136 PHYSIOLOGY CHAP. 



sweetish, the latter is bitter at the base ; alum, on the contrary, 

 is acid at the tip and sweet at the base. The number of substances 

 that taste differently at the two ends of the tongue are continually 

 being added to. Bromo-saccharine (Howell and Kastel), which 

 tastes sweet at the apex and bitter at the base, is typical. The tip 

 of the tongue is, however, able to perceive the bitter taste of 

 quinine and of many other substances. Generally speaking, it 

 may be' said that every part of the tongue that is provided with 

 taste-buds can distinguish the primitive qualities of taste ; but 

 there are distinct differences in sensibility between the different 

 points of the tongue. 



The latency of sensations to various tastes is also different at 

 the apex and the base. This fact, demonstrated by v. Vintschgau 

 and Honigschmied, was confirmed by others, as shown by the 

 following table : 



Sodium 



Chloride. Sugar. Quinine, 



sec. sec. sec. 



Tip of the tongue . . . 0-597 0-752 0-993 



Base of the tongue . . . 0-534 0-552 0-501 



The dissimilar capacity of the base and the apex of the tongue in 

 appreciating tastes has been referred to the different origins of 

 the nerves that supply these regions, but although the lingual 

 nerve ramifies in the anterior part of the tongue, and the glosso- 

 pharyngeal in the base, the gustatory fibres of the lingual probably 

 come from the glosso-pharyngeal (Vol. III. pp. 401-5). It seems 

 probable, therefore, that these differences are accounted for by the 

 fact that the 1 specific organs for the several tastes are unequally 

 distributed over the different gustatory regions of the tongue. 



Kiesow, by an exact method, obtained the following reaction 

 times for the tip of the tongue alone : 



sec. 

 Sodium chloride . . . . 0-308 



Sugar 0-446 



Hydrochloric acid 0-536 



Quinine 1-082 



He points out that these values agree perfectly with the general 

 fact already established by Schirmer, that in a mixture of the four 

 sapid substances applied to the tongue salt is appreciated first, 

 then sweet, thirdly acid, and lastly bitter. 



According to Schreiber (1892) the insensitive central area on 

 the dorsum of the tongue varies in extent according as sweet, acid, 

 salt or bitter substances are employed. As shown by the diagram 

 (Fig. 60) the area insensitive to acid is the smallest, to bitter the 

 most extended. The area that is insensitive to acid is insensitive 

 also to almost all other tastes. But we must not assume this to 

 be a general rule; without criticising the method employed by 



