Histochemistry of the tongue epithelium in four mammals with respect to keratinization

The tongue epithelium was examined in the laboratory rat, guinea pig, rabbit and Domestic cat, using light microscopical, histological fluorescent and histochemical methods. The distributions of the enzymes, acid and alkaline phosphatase were examined. Protein-bound phospholipid and calcium were investigated, together with thiol sulphydryl groups and cysteine disulphide bonds of proteins. A variety of different types of keratinization were shown in the various species, as well as in the same species in different regions of the tongue. The most strongly keratinized structures were the filiform and conical papillae which varied widely from species to species. Those of the rat dorsum were similar to papillae described previously in the House mouse and have strongly keratinized spines. The guinea pig showed some differences but also had keratinized spines. In contrast the rabbit papillae did not have spines but the horny layer over the posterior sides was hardened instead to form pointed edges. Human filiform papillae are similar to the rabbit without spines but the horny layer is less strongly keratinized. In the Domestic cat the conical papillae were also without spines but the horny layer on the anterior and posterior surface was hardened to form claw-like structures.