31.8 THE SENSES 



two-thirds of the tongue, and (b) the glosso-pharyngeal to 

 the posterior third of that organ. It is probable that only the 

 dorsum of the tongue, the lateral parts of the soft palate, the 

 uvula and the upper pharynx are concerned in gustation. On 

 the tongue are found special papillae, ( i ) the circumvallate, 

 large and few in number, near the base of the organ, and (2) 

 the fungiform, about 200 in number, over the remaining area. 

 The circumvallate and some of the fungiform papillae contain 

 taste beakers, true gustatory organs. They are ovoid col- 

 lections of cells beneath the epithelial covering of the, mu- 

 cous membrane. Sapid substances enter these beakers in so- 

 lution and come in contact with the taste cells, which are 

 connected with the filaments of the gustatory nerves. Thus 

 are produced specific impressions which are conveyed to the 

 gustatory center, and the sense of taste is excited. The lim- 

 ited distribution of the taste beakers makes it impossible that 

 they should be the only organs capable of receiving special 

 gustatory impressions. The taste center has been indefi- 

 nitely located in the uncinate gyrus near the olfactory center. 



Since it is necessary to the tasting of substances that they 

 come in actual contact with the taste organs, and since to do 

 so they must be in solution, it follows that dryness of the 

 mouth interferes with, or abolishes, this sense. 



The most marked tastes are the sweet, bitter, saline, and 

 alkaline. The more delicate flavors involve also the special 

 sense of smell, and it has been seen that dissociation of the 

 two kinds of impressions is often impossible. Taste is also 

 subject to variations by reason of education, age, association, 

 caprice, etc. Bitters are most easily appreciated at the back, 

 salts and sweets at the tip, and acids at the sides at the 

 tongue. 



5. The Sense of Hearing. 



The ear consists of a complicated apparatus for the pur- 

 pose of the reception of special impressions which are appre- 

 ciated by the brain as sounds. Anatomically it consists of 



