2. Human Duality

And then we have the third of these systems of organs, the blood-vessel system itself, with its larger and smaller tubes extending throughout the entire human organism and having the heart as the central point of all its work. We know also that, going out from the heart, those blood-vessels or blood-filled vessels which are called arteries, convey the blood to all parts of our organism; that the blood goes through a certain process in the separate parts of the human organism, and then is carried back to the heart by means of other similar vessels which bring it back, however, in a transformed condition as so called “blue blood” in contrast to its red state. We know that this transformed blood, no longer useful for our life, is conducted from the heart into the lungs; that it there comes into contact with the oxygen taken up from the outer air; and that, by means of this, it is renewed in the lungs and conducted back again to the heart, to go its way afresh throughout the whole human organism.