Chemicals of diverse structures can elicit sweet response in humans, but marked species difference in response to sweet-tasting compounds exists among mammalinan species. In a number of species a distinct group of chorda tympani nerve fibers predominantly responds to sucrose and Na saccharin. Sweet response in certain mammals can be selectively blocked by a number of compounds, including gymnemic acid and ziziphin. Cu and Zn salts also selectively suppress chorda tympani nerve response to sweet stimuli in rodents. Probably Cu²⁺and Zn²⁺ compete with sweet stimuli for binding to receptor molecules. A recent attempt to isolate a protein from monkey tongues revealed the presence of a thaumatin-binding protein of M.W. of approximately 50, 000. This protein was predominantly found in taste papillae, with lesser amounts found in non-taste tissue.