76 4 SPECIAL SENSES. 



Experiments upon the glosso-pharyngeal are not very definite and satisfactory 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 MeckeFs ganglion. Experiments show, also, 

 that the reflex phenomena 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. 



With these remarks, we dismiss the functions of the glosso-pharyngeals as nerves of 

 general sensibility and shall consider in detail their relations to the sense of taste. 



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

 on the inferior animals, particularly dogs, it seems pretty certain that there are two 

 nerves presiding over the sense of taste : The chorda tympani gives this sense to the 

 anterior portion of the tongue exclusively, probably the anterior two-thirds ; the glosso- 

 pharyngeal supplies this sense to the posterior portion of the tongue ; the chorda tympani 

 seems to have nothing to do with general sensibility ; 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 

 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. The mode in which sapid substances are brought in con- 

 tact with the organ of taste is so simple, that we need only allude to it, before we study 

 the anatomy of the parts directly concerned and their connections with the terminal 

 filaments of the gustatory nerves. In the first place, the articles which make the special 

 impression 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 usu- 

 ally more or less mastication, which increases the flow of the parotid saliva ; and, during 

 the acts of mastication and the first stages of deglutition, the sapid substances are dis- 

 tributed over the gustatory membrane, so much so, indeed, that it is difficult to exactly 

 locate the seat ot the special impression. In this way, by the movements of the tongue, 

 aided by an increased flow of saliva, the actual contact of the savory articles is rapidly 

 effected. The thorough distribution of these substances over the tongue and the mucous 

 membrane of the general buccal cavity leads to a certain amount of confusion in our 

 appreciation of the special impressions ; and, in order to ascertain if different portions 

 of the membrane possess different properties, it is necessary to make careful experiments, 

 limiting the points of contact as closely as possible. This has been done, with the result 

 of showing that the true gustatory organ is quite restricted in its extent, and, as such, it 

 demands special anatomical description. 



Physiological Anatomy of the Organ of Taste. Recent anatomical and physiological 

 researches have shown that, at least in the human subject, the organ of taste is probably 

 confined to the dorsal surface of the tongue. When we examine the structure of the 

 mucous membrane of the mouth, tongue, and palate, we find that the upper surface of 

 the tongue presents numerous papillae, called, in .contradistinction to the filiform papilla?, 

 fungiform and circumvallate. These are not found on its under surface or anywhere 

 except on the superior portion. It is now pretty well established that the circumvallate 

 and fungiform papillae alone are the organs of taste. Camerer, in some recent experi- 

 ments upon the gustatory organs by the application of solutions to different parts through 

 fine glass tubes, concluded that the parts around a papilla have no gustatory sensibility, but 

 that different savors can be distinguished when a single papilla is touched. These obser- 

 vations give a new importance to the peculiar papillae of the tongue, and we therefore 

 present a description of their arrangement and structure. 



