On The Parts Of Animals   

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