MECHANISM OF GUSTATION. 6G7 



Near the base of the tongue branches are sent to the mucous membrane 

 covering the tonsils and the soft palate. 



The lingual branches penetrate the tongue about midway between its 

 border and centre, are distributed to the mucous membrane at its base and 

 are connected with certain of the papillae. 



General Properties of the Glosso-Pharyngeal. To ascertain the general 

 properties of this nerve, it must be stimulated at its root, before it has con- 

 tracted anastomoses with other nerves, and the nerve must be divided in 

 order, to avoid reflex phenomena. Taking these precautions it has been 

 found that stimulation of the peripheral end of the nerve does not give rise 

 to muscular movements (Longet). There can be no doubt of the fact that 

 the nerve is sensory, although its sensibility is somewhat dull. In experi- 

 ments in which the nerve has seemed to be insensible to ordinary impressions, 

 it is probable that the animals operated upon had been exhausted more or 

 less by pain and loss of blood in the operation of exposing the nerve, which, 

 it is well known, abolish the sensibility of some of the nerves. 



Experiments upon the glosso-pharyngeal are not very definite and satis- 

 factory in their results as regards the general sensibility of the base of the 

 tongue, the palate and the pharynx. The sensibility of these parts seems to 

 depend chiefly upon branches of the fifth, passing to the mucous membrane, 

 through Meckel's ganglion. Experiments show, also, that the reflex phe- 

 nomena of deglutition take place mainly through these branches of the fifth, 

 and that the glosso-pharyngeal has little or nothing to do with the process. 

 In fact after division of both glosso-pharyngeal nerves, deglutition does not 

 seem to be affected. 



Relations of the Glosso-Pharyngeal Nerves to Gustation. Relying upon 

 experiments on the inferior animals, particularly dogs, it seems certain that- 

 there are two nerves presiding over the sense of taste : The chorda tympani 

 gives this sense to the anterior two-thirds portion of the tongue exclusively ; 

 the glosso-pharyngeal supplies this sense to the posterior portion of the 

 tongue ; the chorda tympani seems to have nothing to do with general sensi- 

 bility ; while the glosso-pharyngeal is an ordinary sensory nerve, as well as a 

 nerve of special sense. 



Where there are such differences in the delicacy of the sense of taste as 

 exist usually in different individuals, it must be difficult to describe with 

 accuracy delicate shades of savor, particularly in alimentary substances ; but 

 the distinct impressions of acidity or of bitter quality are easily recognizable. 

 It is certain, however, that saline, acid and styptic tastes are best appreciated 

 through the chorda tympani, and that sweet, alkaline, bitter and metallic 

 impressions are received mainly by the glosso-pharyngeal. 



Mechanism of Gustation. Articles which make the special impression 

 upon the gustatory organ are in solution ; introduced into the mouth, they 

 increase the flow of saliva, the reflex action involving chiefly the submaxillary 

 and sublingual glands ; there is usually more or less mastication, which in- 

 creases the flow of the parotid saliva ; and during the acts of mastication and 

 the first stages of deglutition, the sapid substances are distributed over the 



