The Alkaline Taste: A Comparison of Absolute Thresholds for Sodium Hydroxide on the Tip and Mid-Dorsal Surfaces of the Tongue

At present the modality of taste is generally considered to have four primary qualities: sweet, salt, sour, and bitter. Earlier writers have, however, accepted additional categories, one of which was the alkaline taste. The status of alkaline as a primary taste was made doubtful by the work of Oehrwall1 and Von Frey.2 Oehrwall considered the alkaline taste to be a complex excitation of one or more of the four primary tastes with touch. Von Frey suggested that the alkalies excited taste receptors and probably also stimulated olfactory receptors, due to their reactions on the surface of the tongue. More recently Moncrieff has considered the alkaline taste to be a function, not of taste but of the 'common chemical sense, since the alkalies are chemically irritating to other parts of the body as well as the tongue.3 He suggests further that more information on the alkaline taste might be obtained through a comparison of the thresholds of alkaline solutions on the tip of the tongue where there are taste buds and the mid-dorsal surface of the tongue where no taste buds exist. The inference from this suggestion is that a lack of difference in thresholds in the two areas would support his theory. The present experiment is an attempt to determine whether there is a difference between the absolute thresholds for sodium hydroxide at those areas.