ABSTRACT
Amyloid is a proteinaceous material of diverse composition and origin deposited in the extracellular space of different tissues under various pathologic conditions. One of them is the well known fact that polarization microscopy is widely used for routine histopathologic diagnosis of amyloid, and amyloid was one of substances in which the ultrastructure had been revealed by the polarization microscopy prior to the first relevant electron microscopic observations. This chapter suggests that the old assumption that orthochromatically stained tissue constituents are isotropic, consequently amorphous materials, is no longer valid. Amyloid deposits contain fibrils and nonfibrillar materials. Chemical analyses of isolated amyloid fibrils reveal the presence of different classes of proteins in the fibrils. Amyloid can be stained metachromatically by certain cationic dyes such as crystal violet and toluidine blue. This staining pattern may be attributed to the presence of sulfated glycosaminoglycans in the amyloid deposits.
