134 PHYSIOLOGY CHAP. 



can be avoided by employing discs of gelatin or elder pith with a surface of 

 the desired form, impregnated with the solution (Zwaardemaker, Quix). 

 Kiesow stained his fluids slightly, to avoid the errors that may arise from 

 diffusion. 



In making a methodical research it is well to have a series of substances 

 corresponding with the primitive tastes. Sugar can be used for the sweet 

 tastes, quinine for the bitter, common salt for the saline, hydrochloric or 

 sulphuric acid for the sour taste. Concentrated stock solutions can be kept 

 of all these substances, from which solutions of different strengths can be 

 prepared at any moment. Kiesow (1894) and Hanig (1901) used the follow- 

 ing solutions for their important researches in Wundt's laboratory sugar 

 10 per cent, hydrochloric acid 0*2 per cent, quinine sulphate O'l per cent. 



The mode of application differs according to whether the taste-property 

 of a certain substance is to be tested, or if it is desired to map out the sensi- 

 bility to taste with the oral mucous membrane. In the first case it suffices 

 to pour a given amount (about | c.c.) of the chosen solution on the tongue, at 

 a temperature of about 37 C. The subject then withdraws his tongue and 

 applies it to the palate, and has to say immediately whether the solution has 

 any taste, and if possible, what the taste is. 



He must not know beforehand what substance is being used. The mouth 

 must be rinsed with distilled water before passing from one substance to 

 another. The sensation aroused by one substance must have entirely dis- 

 appeared before proceeding to the next. This requires about five minutes. 

 If the titration of the respective solutions is known, it is easy to determine 

 the liminal stimulus, that is the minimal quantity of the substance that can 

 arouse a definite sensation. 



The above rules and precautions must be observed whenever the taste 

 sensibility in the oral cavity is to be mapped out. In every experiment it is 

 essential to find the liminal value for each individual and for each substance, 

 i.e. the weakest solution that can be appreciated as taste in general or as a 

 specific taste. It should be noted that with increased concentration of the 

 solutions of some substances the quality of the taste alters as well as its 

 intensity. 



In order to control the veracity of the subject's judgments, and to test his 

 attention, pure distilled water can be used on the brush at the outset or 

 occasionally during the experiment. 



Physiological investigation confirms our daily experience that 

 the tongue is the principal organ of taste sensibility, but other 

 areas, even beyond the oral cavity, are capable of perceiving taste. 

 In children, as we have seen, the central part of the dorsum of the 

 tongue is gustatory, but ceases to be so after a certain age : we 

 must now discuss the localisation of the taste sense in adults, on 

 whom it has been studied more accurately. 



Every one admits, in accordance with the facts of histology, 

 that the mucous membrane of the lips, gums, inner surface of the 

 cheek, hard palate, lower surface of the tongue and central part 

 of the dorsum are insensitive to taste. The evidence is less 

 positive in regard to the tonsils and anterior and posterior pillars 

 of the fauces, in which there are marked individual differences. 

 According to Hanig these regions are sensitive to taste stimuli ; 

 according to Kiesow they are usually insensitive, particularly the 

 posterior pillars. As regards the uvula the results were con- 

 tradictory, owing to the rapidity with which the solutions diffuse. 





