484 THE SPECIAL SENSES. 



Finally, the muscles of the tongue, it will be remembered, are 

 animated exclusively by the filaments of the hypoglossal nerve. 



The exact seat of the sense of taste has been determined by 

 placing in contact with different parts of the mucous membrane a 

 small sponge, moistened with a solution of some sweet or bitter 

 substance. The experiments of Verniere, Longet and others have 

 shown that the sense of taste resides in the whole superior surface, 

 the point and edges of the tongue, the soft palate, fauces, and part 

 of the pharynx. The base, tip, and edges of the tongue seem to 

 possess the most acute sensibility to savors, the middle portion of 

 its dorsum less of this sensibility, and its inferior surfaces little or 

 none. Now as the whole anterior part of the organ is supplied by 

 the lingual branch of the fifth pair alone, and the whole of its 

 posterior portion by the glosso-pharyngeal, it follows that the sense 

 of taste, in these different parts, is derived from these two different 

 nerves. 



Furthermore, the tongue is supplied, at the same time and by the 

 same nerves, with- general sensibility and with the special sensibility of 

 taste. The general sensibility of the anterior portion of the tongue, 

 and that of the branch of the fifth pair with which it is supplied, 

 are sufficiently well known. Section of the fifth pair destroys the 

 sensibility of this part of the tongue as well as that of the rest of 

 the face. Longet has found that after the lingual branch of this 

 nerve has been divided, the mucous membrane of the anterior two- 

 thirds of the tongue may be cauterized with a hot iron or with 

 caustic potassa, in the living animal, without producing any sign of 

 pain. Dr. John Keid, on the other hand, together with other experi- 

 menters, has determined that ordinary sensibility exists in a marked 

 degree in the glosso-pharyngeal, and is supplied by it to the parts 

 to which this nerve is distributed. 



Accordingly we must distinguish, in the impressions produced 

 by foreign substances taken into the mouth, between the special 

 impressions derived from their sapid qualities, and the general sensa- 

 tions produced by their ordinary physical properties. As the tongue is 

 exceedingly sensitive to ordinary impressions, and as the same body 

 is often capable of exciting both the tactile and gustatory functions, 

 these two properties are sometimes liable to be confounded with 

 each other by careless observation. The truly sapid qualities, 

 however, the only ones, properly speaking, which we perceive by 

 the sense of taste, are such savors as we designate by the term 

 sweet, bitter, salt, sour, alkaline, and the like. But there are many 



