Tim. but as regards the thinness of its sides and the acuteness of its angles and the smallness of its particles and the rapidity of its motion—owing to all which properties fire is intense and keen and sharply cuts whatever it encounters,—these properties we must explain by recalling the origin of its form, how that it above all others is the one substance which so divides our bodies and minces them up as to produce naturally both that affection which we call heat and its very name. i.e., θερμόν (quasi κερμόν ) is derived from κερματίζω ( minced up or mint ). 

 The opposite affection is evident, but none the less it must not lack description. When liquids with larger particles, which surround the body, enter into it they drive out the smaller particles; but as they cannot pass into their room they compress the moisture within us, so that in place of non-uniformity and motion they produce immobility and density, as a result of the uniformity and compression. But that which is being contracted contrary to nature fights, and, in accordance with its nature, thrusts itself away in the contrary direction. And to this fighting and shaking we give the names of trembling and shivering ; while this affection as a whole, as well as the cause thereof, is termed cold. 

 By the term hard we indicate all the things to which our flesh gives way; and by the term soft all those which give way to our flesh; and these terms are similarly used relatively to each other. Now a substance gives way when it has its base small; but when it is constructed of quadrangular bases, being very firmly based, it is a most inelastic form; and so too is everything which is of very dense composition and most rigid.

 The nature of heavy and light would be shown most clearly if, along with them, we examined also the nature of above and below, as they are called. That there really exist two distinct and totally opposite regions, each of which occupies one-half of the Universe—the one termed below, towards which move all things possessing any bodily mass, and the other above, towards which everything goes against its will,— this is a wholly erroneous supposition The reference here is, probably to Democritus (Aristotle also speaks of τὸ ἄνω φύσει , Phys . 208 b 14). For inasmuch as the whole Heaven is spherical, all its outermost parts, being equally distant from the center, must really be outermost in a similar degree; and one must conceive of the center, which is distant from all the outermost parts by the same measures, as being opposite to them all. Seeing, then, that the Cosmos is actually of this nature, which of the bodies mentioned can one set above or below without incurring justly the charge of applying a wholly unsuitable name? For its central region cannot rightly be termed either above or below, but just central ; while its circumference neither is central nor has it any one part more divergent than another from the center or any of its opposite parts. But to that which is in all ways uniform, what opposite names can we suppose are rightly applicable, or in what sense? Tim. For suppose there were a solid body evenly-balanced at the center of the universe, it would never be carried away to the extremities because of their uniformity in all respects; nay, even were a man to travel round it in a circle he would often call the same part of it both above and below, according as he stood now at one pole, now at the opposite. i.e., above and below are purely relative terms. For seeing that the Whole is, as we said just now, spherical, the assertion that it has one region above and one below does not become a man of sense.

 Now the origin of these names and their true meaning which accounts for our habit of making these verbal distinctions even about the whole Heaven, we must determine on the basis of the following principles. Suppose that a man were to take his stand in that region of the Universe in which the substance of fire has its special abode, and where also that substance to which it flies is collected in largest bulk; and suppose that, having the power to do so, he were to separate portions of the fire and weigh them, putting them on scales and lifting the balance and pulling the fire by force into the dissimilar air, it is obvious that he will force the smaller mass more easily than the larger. For if two masses are lifted up simultaneously by a single effort, the smaller will necessarily yield more and the larger less, owing to its resistance, to the force exerted; and the large mass will be said to be heavy and moving down, the small light and moving up. Now this is just what we ought to detect ourselves doing in our region here. Standing on the earth and detaching various earthy substances, and sometimes pure earth, we pull them into the dissimilar air by force and against nature, since both these kinds cleave to their own kindred; and the smaller mass yields more easily, and follows first, as we force it into the dissimilar kind; wherefore we name it light, and the region to which we force it above ; and the conditions opposite thereto we name heavy and below. Thus, these must necessarily differ in their mutual relations, because the main masses of the Kinds occupy regions opposite to one another; for when we compare what is light in one region with what is light in the opposite region, and the heavy with the heavy, the below with the below, and the” above with the above, we shall discover that these all become and are opposite and oblique and in every way different in their mutual relations. There is, however, this one fact to be noticed about them all, that it is the passage of each kind to its kindred mass which makes the moving body heavy, and the region to which such a body moves below ; while the opposite conditions produce the contrary results. i.e., the attraction takes different directions, therefore up and down are relative terms. Let this, then, stand as our account of the causes of these conditions. Tim. Of smoothness and roughness anyone might be able to discern the causes and explain them also to others. For the cause of the latter is hardness combined with irregularity, and of the former regularity combined with density.

 In respect of the affections common to the whole body a very important point, which still remains, is the cause of the pleasures and pains attaching to the sense-affections we have been discussing; and the cause also of those affections which have become perceptible by means of the bodily parts and involve in themselves concomitant pains and pleasures. Let us, then, try to grasp the causes in connection with every perceptible and imperceptible affection in the following way, bearing in mind the distinction we previously drew Cf. 54 B ff., 57 D, E. between mobile and immobile substances; for it is in this way that we must track down all those facts that we intend to grasp. Whenever what is naturally mobile is impressed by even a small affection, it transmits it in a circle, the particles passing on to one another this identical impression until they reach the organ of intelligence and announce the quality of the agent. But a substance of the opposite kind, being stable and having no circular movement, is only affected in itself and does not move any other adjacent particle; consequently, since the particles do not transmit to one another the original affection, it fails to act upon the living creature as a whole, and the result is that the affected body is non-percipient. This is the case with the bones and the hair and all our other parts that are mainly earthy whereas the former character belongs especially to the organs of sight and of hearing, owing to the fact that they contain a very large quantity of fire and air.

 Now the nature of pleasure and pain we must conceive of in this way. When an affection which is against nature and violent occurs within us with intensity it is painful, whereas the return back to the natural condition, when intense, is pleasant Cf. Rep . 583 C ff., Phileb . 31 D ff. ; and an affection which is mild and gradual is imperceptible, while the converse is of a contrary character. And the affection which, in its entirety, takes place with ease is eminently perceptible, but it does not involve pain or pleasure; such, for example, are the affections of the visual stream itself, which, as we said before, Cf. 45 B. becomes in the daylight a body substantially one with our own. For no pains are produced therein by cuttings or burnings or any other affections, nor does its reversion to its original form produce pleasures; but it has most intense and clear perceptions concerning every object that affects it, and every object also which it strikes against or touches; for force is wholly absent both from its dilation and from its contraction. Tim. But those bodies which are composed of larger particles, since they yield with difficulty to the agent and transmit their motions to the whole, feel pleasures and pains— pains when they suffer alteration, and pleasures when they are restored to their original state. And all those bodies which undergo losses of substance and emptyings that are gradual, but replenishings that are intense and abundant, become insensitive to the emptyings but sensitive to the replenishings; consequently, they furnish no pains to the mortal part of the soul, but the greatest pleasures—a result which is obvious in the case of perfumes. But all those parts which undergo violent alterations, and are restored gradually and with difficulty to their original condition, produce results the opposite of those last mentioned; and it is evident that this is what occurs in the case of burnings and cuttings of the body.

 And now we have given a fairly complete statement of the affections which are common to the body as a whole, and of all the names which belong to the agents which produce them. Next we must try, if haply we are able, to describe what takes place in the several parts of our bodies, both the affections themselves and the agents to which they are ascribed. 

 Firstly, then, we must endeavor to elucidate so far as possible those affections which we omitted in our previous account of the flavors, they being affections peculiar to the tongue. It is evident that these also, like most others, are brought about by means of certain contractions and dilations Cf. 64 E. ; and, more than other affections, they involve also conditions of roughness and smoothness. For all the earthy particles which enter in by the small veins—which, extending as far as to the heart, serve as it were for testing-instruments The function of the nerves is here assigned to the veins. of the tongue,—when they strike upon the moist and soft parts of the flesh and are melted down, contract the small veins and dry them up; and these particles when more rough appear to be astringent, when less rough harsh. And such as act on these veins as detergents and wash out all the surface of the tongue, when they do this excessively and lay such hold on the tongue as to dissolve part of its substance—and such, for example, is the property of alkalies,— are all termed bitter ; while those which have a property less strong than the alkaline, being detergent in a moderate degree, seem to us to be saline, and more agreeable, as being devoid of the rough bitterness. Tim. And those which share in the heat of the mouth and are made smooth thereby, when they are fully inflamed and are themselves in turn burning the part which heated them, fly upwards because of their lightness towards the senses of the head and cut all the parts on which they impinge; and because of these properties all such are called pungent. Again, when particles already refined by putrefaction, entering into the narrow veins, are symmetrical with the particles of earth and air contained therein, so that they cause them to circulate round one another and ferment, then, in thus fermenting they change round and pass into fresh places, and thereby create fresh hollows which envelop the entering particles. By this means, the air being veiled in a moist film, sometimes of earth, sometimes of pure moisture, moist and hollow and globular vessels of air are formed; and those formed of pure moisture are the transparent globules called by the name of bubbles, while those of the earthy formation which moves throughout its mass and seethes are designated boiling and fermenting ; and the cause of these processes is termed acid. 

 An affection which is the opposite of all those last described results from an opposite condition. Whenever the composition of the particles which enter into the moist parts is naturally akin to the state of the tongue, they oil its roughened parts and smooth it, contracting the parts that are unnaturally dilated or dilating those that are contracted, and thus settling them all, so far as possible, in their natural condition; and every such remedy of the forcible affections, being pleasant and welcome to everyone, is called sweet. 

 For this subject, then, let this account suffice. Next, as regards the property of the nostrils, it does not contain fixed kinds. For the whole range of smells is a half-formed class, and no kind possesses the symmetry requisite for containing any smell; for our veins in these organs are of too narrow a construction for the kinds of earth and of water and too wide for those of fire and air, so that no one has ever yet perceived any smell from any of these, but only from substances which are in process of being moistened or putrefied or melted or vaporized. For smells arise in the intermediate state, when water is changing into air or air into water, and they are all smoke or mist; and of these, the passage from air to water is mist, and the passage from water to air is smoke whence it is that all the smells are thinner than water and thicker than air.