(1) A single fungiform papilla was stimulated by a fine capillary containing various taste solutions and it was found that a single papilla responded to mechanical stimuli (touch and pressure) and four fundamental kinds of taste solutions (salty, bitter, acid and sweet). It also responded to distilled water. (2) It was shown that frog's tongue responded to sucrose solutions of more than 1/8M and to saccharin solutions of more than 1/32M. (3) The water response was depressed by not only such common salts as NaCl, NaNO3, NaHCO3, NaOH, KCl, KBr, KI and NH4Cl but also by sodium acetate and sodium sacchrin, while CaCl2 and MgCl2 failed to depress it. (4) The possibility that the withdrawal of some cations, possibly potassium ions, from cell interior may initiate the water response was discussed.