Thermal stimuli when applied to the tongue do not cause taste sensations, but only sensations of warmth and cold. Thermal stimuli, however, are recognized to have considerable influence upon the effect of taste stimuli. Two cases are to be noted, that in which the sapid substance itself is either warm or cold and that in which the mouth has been subjected to warm or cold stimuli before the sapid substance is introduced into the mouth. The first condition has received the more attention on account of the importance of temperature in the supposed chemical reaction in the taste buds and the consequent possibility of interpreting the facts in favor of a chemical theory of taste. Both problems have been investigated by Kiesow and others, and the conclusions are conflicting. Some find that there is a certain optimum temperature for sapid bodies at which the taste sensations are best obtained, although there is no perfect agreement as to what this optimum temperature is. It varies from 55 to 120 degrees F. for different authors. At the optimum temperature the least quantity of the sapid substance is necessary to arouse a taste sensation, while a deviation from this temperature in either direction requires a stronger stimulus to arouse the same sort of a sensation. Kiesow, on the other hand, believes that the temperature of the sapid substance makes no difference, but only the temperature of the mouth previous to receiving the sapid substance. For instance, he holds that the sensitivity is just as acute when the temperature of the sapid substance is 32 degrees F. as when it is 100 degrees F. But if the tongue is placed in water at 32 degrees F. for a few minutes it then becomes insensitive to sapid substances,—a kind of anesthesia results. He believes that the conflicting results obtained by the other investigators are merely the results of distraction of the attention. Whenever the temperature rises or falls beyond a certain point, then this temperature sensation becomes more impressive than the weaker taste sensation, and the taste sensation drops out of consciousness. It is a well-established fact, at any rate, that thermal stimuli cannot directly arouse taste sensations.