All substances do not taste alike to different tongues. We have noted the difference in appreciation of certain foods in infancy and in mature years. Water tastes differently to the fever patient and to the well man. As substances taste differently at different times to the same person, so they vary with individuals. One tongue is found on careful examination to have three times as many papillæ as another, one system is more susceptible to chemical action than another, and the nervous system varies enough in different subjects to make a considerable difference in the powers of taste. One guest at table is delighted with a dish which appeals not at all to the palate of his neighbor. In fact there are cases where the power of taste has been temporarily or entirely lost. In such cases the patient goes on with his daily eating in a mechanical way, not because it tastes good, but because he must. There seem to be different nerves for sweet, for bitter, for salty things, and for acids. Substances are known to chemistry which act differently on the nerves of the front and those of the back of the tongue. They very curiously taste sweet to the nerves of the tip of the tongue and at the same instant bitter to those at the base. If leaves of the _Gymnema sylvestre_ be chewed, sweet and bitter things are tasteless for awhile although acids and salts are tasted as usual. Let an electric current pass through the tongue from the tip to the root and a sour taste will be experienced at the tip. But no one has yet explained why when the same sort of current is passed through in the opposite direction the taste is alkaline. Place a small piece of zinc under the tongue and a dime on top. The saliva which moistens them will cause them to form a small galvanic battery. As they are allowed to touch each other at the tip of the tongue a sour taste will be experienced and in the dark a spark will appear to the eyes.