664 SPECIAL SENSES. 



regarded as a violation of strictly hygienic principles, but it none the less 

 exemplifies the cultivation of the sense of taste. 



Nerves of Taste. Two nerves, the chorda tympani and the glosso-pharyn- 

 geal, are endowed with the sense of taste. These nerves are distributed to 

 distinct portions of the gustatory organ. The chorda tympani has already 

 been referred to as one of the branches of the facial ; the glosso-pharyngeal 

 has not yet been described. 



Chorda Tympani. In the description already given of the facial, the 

 chorda tympani is spoken of as the fourth branch. It passes through the 

 tympanum, between the ossicles of the ear, and joins the inferior maxillary 

 division of the fifth, at an acute angle, between the two pterygoid muscles, 

 becoming so closely united with it that it can not be followed farther by dis- 

 section. The filaments of this branch probably originate from the interme- 

 diary nerve of Wrisberg. 



The course of the filaments of the chorda tympani, after this nerve has 

 joined the fifth, is shown by the effect upon the sense of taste and the altera- 

 tion of the nerve-fibres following its division. Vulpian and Prevost, by the 

 so-called Wallerian method, after dividing the chorda tympani, found degen- 

 erated fibres at the terminations of the lingual branch of the fifth, in the 

 mucous membrane of the tongue, the fibres being examined ten days or 

 more after the section. Observations upon the sense of taste show that the 

 chorda tympani is distributed to the anterior two-thirds of the tongue. 



The general properties of the chorda tympani have been ascertained only 

 by observations made after its paralysis or division. All experiments in 

 which a stimulus has been applied directly to the nerve in living animals 

 have been negative in their results. According to Longet, when the nerve 

 has been isolated as completely as possible and all reflex action is excluded, 

 its stimulation produces no movement in the tongue. 



In cases of facial palsy in which the lesion affects the root so deeply as 

 to involve the chorda tympani, there is loss of taste in the anterior two- 

 thirds of the tongue, tactile sensibility being unaffected ; and many cases 

 illustrating this fact have been recorded. Aside from cases of paralysis of 

 the facial with impairment of taste, in which the general sensibility of the 

 tongue is intact, instances are on record of affections of the fifth pair, in 

 which the tongue was absolutely insensible to ordinary impressions, the 

 sense of taste being preserved. A number of such cases have been reported, 

 which show conclusively that the fifth pair presides over general sensibility 

 only, and that it is not a gustatory nerve, except by virtue of filaments de- 

 rived from the chorda tympani. 



Passing from the consideration of pathological facts to experiments 

 upon living animals, the results are equally satisfactory. Although it is 

 somewhat difficult to observe impairment of taste in animals, Bernard and 

 others have succeeded in training dogs and cats so as to observe the effects 

 of colocynth and various sapid substances applied to the tongue. In a great 

 number of experiments of this kind, it has been observed that after section 

 of the chorda tympani, or of the facial so as to involve the chorda tympani, 



