138 



PHYSIOLOGY 



CHAP. 



tip, afterwards more slowly, while there is a gradual diminution 

 from without inwards. 



(c) Sensibility to acid is maximal in the median part of the 

 border of the tongue, and diminishes towards both base and apex, 

 and from without inwards towards the central anaesthetic zone. 



(d) Sensibility to salt is maximal at the apex and margin of 

 the tongue, minimal at the base. From both the apex and the 

 base it remains approximately constant up to the anaesthetic 

 region, and only diminishes perceptibly in the lateral portions. 



These conclusions, at least in so far as concerns the general 



J:: 



:il 



lit! 



::: 



FIG. 61. Diagram of topographical distribution of gustatory sensibility to the four primitive 

 qualities of taste on the dorsal surface of the tongue. (Hanig.) The sensory spots for each of 

 the four qualities of tastes are arranged in parallel isogustatory lines (isochymes). Those for 

 s\yeqt (marked blue) are most dense at the apex of the tongue ; those for bitter (red) at the 

 base ; those for aqid (green) at the borders ; those for salt (yellow) at the borcTfers and tip of 

 the tongue. 



topography of the taste sense in the tongue, are confirmed by the 

 fact that they agree essentially with the early observations of 

 Guzot and Admirauld (1830), and of Stich and Klantsch (1858), 

 as well as those obtained by Eosenthal (1860) and Neumann 

 (1864) with galvanic stimulation. 



In infants, as has been said, the whole surface of the tongue 

 is sensitive to taste, and has no anaesthetic zone such as is con- 

 stantly present in adults. To account for the change, Kiesow 

 assumes that in adults it is more necessary to have the control of 

 taste in the marginal portion of the tongue which is nearer the 

 teeth, the instruments of mastication, while the sensibility of the 

 central area of the tongue in early life is correlated with the 



