Tannic Acid in Histology: An Historical Perspective

The development of tannic add as a reagent in histological methods is traced against a background of widespread use in science and technology from times of antiquity. Numerous light microscopic methods involving tannic add, particularly in conjunction with iron and silver, have been described for a variety of tissue components. In most applications, tannic add functions as a mordant. Current use is generally restricted to methods based on its affinity for collagen. The most significant histological use of tannic add in contemporary times is as an adjunct to conventional glutaraldehyde-osmimn-heavy metal fixation and staining for ultrastructural studies of tissue structures not normally clearly demonstrated. Tannic add reacts with various components by mechanisms which are often not fully understood.