Now, to go beyond physical nourishment and include also breathing presents no difficulty to the man of the present day; for breathing too is a form of assimilation. But it would not occur to him to go any farther. The earlier student of Nature went farther. It was clear to him that when man uses his eye to perceive things, he does not merely see with the eye, but during the process of perception he receives through the eye in infinitely minute quantities something of the substance of the World-All. And not through the eye alone, but through the ear and through other portions of the organism. And the medieval student of Nature was fully aware of the very great importance of those substances which occur in a slight measure only in the human organism, such as, for example, lead, and which man receives in infinitely minute quantities that may be found where we little suspect their presence. (Steiner 2012:29)
Lead is a metal that cannot immediately be demonstrated as occurring in man. But lead is, as a matter of fact, distributed throughout the entire physical Cosmos in a state of very fine dilution, and the human being takes up lead from the Cosmos by means of processes that are many times more delicate than the process of breathing. The human being is perpetually excreting substances, throwing them off from the periphery. You not only cut your nails, you continually throw off substances from your skin. But whilst substance is thus given off, other substance is taken up and received into the organism. (Steiner 2012:29)
STEINER, Rudolf. 2012. World History in the light of Anthroposophy. (Trans.: George Adams; Mary Adams; Dorothy Osmond) London: Rudolf Steiner Press.