GUSTATORY SENSATIONS. 919 



even when the tongue is moistened with an acid solution, the alkaline taste per- 

 sists at the negative pole. The most probable explanation is that electrolytes 

 are formed in the interior of the taste-bud that irritate the end-organ during the 

 passage of the current. This is proved by the fact that the taste-sensation changes 

 on the use of currents of different tension, so that it is dependent upon the ions 

 liberated by the current. The constant current as such irritates the end-organs 

 of the gustatory nerves directly only at the moment of closure and of opening. 

 The sensation thus produced is added to the preceding excitation. If one electrode 

 is placed on the tongue and the other (indifferent) in the hand the following 

 phenomena appear: Kathodal closure and the passage of the current excite no 

 taste-sensation on the root of the tongue ; and the same is true of anodal opening. 

 If, however, the anode is placed on the tongue, a sour taste is excited, both on 

 closure and during the passage of the current, and also on kathodal opening. 

 On the tip of the tongue, and on its middle portion, a salty or a bitter taste is excited 

 when the kathode is placed on the tongue, upon closure and while the current 

 is passing; likewise on opening, when the anode is placed on the tongue. No 

 sensation results on anodal closure, or while the current is passing, or on kathodal 

 opening. Rapidly interrupted currents cause no taste-sensation. Applications 

 of cocain to the tongue abolish the electrical taste temporarily. The experiments 

 of v. Vintschgau, whose taste was imperfect at the tip of the tongue, showed that 

 the electrical current never excited a taste-sensation when applied there (although 

 a distinct tactile sensation). 



In experiments on Honigschmied, who had normal taste-sensation at the tip 

 of the tongue, the positive pole often excited a metallic taste at the tip but not 

 rarely also an acid taste; while at the negative pole, taste was often absent, and 

 when present, it was almost always alkaline, exceptionally acid. It is important 

 to note that after interruption of the current a metallic after-taste could be recog- 

 nized with both directions of the current. 



Pathological. Diseases of the tongue, coating of the tongue, and dryness 

 disturb or destroy the sensation. Subjective tastes are common among insane 

 or nervous patients, probably from irritation of the psychogeusic center. A 

 bitter taste has been noted after poisoning with santonin, bitter and acid tastes 

 after subcutaneous injections of morphin. Gymnemic acid is capable of de- 

 stroying subjective tastes and parageusis. 



The designations hypergeusis, hypogeusis and ageusis are applied respectively 

 to increase, decrease and abolition of taste-sensations. Many forms of tactile 

 sensation on the tongue are confused with gustatory sensations, for example 

 so-called biting, cooling, pricking, sandy, mealy, pasty, astringent, bitter tastes. 



Comparative. In cattle there are as many as 1760 taste-buds to a circum- 

 vallate papilla. A large taste-organ, with numerous folds is described as the 

 foliate papilla in the lateral posterior portion of the tongue in rabbits. This 

 has an analog in man in the form of parallel furrows on the posterolateral edge 

 of the tongue, the fimbrise linguae. Reptiles and birds have no taste-buds, 

 which are numerous in the gill-slits of the tadpole, although the tongue of the 

 adult frog is lined only with an epithelium suggestive of taste-cells. The goblet- 

 shaped organs in the epidermis of fishes and tadpoles are similar in structure to 

 the taste-buds, and probably have the same function. Taste-buds are present 

 on the palate of the carp, and in the mouth of the shark and ray. In aquatic 

 amphibians and in fish, the end-organ of the olfactory nerve is probably stimu- 

 lated like the taste-buds, that is the stimulation takes place through the action of 

 substances dissolved in the water. 



The tongue of the cyclostomes serves as a suction-apparatus, while in other 

 fish it has no muscular tissue. Salamanders and most of the batrachians can 

 extrude the tongue from the mouth and again withdraw it. In many of the lower 

 vertebrates the entoglossal bone serves as a support for the tongue, while in the 

 higher forms it is replaced by the cartilage or the septum of the tongue. The 

 nerve-endings in the proboscis (flies), jaw and tongue (ants), palate and epi- 

 pharynx are the seat of the taste-organs in insects. Taste-organs have been 

 found also in snails. 



Historical. Bellini considered the papilla? of the root of the tongue as the 

 gustatory organs (1665). Sulzer reported in 1760 as to electrical taste-sensations. 

 Baur was the first to describe accurately the course and the division of the muscles 

 in the tongue; and Rudolphi the course of the nerves. Elsasser (1834) showed 

 that the sensation of taste was most intense for all substances on the vallate 

 papillae, and on the posterior portion of the lateral margin of the tongue. 



