Nature uses various natural membranes to eliminate toxic substances from the blood, mainly in renal failure. The membranes used for this purpose are predominantly those of the gastrointestinal system and the skin. Humans tried to imitate nature, and employed the same membranes for blood purification in patients with renal failure. The beginning of the practice can be dated to at least 4,000 years ago. However, the initiative for such clearing maneuvers was given by the human mind’s conception for purifying the cosmos, the polis and the soul. This article traces similarities between such metaphysical tactics and procedures of the applied sciences. It also describes the historical evolution of the use of natural membranes for medical reasons in nephrological patients.