Effect of formalin fixation on the ultrastructure of connective tissue components

Electron microscopic examinations of fibrillar components and the ground substance of human skin derma fixed in formaldehyde showed good preservation of the fibrillar structures. The typical changes in fixed collagen fibrils in negative staining include the lack of transversal lines in the zone A and poor manifestation of microfibrillarity in the zone B. Alterations in the ground substance are more significant. Staining with rutenium red reveals no reticular structure here, but floccular formations appear in the amorphous interfibrillar substance. Other species of rutenium-positive structures (sheaths of elastic fibers and collagen fibrils as well as lines of thin cross-striation of the latter) are well preserved. All these alterations should be taken into consideration in ultramicroscopical examinations of formalin-fixed connective tissue.