Aristotle

by Various Works [lit]

  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