I. Soul and Spirit in the Human Physical Constitution

This indicates how, for example, we should look for the way in which the Ego works in the circulating blood. It works in the circulating blood by way of the warmth organism—works as the spiritual entity which, as it were, sends down the will out of the warmth, via the air, into the fluid organism. Thus everything in the human organism works upon everything else. But we will get nowhere if we have only general abstract ideas of this interpenetration; we will reach a result only if we can evolve a concrete idea of our constitution and of how everything that is around us participates in our make-up.