760 SPECIAL SENSES. 



sometimes lends a delicious flavor to the simplest articles of food. The taste for certain 

 articles is certainly acquired, and this is almost always true of tobacco, now so largely 

 used in civilized countries. 



Any thing more than the simplest classification of savors is difficult, if not impossible. 

 We recognize that certain articles are bitter or sweet, empyreumatic or insipid, acid or 

 alkaline, etc., but, beyond these simple distinctions, the shades of difference are closely 

 connected with olfaction and are too delicate and numerous for detailed description. 

 Many persons are comparatively insensible to nice distinctions of taste, while others recog- 

 nize with facility the most delicate differences. Strong impressions may remove, for a 

 time, the appreciation of less powerful and decided flavors. The tempting of the appetite 

 by a proper gradation of gustatory and odorous impressions is illustrated in the modern 

 cuisine, which aims at an artistic combination and succession of dishes and wines, so that 

 the agreeable sensations are prolonged to the utmost limit. This may often be regarded 

 as a violation of strictly hygienic principles, but it none the less exemplifies the cultiva- 

 tion of the sense of taste. 



In discussing the physiology of taste, we shall avoid an elaborate and artificial classi- 

 fication of savory articles, arid shall use the terms sweet, acid, bitter, etc., as they are 

 commonly understood. We shall first describe the physiological anatomy and properties 

 of the gustatory nerves, and then consider the mechanism of gustation, the special organs 

 of taste, and the probable mode of connection between the organs of taste and the nerves. 



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

 over the sense of taste. These nerves seem to be distributed to distinct portions of the 

 gustatory apparatus and to have somewhat different functions. The chorda tympani has 

 already been referred to as one of the branches of the facial ; the glosse-pharyngeal, one 

 of the nerves of the eighth pair, has not yet been described. 



Chorda Tympani. In the description we have 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 cannot be followed 

 farther by ordinary dissection. (See Fig. 202, p. 622.) It is impossible to determine with 

 certainty from what root the filaments of this branch derive their origin, whether from 

 the main trunk or the intermediary nerve of Wrisberg; but experiments have shown that 

 it possesses functions entirely distinct from those of the other branches of the facial. The 

 lingual branch of the inferior maxillary division of the fifth has been called the gustatory 

 branch ; but this is an error ; for, as we shall see, the fifth has nothing to do with gusta- 

 tion, except that it is joined with filaments of the chorda tympani, which reach the tongue 

 through the lingual branch. 



As regards the course of the filaments of the chorda tympani after this nerve has joined 

 the fifth, there can be no doubt, both from the effect upon taste and the alteration cf 

 the nerve-fibres following its division. Vulpian and Prevost, by the so-called Wallerian 

 method, after dividing the chorda tympani, found degenerated 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. It is well known that, a number of days 

 after the section of a nerve, its fibres of distribution undergo change, and these observa- 

 tions leave no doubt of the fact that the chorda tympani is really distributed to the lingual 

 mucous membrane. Observations upon the sense of taste show that the chorda tympani 

 is distributed to about the anterior two-thirds of the tongue. 



The general properties of the chorda tympani have only been ascertained by observa- 

 tions made after its paralysis or division. All experiments in which excitation has been 

 applied directly to the nerve in living animals have been negative in their results. 

 Longet states that, when the nerve has been isolated as completely as possible and all 

 reflex action is excluded, its galvanization produces no movement in the tongue. 



