896 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



The galvanic current is likewise capable of producing the sensation 

 of taste, which varies according to the direction of the current. Thus, 

 a bitter metallic taste is developed when the anode, and an acid taste 

 when the cathode, is placed on the tongue. In this instance it is 

 doubtful whether the sensation of taste is due to a direct stimulation of 

 the taste bulbs or to electrolytic changes occurring through the action 

 of the galvanic current. 



All the localities in which the taste bulbs have been detected are 

 probably possessed of the sense of taste, although certain regions, as 

 the entrance to the larynx and the hard palate, do not admit of experi- 

 mental demonstration as regards this point. Without doubt the root of 

 the tongue and its tip and margins are gustatory, while it is probable 

 that the under surface of the tongue possesses no power of taste. 



The nerves which preside over the sense of taste are certain fibres 

 of the lingual and the glosso-pharyngeal. After the lingual nerve is 

 divided the sense of taste disappears from the tip of the tongue. When 

 the glosso-pharyngeal is divided the sense of taste is lost in the posterior 



FIG. 412. TASTE FURROW IN MAYER'S FIG. 413. SECTION or MAYER'S ORGAN IN THE 

 ORGAN IN THE HOG. (Csokor.) HORSE. (Csokor.) 



part of the dorsum of the tongue. Contrary to our experience with the 

 other nerves of special sense, stimulation of the trunks of these nerves 

 does not give rise to the sense of taste, probably owing to the fact that 

 both of these nerves are mixed nerves, and contain other afferent fibres 

 as well as those of the sense of taste. 



Certain substances seem to possess the power of antagonizing the 

 impressions which others ordinarily make on the terminal filaments of 

 the nerves of taste ; thus the taste of bitter and sour substances may to 

 a certain extent be corrected by the admixture of sugar, even without 

 any chemical change occurring in the mixture. Such a result is only to 

 be explained as some kind of interference of the sensations; on the other 

 hand, substances having a sweet taste do not possess the power of modi- 

 fying saline tastes. 



Any explanation as to why certain substances possess one peculiar 

 taste and others another is in our present state of knowledge impossible, 

 with the single exception of the characteristic taste of acids and alkalies, 

 where we find the characteristic taste associated with certain definite 

 chemical characteristics. 



