Diogenes of Apollônia (probably on the Black Sea), lived in the later half of the fifth century B.C.

His longest surviving work was that On Natural Science; he also wrote, and mentioned in his main work, separate treatises on Meteorology, and On the Nature of Man; and an attack on the Natural Scientists, whom he called Sophists.

1. In starting any thesis, it seems to me, one should put forward as one's point of departure something incontrovertible; the expression should be simple and dignified.

2. It seems to me, to sum up the whole matter, that all existing things are created by the alteration of the same thing, and are the same thing. This is very obvious. For if the things now existing in this universe—earth and water and air and fire and all the other things which are seen to exist in this world: if any one of these were different in its own (essential) nature, and were not the same thing which was transformed in many ways and changed, in no way could things mix with one another, nor could there be any profit or damage which accrued from one thing to another, nor could any plant grow out of the earth, nor any animal or any other thing come into being, unless it were so compounded as to be the same. But all these things come into being in different forms at different times by changes of the same (substance), and they return to the same.

3. Such a distribution would not have been possible without Intelligence, (namely) that all things should have their measure: winter and summer and night and day and rains and winds and periods of fine weather; other things also, if one will study them closely, will be found to have the best possible arrangement.

4. Further, in addition to these, there are also the following important indications: men and all other animals live by means of Air, which they breathe in, and this for them is both Soul (Life) and Intelligence, as had been clearly demonstrated in this treatise; and if this is taken from (them), Intelligence also leaves them.

5. And it seems to me that that which has Intelligence is that which is called Air by mankind; and further, that by this, all creatures are guided, and that it rules everything; for this in itself seems to me to be God and to reach everywhere and to arrange everything and to be in everything. And there is nothing which has no share of it; but the share of each thing is not the same as that of any other, but on the contrary there are many forms both of the Air itself and of Intelligence; for it is manifold in form: hotter and colder and dryer and wetter and more stationary or having a swifter motion; and there are many other differences inherent in it and infinite (forms) of savour and colour. Also in all animals the Soul is the same thing, (namely) Air, warmer than that outside in which we are, but much colder than that nearer the sun. This degree of warmth is not the same in any of the animals (and indeed, it is not the same among different human beings), but it differs, not greatly, but so as to be similar. But in fact, no one thing among things subject to change can possibly be exactly like any other thing, without becoming the same thing. Since therefore change is manifold, animals also are manifold and many, and not like one another either in form or in way of life or in intelligence, because of the large number of (the results of) changes. Nevertheless, all things live, see and hear by the same thing (Air), and all have the rest of Intelligence also from the same.

6. The blood-vessels in man are as follows: there are two main blood-vessels; these extend from the abdomen along the spinal column, one to the right, one to the left, going (down) to each of the legs correspondingly, and up to the head past the collar-bone through the throat. From these, blood-vessels extend throughout the whole body: from the right-hand one to the right side, from the left-hand one to the left side; the two biggest to the heart along the spine, and others a little higher through the chest below the armpit to each of the corresponding arms. And the one is called splenetic (after the spleen), the other (after the liver) hepatic. The extreme end of each of them divides, one branch going to the thumb, the other to the wrist, and from these go fine and many-branched veins to the rest of the hand and the fingers. (Two) other finer blood-vessels lead from the original (main) blood-vessels on the right to the liver, and on the left to the spleen and the kidneys. Those extending to the legs divide at the point of attachment (to the body) and extend throughout the thigh; the largest of them goes behind the thigh and is thick where it emerges; a second goes inside the thigh and is a little less thick. Then they travel past the knee to the shin and the foot, as in the hands; and they descend into the ankle and thence to the toes.

From the chief blood-vessels, many fine veins divide off also to the abdomen and the sides. Those which extend to the head through the throat come into view as large blood-vessels in the neck; and from each of these, at its extremity, many divide off to the head, those on the right going to the left, those on the left going to the right; and they each end at the ear.

There is another blood-vessel on each side of the neck parallel to the large one, a little smaller than the latter; into this the majority of those from the head itself unite. These extend through the throat inside, and from each of them (blood-vessels) travel below the shoulder-blade and to the arms. And beside the splenetic and hepatic blood-vessels others a little smaller appear: these are opened when there is any pain under the skin, but if the pain is in the abdomen, the hepatic and splenetic vessels are bled. There are others also leading from these below the breasts. There are other fine ones again which lead from each (of the main vessels) through the spinal marrow to the testicles in men, and in women to the womb. (The main blood-vessels, which come from the abdomen, are broader, and then become finer, until they change over from right to left and from left to right). These are called after the semen. The thickest blood is swallowed up by the fleshy parts; but if any is left over after passing through these parts, it becomes fine and warm and foamlike.

7. And this (Element) itself is a body both everlasting and immortal; whereas of other things, some come into being and others pass away.

8. But this seems to me to be clear, that it is great and strong, everlasting and immortal and manifold in form.

9. (GALEN, quoting Rufus of Ephesus: All medical men agree that the male foetus is formed sooner and moves sooner than the female; Diogenes alone says the contrary).

10. (Contracted form of the word 'full').