Descemet's membrane was isolated from the corneas of cows and observed by electron microscopy after negative staining with 1% phosphotungstic acid solution, pH 7.2. Ultrastructurally, bovine Descement's membrane had a very regular hexagonal pattern. Nodes were connected to the six others around each of them by thin filaments to form a hexagon. The distance between the nodes was approximately 120 nm, the diameter of the nodes approximately 30 nm, and the width of the connecting filaments approximately 10 nm. Bovine Descement's membrane was a molecular sieve composed of nodes and filaments substantiating our molecular sieve theory of basement membranes.</p
