SENSES OF SMELL, TASTE, HUNGER AND THIRST 751 



facts are at our disposal which could be used to exclude the second 

 view, and hence, we must regard the excitation of the taste buds by- 

 inadequate stimuli as not proven, 



The Power of Reaction of the Taste Buds. Gustometry. — ^The 

 acuity of the sense of taste may be tested by bringing solutions of 

 different concentration in relation with different points of the tongue 

 and ascertaining the dilution which barely suffices to incite a sensation. 

 These fluids may be applied either with a camel's hair brush or a drop- 

 per, but inasmuch as the tongue is also equipped with tactile, temper- 

 ature and pain receptors, they must be non-irritating and should be 

 heated to a few degrees below the temperature of the body. Very 

 cold and very warm solutions diminish the sensitiveness of these end- 

 organs. Care must also be taken that the substances selected for 

 these tests, do not activate the olfactory cells, and that they are not 

 spread to other regions of the oral cavity by movements of the tongue. 



All sensations of taste are preceded by a definite latent period, 

 which is caused in part by the delayed action of the sense-organs 

 themselves, and in part by the fact that the substances must first be 

 dissolved. Other factors to be controlled are the size of the field 

 stimulated, the length of the period during which the stimulus is allowed 

 to act and the general sensitiveness of the mucous membrane. It is 

 a matter of common experience that the receptive power of the latter 

 is materially altered by habits, such as the use of alcohol and tobacco. 

 The values of the latent period for the tip of the tongue are as follows:^ 



Sodium chlorid . 308 sec. 



Sugar . 446 sec. 



Sulphuric acid 0. 536 sec. 



Quinine 1 . 082 sec. 



The Topography of the Sense of Taste. — While the sensations of 

 taste are very numerous, it is possible to arrange them in four funda- 

 mental groups, namely, as sweet, bitter, acid and salty. Such modali- 

 ties as burning, astringent, aromatic and oily are composite in their 

 nature and require the simultaneous activation of the olfactory cells 

 as well as of the sense-organs for touch and temperature. Thus, 

 weak acids give an astringent sensation in addition to a distinct taste 

 of sour, while strong acids amphfy the primary impression by a 

 burning sensation. A similar amplification of common sensibility is 

 effected by alum and pepper. 



Even the fundamental taste sensations may be combined to give 

 a fused or compound effect. Thus, weak solutions of sweet and salty 

 substances may yield a sensation of flatness or alkalinity, and a weak 

 sensation of sweet may be completely neutraUzed by the addition of 

 a few grains of sodium chlorid. Quite similarly, the addition of 

 sugar to lemon juice diminishes the acidity of the latter and gives rise 

 to a mixed sensation in which the components may be clearly recognized. 



^Kiesow, Wundt's philos. Studien, ix, x and xii, 1894-96; also Zeitschr. fiir 

 Psych, and Physiol, der Sinnesorgane, xxvii, 1901. 



