The oyster expels its shell because keeping that formative process inside would kill it, so Steiner reads the shell as life preserved by ejection.
The Oyster Shell Process in Anthroposophy is Rudolf Steiner's name for the formative activity an oyster must drive out of its own body as carbonate of lime, because a force of that strength, retained inside, would kill the creature. Steiner set it out across three lectures of Spiritual Science and Medicine (GA 312, Dornach, March and April 1920). In Lecture V the shell carries off the force that in a human being becomes thinking, so the oyster stays lowly in the animal kingdom while standing relatively high in the cosmos. In Lecture XI the shell is earth formation held back at an earlier stage, kept primitive by the creature's persistent link with the sea, and named as the polar opposite of the inward formative work of the human lung. In Lecture XIX eating the oyster takes that albuminising process into the abdomen, draws formative force downward, and empties the head. Homeopathic and anthroposophic pharmacy still prepare Calcarea carbonica from the shell.
The Oyster Shell Process is the clearest picture Steiner gives of a life force that can only be carried at a distance. The oyster secretes outward what it cannot afford to keep, and the discarded carbonate of lime is not waste but the visible record of a formative activity too strong for the small body that produced it.
In Steiner's Own Words
What precisely is an oyster shell and egg shell? It is a product that the oyster or the essential substance of the egg must eject, because were it retained it would kill them. This shell formation is necessary for the preservation of life. And so, when eating oysters, we consume that life process which is manifested externally in the formation of the shells. (I put the facts to you in these simple terms; if I sought to impress current science, more intricate and technical terms would of course be necessary.) In eating the oyster we eat this albuminising process, a process which is the antithesis to the antimonising process. Through its absorption we promote and stimulate all that leads in man to typhoid manifestations.
What it Means Today
The substance Steiner keeps pointing at already had a documented pharmaceutical history when he lectured. Samuel Hahnemann introduced Calcarea carbonica in Die chronischen Krankheiten (The Chronic Diseases), published from 1828, and he was exact about its origin: the remedy is not chalk and not limestone but calcarea carbonica ostrearum, the soft middle layer of the shell of the edible oyster, Ostrea edulis. Hahnemann's provings recorded what the preparation did without explaining why that particular source mattered, and pharmacists have repeated the specification for nearly two centuries without one. Steiner's 1920 lectures supply a reason. If the shell is the trace of a formative force expelled under the pressure of staying alive, then the middle layer is where that expulsion is still legible in the substance, and a potentised preparation of it carries the same gesture: drawing soul and spirit activity outward and upward from a lower bodily region where it has settled and become illness. The anthroposophic pharmacy that grew from Ita Wegman's clinical institute at Arlesheim, opened in 1921, inherited that preparation and worked with it on exactly those terms.
Thalira synthesis: the oyster shows that some faculties are survivable only at a distance, which is why a human being does not carry thinking in the abdomen but holds it at the head, one body-length away from the organs it would otherwise consume.
Where to Read More