same
individual or the bloods of different animals. For, in the individual,
all the differences just enumerated distinguish the blood of the upper
and of the lower halves of the body; and, dealing with classes, one
section of animals is sanguineous, while the other has no blood, but
only something resembling it in its place. As regards the results of
such differences, the thicker and the hotter blood is, the more
conducive is it to strength, while in proportion to its thinness and
its coldness is its suitability for sensation and intelligence. A like
distinction exists also in the fluid which is analogous to blood. This
explains how it is that bees and other similar creatures are of a more
intelligent nature than many sanguineous animals; and that, of
sanguineous animals, those are the most intelligent whose blood is
thin and cold. Noblest of all are those whose blood is hot, and at the
same time thin and clear. For such are suited alike for the
development of courage and of intelligence. Accordingly, the upper
parts are superior in these respects to the lower, the male superior
to the female, and the right side to the left. As with the blood so
also with the other parts, homogeneous and heterogeneous alike. For
here also such variations as occur must be held either to be related
to the essential constitution and mode of life of the several animals,
or, in other cases, to be merely matters of slightly better or
slightly worse. Two animals, for instance, may have eyes. But in one
these eyes may be of fluid consistency, while in the other they are
hard; and in one there may be eyelids, in the other no such
appendages. In such a case, the fluid consistency and the presence
of eyelids, which are intended to add to the accuracy of vision, are
differences of degree. As to why all animals must of necessity have
blood or something of a similar character, and what the nature of
blood may be, these are matters which can only be considered when we
have first discussed hot and cold. For the natural properties of
many substances are referable to these two elementary principles;
and it is a matter of frequent dispute what animals or what parts of
animals are hot and what cold. For some maintain that water animals
are hotter than such as live on land, asserting that their natural
heat counterbalances the coldness of their medium; and again, that
bloodless animals are hotter than those with blood, and females than
males. Parmenides, for instance, and some others declare that women
are hotter than men, and that it is the warmth and abundance of
their blood which causes their menstrual flow, while Empedocles
maintains the opposite opinion. Again, comparing the blood and the
bile, some speak of the former as hot and of the latter as cold, while
others invert the description. If there be this endless disputing
about hot and cold, which of all things that affect our senses are the
most distinct, what are we to think as to our other sensory
impressions?
The explanation of the difficulty appears to be that the term
'hotter' is used in several senses; so that different statements,
though in verbal contradiction with each other, may yet all be more or
less true. There ought, then, to be some clear understanding as to the
sense in which natural substances are to be termed hot or cold,
solid or fluid. For it appears manifest that these are properties on
which even life and death are largely dependent, and that they are
moreover the causes of sleep and waking, of maturity and old age, of
health and disease; while no similar influence belongs to roughness
and smoothness, to heaviness and lightness, nor, in short, to any
other such properties of matter. That this should be so is but in
accordance with rational expectation. For hot and cold, solid and
fluid, as was stated in a former treatise, are the foundations of
the physical elements.
Is then the term hot used in one sense or in many? To answer this we
must ascertain what special effect is attributed to a hotter
substance, and if there be several such, how many these may be. A body
then is in one sense said to be hotter than another, if it impart a
greater amount of heat to an object in contact with it. In a second
sense, that is said to be hotter which causes the keener sensation
when touched, and especially if the sensation be attended with pain.
This criterion, however, would seem sometimes to be a false one; for
occasionally it is the idiosyncrasy of the individual that causes
the sensation to be painful. Again, of two things, that is the
hotter which the more readily melts a fusible substance, or sets on
fire an inflammable one. Again, of two masses of one and the same
substance, the larger is said to have more heat than the smaller.
Again, of two bodies, that is said to be the hotter which takes the
longer time in cooling, as also we call that which is rapidly heated
hotter than that which is long about it; as though the rapidity
implied proximity and this again similarity of nature, while the
want of rapidity implied distance and this again dissimilarity of
nature. The term hotter is used then in all the various senses that
have been mentioned, and perhaps in still more. Now it is impossible
for one body to be hotter than another in all these different
fashions. Boiling water for instance, though it is more scalding
than flame, yet has no power of burning or melting combustible or
fusible matter, while flame has. So again this boiling water is hotter
than a small fire, and yet gets cold more rapidly and completely.
For in fact fire never becomes cold; whereas water invariably does so.
Boiling water, again, is hotter to the touch than oil; yet it gets
cold and solid more rapidly than this other fluid. Blood, again, is
hotter to the touch than either water or oil, and yet coagulates
before them. Iron, again, and stones and other similar bodies are
longer in getting heated than water, but when once heated burn other
substances with a much greater intensity. Another distinction is this.
In some of the bodies which are called hot the heat is derived from
without, while in others it belongs to the bodies themselves; and it
makes a most important difference whether the heat has the former or
the latter origin. For to call that one of two bodies the hotter,
which is possessed of heat, we may almost say, accidentally and not of
its own essence, is very much the same thing as if, finding that
some man in a fever was a musician, one were to say that musicians are
hotter than healthy men. Of that which is hot per se and that which is
hot per accidens, the former is the slower to cool, while not rarely
the latter is the hotter to the touch. The former again is the more
burning of the two-flame, for instance, as compared with boiling
water-while the latter, as the boiling water, which is hot per
accidens, is the more heating to the touch. From all this it is
clear that it is no simple matter to decide which of two bodies is the
hotter. For the first may be the hotter in one sense, the second the
hotter in another. Indeed in some of these cases it is impossible to
say simply even whether a thing is hot or not. For the actual
substratum may not itself be hot, but may be hot when coupled witb
heat as an attribute, as would be the case if one attached a single
name to hot water or hot iron. It is after this manner that blood is
hot. In such cases, in those, that is, in which the substratum owes
its heat to an external influence, it is plain that cold is not a mere
privation, but an actual existence.
There is no knowing but that even fire may be another of these
cases. For the substratum of fire may be smoke or charcoal, and though
the former of these is always hot, smoke being an uprising vapour, yet
the latter becomes cold when its flame is extinguished, as also
would oil and pinewood under similar circumstances. But even
substances that have been burnt nearly all possess some heat, cinders,
for example, and ashes, the dejections also of animals, and, among the
excretions, bile; because some residue of heat has been left in them
after their combustion. It is in another sense that pinewood and fat
substances are hot; namely, because they rapidly assume the
actuality of fire.
Heat appears to cause both coagulation and melting. Now such
things as are formed merely of water are solidified by cold, while
such as are formed of nothing but earth are solidified by fire. Hot
substances again are solidified by cold, and, when they consist
chiefly of earth, the process of solidification is rapid, and the
resulting substance is insoluble; but, when their main constituent
is water, the solid matter is again soluble. What kinds of substances,
however, admit of being solidified, and what are the causes of
solidification, are questions that have already been dealt with more
precisely in another treatise.
In conclusion, then, seeing that the terms hot and hotter are used
in many different senses, and that no one substance can be hotter than
others in all these senses, we must, when we attribute this
character to an object, add such further statements as that this
substance is hotter per se, though that other is often hotter per
accidens; or again, that this substance is potentially hot, that other
actually so; or again, that this substance is hotter in the sense of
causing a greater feeling of heat when touched, while that other is
hotter in the sense of producing flame and burning. The term hot being
used in all these various senses, it plainly follows that the term
cold will also be used with like ambiguity.
So much then as to the signification of the terms hot and cold,
hotter and colder.
3
In natural sequence we have next to treat of solid and fluid.
These terms are used in various senses. Sometimes, for instance,
they denote things that are potentially, at other times things that
are actually, solid or fluid. Ice for example, or any other solidified
fluid, is spoken of as being actually and accidentally solid, while
potentially and essentially it is fluid. Similarly earth and ashes and
the like, when mixed with water, are actually and accidentally
fluid, but potentially and essentially are solid. Now separate the
constituents in such a mixture and you have on the one hand the watery
components to which its fluidity was due, and these are both
actually and potentially fluid, and on the other hand the earthy
components, and these are in every way solid; and it is to bodies that
are solid in this complete manner that the term 'solid' is most
properly and absolutely applicable. So also the opposite term
'fluld' is strictly and absolutely applicable to that only which is
both potentially and actually fluid. The same remark applies also to
hot bodies and to cold.
These distinctions, then, being laid down, it is plain that blood is
essentially hot in so far as that heat is connoted in its name; just
as if boiling water were denoted by a single term, boiling would be
connoted in that term. But the substratum of blood, that which it is
in substance while it is blood in form, is not hot. Blood then in a
certain sense is essentially hot, and in another sense is not so.
For heat is included in the definition of blood, just as whiteness
is included in the definition of a white man, and so far therefore
blood is essentially hot. But so far as blood becomes hot from some
external influence, it is not hot essentially.
As with hot and cold, so also is it with solid and fluid. We can
therefore understand how some substances are hot and fluid so long
as they remain in the living body, but become perceptibly cold and
coagulate so soon as they are separated from it; while others are
hot and consistent while in the body, but when withdrawn under a
change to the opposite condition, and become cold and fluid. Of the
former blood is an example, of the latter bile; for while blood
solidifies when thus separated, yellow bile under the same
circumstances becomes more fluid. We must attribute to such substances
the possession of opposite properties in a greater or less degree.
In what sense, then, the blood is hot and in what sense fluid, and
how far it partakes of the opposite properties, has now been fairly
explained. Now since everything that grows must take nourishment,
and nutriment in all cases consists of fluid and solid substances, and
since it is by the force of heat that these are concocted and changed,
it follows that all living things, animals and plants alike, must on
this account, if on no other, have a natural source of heat. This
natural heat, moreover, must belong to many parts, seeing that the
organs by which the various elaborations of the food are effected
are many in number. For first of all there is the mouth and the
parts inside the mouth, on which the first share in the duty clearly
devolves, in such animals at least as live on food which requires
disintegration. The mouth, however, does not actually concoct the
food, but merely facilitates concoction; for the subdivision of the
food into small bits facilitates the action of heat upon it. After the
mouth come the upper and the lower abdominal cavities, and here it
is that concoction is effected by the aid of natural heat. Again, just
as there is a channel for the admission of the unconcocted food into
the stomach, namely the mouth, and in some animals the so-called
oesophagus, which is continuous with the mouth and reaches to the
stomach, so must there also be other and more numerous channels by
which the concocted food or nutriment shall pass out of the stomach
and intestines into the body at large, and to which these cavities
shall serve as a kind of manger. For plants get their food from the
earth by means of their roots; and this food is already elaborated
when taken in, which is the reason why plants produce no excrement,
the earth and its heat serving them in the stead of a stomach. But
animals, with scarcely an exception, and conspicuously all such as are
capable of locomotion, are provided with a stomachal sac, which is
as it were an internal substitute for the earth. They must therefore
have some instrument which shall correspond to the roots of plants,
with which they may absorb their food from this sac, so that the
proper end of the successive stages of concoction may at last be
attained. The mouth then, its duty done, passes over the food to the
stomach, and there must necessarily be something to receive it in turn
from this. This something is furnished by the bloodvessels, which
run throughout the whole extent of the mesentery from its lowest
part right up to the stomach. A description of these will be found