Microfibrils: Fine filamentous components of the tissue space

Fine extracellular filaments were first observed in sectioned connective tissue by Jakus ('54) in the rat cornea and later by Robertson ('56) in reptilian skeletal muscle. Karrer ('58), using methacrylate sections stained with phosphotungstic acid (PTR), described thin filaments in mouse connective tissue and collated his observations with those of other workers. More conspicuous visualization of these filaments is afforded by tissue embedded in the polyester, Vestopal-W by the method of Ryter and Kellenberger ('58). They are especially striking after heat and solvent clearing of sections, and solvent staining (Low, '61b). In recent studies of polyester-embedded lung (Low, '61a) and heart (Battig and Low, '61) they became so conspicuous that they were designated "microfibrils." They are now routinely observed in normal (Karrer, '61) and experimental material (Chapman, '61) and are recognizable as one of the structurally organized entities of the connective tissue (Low, '61c). It therefore seems appropriate to present a brief account of their morphology and their physical relationships to other formed elements in the tissue space: and to assign them a specific name.